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Raw
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Effects of Drying Conditions
on the Technological Properties of Sheet Natural Rubber
M.M. Jayasuriya et al. J. Rubb. Res., 3(3), 185
- 192
Attempts were made to prepare natural rubber
sheets by varying the drying time and drying conditions. Rheological and
techno-logical properties of rubber compounds based on ACS-1 and tread
formula were evaluated. It was found that sun drying of rubber sheets for
up to 2 days, followed by smoking for up to 2 days could impart
equivalent physical properties with that of purely smoked rubber. In
addition, it was found that drying of rubber sheets under sunlight for
2-4 days did not impart inferior physical properties.
Production of soluble protein free latex by
radiation process
S. Varghese et al. Department of Quantum
Engineering and Systems Science, Faculty of Engineering, University of
Tokyo, Japan. Rubber Chemistry and Technology, March-April, Vol.73.
Number 1, page 80 - 88.
During irradiation of natural rubber (NR) latex
for vulcanisation, the latex proteins undergo disintegration, which
leaves a high soluble protein content in latex products. In order to
follow up the effects of radiation on NR proteins, field latex was
irradiated with g-rays and the soluble protein concentration in the
rubber phase and the serum phase were analyzed. It was found that the
water solubility of the proteins increases with increasing dose. The
soluble protein content in the cream phase (rubber) decreased where as
that in the serum phase increased with radiation dose. SDS-PAGE analysis
revealed that the 27 kD protein together with 14 kD appear in the
radiation vulcanised latex up to a radiation dose of 160 kGy and at 320
kGy they disappear due to the disintegration by radiation. A new process
for the preparation of protein free latex has been developed. In the new
process the radiation-vulcanised, centrifuged latex is subjected to
dilution and then centrifuged. In the case of field latex, it is
irradiated first and then centrifuged after dilution. The new process
results in pre-vulcanised latex almost free from soluble proteins.
Tensile strength of samples produced by the new process is comparable to
that from conventional radiation process.
Crystallisation behavior and strength of
natural; rubber isolated from different Hevea clone
S. Kawahara et.al. Department of Chemistry,
Faculty of Engineering, University
of Technology, Nagaoka,
Japan. Rubber
Chemistry and Technology, March-April 2000, Vol.73. Number 1, page 39 -
46.
Crystallisation behavior of natural rubbers of
different clonal origins, i.e. RRIM 600, 60/2, 2025, 2026, and skim
rubbers, was investigated by dilametry at –25ºC. The latex samples
were deproteinised with a proteolytic enzyme in the presence of a
sulfactant. Skim rubbers were purified by centrifugation followed by
acetone-extraction. The over-all crystallisation rate of
acetone-extracted rubbers could be divided in two categories: one
includes RRIM 600, 60/2 and 2025, and other RRIM 2026 and skim rubbers.
This is attributed to the different levels of linked fatty acid groups
and gel contents. The minimum level of linked fatty ester groups required
to promote crystallisation of natural rubber is about 2.8 mmol/kg. The
green strength of the rubber is dependent on the level of linked fatty
acid ester groups.
Guayule Rubber: A new possible World Scenario
for the Production of NR?
F. Catalo. Trelleborg Wheel Systems - Pirelli,
Progress in Rubber and Plastics Technology, Vol. 16, No. 1, 2000.
Natural Rubber is a particularly precious to the
rubber industry. The regularity of its chemical structure and its trend
to crystalisation, makes natural rubber an irreplaceable material in
rubber compounding. The increasing demand for this product could cause
the disruption of other tropical forests to increase natural rubber
production. Thus the best answer to avoid further deforestation is to
start the production of guayule rubber. This can be cultivated in
semi-desert, abandoned lands, avoiding further deforestation of tropical
lands currently dedicated to the production of hevea. An additional item
is the discovery that contrary to hevea, guayule rubber has a low protein
content, while these proteins are different from those of hevea and do
not cause allergy to sensitive individuals. The history of guayule rubber
is also reviewed, the aspects concerning its cultivation, equivalence to
natural rubber from the chemical standpoint. Finally typical mechanical
properties of guayule rubber are presented together, with the advantages
and didadvantages offered by guayule in comparison to hevea.
Standard for Rubber Powders
H.J. Manuel. Vredestein Rubber Resources B.V.
Paper presented at the 7th ETRA Conf. Brussels, March 29-31, 2000.
Rubber powders (or granulate) from rubber scrap
materials are used in many applications in different fields. These
applications ask for different properties of the rubber powders. In his
paper a number of suggestions to classify powders are given. A reference
is being made toward ASTM D5603, that classifies powders with respect to
feed stock and sieve analysis. It will be shown that the American
situation does not comply as such to the European situation, due to
different materials being used on both continents.
By using a classification system it should become more clear what type of
material the customer is dealing with. Applications with more demanding
properties and/or consistency can then choose from a material that will
live up to these requirements.
For applications where properties are at a low level, or where the basic
properties that come from the proposed classification list. Some examples
will be given of the current ‘Vredestein’ grades and their
properties to supply data for a classification system. In a few examples
it is shown how different powders can affect the properties of products.
Production, classification and
properties of Natural Rubber, Part 1
Production, classification and properties
of Natural Rubber, Part 2
M. Brendan Rogers, Donald S. Tracy
and Walter H. Waddell, ExxonMobil Chemical. Rubber World,
August/September 2005.
In this review the production, classification and properties of natural
rubber are discussed. Several key factors will determine its continued
use in the future such as, availability, Technical specifications,
quality and chemical modification. The greatest challenge in the future,
however, may not be with regard to technical properties, but with supply and
availability.
Elastomers for shoe applications
K. A. Ames, Rubber Chem.& Techn.,
Vol. 77, No. 3, p. 413-475
Reviews the improvements made over the last 15 years in the production of
outsoles and midsoles for footwear by using various materials.
Development
of a new procedure for lipid extraction from Hevea brasiliensis natural
rubber
S.
Liengprayoon, F. Bonfils, J. Sainte-Beuve, K. Sriroth, E. Dubreucq, L.
Vaysse
European
Journal of Lipid Science and Technology, 110 (6), 563-569
(2008)
Attempts
were made to extract lipids which have been reported to have influences
in some key properties of natural rubber. The lipid extraction from
natural rubber was carried out either in the liquid state (latex) or in
the dry state (unsmoked sheets). Different combinations of organic
solvents (chloroform/methanol and hexane/isopropanol mixes) were used to
extract unsmoked sheets from the RRIM 600 clone, and chloroform/methanol
(2:1 vol/vol) was found to be the most suitable solvent. By increasing
the exchange surfaces by grinding rubber under liquid nitrogen and
extracting the ground rubber for 6 h at room temperature, the lipid
extraction yield was improved to 1.82% (versus dry rubber). For the latex
extraction, the problem of lipid entrapment in the coagulum from immediate
coagulation of latex in the solvent was solved by preliminary two times
dilution, giving a 3.24% extract (versus dry rubber) containing a minimum
quantity of contaminating polyisoprene.
Pulsed
NMR studies on long-term crystallization behavior and melting process of
natural rubber under elongation
M.
Komura, K. Nakajima, T. Nishi, T. Ikehara, Q. Zhaobin
Rubber
Chemistry and Technology, 81 (1), 110-120 (2008)
Spin-spin
relaxation time T-2 was measured by pulsed nuclear magnetic resonance
(NMR) in order to investigate the long-term crystallization and melting
process of natural rubber under elongation. The dependence of the
both processes on extension ratio, crystallization temperature and crosslink
density were examined. The crystallization of natural rubber was
found to be continued over 3 months even at 10 degrees C. According
to the two-step melting process found for the first time under
elongation, this present work proposed a model that crystalline part of
natural rubber under large elongation is composed of two kinds of
crystallites from highly extended and loose chains. The situation is
caused by the microscopic distribution of extension ratio of the chains
between crosslink points.
Highly-purified
natural rubber by saponification of latex: Analysis of residual proteins
in saponified natural rubber
J.
Yunyongwattanakorn, Y. Tanaka, J. Sakdapipanich, V. Wongsasuthiukul
Rubber
Chemistry and Technology, 81 (1), 121-137 (2008)
Fresh
latex (FL-latex) and preserved high-ammonia latex (HA-latex) were
purified by saponification in the presence of surfactant to reduce the
residual proteins in resulting solid NR and hence to have a highly
purified natural rubber (NR). The latex was diluted to 30%DRC and
then saponification was carried out with 1-7% (w/v) sodium hydroxide at
room temperature for 1-7 hr at 70 oC. The latex was
later coagulated with formic acid. The nitrogen content of NR obtained by
coagulation of the saponified latex decreased to less than 0.014% by
centrifugation of the saponified latex or soaking the coagulum in aqueous
sodium hydroxide solution. The nitrogenous compounds from saponified NR
(SAP-NR) were extracted with sodium dodecyl sulphate (SDS) aqueous
solution and subjected to SDS-Polyacrylamide Gel Electrophoresis
(SDS-PAGE) analysis to check the molecular weight of extracts. Analysis
of allergic protein by FIT Kit method, based on Enzyme-Linked
Immunosorbent Assay (ELISA) method was also carried out for the extract from
SAP-NR in comparison with a deproteinized NR by protease (DPNR). It
was found that no extractable protein was observed in SAP-NR, whereas
DPNR contained 1.5 mu g/ml proteins. The results from SDS-PAGE analysis
and FIT Kit test demonstrated that NR free from allergic proteins is
obtainable by saponification of FL-latex with 1.5% NaOH at 70 oC
for 1 hr or at room temperature for 24 hr.
Effects
of coagulation processes on properties of epoxidized natural rubber
Z. Q. Zeng, H. P. Yu, Q. F. Wang, L.
Guang
Journal
of Applied Polymer Science, 109 (3), 1944-1949 (2008)
The
structures, processing performances, antioxidative behaviors, cure
characteristics, and dynamic mechanical properties of the epoxidized
natural rubber (ENR) with epoxy group contents of 48.4%, which was
coagulated with ethanol and steam, were analyzed using infrared
spectroscopy, rubber processing analyzer, thermogravimetric analyzer,
rheometer, and dynamic thermomechanical analyzer, respectively. The ENR
coagulated with ethanol (ENR-e) was found to exhibit a compact structure
and the contents of residual low-molecular-weight substances are higher
than those of unconsolidated ENR coagulated with steam (ENR-s).
These results in the poorer processing performance and antioxidative behavior
as well as the curing characteristics of ENR-e compared with those of
ENR-s. The ENR-s vulcanizate exhibits poorer mechanical properties
and wet skid resistance, but better heat build-up or rolling resistance
than those of ENR-e.
Energy
efficiency enhancement of natural rubber smoking process by flow
improvement using a CFD technique
P.
Tekasakul, M. Promtong
Applied
Energy, 85 (9), 878-895 (2008)
Computational
fluid dynamics (CFD) simulation has been applied to improve flow
uniformity and temperature variation in a natural rubber smoking-room for
a more efficient use of energy. The effects of the size, position
and number of gas supply ducts and ventilating lids which were at the
inlets and the outlets of the smoking-room were investigated. The optimal
rubber smoking-room of size 2.6 m x 6.2 m x 3.6 m contains 154 50
mm-diameter hot gas supply ducts, and four 0.25 x 0.25 m and four 0.25 x
0.20 m ventilating lids. The temperatures at 54 positions were monitored
and an average of 62.1 oC was recorded. By using this
model, the temperature variation could reduce by a factor of three from
the original room model, i.e., from 15 to 5.5 oC.
Furthermore, the heat input of an appropriate room model was finely
adjusted to obtain a suitable temperature (60 oC) for the
smoking process where the temperature variation was reduced to 5.3 oC.
An appropriate heat supply at this temperature was found to be 11
kW. The improved model should help the rubber smoking cooperatives
to achieve at least a 31.25% saving in energy.
Processing
characteristics and thermal stabilities of gel and sol of epoxidized
natural rubber
H. Yu, Z. Q. Zeng, G. Lu, Q. F. Wang
European
Polymer Journal, 44 (2), 453-464 (2008)
Gel
and sol of epoxidized natural rubber (ENR) were separated by using
organic solvents and then subjected to study for their processing
performances and aging behaviours by means of rubber processing analyzer
(RPA), thermogravimetric analysis (TGA) and difference FT-IR
method. The molar percentage of epoxy groups of gel is lower than
that of sol, since the gel with intermolecular ether structure is formed
by the ring-opening reactions of a part of epoxy groups during the
preparation and storage of ENR. The gel shows higher elastic moduli
to temperature and frequency responses, lower tan delta to frequency and
strain response and higher elastic torque to strain response as comparing
to those of sol. The formation of gel will therefore reduce
processing performance of ENR. The aging behaviours of gel and sol
were analyzed by different methods, and the differences of aging
conditions led to the different aging reactions and their degrees.
Compared to gel, the sol is easy to be crosslinked, leading to a higher
tan delta difference from the RPA analysis and it is also easy to be
oxidized into small molecules, leading to lower onset temperature and
apparent activation energy when being analyzed by TGA. However, the gel
shows more variations of functional groups than those of sol when
analyzed by difference FT-IR method. As the variations of molecular
structures have an influence on the mechanical properties of ENR, the
formations of gel during preparation and storage of ENR will reduce the
oxidative aging resistance of ENR.
Removal
of proteins from natural rubber with urea and its application to
continuous processes
Y.
Yamamoto, P. T. Nghia, W. Klinklai, T. Saito, S. Kawahara)
Journal
of Applied Polymer Science, 107 (4), 2329-2332 (2008)
Deproteinized
natural rubber (DPNR) was prepared in a batch process by the incubation
of the rubber latex with urea in the presence of sodium dodecyl
sulfate. The total nitrogen content of DPNR was decreased from 0.38
to 0.02 wt % after incubation for 10 min under suitable conditions; this
was similar to that of the rubber deproteinized with a proteolytic enzyme
for 12 h. To scale up DPNR preparation, continuous incubation and
centrifugation were individually investigated by the use of a
semicircular channel and a continuous centrifuge, respectively.
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Modification of Natural Rubber
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Modification of deproteinised natural rubber by
graft-copolymerisation of methyl methacrylate
N. H.
Yusof, S. Kawahara, M. M. Said
Journal
of Rubber Research, 11 (2), 97-110 (2008)
Deproteinised
Natural Rubber (DPNR) latex was prepared by incubation with urea in the
presence of sodium dodecyl sulfate (SD). The Urea deproteinised NR
(U-DPNR) latex was then graft-copolymerised with methyl methacrylate
(MMA) at a monomer feed of 5, 10, 15 and 20 wt % on rubber. The monomer
content, monomer conversion and grafting efficiency of the
copolymerisation reaction were investigated. The graft copolymers were
characterised by FT-IR spectroscopy and morphology observed using a
transmission electron microscope (TEM). In addition, the monomer content,
conversion and grafting efficiency of NR-g-PMMA, U-DPNR-g-PMMA and
E-DPNR-g-PMMA were compared. The suitable conditions to obtain high MMA
content, high conversion and high grafting efficiency were found when the
MMA feed of 15 wt % on rubber, initiator concentration of 6.6 x 10-5
mol/g-rubber and reaction temperature at 30 oC were
used. The highest grafting efficiency was about 80% at 15 wt % on
rubber feed of MMA for U-DPNR-g-PMMA and E-DPNR-g-PMMA.
Modification
of epoxidised natural rubber film surface by polymerisation of methyl
methacrylate
C.
Amornchaiyapitak, W. Taweepreda, P. Tangboriboonrat
European
Polymer Journal, 44 (6), 1782-1788 (2008)
The
film surface of epoxidised natural rubber (ENR) latex having 25% of
epoxide content was modified by immersing into methyl methacrylate (MMA)
emulsion and then alkaline aqueous solution of ferrous ion/fructose for
redox-initiated polymerisation. A percent conversion of MMA swelled
in ENR sheet was increased with increasing polymerisation time. The
presence of poly(methyl methacrylate) on the ENR surface was examined by
attenuated total reflection-Fourier transform infrared
spectroscopy. The nano-scale indentation experiment performed on
the cross-section of the modified ENR sheet revealed that the MMA
polymerization occurred mainly near the rubber's surface. The
friction coefficient of ENR surface was decreased as a result of a
pronounced roughness on the surface observed under scanning electron
microscopy and atomic force microscopy.
Effect
of grafted methyl methacrylate on the catalytic hydrogenation of natural
rubber
S.
Kongparakul, P. Prasassarakich, G. L. Rempel
European
Polymer Journal, 44 (6), 1915-1920 (2008)
The
graft copolymer of natural rubber and poly(methyl methacrylate) was
prepared by using a cumene hydroperoxide redox initiator. The graft
copolymer was purified by extraction and then hydrogenated in the
presence of OsHCl(CO)(O2)(PCY3)2. The
graft copolymer and hydrogenated product were characterized by proton
nuclear magnetic resonance (1H NMR). The hydrogenation rate
was investigated using a gas-uptake apparatus, and it was found that the
hydrogenation was inverse first-order with respect to rubber
concentration. The presence of a small amount of poly(methyl
methacrylate) demonstrated a beneficial effect on the hydrogenation of
the grafted copolymer.
Blends
of sulphur prevulcanised natural rubber latex and 2-(Dimethylamino) ethyl
methacrylate-grafted latex for improved static dissipative properties
K.
Vivayganathan, M. Asrul, M. Y. Amir-Hashim
Journal
of Rubber Research, 11 (1), 36-42 (2008)
This
work demonstrates an improvement in static dissipative properties of cast
films prepared from blends of natural rubber latex and 2-(Dimethylamino)
ethyl methacrylate (DMAEMA)-grafted NR latex. Various techniques: surface
resistivity measurements, contact angle and Fourier Transform
Infrared-Attenuated Total Reflectance (FTIR-ATR) were applied to
investigate the relative changes in surface properties of the cast films
prepared from latex blends. Providing that an appropriate blend
ratio of the DMAEMA-grafted NR latex and an effective amount of monomer
was used in the preparation of the grafted NR latex, the static
dissipative properties and surface related properties, such as surface
energy and wettability could be enhanced. Furthermore, differences
in the film surface properties, the air-facing and former-facing surfaces
are also described.
Morphology
and mechanical properties of natural rubber and styrene-grafted natural
rubber latex compounds
W.
Arayapranee, G. L. Rempel
Journal
of Applied Polymer Science, 109 (3), 1395-1402 (2008)
Styrene-grafted
natural rubber (styrene-GNR) latex was synthesized via emulsion
copolymerization using cumene hydroperoxide/tetraethylene pentamine as an
initiator. It was then mixed with natural rubber latex (NRL) with
various latex compounding contents and then prevulcanization was carried
out. The mechanical properties and heat, weathering, and ozone
resistance of NRL modified with styrene-GNR latex were investigated as a
function of the grafted NR content. At high content of styrene-GNR,
the tensile and tear strength were decreased, whereas Young's modulus and
hardness were increased. The resistance of the compounds to heat
and weathering ageing was also improved with an addition of
styrene-GNR. The ozone resistance of the compound containing
styrene-GNR is superior to that of the NR-rich compound. The results
indicated that NR/styrene-GNR latex compounds maintained good antiageing
properties required for outdoor applications. The SEM analysis of tensile
fracture surface confirmed a shift from ductility failure to brittle with
an increase of the styrene-GNR content in the compounds.
Hydrogenation
of natural rubber having epoxy group
P. T.
Nghia, H. Onoe, Y. Yamamoto, S. Kawahara S
Colloid
and Polymer Science, 286 (8-9), 993-998 (2008)
The
epoxidized deproteinized natural rubber (EDPNR) was prepared by
epoxidation of DPNR with peracetic acid in latex stage.
Hydrogenation of EDPNR was then performed with p-toluenesulfonylhydrazide
in p-xylene in order to introduce hydroxyl group to hydrogenated natural
rubber. The resulting hydrogenated EDPNR (HEDPNR) was characterized
by nuclear magnetic resonance spectroscopy with various pulse sequences,
i.e. two-dimensional correlation spectroscopy, two-dimensional
heteronuclear correlation measurements. Carbons linking up to hydroxyl
group were assigned to be quaternary and tertiary groups. The HEDPNR
displayed a characteristic of polyolefin elastomer through differential
scanning calorimetry.
Grafting
characterization of natural rubber latex particles: wet-STEM imaging
contributions
A.
Bogner, A. Guimaraes, R. C. O. Guimaraes, A. M. Santos, G. Thollet, P. H.
Jouneau, C. Gauthier Colloid and Polymer Science, 286 (8-9), 1049-1059,
(2008)
The
present article focuses on the grafting characterization of the modified
natural rubber latexes which have been chemically modified by seeded
emulsion polymerization using monomers with different water affinity (MMA
or DMAEMA). The expected result was the grafting of the
corresponding polymer inside or on the surface of the latex
particles. A recent imaging characterization mode called wet-STEM
which consists of transmission imaging in an Environmental SEM operating
in the wet-mode, allowing transmission observations of particles
suspended in a liquid layer with good resolution and contrast, was
applied in this work. A comparative characterization approach
between a non-grafted natural rubber latex and two grafted ones has been
adopted, and this approach contributes to highlight the particles
morphology resulting from chemical modification using either MMA or
DMAEMA. Transmission images in SEM of thin foils are relatively
well interpreted and are completed with wet-STEM images of latexes in
their native state, bringing important contributions for grafting
characterization.
Properties
of styrene-methyl methacrylate grafted DPNR latex at different monomer
concentrations
S. H.
C. Man, A. S. Hashim, H. M. Akil
Journal
of Applied Polymer Science, 109 (1), 9-15 (2008)
The
graft copolymerization of deproteinized natural rubber (DPNR) latex with
styrene and methyl methacrylate (MMA) was investigated. The effect of
monomer concentrations on grafting efficiency, thermal and mechanical
properties was studied. The graft copolymers were characterized by proton
nuclear magnetic resonance (1H NMR) and the highest grafting
efficiency was found at 20 wt % monomer concentration. It was found
that the grafting was not significant at low monomer concentration (10 wt
%) and the grafting efficiency was slightly decreased at 30 wt % monomer
concentration. The thermal properties of graft copolymers were
analyzed using differential scanning calorimeter (DSC) and thermal
gravimetric analysis (TGA). The increase of monomer concentration results
in an increase of the degradation temperature of the graft copolymer
indicating the improvement in thermal stability. The improvement in
miscibility between the components as the monomer concentration increased
was also observed from the DSC results. In term of the mechanical
properties of gum and filled modified NR, the tensile strength and
elongation at break decreased with an increase in monomer concentration
while tensile modulus increased as the monomer concentration
increased.
Mechanism
of graft copolymerization of styrene onto deproteinized natural rubber
N.
Pukkate, Y. Yamamoto, S. Kawahara
Colloid
and Polymer Science, 286 (4), 411-416 (2008)
This
work investigated the graft copolymerization of styrene onto
deproteinized natural rubber (DPNR) with respect to the molecular weight
of grafted polystyrene. The graft copolymerization was performed
using tert-butyl hydroperoxide/tetraethylenepentamine as an initiator
after deproteinization of natural rubber with urea. Grafted
polystyrene was subsequently isolated from the resulting graft copolymer
by ozonolysis reaction, and the molecular weight of grafted polystyrene
was determined by size exclusion chromatography. Effects of initiator and
monomer concentrations were investigated with respect to the molecular
weight of the grafted polystyrene, which was found to depend on not only
the number of active site generated on the rubber particle but also the
feed of styrene. It was found that deactivation and chain transfer
of the active sites influenced an effective amount of styrene used for
the graft copolymerization.
Grafting
of methyl methacrylate onto natural rubber in supercritical carbon
dioxide
S. Y.
Zhang, L. Q. Cao, F. Shao, L. P. Chen, J. Q. Jiao, W. Gao
Polymers
for Advanced Technologies, 19 (1), 54-59 (2008)
Attempts
were made to prepare the graft copolymer of natural rubber (NR) with
poly(methyl methacrylate by supercritical carbon dioxide (scCO2)
swelling polymerization with benzoyl peroxide (BPO) as an initiator. The
graft copolymer was characterized by Fourier transform-infrared
spectroscopy (FT-IR) and the formation of graft copolymers was confirmed
with the characteristic bands of symmetric C=O and C-O-C stretching vibrations
at 1728cm-1 and 1147cm-1, respectively. The effects
of the rubber-to-monomer ratio, amount of initiator, reaction time, and
pressure on the monomer grafting level (GL) and grafting efficiency (GE)
were investigated. The optimum conditions for the preparation of
NR-g-MMA were found to be 70:30 of the rubber-to-monomer ratio, 1.2% of
the initiator content, and the reaction pressure of 23 MPa for 6 h. The
thermal behavior of the NR and the grafted copolymers with different
NR/MMA molar ratios was studied by differential scanning calorimetry
(DSC). The tensile strength, modulus, elongation at break,
hardness, and oil resistance of graft copolymers were determined and
compared with the values of NR and that of graft copolymers prepared in
traditional toluene solution. The results showed that the tensile
strength, modulus, hardness and oil resistance were improved after
modification in scCO2.
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Processing and Treatment
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The effect of cure system on NR bonding
J.R. Halladay and F.J. Krakowski, Lord
Corpotation. Rubber World, December 1999, page 18-22.
This article continues the bond investigations
on the influence of sulphur and accelerator choices in natural rubber.
The authors came to the conclusion that there is no correlation between
the adhesion results obtained using two different adhesion test methods
(peel and buffer specimens), i.e., geometry affects the adhesion test
results. The peel test shows a strong correlation with both tear and
modulus; the buffer test shows no correlation. There is no difference
between solvent- and water based bonding systems. There is no absolute
trend to suggest that high-sulphur cures are easier to bond than
low-sulphur cures in natural rubber, also for peroxide cures. The use of
PVI does not inhibit the bonding of thiuram and sulphur cured NR. The
choice of the adhesive system has a greater impact on bond strength than
the choice of the cure system.
Blends of Natural Rubber, Novel techniques for
blending with speciality polymers.
Andrew J.Tinker and Kevin P. Jones. Chapman
& Hall, 1998, London. ISBN
0-412-81940-6.
The idea of blending synthetic rubbers with natural rubber is certainly
not a new one, but it is only now that this can be shown to be possible
with consistently positive results, by the use of new techniques
developed over the last five years. It are these new techniques which
this book describes, giving valuable information on the technology
required and the results which can be achieved.
Processing effects on NR aging characteristics
J. Shell, T. Wang, V. Vejins, Y. L.
Wong, Rubber World, Vol. 231, No. 2, p. 21-28
Demonstrates that latex-phase mixing of NR-compounds results in
improvement of ageing resistance and performance properties compared to
conventional dry mixed compounds.
Mold fouling during rubber
vulcanization
B. van Baarle, Rubber World, Vol. 231,
No. 3, p. 25-29+38
To prevent mold fouling the role of ZnO in rubber compounds has to be
diminished through reduction of its level or its replacement by nano-ZnO.
The approach through modification of the mold surface shows very
promising first results for magnetite coatings.
Effect analysis of mixing process
variables on viscoelastic properties of NR tread compounds
A. M. Marks, A. Adhikary, R.
Mukhopadhyay, Rubber World, Vol. 231, No. 2, p. 29-32+63
Factorial designs allow for the simultaneous study of the effects that
several factors may have on a process. This article shows that a
two-level fractional factorial design can be used as an effective tool in
screening rubber compound mixing processing variables having different
degrees of effects on viscoelastic behaviour.
Carbon black dispersion measurement in rubber
vulcanizates via interferometric microscopy
A. P. Smith, T. L. Aybar, R. W.
Magee, C. R. Herd, Rubber Chem.& Techn., Vol. 77, No. 4, p. 691-710
Surface roughness of razor cut samples of black-filled rubber compounds,
determined by interferometric microscopy, correlates to the carbon black
dispersion level in the measured compound.
Einmischen von Recyclat und seine Auswirkung auf
den bound rubber (Mixing-in of recyclate and its influences on bound
rubber)
K. Thiele, U. Winkler, GAK 12/2004,
p. 779-782
Investigation of the influence of recyclate on processing and mechanical
properties.
Controlled sulfur vulcanization
of NR
Keeping the vulcanizing chemicals in active in the rubber compound at the
mixing temperature by encapsulation in a (polymer) particle may be a
possibility to circumvent the problem of premature crosslinking.
Possibilities are one-component room temperature vulcanization systems or
systems that vulcanize on demand. Upon applying a suitable trigger,
like an increase in temperature, the encapsulated chemical(s) can be
released from the microspheres, enabling instantaneous crosslinking.
A new series of Natural Rubber and Processing
will be published in GAK (Gummi, Fasern und Kunststoffe)
Prof. Dr. Jorgen Schnetger
“Die Geschichte des
Kautschuks und siene Verarbeitung”
Teil 1: Naturkautschuk
Teil 2: Synthetic rubber
The paper(s) doesn’t give fundamental news to those who work with
the matter since long; however it is dedicated to the young people,
who always cone into this sticky business.
Teil 3: Processing and Inspection
This paper continues the series on rubber processing.
Tensile
properties of vulcanized field natural rubber latex by electron beam
C. C. Keong, S. H. Ahmad, W. M. W. Zin
Sains
Malaysiana, 37 (1), 79-84 (2008)
This
work aims to develop an electron beam vulcanization of natural rubber
latex as an alternative to the conventional sulphur vulcanization method.
The effects of electron beam dose, beam current and centrifugation to the
tensile properties of field natural rubber latex were determined.
Irradiation dose and beam current ranged from 50 to 300kGy and 1 to 15 mA
respectively. The tensile properties of cast film prepared from irradiated
field latex before and after centrifugation were investigated. The
tensile properties were found to increase with radiation dose but
decrease with beam current. Rubber films made from centrifuged irradiated
field latex were softer and showed higher tensile strength.
A
study of heat transfer during molding of elastomers
B.
Likozar, M. Krajnc
Chemical
Engineering Science, 63 (12), 3181-3192 (2008)
Heat
transfer in several elastomers, including natural rubber, polybutadiene,
hydrogenated butadiene-acrylonitrile copolymer, poly-chloroprene and
polyisoprene, was studied on a pilot scale mold utilizing various
expressions for description of temperature dependent elastomer densities,
heat capacities and thermal conductivities, which were applied in the
governing heat equation. The latter was solved by means of quasi-exact
and explicit finite difference algorithms. The molding experiments
were applied for determination of the temperature dependent thermal
conductivities, whereas the temperature dependent densities and heat
capacities were determined separately using pycnometry and differential
dynamic calorimetry, respectively. The experimental and the predicted
temperatures were in good agreement throughout the temperature range
between 20 and 200 oC. Moreover, the determined parameters of
the temperature dependent thermodynamic quantities may be correlated to
the parameters of other, non-elastomeric polymers. The developed model
along with its determined parameters may be readily applied for a wide
range of elastomers and processing operating conditions or even combined
with other aspects of a certain operation, such as kinetics or
mechanics.
Continuous
ultrasonic devulcanization comparison of carbon black filled synthetic
isoprene and natural rubbers
X. M.
Sun, A. I. Isayev
Rubber
Chemistry and Technology, 81 (1), 19-46 (2008)
Continuous
ultrasonic devulcanization of carbon black (CB) filled isoprene rubber (IR)
was carried out, and it was found that power consumption during the
devulcanization of the filled IR increased with the increase of
ultrasonic amplitude indicating a greater extent of
devulcanization. This behaviour is similar to that of unfilled IR,
but in contrast with the devulcanization of CB filled natural rubber (NR)
where power consumption showed a maximum at an intermediate amplitude
suggesting a lesser extent of devulcanization at higher amplitude.
Gel fraction and crosslink density of the virgin vulcanizates,
devulcanizates and revulcanizates were characterized. In addition,
kinetics of revulcanization, rheological properties of the devulcanizates
and mechanical properties of revulcanizates were compared with those of
virgin uncured IR and their vulcanizates. The addition of processing oil
resulted in a slight delay of the vulcanization and lower torque without
affecting the degree of reversion. The oil caused more
devulcanization as indicated by an increase in the ultrasonic power consumption
and a reduction of the gel fraction and crosslink density of devulcanized
rubbers. The revulcanization of the IR occurred without the induction
period, regardless of the presence of CB and processing oil. The
use of retarder in the recipe was effective in improving the scorch
safety and minimizing the reversion in revulcanization. It was
found that the experimental data on normalized gel fraction versus
crosslink density of filled IR and NR at low CB loadings fell into the
master curve, which is probably determined by the main chain structure of
both rubbers consisting of cis-1, 4 isoprene.
Study
of natural rubber crosslinked in the state of uniaxial deformation
I.
Dubrovic, D. Klepac, S. Valic, G. Zauhar
Radiation
Physics and Chemistry, 77 (6), 811-817 (2008)
The
amount of gel and sol phase of natural rubber (NR) in the 1 mm thick NR
films crosslinked by gamma-irradiation in the relaxed state and in the
state of uniaxial deformation were comparatively investigated. The
total irradiation dose varied from 0 kGy (for non-irradiated NR) to 400
kGy and the degree of deformation, defined as lambda = l/l0 (l0
and l being the lengths of relaxed and uniaxially deformed sample,
respectively) varied at lambda = 1.0 (relaxed state), lambda = 1.5 and lambda
= 2.0. The amount of sol and gel phase of NR was determined by extracting
the sol component in toluene. Increasing the irradiation dose resulted in
a significant decrease in the amount of the sol component (from 14.2% to
33.5%, depending on irradiation dose). It was found that the application
of deformation during the crosslinking leads to the lower crosslink
density which is attributed to the loss of the gel component induced
mechanically. The electron spin resonance (ESR) spectra of spin probe diffusing
in the NR matrix crosslinked under deformation are influenced by both,
the local dynamics of the chain segments and their spacious orientation.
The
mastication characteristics of powdered carbon black filled natural
rubber during internal mixing
A. Q. Zhang, Y. L. Lin, L. S. Wang
Polymer
Engineering and Science, 48 (4), 815-822 (2008)
This
work aims to study a powdered carbon black filled natural rubber or
called P(NR/HAF) which is a premixture of natural rubber and carbon black
in powdered form with good carbon black dispersion throughout the rubber
matrix. The mastication properties of P(NR/HAF) were investigated
under a temperature range of 50-110 oC and rotor speed of
30-100 rpm, using a mixing head attached to Brabender Plasticorder.
The P(NR/HAF) showed different mastication characteristic when compared
with the traditional internal mastication theories of natural
rubber. Poor masticating properties of P(NR/HAF) are observed with
low rotor speed and high temperature and a "stable zone" with
middle rotor speed and lower temperature. It was considered that
the higher temperature build-up of the mixing batch of P(NR/HAF) during
the early stage of internal mixing results in the special mastication
properties. A quadratic mastication model of P(NR/HAF), based on the
multivariate regression analysis and stepwise regression analysis, was
used to predict the mastication characters of P(NR/HAF) in internal mixer
under varied temperature and rotor speed.
Surface
modification of natural rubber by TiO2 film
M. Jin, X. Zhang, A. V. Emeline, T. Numata, T.
Murakami, A. Fujishima
Surface
& Coating Technology, 202 (8), 1364-1370 (2008)
Attempts
were made to deposit a titanium dioxide (TiO2) layer on a
natural rubber (NR) substrate through liquid phase deposition (LPD)
method, for a possible application such as the anti-aging layer of
NR. Thin SiO2 layer serving as intermediate layer
between TiO2 and NR, was produced through vapor-phase
chemisorption followed by UV/ozone treatment. This stepwise modification
process was monitored by FT-IR spectroscopy, water contact angles and
scanning electron microscopy (SEM) techniques. The formed TiO2
layer was characterized by UV-visible spectra, XRD, and EDX spectra, and
it demonstrates photocatalytic and photoinduced hydrophilic conversion
properties.
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Rubber
vulcanizates degradation and stabilization
R.N. Datta, et al. Teijn Twaron BV, Westervoortsedijk
73, 6800 TC Arnhem. The Netherlands and A.G. Talma, Akzo Nobel
Polymer Chemicals, Zutphenseweg 10, 7418 AJ Deventer, The Netherland. Rubber Chemistry and Technology, Volume 80 number 3, 2007
Degradation of rubber vulcanizates in the presence and absence of
air as in presence of ozone is reviewed in this paper. The paper also
outlines the means to overcome this undesirable phenomenon.
Stabilization of tyre compounds with QDI
F. Ignats-Hoover, Flexsys America and R. Datta, Flexsys
NV. Rubber World, August 2000, page 43 -
46.
Protecting vulcanizates, based on NR or NR
blends, with quinonediimine antidegradants provides protection similar to
that achieved with conventional PPD antidegradants. In an oxidative
environment, reversion is reduced when compounds are protected with QDI
antidegradants. Dynamic mechanical proper-ties are maintained better with
quinone-diimine antidegradants compared to PPDs due to a reduction in
reversion chemistry upon aging.
Some aspects on the crosslink reaction of
natural rubber with dipentamethylene thiuram tetrasulfide
L. González et.al. Instituto de Ciena y
Technología de Polímeros (CSIC) Madrid, Spain. Rubber Chemistry and
Technology, March-April 2000, Vol.73. Number 1, page 89 - 100.
The mechanism of vulcanization of natural rubber
with the sulfurating agent dipentamethylene thiuram tetrasulfide was
studied. On the transformation from crosslink precursor to crosslink, the
route via disproportionation is preferred. In the presence or absence of
zinc oxide and stearic acid as activators, the formation of the crosslink
precursor follows similar processes, while the main difference is in the
reaction induction times. In addition, the desulfuration reaction was
favored by the presence of zinc oxide.
Advances in Precipitated Silicas for Passenger
and Truck Tyre Treads.
Timothy A. Okel et al. PPG Industries Inc. Paper
presented at Tyre Tech 1998.
For the all-natural rubber low rolling resistance truck tread formulation
at a constant level of accelerator(s), increasing silica surface area or
increasing the loading of silica significantly reduces the cure-related
compound physical properties. Therefore, with the appropriate level of
accelerator to compensate for the surface area and the loading of silica,
the perturbation of the cure system due to the reactive nature of the
silica relative to carbon black is overcome allowing a reduction in the
level of silane required to achieve the disired balance of cure-ralated
properties.
For this natural rubber-based tread formulation, no significant effect of
either silica loading or level of silane on Mooney viscosity was found at
the levels studied.
Cure system and carbon black effects on NR
compound performance in truck tires
Bin Ching, et al. Cheng Shin rubber
USA/Maxxis International, and Hung-yu, Chin-fang and Wally Chen, Cheng
Shin Rubber. Rubber World, November 2002.
The influence of the cure system on Natural Rubber properties were
investigated. The results are based on the consistent trends observed from
this study on NR compound performance with different carbon black types
and loadings.
Reinforcement of Natural Rubber Latex by
nanosize montmorillonite clay
R. Tantathertdtam, Thesis in Material
Science and Engineering. The PennsylvaniaStateUniversity.TheGraduateSchool.
Based on the unique character of montmorillonite namely its layer
structure and the ability of silicate particles to separate into
nanometer-size platelets, natural rubber / clay composites were obtained
by mixing latex with clay-water dispersion and coagulate the mixture. The
resulting film had greatly improved mechanical properties compared with
films using micron-sized fillers. The observed considerable improvement
in mechanical properties, coupled with a theoretic model suggests a dispersed
structure of clay in the composite.
Compounding and manufacture of thin-wall latex
products
Ray Rusel-Fell, Retired Rubber
technologist. Latex 2004 Conference, Hamburg,
Germany.
Chemical
aspects of raw latex concentrate Lots need equal consideration with
mechanical stability, and a numerically-quantifiable method of chemical
stability measurement outlined. Choice and preparation of compounding
ingredients, and heat versus room-temperature pre-vulcanisation of NRL
compounds is discussed. Benefits of statistical process control are also
discussed. Effects of different, final process methods on skin-contact
products’ Type I & Type IV allergenic potential are discussed.
QDI antidegradant for cost saving, productivity
in various grades of NR
F. Ignatz-Hoover, B. H. To, Rubber
World, Vol. 230, No. 5, p. 22-28
Demonstrates that Quinonediimine antidegradant (QDI) can reduce mix times
up to 25%.
Ozone attack and tire sidewall protection
A. Adhikary, R. Mukhopadhyay, Rubber
World, Vol. 230, No. 6, p. 16-20
Reviews the protection of tires against ozone in relation to higher
performance needs and rising ozone concentrations in the atmosphere.
Activators in accelerated sulfur vulcanization
G. Heideman, R. N. Datta, J.W.M.
Noordermeer, B. van Baarle, Rubber Chem.& Techn., Vol. 77, No. 3, p.
512-541
In conventional rubber compounding ZnO is difficult to substitute.
Reduction of ZnO levels would only be possible with different
activator/accelerator systems.
Non-carcinogenic tire extender oils providing
good dynamic performance.
Marika Joona, Nynas Naphthenics AB.
Rubber World, Vol. 235 No.4, January 2007
Non-carcinogenic mineral oil based plasticizers and extender oils are
utilized more and more in rubber and tire compounds. The interest is
driven by health and environmental consciousness, as well as the coming
European Union legislation prohibiting the use of high-aromatic tire
extender oils. Highly refined naphthenic oils comply with the set health
and safety criteria and are, considering their chemistry, one of the best
alternatives when it cones to compatibility with the common polymers. By
taking into account certain characteristics features when choosing the
plasticizer of extender oil, it is possible to find a safe product that
performs in a similar manner as the high aromatic oils, not only when it
comes to physical and mechanical characteristics, but also the dynamic
properties.
Controlled sulfur vulcanization of natural
rubber
R. Heijkants and A. Boersma. TNO
Science and Industry (DPI). B .van Baarle TNO Science and Industry,
Innovative Materials and M.van Duin, DSM Research. Rubber World, Vol. 235
No. 2. November 2007
Most of the rubber product currently applied consists of mixtures of
polymers, fillers, plasticizers, crosslinking agents and corresponding
accelerators that require a specific heat treatment in order to obtain
the desired properties. Keeping the vulcanizing chemicals inactive at the
mixing temperature by encapsulation them in a (polymer) particle be a
possibility to circumvent the problem of premature crosslinking. This
article describes different methods and gives some results for
encapsulation.
A study on the Use of Coconut Oil as Plasticiser
in Natural Rubber Compounds
Raju, et al. Dept of Polymer Science
and Rubber technology, Cochin University of Science ant Technology,
Kochi, Kerala, India. Journal of Rubber Research, Volume 10(1), 1st
Quarter 2007
Mechanical properties and thermal degradation was studied of natural
rubber compounds containing coconut oil were compared with that of a
control compound containing naphthenic oil. Mechanical properties were
better than naphthenic oil-based compounds. Physical properties were
marginally inferior but thermal studies show an increase in the thermal
degradation temperature.
Studies
on a new binary accelerator system in sulfur vulcanization of natural
rubber
C. V.
Marykutty, E. J. Mathew, S. Thomas
KGK-Kautschuk
Gummi Kunststoffe, 61 (7-8), 383-389 (2008)
Natural
rubber (NR) was sulphur cured with N-cyclohexyl benzothiazyl sulphenamide
(CBS) in the presence of 1-phenyl 5-(o, p, m) tolyl derivatives of 2,4
dithiobiurets (o-DTB, p-DTB and m-DTB) as secondary accelerators. These
binary accelerator systems could reduce the optimum vulcanization time and
the vulcanizates containing DTB showed an increase in tensile properties.
These vulcanizates also showed better retention of tensile properties
after ageing. This binary systems also show a beneficially to
hardness, compression set, heat build up, resilience and tear strength.
The concentration of crosslinks and the relative proportions of different
types of crosslinks were determined. An optimum concentration is
suggested for this new system based on the processing, mechanical and
chemical characterization.
Novel
blocked mercaptosilane (3-propionylthio-1-propyltrimethoxylsilane) for
natural rubber/silica composite reinforcement in various curing systems
H.
Peng, L. Liu, Y. F. Luo, D. M. Jia, W. W. Fu
E-Polymers,
article no. 104 (2008)
The
work reports the effect of novel blocked mercaptosilane(3-propionylthio-
1-propyltrimethoxylsilane) (PXT) on structure and dynamic mechanical
properties of natural rubber/silica (NR/silica) composites. The compounds
were vulcanized using efficient, semi-efficient and conventional
vulcanization systems. The crosslink density of composites determined by
equilibrium swelling method was enhanced by the use of PXT.
In addition, PXT was reported to enhance the strength,
resistance to flex cracking and abrasion of NR/silica composites.
The PXT possess two functionally active end groups which can chemically
react with both silica and rubber. The optimum comprehensive
dynamic mechanical properties of NR/silica composites were obtained when
2 phr of the PXT was used.
Synthesis
of polyisoprene-grafted silicas by free radical photopolymerisation of
isoprene initiated from silica surface
D. Derouet, C. N. H. Thuc
Journal
of Rubber Research, 11 (2), 78-96 (2008)
The
use of synthetic silicas as fillers for hydrophobic rubbers (synthetic
polydienes, natural rubber) requires a silane-coupling agent in order to
bind the silica to the rubbers and to prevent it from interfering with
the reaction mechanism of the sulphur-cure system. This work reports a
synthesis of polyisoprene-grafted silicas in order to improve the
interphase strengths between silica and hydrophobic rubbers as well as to
suppress the effects of silanol groups on sulphur-cured systems.
The principle of the synthesis was based on the "living"
radical photopolymerisation initiated from the silica surface, and a
two-step procedure was adopted. First, silica particles were
functionalised with N,N-diethyldithiocarbamate iniferter groups, by using
a SN2 substitution of chlorine atoms previously bound on silica surface.
Then, photopolymerisation of isoprene was carried out from the N,
N-diethyldithiocarbamate iniferter groups. The polymerisation
progress was simultaneously followed by HPLC and NMR, and functionalised
silicas as well as polyisoprene-grafted silicas were characterised by
solid-state C-13 and Si-29 CP/MAS NMR.
Amidino
phenyl thiourea as a secondary accelerator for the vulcanisation of
natural rubber - Polychloroprene blends
A. P.
Susamma, A. M. Mini, A. P. Kuriakose
Journal
of Rubber Research, 11 (2), 111-123 (2008)
Thiourea
(TU) and its derivatives are widely used in CR and NR latex
vulcanisation. It is well-known that ethylene thiourea (NA22), the
conventional accelerator used in CR vulcanisation is toxic in nature.
This work reports a use of synthesized non-toxic thiourea derivative viz.
N-amidino-N'-phenyl thiourea (APT) as a secondary accelerator for the
vulcanisation of NR-CR blends. The unfilled and filled blend compounds
with varying concentrations of APT along with tetramethyl thiuram
disulphide (TMTD) and other compounding ingredients were prepared.
TMTD-TU and TMTD-NA22 binary combinations were taken as controls. Cure
characteristics and various physical properties of the experimental and
control systems were investigated. It was found that APT could be
advantageously used as a secondary accelerator along with TMTD. The
vulcanisates with this APT accelerator showed better/comparable tensile
and other physical properties when compared with the reference
formulations.
Reinforcement
of maleated natural rubber by precipitated silica
K.
Sahakaro, S. Beraheng
Journal
of Applied Polymer Science, 109 (6), 3839-3848 (2008)
Maleated
natural rubber (MNRs) or graft copolymers of maleic anhydride and natural
rubber were prepared in a molten state with varying maleic anhydride
contents from 4 to 10 phr, in order to be used to investigate the
filler-filler and filler-rubber interactions of the MNR and precipitated
silica. The MNR compounds with 40 phr of silica were prepared, both with
and without 9 wt % of silane coupling agent. Increasing the maleic
anhydride contents resulted in an increase of Mooney viscosity and cure
time, but a decrease of torque difference and cure rate index. Bound
rubber was found to increase with increasing maleic anhydride content
which indicates an increase of filler-rubber interaction. For the
compounds without silane, the use of MNR with 6 phr of maleic anhydride
gave the lowest filler-filler interaction. This indicates by a
decrease of storage modulus upon an increase of strain in the filled
compound i.e., Payne effect. This MNR compound also showed the
optimum mechanical properties. This work demonstrated that the use
of MNR with suitable maleic anhydride content could dramatically reduce
the filler-filler interaction and hence improve silica dispersion,
resulting in an enhancement of the mechanical and dynamical properties.
The improved silica dispersion was confirmed by SEM
micrographs.
Effects
of cyclohexylamine modified silica on the mechanical properties of filled
natural rubber
J. W. Liu, C. F. Wu, P. Zhang, S. G. Zhao
Journal
of Macromolecular Science Part B-Physics, 47 (4), 689-700
(2008)
Modification
of silica surface by using a basic cyclohexylamine (CA) solution in order
to optimize the mechanical properties of filled natural rubber was
investigated in this work. The modification was confirmed by FT-IR,
TGA and XPS analysis. The use of CA modified silica showed the
improved mechanical properties of the filled natural rubber when compared
with the use of pure silica. From the DMA results, the filled
compounds with the CA modified silica also showed a decrease of tan delta
values at 60 degrees C and 90 degrees C which corresponds to a lower
rolling resistance and heat generation of the filled natural rubber
vulcanizates. The improvement in properties was attributed to a
high cross linking density and a good dispersion of the modified silica
in rubber.
Comparing
effects of silanized silica nanofiller on the crosslinking and mechanical
properties of natural rubber and synthetic polyisoprene
S.
Ostad-Movahed, K. A. Yasin, A. Ansarifar, M. Song, S. Hameed
Journal
of Applied Polymer Science, 109 (2), 869-881 (2008)
The
effect of the precipitated silica nanofiller on the curing and mechanical
properties of natural rubber and synthetic polyisoprene was investigated.
The silica surfaces were pretreated with bis(3-triethoxysilylpropyl)
tetrasulfide (TESPT) and the rubbers were primarily cured by using sulfur
in TESPT. The cure was optimized by the addition of accelerator and
activator which helped to form sulfur chemical bonds between the filler
and rubber. Different amounts of accelerator and activator were required
to fully crosslink the filled rubbers. The incorporation of the
filler in the rubber resulted in the improved hardness, tensile strength,
elongation at break, stored energy density at break, tearing energy, and
modulus of the vulcanizates. This was attributed to a formation of
chemical bonds between the rubber and TESPT, and the improved
rubber-filler adhesion. It was found that natural rubber benefited more
from the filler than did synthetic polyisoprene.
Silica-reinforced
natural rubber prepared by the sol-gel process of ethoxysilanes in rubber
latex
V.
Tangpasuthadol, A. Intasiri, D. Nuntivanich, N. Niyompanich, S.
Kiatkamjornwong
Journal
of Applied Polymer Scienc, 109 (1), 424-433 (2008)
The
silica was generated in situ inside the rubber by the sol-gel
process of tetraethoxysilane (TEOS) which was mixed directly into
commercial-graded NR latex having 60% dry rubber content and 0.7%
ammonia. The conversions of TEOS to silica inside the rubber were ranging
from 90 to 97%. The SEM micrographs demonstrated that silica particles
were dispersed evenly without extensive aggregation with sizes between
100 and 500 nm. This work employed an experimental design
methodology, namely "two-level factorial design," to evaluate
the influence of the amounts of TEOS, ammonia, and gelation time on the
tensile modulus, tensile strength, and tear strength of the vulcanizates.
The mechanical properties were significantly affected by the amount of
TEOS added into the latex. Ammonia in the amount of 0.7% (w/w) present in
the commercial latex was found to be sufficient for the conversion
reaction of TEOS to silica. An addition of
bis-(3-triethoxysilylpropyl)tetrasulfide or TESPT with TEOS in a process
of silica-filled composite preparartion resulted in an increase of the
mechanical properties and the sulfur cure rate.
Effect
of silica reinforcement on natural rubber and butadiene rubber
vulcanizates by a sol-gel reaction with tetraethoxysilane
K. H.
Chung
Journal
of Applied Polymer Science, 108 (6), 3952-3959 (2008)
Natural
rubber (NR) and butadiene rubber (BR) vulcanizates were reinforced with
silica formed in situ in the rubber by a sol-gel reaction of
tetraethoxysilane at different temperatures. The formation of silica was
investigated analytically with Fourier transform infrared spectroscopy
and energy-dispersive X-ray analysis. The effects of silica filling on
the mechanical and dynamic properties of the NR and BR vulcanizates were
investigated. The silica filled rubber vulcanizates showed an increase of
hardness and the moduli at 50, 100, and 300% elongation, but a decrease
of tensile strength and elongation at break. The storage modulus of
silica-filled rubber vulcanizates was higher when compared with that of
pure rubber vulcanizates.
Synthesis
of silica in natural rubber solution via sol-gel reaction
S.
Poompradub, B. Chaichua, C. Kanchanaamporn, T. Boosalee, P.
Prasassarakich
KGK-Kautschuk
Gummi Kunststoffe, 61 (4), 152-155 (2008)
The in
situ silica was generated in natural rubber by sol-gel reaction using
tetraethoxysilane (TEOS) as the precursor for silica generation. The
effects of solvent, catalyst type and concentration, mole ratio of
tetraethoxysilane (TEOS) to water, and reaction temperature on in situ
silica formation were investigated. The base catalysts used were
N-butylamine and n-hexylamine. At optimum conditions, 41% in
situ silica was obtained for sol-gel reaction.
Preparation
and characterization of the natural rubber composites reinforced by epoxy
natural rubber grafted silica with good dispersibility
J. Liu, H. Xu, C. Wu
Acta
Polymerica Sinica, 2, 123-128 (2008) (This article is
written in Chinese)
Silica
was grafted with epoxidized natural rubber (ENR) in order to improve its
hydrophobic and dispersibility in rubber matrix. The silica and ENR
were blended in Haake internal mixer at high temperature (170 oC),
resulting in the grafted silica made through in-situ grafting reaction
between the hydroxyl groups of silica and the epoxy groups of ENR.
The weight proportions between silica and ENR were chosen to be 1: 1, 2:
1 and 3: 1 separately in this study. The ENR was mixed in the internal
mixer about 1 min, then pre-dried silica was added to react with the ENR
for another 15 min before discharged. The ENR-grafted silica was
characterized via FTIR, TGA and TEM analysis. The appropriate
proportion between silica and ENR at 3: 1 was found to give the optimum
reinforcement effect. The properties of NR filled with grafted
silica were investigated in comparison with those of rubber filled with
unmodified silica. The use of ENR grafted silica resulted in a
reduction of the silica-silica interaction, i.e. Payne effect, so the
grafted silica had better dispersibility in natural rubber (NR).
The mechanical properties of NR composites with the grafted silica were
also improved.
Rare
earth compounds modified carbon black filled powdered natural rubber: Preparation,
morphology and properties
Y. L. Lin, A. Q. Zhang, L. S. Wang
Journal
of Applied Polymer Science, 108 (3), 1393-1401 (2008)
High
abrasion furnace (HAF) black was modified with ten types of rare earth
(RE) compounds using chemical-deposit method. The HAF-RE were mixed
with natural rubber latex to prepare HAF-RE filled powdered natural
rubber [P(NR/HAF-RE)] by a carbon black/rubber latex coagulation
method. The results revealed that most of the P(NR/HAF-RE)
vulcanizates showed better mechanical properties, especially higher
tensile modulus, and tensile strength, compared with none-rare earth
modified carbon black filled powdered natural rubber [P(NR/HAF)].
Further investigation was carried out using Dysprosium (Dy) modified
carbon black (HAF-Dy) filled powdered natural rubber
[P(NR/HAF-Dy)]. The addition of Dy compound could help to get
smaller particles with narrower particle size distribution, of carbon
black. The SEM analysis showed that carbon black has been dispersed
in rubber matrix uniformly with diameter of 50-150 nm and the TEM
analysis showed that Dy compounds could obviously reduce the aggregation
of primary particles of carbon black, and promote the dispersion of
carbon black in P(NR/HAF-Dy) particles.
Synthesis
and aging properties of reactive antioxidant NAPM in natural rubber
vulcanizates
Y. Lu, J. Yang, D. Yin, M. Tan, J. Wang
Journal
of Applied Polymer Science, 108 (1), 576-582 (2008)
The
antioxidant N-(4-anilinophenyl) methacrylamide (NAPM) was synthesized by
a two-step reaction using thionyl chloride (SOCl2) with
methacrylic acid (MAA) and consequently 4-aminodiphenylamine (ADPA) as
precursors. The resulting product was characterized by IR, 1H
NMR and elemental analysis. Thermal stability, aging property of NAPM and
mechanical properties of natural rubber (NR) vulcanizates containing NAPM
were investigated and compared with two other commercial antioxidants
N-isopropyl-N'-phenyl-p-phenylene diamide (4010NA) and N-(1, 3-dimethyl
butyl)-N'-phenyl-p-pheny1ene diamide (4020). The NAPM was found to
be an effective antioxidant with a better thermal stability and higher
antiaging resistance than 4010NA and 4020. It was also found that an
unsaturation level of NR vulcanizates containing NAPM was lower than that
of 4010NA and 4020. An antiaging resistant mechanism of a surface
reaction between NAPM and cis-1, 4-polyisoprene in NR was proposed based
on the IR and SEM analyses.
Organomodified
kaolin as a reinforcing filler for natural rubber
R.
Sukumar, A. R. R. Menon
Journal
of Applied Polymer Science, 107 (6), 3476-3483 (2008)
China
clay (kaolin) has been modified with sodium salt of rubber seed oil
(SRSO) and characterized using X-ray diffraction (XRD), infrared
spectroscopy (FTIR), and differential thermal analysis (DTA). XRD of
SRSO-modified kaolins showed an increase in the d-(001) spacing of kaolin
platelets from 7.15 to 14 when compared with the unmodified one.
FTIR spectra indicated possible grafting of the organic moiety of
rubber seed oil (RSO) onto the clay surface, and DTA results of the
SRSO-modified kaolin indicated that the SRSO is more strongly bound in a
constraint environment within the lamellae of kaolin. Natural rubber (NR)
compound filled with 10 phr of SRSO-modified kaolin showed a shorter cure
time when compared with that of a similar compound containing unmodified
kaolin. In addition, the vulcanizates with SRSO-modified kaolin
showed considerable increase in modulus, tensile strength, and elongation
at break indicating its potential as an organomodified nanofiller.
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Blends and Thermoplastic Vulcanizates
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Characterization
of natural rubber latex/chitosan blends
J.
Johns, V. Rao
International
Journal of Polymer Analysis and Characterization, 13 (4), 280-291 (2008)
Attempts
were made to prepare biodegradable materials based on blends of natural rubber
latex/chitosan (NR/CS) containing different compositions. The
blends were prepared by solution casting followed by compression, and
then characterized by thermogravimetry, Fourier transform-infrared
spectroscopy (FT-IR), X-ray diffraction, and scanning electron microscopy
(SEM) techniques. Thermal stability of the blends containing different
percentages of natural rubber latex and the water absorption of the
blends were investigated. The percentage of bound rubber content and
fraction of rubber dissolved in benzene was also determined. The IR
spectrum indicates that better interfacial adhesion between chitosan and
natural rubber is achieved in the blend NR95/CS5. Moreover, X-ray
diffraction study shows that the addition of chitosan resulted in a decrease
in crystallinity in natural rubber.
Electrically conductive
epoxidised natural rubber-polyaniline dodecylbenzenesulfonate blends
prepared by solution mixing
K. C.
Yong, P. J. S. Foot, H. Morgan, S. Cook, A. J. Tinker, M. A.
Ahmad
Journal
of Rubber Research, 11 (2), 59-77 (2008)
Based
on simple solubility parameter calculations, epoxidised natural rubber
(ENR) and polyaniline dodecylbenzenesulfonate (PAni.DBSA) were predicted
to be miscible. Blends with electrical conductivities zip to 10-3S.cm-1
were prepared by solution mixing, and the lowest estimated electrical
conductivity percolation threshold was 2.9 wt% or 2.5 volume% of added
PAni.DBSA. Based on NMR result, an increase of PAni.DBSA loading
decreased the epoxide level of the ENR due to the sensitive nature of ENR
to acidic conditions. This decrease indicates a ring opening in the
ENR molecular structure. An increase of absorption value of FT-IR
peaks in the region of 3390 cm-1 and a result obtained by
differential scanning calorimetry (DSC) also indicate the ring opening of
ENR. However, the ring opening was not found to affect the
electrical properties of the blends.
Influences
of blend compatibilizers on dynamic, mechanical, and morphological
properties of dynamically cured maleated natural rubber and high-density
polyethylene blends
S.
Pichaiyut, C. Nakason, A. Kaesaman, S. Kiatkamjornwong
Polymer
Testing, 27 (5), 566-580 (2008)
Influences
of various types and loadings of blend compatibilizers on properties of
thermoplastic vulcanizates (TPVs) based on maleated natural
rubber/high-density polyethylene (MNR/HDPE) were investigated.
Addition of compatibilizers enhanced the mechanical and dynamic
properties of the TPVs. The phenolic modified polyethylene
compatibilizers (i.e., PhSP-PE and PhHRJ-PE) showed a better
compatibilizing effect than HDPE-g-MA. Among the three types of
compatibilizer investigated, the TPVs with PhHRJ-PE exhibited the best
mechanical and dynamic properties. The smallest dispersed
vulcanized rubber domains in the HDPE matrix were also observed. By
varying loading amounts of PhHRJ-PE, the best overall properties were
achieved when a loading amount of 5 wt% was
used.
Thermoplastic
natural rubber based on oil extended NR and HDPE blends: Blend
compatibilizer, phase inversion composition and mechanical properties
W.
Pechurai, C. Nakason, K. Sahakaro
Polymer
Testing, 27 (5), 621-631 (2008)
The oil
extended natural rubber (OENR) and HDPE blends at various blend ratios
(i.e., OENR/HDPE = 0/100, 20/80, 30/70, 40/60, 50/50, 60/40, 70130, 80/20
and 100/0) were prepared by a melt mixing process at 160 oC.
Effect of phenolic modified polyethylene (PhHRJ-PE) as blend
compatibilizer and proportions of OENR/HDPE in the blends on rheological,
tensile, morphological and hardness properties were investigated.
The blend containing compatibilizer exhibited higher flow and viscosity
curves as well as mechanical properties. SEM micrographs and
rheological properties indicated that the blends of OENR/HDPE are
two-phase systems in which the lower proportion component was found to be
a dispersed phase in the major continuous matrix phase. The 50/50
and 60/40 OENR/HDPE blends were found to have co-continuous phase
morphology where the materials behave as thermoplastic elastomers.
The experimental results were in agreement with the phase inversion
composition predicted by using various models. The blend
proportions have a profound effect on tensile strength, elongation at
break, tension set and hardness properties of the blends.
Spectroscopic
analysis and mechanical properties of electron beam irradiated
polypropylene/epoxidized natural rubber (PP/ENR) polymer blends
M. M.
H. Senna, A. A. Abdel-Fattah, Y. K. Abdel-Monem
Nuclear
Instruments & Methods in Physics Research Section B-Beam Interactions
with Materials and Atoms, 266 (11), 2599-2606 (2008)
Polypropylene
(PP) and epoxidized natural rubber (ENR) blends with different blend
ratios were prepared by melt extrusion into sheets. The PP/ENR blends
were exposed to various doses of accelerated electrons. The effect
of electron beam irradiation on the mechanical and structural morphology
was investigated by stress-strain behavior and scanning electron
microscope (SEM). Improved mechanical properties and structural
morphology were observed after the blends were subjected to electron beam
irradiation. The formation of free radicals during and after
electron beam irradiation was illustrated by electron spin resonance
(ESR). The ESR spectra indicated the formation of alkyl and allyl
radicals during electron beam irradiation and peroxyl radicals during the
post effect. In addition, the rate of radical decay was found to be
second-order kinetics.
Preparation
and characterization of blends containing natural and some synthetic
rubbers with synthesized aromatic polyester
S. H.
El-Sabbagh, M. E. Tawfik
Journal
of Applied Polymer Science, 109 (5), 2823-2835 (2008)
Aromatic
polyester (AP) was synthesized from polyarylate [Bisphenol A
(BPA)/dimethyl terephalate (DMT)/ethylene glycol (EG)] and maleic
anhydride (MA) in presence of dibutyl tin oxide (DBTO) as a
catalyst. Candidated AP (10-30 phr) was blended with different
types of rubber; natural rubber (NR), acrylonitrile butadiene rubber
(NBR), styrene butadiene rubber (SBR) and ethylene-propylenediene monomer
(EPDM). The blends were then subjected to physicomechanical measurements
to evaluate their properties as efficient blends for economic industrial
applications. For all types of the tested blends, the fatigue life values
were found to decrease with increasing the AP contents. The blends
exhibited different equilibrium swelling (%) in solvents like toluene and
motor oil. The addition of N-isopropyl-N'-phenyl-p-phenylene diamine
(IPPD), as antioxidant, affects the properties of all the blends.
The morphological structure was studied by using scanning electron microscope
(SEM) and the SEM results show the changes in surface of the rubber
before and after being blended with AP.
Thermal
behavior of chitosan/natural rubber latex blends - TG and DSC analysis
V.
Rao, J. Johns
Journal
of Thermal Analysis and Calorimetry, 92 (3), 801-806
(2008)
Thermogravimetry
(TG) and differential scanning calorimetry (DSC) techniques have been
applied to characterize the thermal behavior of chitosan (CS)/natural
rubber latex (NRL) blends with different blend compositions. The
addition of NRL affects decomposition behavior of CS. Activation
energies of degradation have been calculated using Horowitz-Metzger
equation. Among the series of the blend compositions, CS15NRL85 was found
to exhibit better thermal stability. The presence of two glass
transitions corresponding to CS and NRL phases in the blend from the DSC
studies reveals that the CS/NRL blends are thermodynamically
incompatible.
The
effect of HVA-2 on properties of irradiated epoxidized natural rubber
(ENR-50), ethylene vinyl acetate (EVA), and ENR-50/EVA blend
M.
Zurina, H. Ismail, C. T. Ratnam
Polymer
Testing, 27 (4), 480-490 (2008)
Melt
blended ENR-50, EVA, and ENR-50/EVA (50/50) containing N,N'-m-phenylene
dimaleimide (HVA-2) were irradiated using a 3.0 MeV electron beam machine
with doses ranging from 20 to 100 kGy. A study on influence of a coagent
(HAV-2) on the properties of irradiated ENR-50, EVA, and ENR-50/EVA blend
revealed that HVA-2 was more effective in enhancing the
irradiation-induced crosslinking in the ENR-50 phase than in EVA.
The addition of HVA-2 enhanced the tensile properties and the
irradiation-induced crosslinking in ENR-50/EVA blend. The
compatibility of the blend was also improved by the addition of HVA-2.
Thermoplastic
elastomers based on epoxidized natural rubber and high-density
polyethylene blends: Effect of blend compatibilizers on the mechanical
and morphological properties
C. Nakason, M Jarnthong, A. Kaesaman, S.
Kiatkamjornwong
Journal
of Applied Polymer Science, 109 (4), 2694-2702 (2008)
Epoxidized
natural rubber (ENR)/high-density polyethylene (HDPE) blends at various
blend ratios were investigated. The ENR consisting of 20 mol %
epoxide groups was prepared via the performic epoxidation method.
Three types of blend compatibilizers; a graft copolymer of HDPE and
maleic anhydride (HDPE-g-MA) and phenolic modified HDPEs using phenolic
resins SP-1045 and HRJ10518 (i.e., PhSP-PE and PhHRJ-PE), were prepared.
When compared with the blend without compatibilizer, the addition of
compatibilizer resulted in the blend with superior tensile strength,
hardness, and set properties. Blend compatibility is promoted by
interaction between the polar functional groups of the compatibilizer and
the oxirane groups in the ENR molecules. In addition, HDPE segments
at another end of the compatibilizer molecules were compatibilizing with
the HDPE molecules in the blend components. The blend with compatibilizer
showed smaller phase morphology than the blend without
compatibilizer. Among the three types of the blend compatibilizer,
HDPE-g-MA provided the blend with the greatest strength and hardness
properties but the lowest set properties.
Coupling
of various methods for the investigation of the morphology of blends of
natural rubber and polybutadiene
J.
Portal, C. Carrot, J. C. Majeste, S. Cocard, V. Pelissier, K. Baran, I. Anselme-Bertrand
Polymer
Engineering and Science, 48 (6), 1068-1076 (2008)
Attempts
were made to develop a set of experimental methods to investigate the
morphology of two immiscible elastomer blends of natural rubber (NR) and
polybutadiene (PB). The unfilled and uncured blends were used for
this investigation. Selective extraction was done by using
1,2-dichloroethane and 4-methyl-2-pentanone (MIBK) to dissolve
selectively NR and PB in specific conditions to assess the continuity of
the phases. In oscillatory shear flow at low frequencies and low
volume fractions of the minor phase in the melt, the storage modulus
shows an excess of elasticity that increases with the dispersed phase
content. At higher concentration of the minor phase, the elasticity
decreases in relation to the morphology. Ultra cryo-microtomed
samples were also analyzed by transmission electron microscopy
(TEM). The superposition of the three methods highlights the
existence of a phase-inversion point for these blends.
A
comparative study of the cure characteristics, processability, mechanical
properties, ageing, and morphology of rice husk ash, silica and carbon
black filled 75 : 25 NR/EPDM blends
W.
Arayapranee, G. L. Rempel
Journal
of Applied Polymer Science, 109 (2), 932-941 (2008)
Rice
husk ash (RHA) was used as a filler for natural rubber
(NR)/ethylene-propylene-diene monomer (EPDM) blends in comparison with
two commercial reinforcing fillers, silica and carbon black. A 75:25 (wt
%) NR/EPDM was prepared using a two-stage conventional mixing procedure,
and filler loading was varied from 0 to 60 phr at 15 phr intervals. The
results indicated that RHA offers processing advantages over silica and
carbon black, however, the use of RHA as an additional filler provided
almost no improvement in the tensile strength and abrasion resistance of
the blends. The ozone resistance of the blends was inferior to those
obtained from the addition of RHA. Scanning electron micrographs
revealed that the RHA filler was dispersed discontinuously in the rubber
matrix, therefore generates weak structure when compared with carbon
black and silica. The results indicated that RHA could be used as a
diluent filler for the 75:25 NR/EPDM blend.
Thermal
properties in cured natural rubber/styrene butadiene rubber blends
S.
Goyanes, C. C. Lopez, G. H. Rubiolo, F. Quasso, A. J. Marzocca
European
Polymer Journal, 44 (5), 1525-1534 (2008)
Natural
rubber (NR) and styrene butadiene rubber (SBR) blends with sulfur and
n-tert-butyl-2-benzothiazole sulfonamide (TBBS) as accelerator were prepared,
varying the amount of each polymer in the blend. Samples were cure
characterized by rheometer at 433 K to their maximum torques.
Differential scanning calorimetry was employed to study the miscibility
among the constituent polymers of the cured compounds in a broad range of
temperatures. The glass transition temperatures of the samples were
analyzed and the specific heat capacity of the compounds was also
determined. A new device that performs measurements in vacuum was applied
to measure thermal diffusivity of the samples in the temperature range
from 130 to 400 K. The thermal results are explained on the basis
of the structure formed during the vulcanization of the samples
considering the variation of the crosslink density of each phase. Finally,
a serial thermal conduction model that takes into account the
contribution of each phase to the thermal diffusivity was used to fit the
experimental results.
Improving
the mechanical properties of ENR/NBR blends via masterbatches with
initial accelerator concentration gradients
K.
Sahakaro, N. Pantupon
International
Polymer Processing, 23 (2), 140-145 (2008)
Epoxidized
natural rubber with 30 mol. % of epoxide (ENR-30) and medium nitrile
rubber (NBR) were blended at the 30/70 and 70/30 blend ratios (wt %)
using simple mixing and masterbatch techniques. TBBS was employed
as an accelerator. The masterbatches of ENR-30 initially contained higher
accelerator concentrations compared with those of NBR in order to
compensate an effect of accelerator partition towards NBR phase. The
initial accelerator concentration ratios in ENR-30 and NBR masterbatches
before cross-blending were 50/50, 60/40, 70/30 and 80/20, respectively.
The blend vulcanizates prepared by masterbatch technique showed a
dramatic improvement in tensile properties in comparison with those
prepared by simple blend. The initial accelerator concentration
ratio in ENR-30/NBR masterbatches at 70/30 was found to give the highest
ultimate tensile properties. The improvement in tensile properties was
clearly observed for all the blends vulcanized with conventional, semi-EV
and EV sulfur systems. The increase of tensile properties does suggest a
better curative distribution and hence a better crosslink distribution.
Effect
of the processing conditions and the addition of trans-polyoctenylene
rubber on the properties of natural rubber/styrene-butadiene rubber
blends
C. M. P.
Bizi, N. R. Demarquette
Journal
of Applied Polymer Science, 109 (1), 445-451 (2008)
Trans-
polyoctenylene rubber (TOR) was added to natural rubber/styrene-butadiene
rubber blends, and the processing conditions, Mooney viscosity, tensile
properties, hardness, tearing resistance, and resilience were
investigated. Finer blend morphology was obtained when processing
time was increased. This resulted in an improvement in the
mechanical properties. The addition of TOR also resulted in an increase
in hardness, a decrease in tear resistance, and no effect on the
resilience. If the components of the compounds were not properly mixed, a
large decrease in the Mooney viscosity and a slight decrease in the
tensile properties were observed. Dynamic mechanical and
morphological analyses were applied to explain the results, and TOR was
found to act more as a plasticizer than a compatibilizer.
Mechanical
and sorption properties of poly(ethylene-co-vinyl acetate)(EVA)
compatibilized acrylonitrile butadiene rubber/natural rubber blend
systems
P.
Kumari, C. K. Radhakrishnan, S. George, G. Unnikrishnan
Journal
of Polymer Research, 15 (2), 97-106 (2008)
Natural
rubber/acrylonitrile butadiene rubber (NR/NBR) blends at a fixed blend
ratio of 50/50 were compatibilized with poly (ethylene-co-vinyl acetate)
(EVA) at varying amounts from 0 to 10 parts per hundred rubber (phr). The
compatibility of the blend components in presence of EVA has been
evaluated in terms of mechanical and sorption characteristics. The
addition of EVA upto 6 phr could improve the mechanical properties.
The blends with EVA compatibilizer showed better solvent resistance when
compared with the uncompatibilized blends. This is attributed to
the increased interfacial adhesion between the blend components.
A shift of glass transition temperatures of the blend components
towards higher temperatures was observed by DSC studies, indicating
increased rigidity of the matrix in presence of EVA.
Thermoplastic
elastomer based on high-density polyethylene/natural rubber blends:
rheological, thermal, and morphological properties
C.
Nakason, S. Jamjinno, A. Kaesaman, S. Kiatkalmjornwong
Polymers
for Advanced Technologies, 19 (2), 85-98 (2008)
Thermoplastic
elastomer (TPE) based on natural rubber (NR) and high-density
polyethylene (HDPE) was prepared by a simple blending technique at 180 oC
in an internal mixer using phenolic compatibilizer (HRJ-10518 or SP-1045)
or liquid natural rubber (LNR) as a compatibilizer. The mixing
torque, shear stress, and shear viscosity of the blends were found to
increase with increasing NR content. Positive deviation blend (PDB) for
the blends containing active hydroxyl methyl phenolic resin in HRJ-10518
or dimethyl phenolic resin in SP-1045 was obtained, but PDB was not
observed for the blends with LNR or without the compatibilizers. In the
phenolic compatibilized blends, different blend ratios gave different
blend morphology. NR dispersed in the HDPE matrix was found in the
NR/HDPE blends of 20/80, 40/60, and 50/50 ratios, while HDPE dispersed in
NR matrix was obtained in the NR/HDPE blend of 80/20 ratio, and the co-continuous
phase was accomplished in the 60/40 NR/HDPE blend. The 60/40 NR/HDPE
blend compatibilized with HRJ-10518 exhibited higher tensile strength and
elongation at break (EB). Incorporation of parafinic oil caused a
decreasing tendency in tensile strength with increases in EB. The
resulting TPNRs exhibited low-tension set.
Stress-relaxation
Behavior of natural rubber/polystyrene and natural
rubber/polystyrene/natural rubber-graft-polystyrene blends
R.
Asaletha, P. Bindu, I. Aravind, A. P. Meera, S. V. Valsaraj, W. M. Yang,
S. Thomas
Journal
of Applied Polymer Science, 108 (2), 904-913 (2008)
The
effects of strain level, composition, compatibilizer loading, and aging
on the stress-relaxation behavior of natural rubber (NR)/polystyrene (PS)
blends in tension were investigated in detail. The dispersed/matrix phase
morphology showed a two-stage mechanism, whereas the co-continuous
morphology showed a single-stage mechanism. The addition of NR-g-PS as
compatibilizer into 50/50 blends changed the blend morphology to a
matrix/dispersed phase structure, and so a two-step relaxation mechanism
was found in the compatibilized blends. A three-stage mechanism was
observed when the compatibilizer was loaded exceeding the critical
micelle concentration, where the compatibilizer formed micelles in the
continuous phase. The relaxation rate increased with strain levels.
The aging produced interesting effects on the relaxation pattern. The
aged samples showed a two-stage relaxation mechanism, and the relaxation
rate of the samples increased with temperature due to the
degradation.
Characterization
of unvulcanized and dynamically vulcanized ENR-50/EVA blends
M.
Zurina, H. Ismail, C. T. Ratnam
Polymer-Plastics
Technology and Engineering, 47 (1), 1-12 (2008)
Epoxidized
natural rubber (ENR-50) and ethylene vinyl acetate (EVA) blends with
varying proportion of the components were dynamically vulcanized using
sulfur and dicumyl peroxide (DCP) crosslinking systems. Dynamic
mechanical properties, tensile properties and morphology of unvulcanized
and dynamically vulcanized ENR-50/EVA blends were investigated. Dynamic
vulcanization found to improve the compatibility and tensile properties
of the blends, compared to unvulcanized blends. The results of blend
properties indicated that the entire blends are compatible at all blend
ratios. Moreover, DCP cure system produced a more compatible blend
compared to control and sulfur cure system.
Mechanical
properties of thermoplastic elastomeric blends of chitosan and natural
rubber latex
V.
Rao, J. Johns
Journal
of Applied Polymer Science, 107 (4), 2217-2223 (2008)
Thermoplastic
chitosan/natural rubber blends (Cs/NR) were prepared from natural rubber
latex and chitosan by solution casting technique, and characterized by
stress-strain analysis. The mechanical properties were found to
vary with chitosan/natural rubber ratios. Effect of thermal aging on
mechanical properties was investigated. The blends were crosslinked
using dicumyl peroxide, and the effect of crosslinking on mechanical
properties of Cs/NR has been studied. Experimental values were compared
with different theoretical models.
Mechanism
of silica reinforcement in CPE/NR blends by the use of rheological
approaches
P.
Phewphong, P. Saeoui, C. Sirisinha
Journal
of Applied Polymer Science, 107 (4), 2638-2645
(2008)
Blends
of elastomeric chlorinated polyethylene (CPE) and natural rubber (NR) at
blend composition ratio of 80/20 were prepared with various precipitated
silica loadings. A mechanism of silica reinforcement was proposed based
on the use of rheological approaches. The results reveal that the
viscoelastic behavior of blends is influenced remarkably by silica
loadings. A cure promotion phenomenon is observed as silica is loaded due
probably to the strong silica-CPE interaction and/or a reduction in
curative absorption on silica surfaces. An increase of silica
loading induced a stronger Payne effect, implying a formation of
pseudo-crosslink via a physical interaction. Validation of the proposed
mechanism of silica reinforcement based on the formation of
pseudo-crosslink is done by the deactivation of silanol groups on silica
surfaces using silane coupling agents. It was found that
bis-(3-triethoxysilylpropyl) tetrasulfane (Si-69) is more effective in
suppressing the pseudocrosslink than 3-thiocyanatopropyl triethoxy silane
(Si-264).
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Composites and Nanocomposites
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Preparation and characterization of ethylene vinyl
acetate (EVA)/natural rubber (SMR L)/organoclay nanocomposites: Effect of
blending sequences and organoclay loading
H.
Ismail, Y. Munusamy, M. Jaafar, C. T. Ratnam
Polymer-Plastics
Technology and Engineering, 47 (8), 752-761 (2008)
Ethylene
vinyl acetate (EVA)/natural rubber (SMR L)/organoclay thermoplastic
elastomer nanocomposites were prepared in a melt state in an internal
mixer at 120oC and 50rpm rotor speed. This work
demonstrates the effect of different blending sequences and organoclay
loading from 2 to 10phr on the tensile properties, morphology, thermal
degradation, flammability, and water absorption behavior of EVA/SMR
L/organoclay nanocomposites. The nanocomposites were prepared by
three different blending sequences, and each exhibited different tensile
properties. For all blending sequences applied, the presence of
organoclay increases the tensile properties, thermal degradation
resistance, water permeation resistance, and flame retardancy. The
optimum results for all the properties studied were achieved when EVA was
blended with organoclay first and SMR L was incorporated later into the
blend. The optimum organoclay loading was 2phr. The SEM micrographs and
X-ray diffraction (XRD) results revealed that nanostructures of individual
silicate layers were achieved at 2phr organoclay loading, whereas at 8phr
organoclay loading, agglomeration was observed. Increasing organoclay
loading resulted in a decrease of flammability of the nanocomposites.
Preparation
and evaluation of the microstructure and properties of natural
rubber/sodium-montmorillonite nanocomposites
M.
Abdollahi, A. Rahmatpour, J. Aalaie, G. Khanbabae
Iranian
Polymer Journal, 17 (7), 519-529 (2008)
Natural
rubber (NR)/sodium-montmorillionite (Na-MMT) nanocomposites were prepared
by co-coagulating the mixture of NR latex and various amounts of Na-MMT
aqueous suspension. The structure of nanocomposites was characterized by
tapping mode AFM, TEM and XRD. At the low loading of layered
silicates, it was found that fully exfoliated structure could be achieved
by this method. However, when the amount of Na-MMT increased to 10 phr,
both non-exfoliated (stacked layers) and exfoliated structures were
observed in the nanocomposites. The nanocomposites exhibited
greater initial moduli and tensile strength, higher glass
transition temperature and lower tangent peak value in comparison with
Na-MMT-free NR compound. Initial moduli increased with increasing the
Na-MMT loading, indicating the reinforcement effect of Na-MMT on the
mechanical properties of nanocomposites. TGA results indicated an
improvement in decomposition temperature.
Characterization
of high-performance exfoliated natural rubber/organoclay nanocomposites
P. Y.
Li, L. Wang, G. J. Song, L. L.Yin, F. Qi, L. D. Sun
Journal
of Applied Polymer Science, 109 (6), 3831-3838 (2008)
The
exfoliated natural rubber (NR)/organoclay nanocomposites were prepared
with an optimal organoclay by direction blending. The optimal-type
organoclay was chosen from three kinds of organoclay investigated, based
on the results of XRD characterization and the mechanical properties of
the NR/organoclay composites. Well-ordered exfoliated single layers
of organoclay were observed by transmission electron microscopy
(TEM). The tensile strength, tensile modulus, and tear strength
were found to improve remarkably with small amounts of organoclay, whose
contents were below 5.0 phr. At the loading amount of 3.0 phr of
organoclay, the tensile strength and tear strength of nanocomposite were
24.7 MPa and 34.7 kN/m, respectively, which increased similar to 89.5%
and 61.6%. The nanocomposites showed an enhancement of oil resistance and
thermal stability, as indicated by a decrease of the values of the
weight-swelling ratio and the TGA results, respectively. The
nanocomposites demonstrated the gas-barrier properties, and the mechanism
of barrier of clay layers was discussed in this work.
Preparation
of natural rubber/EVA/montmorillonite nanocomposites by latex compounding
S.
Chuayjuljit, B. Nonthaboonlert, S. Limpanart
Polymers
& Polymer Composites, 16 (4), 277-282 (2008)
Nanocomposites
of natural rubber (NR)/poly(ethylene-co-vinyl acetate) (EVA)/ unmodified
montmorillonite (MMT) were prepared by latex compounding. EVA and
MMT were well mixed at room temperature in the latex state and
subsequently blended with NR latex at NR/EVA dry weight ratios of 100/0,
90/10, 80/20, 70/30, 60/40 and 50/50. MMT was added at 4 parts per
hundred of dry rubber and EVA (phr). The sheets were prepared by casting
homogeneous latex mixture on a glass mold, air dried at room temperature
and then in an oven at 70 oC. The sheets were subsequently
cured at 110 oC for 2 h. The cured samples were tested
for their tensile properties, and examined for their structure and
morphology by X-ray diffraction (XRD), scanning electron microscopy (SEM)
and transmission electron microscopy (TEM). The XRD patterns and TEM
images of the nanocomposites showed an exfoliated structure.
Incorporation of MMT substantially improved tensile strength of the
nanocomposite, and the 90NR/10EVA/4MMT exhibited the highest tensile
strength. SEM micrographs revealed that the MMT particles were well
dispersed in the polymer matrix. However, increasing the EVA content to
50 wt% reduced the compatibility between NR and EVA.
Study
on the reinforcing effect of milled carbon fibers in a natural rubber
based composite
F.
Cataldo
Journal
of Macromolecular Science Part B-Physics, 47 (4), 818-828
(2008)
Natural
rubber compound with 45phr of N375 carbon black was filled with milled
carbon fibers (MCF) at 2, 4, and 6 phr. Low elongation moduli were
dramatically increased even with only 2phr of MCF. Anisotropic
properties, which can be measured by an anisotropic factor defined as the
ratio between the modulus parallel to the MCF prevalent direction over
the modulus orthogonal to the MCF prevalent direction, were observed for
the rubber compounds containing MCF. The addition of MCF into the
natural rubber compound reduces the mechanical hysteresis and compression
set, but has an adverse effect on the tear strength properties.
This work demonstrates the feasibility and the advantages derived
by the utilization of the carbon fibers as extra reinforcing filler in
rubber compounds.
A
comparative study of short nylon fiber-natural rubber composites prepared
from dry rubber and latex masterbatch
P. K. Bipinbal, S. K. N. Kutty
Journal
of Applied Polymer Science, 109 (3), 1484-1491 (2008)
Attempts
were made to develop a new method for preparing short nylon fiber-natural
rubber composites. Short fibers were chopped to approximately 6 mm,
incorporated in the latex stage, and processed into sheet form. By using
this method, mixing cycle time and fiber breakage during mixing were
reduced. The new composites when compounded with a dry bonding
system based on hexamethylenetetramine, resorcinol and hydrated silica
(HRH) showed improved modulus, tensile strength and abrasion resistance,
but similar tear strength, resilience, and compression set compared
to conventional composites. Better interaction between matrix
and fibers was also achieved in the case of latex master batch, as
indicated by SEM analysis.
Improving
reinforcement of natural rubber by networking of activated carbon
nanotubes
S.
Bhattacharyya, C. Sinturel, O. Bahloul, M. L. Saboungi, S. Thomas, J. P.
Salvetat
Carbon,
46 (7), 1037-1045 (2008)
Natural
rubber was reinforced with carboxylated multiwalled carbon nanotubes
(c-MWCNT) dispersed with sodium dodecyl sulfate. The reinforced latex
film structure was characterized by TEM and AFM. A strong enhancement in
the Young's modulus (similar to 10-fold), tensile strength (similar to
2-fold) and storage modulus (similar to 60-fold) at low-strain in the
rubbery state with up to 8.3 wt% of MWCNTs, with a small reduction in
elongation at break was observed. Dielectric measurement at room
temperature revealed a low percolation threshold (<1 wt%) associated
with the formation of an interconnected nanotube network. Latex film
formation plays a critical role in the network formation due to the
segregation effect at the surface of latex beads. Large Payne and
Mullins effects due to the mechanical behavior of the nanotube network
were observed. The disruption of the network during stretching induces
both an increase of electrical resistivity and mechanical
stress-softening.
Curing
kinetics and mechanical behavior of natural rubber reinforced with
pretreated carbon nanotubes
G. Sui,
W. H. Zhong, X. P. Yang, Y. H. Yu
Materials
Science and Engineering A-Structural Materials Properties Microstructure and
Processing, 485 (1-2), 524-531 (2008)
This
present work studies the curing kinetics and vulcanizate properties of
carbon nanotubes (CNTs)/natural rubber (NR) nanocomposites. The
CNTs were pretreated by acid bath followed by ball milling with HRH bonding
systems. The CNT/NR nanocomposites were then prepared through
solvent mixing on the basis of pretreatment of CNTs. The surface
characteristic of CNTs and physical interaction between CNTs and NR were
analyzed by Fourier transform infrared spectroscopy (FT-IR). The
vulcanization kinetics of CNT/NR nanocomposites were studied in
comparison with the neat NR. The results indicated that the presence of
CNTs affects the curing process of the NR, and additional heating is
required to cure the nanocomposites due to its higher active
energy. The NR vulcanizates were tested for their static and
dynamic mechanical properties and morphology by scanning electron
microscopy (SEM). The results indicated that the dispersion of
pretreated CNTs in the rubber matrix and interfacial adhesion between
them were obviously improved. The incorporation of the pretreated CNTs
also resulted in a considerable increase of physical and mechanical
properties of the CNT/NR nanocomposites, compared to those of the neat NR
and untreated CNTs-filled NR nanocomposites.
Reinforced
thermoplastic natural rubber hybrid composites with Hibiscus cannabinus,
L and short glass fiber - Part I: Processing parameters and tensile
properties
H.
Anuar, W. N. W. Busu, S. H. Ahmad, R. Rasid
Journal
of Composite Materials, 42 (11), 1075-1087 (2008)
Thermoplastic
natural rubber (TPNR) hybrid composite, based on a blend of polypropylene
(PP), liquid natural rubber (LNR) and natural rubber (NR) at a ratio of
70:10:20, were reinforced with Hibiscus cannabinus, L fiber (kenaf fiber:
KF) and short glass fiber (GF). The composites were prepared via
melt blending method using internal mixer, at various temperatures, speed
and time. Processing parameters were determined from the tensile strength
based on fiber content with 50:50 ratios of GF and KF. Tensile test was
then carried out for reinforced TPNR-KF-GF hybrid composites (0-20% by
volume), with and without silane coupling agent and maleic anhydride
grafted polypropylene, using the optimum processing parameters. The
increasing in kenaf fiber content substantially reduced the tensile
strength and modulus. Scanning electron microscopy (SEM) has shown that
the use of coupling agent or compatibilizer could promote better
fiber-matrix interaction in the composites.
Chemically
modified starch reinforced natural rubber composites
C.
Liu, Y. Shao, D. Jia
Polymer,
49 (8), 2176-2181 (2008)
Starch
paste (MST) was chemically modified with polybutylacrylate (PBA) graft
chains, mixed and finally co-coagulated with natural rubber (NR) latex.
The PBA graft chains are designed to prevent hydrogen bonding and
crystallization of starch and to improve compatibility between starch and
rubber. The results of mechanical properties and phase morphology
revealed that the MST is much superior to unmodified starch paste.
A use of unmodified starch paste caused a decrease of tensile strength,
tear strength and elongation at break. In contrast, optimum MST showed an
increase of tensile strength, elongation at break and tear strength
besides modulus and hardness, as a result of fine starch dispersion and
strong interfacial interaction achieved in NR/MST composites. The
observed reinforcement effect is interpreted based on the results of
X-ray diffraction (XRD), differential scanning calorimetry (DSC) and
scanning electron microscope (SEM) analyses of grafted starch in
comparison with natural starch and gelatinized starch.
Transport
properties of natural rubber latex layered clay nanocomposites
A.
Jacob, P. Kurian, A. S. Aprem
Journal
of Applied Polymer Science, 108 (4), 2623-2629 (2008)
Nanocomposites
of natural rubber latex with low loadings of layered clay were prepared
using conventional compounding technique. Processing difficulties
were encountered when a higher loading of clay was used due to viscosity
build up. Nanocomposites in which layered silicate layers were
either delaminated or ordered as in an intercalated structure were
obtained in this work, as shown by X-ray analysis. Partially exfoliated
structure was observed from TEM photographs of nanocomposites with 3 phr
nanoclay. The transport properties, sorption, diffusion, and permeation
coefficients were investigated using toluene at 303 K. A higher decrease
for the diffusion coefficient for nanocomposites directs the presence of
tortuous path for the diffusing molecules. Thermodynamic parameters show
a better compatibility for the silicates with rubber resulted in the
formation of an elastomeric network. The nanocomposites demonstrated a
better barrier resistance for oxygen molecules even in lower loading of
nanoclay. Different gas transport models (Nielsen, Bharadwaj,
Cussler) were applied to describe the behavior of these nanocomposites.
Preparation
of high performance nanocomposite elastomer: effect of reaction
conditions on in situ silica generation of high content in natural rubber
Y.
Ikeda, S. Poompradub, Y. Morita, S. Kohjiya
Journal
of Sol-Gel Science and Technology, 45 (3), 299-306
(2008)
Silica
was generated in situ in natural rubber via a sol-gel reaction of
tetraethoxysilane. Effect of amines on its generation was
investigated. N-hexylamine, n-heptylamine and n-octylamine were
found to increase the in situ silica content. The nanometer sized silica
particles up to ca. 80 parts per hundred rubber by weight were generated
in situ in the rubber matrix. Silica dispersion in the rubbery matrix was
more homogeneous than that of commercial silica dispersed by a
conventional mechanical mixing. The polarity and solubility in water of amine
were found to be influential factors for controlling the in situ silica
content in the rubbery matrix.
Effect
of montmorillonite modification on mechanical properties of vulcanized
natural rubber composites
J.
Hrachova, P. Komadel, I.
Chodak
Journal
of Materials Science, 43 (6), 2012-2017 (20080
Ca-montmorillonite
Jelsovy Potok (JP; Slovakia)
and Na-montmorillonite Kunipia-F (KU; Japan) were ion exchanged
with octadecyltrimethylammonium (ODTMA) bromide and were used to prepare natural
rubber-clay composites by direct polymer melt intercalation. Silica
Ultrasil VN3 at an amount of 15 phr was also used as conventional filler.
The effect of organoclay loading from 1 up to 10 phr on the tensile
properties (stress at break, strain at break and modulus M100) was
evaluated. Organic modification of both fillers resulted in an increase
of toluene uptake degree. Both ODTMA modified fillers (KU and JP)
exhibited substantial increase in tensile strength and deformation at
break; JP proved to be more effective compared to KU. The natural
rubber composites showed the highest stress and strain at break when 15
phr of silica and 10 phr of montmorillonite were used. An addition
of unmodified KU had no effect on tensile strength and deformation at
break, however, a reinforcing effect was observed for the mixture
containing 10 phr of unmodified JP.
Mechanical
properties and dynamic mechanical analysis of
thermoplastic-natural-rubber-reinforced short carbon fiber and kenaf
fiber hybrid composites
H.
Anuar, S. H. Ahmad, R. Rasid, A. Ahmad, W. N. W. Busu
Journal
of Applied Polymer Science, 107 (6), 4043-4052 (2008)
Mechanical
and thermal properties of thermoplastic natural rubber reinforced by
carbon fiber (CF) and kenaf fiber (KF) were investigated. Hybrid
composites were fabricated via a melt-blending method in an internal
mixer. Samples with overall fiber contents of 5, 10, 15, and 20 vol %
were subjected to flexural testing, and samples with up to 30% fiber
content were subjected to impact testing. The flexural strength and
modulus was found to increase up to 15 vol %, and then decline.
Higher fiber contents resulted in an increment in impact strength in both
treated and untreated composites. Dynamic mechanical analysis was applied
for thermal analysis of composites with 15 vol % fiber content with
fractions of CF to KF of 100/0, 70/30, 50/50, 30/70, and 0/100. It
was found that the storage modulus, loss modulus, and tan delta of the
untreated hybrid composite were more consistent and better than those of
the treated hybrid composites. The glass-transition temperature of the
treated hybrid composite was slightly lower than that of the untreated
composite, which indicated poor damping properties.
Preparation
and properties of natural rubber nanocomposites with solid-state
organomodified montmorillonite
Y. H.
Sun, Y. F. Luo, D. M. Jia
Journal
of Applied Polymer Science, 107 (5), 2786-2792 (2008)
Nanocomposites
of natural rubber and a novel solid-state organomodified montmorillonite
were prepared by traditional rubber mixing and vulcanizing process.
The properties of solid-state organomodified montmorillonite were
investigated by Fourier-transform infrared spectroscopy (FITR) and
thermogravimetric analysis (TGA). The dispersion of the layered
silicate in rubber was characterized by X-ray diffraction (XRD) and
transmission electron microscopy (TEM). The results showed that the
solid-state organomodified montmorillonite can not only accelerate the
curing process, but also improve the mechanical and aging resistance
properties of NR. The improvement in properties is attributed to partial
intercalation of the organophilic clay by NR macromolecules.
The results from dynamic mechanical analysis (DMA) showed a
decrease of tan delta max and increase of Tg when the organoclay is added
to the rubber matrix, which is due to the confinement of the
macromolecular segments into the organoclay nanolayers and the strong
interaction between the filler and rubber matrix.
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Properties and Testing
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Composition of color substances of Hevea
brasiliensis natural rubber
Jitladda Sakdapipanich, et al.
Department of Chemistry of Science, Mahidol University, Bankok, Thailand.
Journal of Rubber Research, Volume 10(2) 2007
It is accepted that NR gives naturally color, which restrict many
applications such as light-color products. Therefore characterization of
color substances presenting NR is very useful to develop the certain
methodology to eliminate them completely or partly from NR in the future.
Rubber friction and its relation
to tire traction
K.A. Grosch, Uelenbenderweg 22,
D-52159, Roetgen Rott, Germany. Rubber Chemistry and Technology,
Volume 80 number 2, 2007
Rubber friction differs from that of hard solid materials in that it is
not linearly related to the normal load and it depend strongly on sliding
speed and temperature. There exits an interrelation between these two
variables on their effect on the friction coefficient. This is a constant
load and can be described by a so-called master curve. .Such master
curves have been obtained on different types of surface and for gum
rubbers as well as filled rubbers on wet and dry surfaces and it is shown
that they may also be obtained on ice.
In this overview different parameters are evaluated.
Numerical simulation of tire traction on various
road conditions
Y. Nakajima, Bridgestone Corporation,
Tire Research Division, 3-1-1, Ogawahogashi-Cho, Kodaira-Shi, Tokyo
187-8531, Japan.
Rubber Chemistry and Technology, Volume 80 number 3, 2007
The tire is the only point of contact between car and the road and the
traction is drastically changed by the road condition. Since the
critical functions performed by the tire are determined by a tiny contact
interface, the numerical simulation has been pursued to analyze the tire
traction on various road conditions. The numerical simulation of tire
traction on various road conditions such as ice, snow, water and soil are
a very challenging problem, because these involve fluid structure
interaction, tire-road contact analysis and difficulty of tire pattern
modeling.
In this paper, the study on the numerical simulation of tire
traction on various road conditions is reviewed.
Monitoring the degradation in shear and bulk
moduli of rubber for inclusion in visco-elastic FE models
B. Chouchaoui, Rubber World, December 2000, p.
32-38
The first two parts of this paper present time
and frequency domains along with calibration of models for FEA and an
overview of CSR tests developed in the rubber industry. The second two
parts will appear in the January 2001 issue, covering a newer method to
monitor shear and bulk moduli of rubber under cycling temperature and the
circulation of fluids, results of modelling samples used in testing, and
the analysis of a seal using data collected under unaxial tension and
compression, planar tension and volumetric compression, along with decay
in shear and bulk moduli with time and temperature.
Vulcanised rubber characterisation for FEA
V. Noparatanakailis, Journal of Rubber
Re-search, Vol. 3(4), 4th quarter 2000, p. 222- 231
Three vulcanised SBR compounds and one vulcanised
NR compound were examined. An agreement of the experimental stress-strain
relation to finite element analysis was found for the four compounds
tested in compression and simple shear modes. This agreement was
confirmed with three other NR compounds. Discrepancy was clearly observed
in the case of high carbon-black loaded SBR compounds tested in tension
mode.
Constitutive models for rubber
Proceedings of the first European
confe-rence,Vienna, Austria, 9-10 September 1999, Al Dorfmann & Alan
Muhr (eds),90 5809 113 9
Constitutive and numerical modelling;
Experimental techniques; Viscoelasticity; Tyres and friction; Softening
phenomena; Applications; 36 papers.
NR elastomer composite: Proces, material and
performance characteristics
J. Shell, T. Wang, N. Tokita and B. Chung,
Cabot. Rubber World, March 2000, page 40-46.
A new process using a mechanical approach to
coagulation has been developed. This new process can continuously produce
emulsion based elastomer composites of similar composition to
conventional masterbatch. While this new process can be equally applied
to natural rubber and synthetic lattices, current commercialization
efforts focus on natural rubber.
The NR compound performance of elastomer composites and similarly
compounded dry-mix counterparts were compared. Laboratory results
indicate that those compounds may demonstrate performance advantages over
dry-mix counterparts in many aspects such as lower hysteresis, better
fatigue life and improved abrasion wear as a result of its unique
characteristics of dispersion, bound rubber formation and molecular
weight. Actual tyre performance must be verified in actual road tests
under various operating conditions.
Modelling of carbon black filled NR vulcanizates
by the standard triboelastic solid
V.A. Coveney and D.E. Johnson. Faculty of
Engineering, University of the West of England,
Bristol. Rubber Chemistry and Technology,
vol. 72, page 673-683.
Mathematical modeling of the dynamic behavior of
vulcanizates is reviewed with the emphasis on carbon black filled natural
rubber (NR). The 3 constant standard triboelastic solid (STS) model and
its behavior are described, in general terms and with reference to low
frequency shear data for a wide range of filled NR vulcanizates. Good
general agreement is found between model and experiment for the data
obtained at strain amplitudes down to 0.01; there is also acceptably good
correlation between carbon black loading and values of STS constant. For
previously published data down to very low strain amplitudes (0.0001),
agreement is much satisfactory.
Longevety of NR structural bearings
K.N.G. Fuller and A.D. Roberts, Tun Abdul Razak
Research Centre. Rubber World, December 1999, page 36-47.
The proposed use of natural rubber bearings to
provide earthquake protection to critical facilities such as nuclear
power plants has increased interest in assessing the longevity of such
bearings and quantifying the expected stiffness changes over the service
life of several decades. This article gives the results over four
decades.
The average of the shear stiffnesses of the two Pelham (UK) bridges
tested after 38 years service is only 7% greater than the stiffness
observed for an original prototype. Mechanical tests on rubber specimen
prepared from a sectioned bearing show a drop in tensile properties of no
more than 30-40% in strength and elongation at break at depths of <10
mm from the surface. Tensile modulus shows a slight increase of 10-15%;
such stiffening, however was not always detected from the hardness
measurements at the surface. Analytical results show that the presence of
significant rubber oxidation and reactions involving the antidegradants
are confined within a surface zone extending to depths of only 10-20 mm.
The mechanical and analytical tests on rubber samples confirm that
aerobic changes were restricted to relatively close to the surface of the
bearings.
Increasing the life of NR pipe joint rings.
D.A. Hills. Materials & Quality Consultancy
Ltd. Rubber World, May 1999.
Many joint failures have occured as a result of microbiological
degradation (MD), and the severity of attack on many samples sighted
indicated that they would have failed within a few years if the affected
joints had not been replaced. In situ treatment of rings placed into
service appears to be possible through the use of a saturated chlorine
solution. This process will markedly increase the service life of the
rings.
The Rubber-Stichting has done a study in the
past on determining the biological attack of natural rubber.
A study of the biodegradation of
vulcanized rubber pipe-seals exposed to inoculated tap water.
G.A. Gerritse and A.O. Hanstveit. TNO Delft,
The Netherlands.
NR Technology 50, Vol. 19, No.3 1988
A new natural rubber vulcanizate has been tested for its resistance to
attack by the rubber-degrading bacterium Nocardia asteroides under
conditions which simulate those of rubber-seals in water supply pipes.
The vulcanizate was exposed to tap water inocculated with
rubber-degrading bacteria. The growth of bacteria on the surface of the
material and any resultant deterioration were monitored by scanning
electron microscopy, transmission electron microscopy, fluorescence
microscopy, visible counts in selective media and the determination of
tensile strength. After exposure for nearly two years the samples were
found to have no significant deteroriation.
Laboratory simulated aging and the effect on the
oxygen content in rubber
D. L. Schwarz, D. W. Askea, B. D.
Lambillotte, Rubber World, Vol. 230, No. 6, p. 26-31+47
It was found that the oxygen concentration in the aging gas directly
impacted the oxygen content in the samples and lead to accelerated
degradation of the samples.
Factors that affect the fatigue life of rubber:
a literature survey
W.V. Mars, A. Fatemi, Rubber
Chem.& Techn., Vol. 77, No. 3, p. 391-412
Describes primary factors of the effects of mechanical loading history,
environmental effects, effects of rubber formulation and effects due to
dissipative aspects of the constitutive response of rubber, and presents
and reviews literature.
Addressing durability of rubber compounds
N. M. Huntink, R. N. Datta, J. W. M.
Noordermeer, Rubber Chem.& Techn., Vol. 77, No. 3, p. 476-511
Reviews the developments on long-term protection of rubber against
aerobic ageing.
Biaxial tensile behavior of rubber vulcanizates;
1. Silica and gum stocks
K. Kajiwara, Y. Kameda, Y. Ikeda, H.
Urakawa, T. Kawamura, K. Urayama, S. Kohjiya, 611-623
Properties of NR samples filled with silica via both conventional and
in-situ methods were compared. Indications were found for differences in
the mechanism of storage of elastic free energy due to the filling
method.
Effect of network-chain length on strain-induced
crystallization of NR and IR vulcanizates
M. Tosaka, S. Kohjiya, S. Murakami,
S. Poompradub, Y. Ikeda, S. Toki, I. Sics, B. S. Hsiao, Rubber Chem.&
Techn., Vol. 77, No. 4, p. 711-723
Due to the lower crystallinity in IR the oriented amorphous component
will bear more stress in IR than in NR.
A comparison of the Hart-Smith model with Arruda-Boyce
and Gent formulations for rubber elasticity
G. Chagnon, G. Marckmann, E. Verron,
Rubber Chem.& Techn., Vol. 77, No. 4, p. 724-735
Describes the ability of the three closely related models to predict
strain responses and establishes equations that relate their material
parameters.
Modeling of stress-softening for elastomeric
materials
L. Gentot, M. Brieu, G. Mesmacque,
Rubber Chem.& Techn., Vol. 77, No. 4, p. 759-775
Describes the main process parameters that govern the stress-softening of
rubber-like materials and gives a model to predict the phenomena.
Effect of silane on the dispersion and
properties of silica in Natural Rubber for use in tyre tread compounds
A. Ansarifar, J. M. D. Lawton, R.
Nijhawan, Journal of Rubber Research, Vol. 7(3), 2004, p. 149-166
The coupling agent bis-(3-triethoxysilylpropyl)tetrasulphane (TESPT) can
improve silica dispersion, bound rubber, hardness, cyclic fatigue life
and cohesive tear strength, but can also detoriate tensile strength,
elongation at break and stored energy density at rupture.
Haftung von Gummi auf Stahlcord – Wirkung
von Mischungsbestandteilen (Effects of compound ingredients on rubber
adhesion to steel cord)
Y. Ishikawa, T. Hotaka, GAK 10/2004,
p. 642-652
Investigation of the influences of accelerators, sulphur and resins on
the adhesion between NR and brass.
Migration von Additiven in Gummi (Fate of
chemical additives migration in rubber)
G. Anthoine, F. Ignatz-Hoover, B. H.
To, GAK 10/2004, p. 653-662
Reviews the mechanisms that underlie the migration of additives in
uncured and cured rubber.
Preparation and characterization of radiopaque
natural rubber. Department of Polymer Science.
Nisha V.S, Rani Joseph. Science and
Rubber technology, Cochin University of Science and Technology, Cochin,
Kerala, India.
Chemistry and Technology, Vol. 79, No. 6, November-December 2006
Currently radiopaque polymers are of great interest to medicine and
dentistry because of their wide area of applications such as catheters,
tools, dental products, radiation shields, etc. Lead has historically
been used as the shielding material, but not without health and
environmental concerns. In this work, we have prepared radiopaque
materials from natural rubber (NR) through different routes. Radiopaque
NR was prepared using radiopacifiers like barites, barium sulfate, zinc
oxide and active zinc oxide. The physical properties of the NR
vulcanizates with different radio pacifiers were studied. Clinical X-ray
techniques have been used to confirm the radiopacity. The optical density
of the samples were measured and compared with that of conventionally
used lead shield.
Shape Factor and Carbon Black Loading Effect on
FEA Prediction of Bearing Behavior.
V.Luksameevanish, et al. Faculty of Science and Technology.
E-mail: mseadan@bunga.pn.psu.th. Journal of Rubber Research
Volume9(3), 3rd Quarter 2006
FEA prediction of shear behavior showed good agreement with the
experimental data of all four bearings compounds and no effect of shape
factor on shear stress was observed. Moreover shear stress did not depend
on the compressive force to which the bearing was subjected before shear;
and the FEA results agreed with the corresponding experimental results.
A new series of Natural Rubber and Processing
will be published in GAK (Gummi, Fasern und Kunststoffe)
Prof. Dr. Jorgen Schnetger
“Die Geschichte des
Kautschuks und siene Verarbeitung”
Teil 1: Naturkautschuk
Teil 2: Synthetic rubber
The paper(s) doesn’t give fundamental news to those who work with
the matter since long; however it is dedicated to the young people,
who always cone into this sticky business.
Physical Properties of NR during longterm
storage.
The physical properties during long term storage
of selected commercial standard Thai Rubbers (STR) showed that
storage-hardening occurred in the rubber samples even after carefully
controlled production processes with respect to storage time, indicating
that depth or positions of specimens in a certain bale did not affect the
storage-hardening phenomenon.
Effects
of rubber type on the curing and physical properties of silica filled
rubber compounds
C. H.
Shin, D. S. Kim
Polymers
for Advanced Technologies, 19 (8), 1062-1068 (2008)
This present
work investigates effects of several different rubber compounds
comprising the same amount of silica on the processability, curing
characteristics, and mechanical and viscoelastic properties.
The performance of the rubber compounds as tire tread materials
were investigated. Among the rubber types studied, SBR1721 compound
comprising natural rubber (NR) and styrene butadiene rubber (SBR) with
high styrene content was considered the most appropriate for application
to tire tread materials.
Comparative
study on strain-induced crystallization behavior of peroxide cross-linked
and sulfur cross-linked natural rubber
Y.
Ikeda, Y. Yasuda, K. Hijikata, M. Tosaka, S. Kohjiya
Macromolecules,
41 (15), 5876-5884 (2008)
This
work employs time-resolved wide-angle X-ray diffraction measurements at
SPring-8 for a comparative study of strain-induced crystallization (SIC)
behavior of natural rubber (NR) crosslinked by peroxide or sulfur.
The stretching ratio at the onset of SIC decreased with an increase of
network chain density for peroxide cross-linked NR (P-NR), while it
remained constant for sulfur crosslinked NR (S-NR). Similar
dependence of relative crystallization rates on network chain density was
found for both P-NR and S-NR. Calculated entropy differences between the
undeformed and the deformed states were equal for P-NR regardless of
network chain density, whereas it became smaller with the increase of
network chain density for S-NR. The SIC behavior of P-NR is in agreement
with the prediction or homogeneous or uniform networks by Flory. Thus,
the network structure of S-NR is supposed to be less homogeneous than
that of P-NR. The mechanical characteristics of S-NR and P-NR are also
discussed from the viewpoint of their SIC behaviors on the basis of the
network structures.
Effective
properties of carbon black filled natural rubber: Experiments and
modeling
B.
Omnes, S. Thuillier, P. Pilvin, Y. Grohens, S. Gillet
Composites
Part A-Applied Science and Manufacturing, 39 (7), 1141-1149
(2008)
Reinforcement
of natural rubber by carbon black comes from the filler-filler and
filler-rubber interactions, leading to an increase of the elastic
modulus, the tensile strength and the hysteresis. This work aims to
develop a model within a generalized self-consistent scheme for filled
rubber to predict the elastic moduli. A morphological pattern, which
takes into account the occluded rubber, the bound rubber and a
percolating network, is proposed and the effective elastic properties are
compared with experimental results obtained in both uniaxial and
oedometric compression. Two types of carbon blacks; N330 and N650,
were investigated in a range of 0% and 18% filler volume fraction.
The influence of the specific surface of the filler is also investigated.
Photooxidation
of dyed styrene-butadiene and natural rubbers
D.
Ruch, C. Becker, A. Riche, S. Etienne, J. Bour
Polymer
Science Series A, 50 (6), 716-720 (2008)
Aging
property of dyed natural rubber (NR) and styrene-butadiene rubber (SBR)
designed for outdoor applications were investigated after an exposure to
accelerated artificial aging in xenon light. A deterioration of the
properties of the exposed surface material was observed, and the
deterioration is largely determined not only by the photochemical
characteristics of the absorbing dyestuff itself but also by the polymer
structure and fillers. Dyed filled NR and SBR samples were found to
behave differently during photooxidation. The photodegradation
products were observed by Fourier transform infrared spectroscopy (FTIR)
to characterize the changes occurring in the rubber during UV aging. The
formation of cracks and the thickness of the degraded area on the dyed
SBR and NR materials were also assessed by environmental scanning
electron microscopy (ESEM). The fading of the dyed polymers and the
degradation thickness were found to be promoted in the NR sample.
For the NR sample, cracks appear initially at the surface and then grow
through the thickness of the specimen, while for the SBR sample cracks
are small and discontinuous.
Uncertainties
in the determination of cross-link density by equilibrium swelling
experiments in natural rubber
J. L.
Valentin, J. Carretero-Gonzalez, I. Mora-Barrantes, W. Chasse, K.
Saalwachter
Macromolecules,
41 (13), 4717-4729 (2008)
This
work discusses the equilibrium swelling method which is popularly used to
determine the cross-link density of networks. The method was
considered to give highly uncertain values and, moreover, the
Flory-Rehner treatment could only give a qualitative evaluation of
cross-link density because of its strong dependence on the thermodynamic
model. In this work, the uncertainties in the determination of the
crosslink density in rubber materials by swelling experiments based on
this model are reviewed. The implications and the validity of some of the
used approximations as well as their influence in the relationship of the
crosslink densities derived from swelling experiments are
discussed. The swelling results are compared with results of a
crosslink density independently determined by proton multiple-quantum
NMR. The correlation observed between the two methods was used to
validate the thermodynamic model.
Prediction
of the ageing of rubber using the chemiluminescence approach and
isoconversional kinetics
F.
Kaser, B. Roduit
Journal
of Thermal Analysis and Calorimetry, 93 (1), 231-237
(2008)
Prediction
of long-term stability is difficult for many product formulations.
This works reports a use of chemiluminescence method to measure the
oxidative aging of rubber and predicting the life time of rubber
items. Kinetic analysis of the oxidation reactions of natural
rubbers with and without stabiliser in an oxygen atmosphere at moderate
temperatures using CL measurements was carried out on a newly-developed
instrumentation. The kinetic parameters of the oxidation process,
calculated from the chemiluminescence's signals by means of the
differential isoconversional method of Friedman, were subsequently
applied for the simulation of the rubber aging under different
temperature profiles.
Rheological
and physico-mechanical properties of natural rubber filled with welder's
used carbide waste
E.
Osabohien, S. H. O. Egboh, J. E. Imanah
Journal
of Polymer Materials, 25 (1), 77-84 (2008)
Welder's
Used Carbide Waste (WUCW) was applied as filler singly and in blends with
carbon black (N330) filler in natural rubber NR) compounding using
efficient vulcanization system. The waste was collected, air dried,
screened with 75nm sieve, and then analysed for its moisture content,
loss on ignition, iodine adsorption number, oil absorption, pH, metal
oxides and silica contents. Various properties, such as scorch
time, cure time, maximum torque, tensile strength, modulus (M100),
elongation at break, specific gravity, resilience and hardness, were
determined. The WUCW-filled NR showed cure enhancement and
significant increase in tensile strength and hardness upto optimum of 50
phr filler loading before decreasing. The modulus (M100), elongation at
break and resilience decreased slightly while specific gravity increased
with increasing filler content. The results of the WUCW-filled NR
vulcanizates showed inferiority in reinforcement compared to standard
carbon black(N330) filled NR vulcanizates.
Mechanical
behavior and microhardness of swollen natural rubber loaded with carbon
black
M.
Abu-Abdeen, A. A. Almulhem, A. Sedky
Journal
of Applied Polymer Science, 109 (5), 3361-3368 (2008)
Swollen
natural rubber loaded with 40 phr high abrasion furnace carbon black was
characterized for its mechanical behavior and microhardness
characteristics. The Young's modulus, tensile strength, elongation
at break, and hardness varied with the swelling time in kerosene. Taken
into account the strain rate sensitivity, different models were applied
to describe this mechanical behavior. It was found that the Mooney-Rivlin
relation agreed with the experimental data at low extension ratios, whereas
the Blatz relation agreed at high extension ratios only. The strain
energy density as a function of the swelling time in kerosene was
calculated with three different equations.
Measurement
of volume changes of elastomers at high strain rates
G. F. Schneider, M. Kerscher, D. Goritz
KGK-Kautschuk
Gummi Kunststoffe, 61 (6), 317-321 (2008)
Volume
changes of elastomers on extension were measured using an in-house made
device. Measurements which could be done within milliseconds were carried
out with strain rates varying up to 1000 % per second. It was found
that the increase of volume of natural rubber filled with both inactive
and active fillers is independent of the strain rate. Moreover, the high
volume change does not relax at constant strain. The stress acting on the
surface caused the onset of void formation at the filler surface.
The
effect of scragging strain on the dynamic mechanical properties of filled
rubber
J.
Kingston
Journal
of Rubber Research, 11 (1), 1-12 (2008)
Filled
natural rubber (NR) and styrene-butadiene rubber (SBR) compounds were
scragged to a series of increasing shear strains, and the effect of this
on the dynamic properties at the lower strains were measured. After a
long period, the tests were repeated to measure the recovery in the
materials. Increasing the scragging strain was found to cause the
rubber stiffness at lower strains to fall continuously, with no sign that
it would reach a constant value. Even though there was some
recovery over time, it is not thought that the rubber would ever recover
its initial stiffness.
A
study on the material properties and fatigue life prediction of natural
rubber component
C. S. Woo, W. D. Kim, J. D. Kwon
Materials
Science and Engineering A-Structural Materials Properties Microsctructure
and Processing, 483, 376-381 (2008)
Attempts
were made to predict fatigue lifetime of the rubber component by
incorporating the finite element analysis and fatigue damage parameter
from fatigue test. Finite element analysis of rubber component was
performed based on a hyper-elastic material model determined from
material test. The Green-Lagrange strain at the critical location
determined from the finite element method was used to evaluate the
fatigue damage parameter of the natural rubber. Fatigue life of rubber
components was predicted by using the fatigue damage parameter at the
critical location. Predicted fatigue life of the rubber component agreed
fairly well with the experimental fatigue lives.
Comparative
study of the elasticity and permeability of vulcanized films made with
skim and cream natural rubber latex
S.
Winsunthorn, F. Bonfils, C. Pochat-Bohatier, D. Bouyer, A. Deratani, C.
Dupuy
Journal
of Applied Polymer Science, 108 (2), 960-968 (2008)
The elasticity
and permeability to acetone of the films made with skim and cream latex
from Hevea brasiliensis were comparatively investigated. Surface
characterization by atomic force microscopy revealed that vulcanization
substantially modified the structure of the films. The vulcanized films
made with cream latex retained their particle identity even after 4 weeks
of aging, which was differed from unvulcanized films. The
vulcanized films made with skim latex showed greater elasticity than
those obtained with cream latex, indicating more entanglements between
polyisoprene chains and associations between proteins. Both skim
and cream vulcanized films showed very similar acetone permeability
despite differences in the structure.
Fatigue
life prediction of vulcanized natural rubber under proportional and
non-proportional loading
Y.
Wang, W. Yu, X. Chen, L. Yan
Fatigue
& Fracture of Engineering Materials & Structures, 31 (1), 38-48
(2008)
The
multiaxial fatigue properties of vulcanized natural rubber (NR) were
investigated through a series of tests including both proportional and
non-proportional loading paths on small specimens. The existing fatigue
life prediction approaches are evaluated with life data obtained in the
tests. It is shown that the equivalent strain approach presents a good
prediction of the fatigue life although it has a certain shortcoming.
Several models for a prediction of the fatigue life of materials were
comparatively tested.
Effects
of hot-air aging and dynamic fatigue on the structure and dynamic
viscoelastic properties of unfilled natural rubber vulcanizates
P.
Zhang, X. Y. Shi, J. Li, G. S. Yu, S. G. Zhao
Journal
of Applied Polymer Science, 107 (3), 1911-1916 (2008)
The network structure and dynamic viscoelastic properties of
unfilled natural rubber (NR) vulcanizates which have been subjected to
hot-air aging and dynamic tensile fatigue were investigated with magnetic
resonance crosslink density spectrometry, Fourier transform infrared
spectroscopy /attenuated total reflection (FTIR-ATR), and dynamic
mechanical analysis. A carbonyl weak absorption peak at 1723 cm-1
in the FTIR-ATR spectra of unfilled NR after hot-air aging was
observed. Increasing ageing times decreased the crosslink density
continuously. An aged specimen showed a considerably declined
dynamic modulus, and a greatly increased value of tan delta. The
FTIR-ATR spectra of unfilled NR vulcanizates before and after tensile
fatigue showed a large difference. The peaks at 1597, 1415, and 1015
cm-1 were found to increase concurrently with the tensile
fatigue time. Initial analysis suggested that structures such as
conjugated dienes appeared in the network structure.
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Product Applications
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An overview of tyre technology
D. Beach and J. Schroeder, Cooper Tire &
Rubber. Rubber World, September 2000, page 45 - 53.
The automotive industry will likely continue to
press the tyre manufactures to design and produce lighter weight, more
fuel-efficient tyres to help conserve our petroleum resour-ces. A tyre
produced today require three to four gallons of oil during the
manufacture of the various polymers and tyre components – as oil
prices rise, both raw material cost and the cost to operate vehicles will
rise. This will likely spur the development of new, less oil dependent
raw materials that will also provide for lower rolling resistance tyres.
Design of EPDM for blends with NR/BR for tyre
sidewalls: Influence of molecular structure and carbon black distribution
on properties
P.M. van de Ven and J. W. M. Noordermeer,DSM
Elastomers. Rubber World, September2000, page 55 - 60.
The physical properties, and especially the tear
and tensile strength of vulcanizates based on NR/BR/EPDM blends, have
been studied as a function of the EPDM's struc-tural parameters. Contrary
to what is commonly assumed, these experiments show that the ethylene
content of EPDM is dominant over molecular weight and unsaturated level.
Therefore, it can be stated that the influence of the filler distribution
plays a much more important role than the degree of crosslinking.
Finally, the present study suggests that the carbon black distribution
over the individual NR/BR and EPDM phases are controlled by the EPDM
structural parameters.
Naval applications of elastomers
C. M. Roland, Rubber Chem.&
Techn., Vol. 77, No. 3, p. 542-551
Describes applications which exploit rubber’s capacity for energy
transmission, storage and dissipation.
Adhesion
properties of pressure-sensitive adhesives prepared from SMR 10/ENR 25,
SMR 10/ENR 50, and ENR 25/ENR 50 blends
B. T.
Poh, A. L. Lim
Journal
of Applied Polymer Science, 109 (1), 115-119 (2008)
Blends
of natural rubber/epoxidized natural rubber with blend ratio ranging from
0 to 100%, together with coumarone-indene resin as the tackifier and
toluene as the solvent, were investigated for their adhesion properties,
i.e. viscosity, tack, and peel strength of pressure-sensitive
adhesives. One grade of natural rubber (SMR 10) and two grades of epoxidized
natural rubbers (ENR 25 and ENR 50) were used to prepare the
blends. Coumarone-indene resin content was fixed at 40 phr in the
adhesive formulation. Results show that the viscosity of the
adhesive, measured by a HAAKE Rotary Viscometer, passes through a minimum
value at 20% blend ratio. For loop tack and peel strength which were
determined using a Lloyd Adhesion Tester operating at 30 cm/min, a
maximum at 60% blend ratio for SMR 10/ENR 25 and SMR 10/ENR 50 systems
was observed. However, for ENR 25/ENR 50 blend, maximum value was
observed at 80% blend ratio. In this study, SMR 10/ENR 25 blend
exhibits the best adhesion property, which is attributed to the optimum
compatibility between rubbers and wettability of adhesive on the
substrate.
Estimation
of shelf life of natural rubber latex exam-gloves based on creep behavior
S. S. Das, L. W. Schroeder
Journal
of Biomedical Materials Research Part B-Applied Biomaterials, 85B (2),
398-408 (2008)
Creep
testing was performed on rectangular specimens of aged and unaged glove
fingers as an assessment of glove loosening during usage. Samples
from chlorinated and nonchlorinated latex medical examination gloves were
aged at 25% relative humidity for various times at several fixed
temperatures, and creep testing was carried out using an applied stress
of 50 kPa. Variations in creep curves obtained were compared to
determine the threshold aging time when the amount of creep became larger
than the initial value. These times were subsequently used in various models
to estimate shelf lives at lower temperatures. Several different methods
of extrapolation were used for shelf-life estimation and comparison.
Characterization
of purified SKIM rubber by alkali treatment for pressure sensitive
adhesive application
K.
Nawamawat, J. T. Sakdapipanich, N. Phuphewkeaw
KGK-Kautschul
Gummi Kunststoffe, 61 (4), 147-151 (2008)
Skim
rubber (SK) shows a good solubility due to the lack of gel phase.
This material was therefore investigated for pressure sensitive adhesive
applications. Non-rubber components in SK were removed via
saponification by alkali treatment under the suitable reaction time and
temperature in order to prepare highly-purified SK (HPSK). The nitrogen
content in SK was reduced to ca. 0.1%w/w, whereas the ester content
slightly decreased. The rolling ball method and 180 degrees peel
tests were applied to evaluate the tackiness and the adhesion properties
of HPSK, respectively. It was found that proteins were an important
factor controlling tackiness property, while the adhesion property
depended on both proteins and phospholipids. The results indicated that
HPSK could be used efficiently as raw material for pressure sensitive
adhesives as its tackiness and adhesion properties are comparable to
those of adhesive tapes prepared from ribbed-smoke sheet (RSS).
Effect
of blend ratio on adhesion properties of pressure-sensitive adhesives
prepared from SBR/SMR L blends
B. T. Poh, S. S. Heng
Polymer-Plastices
Technology and Engineering, 47 (3), 325-329 (2008)
Pressure
sensitive adhesives were prepared from SBR/SMR L blends with a use of
coumarone-indene resin and toluene as the tackifier and solvent,
respectively. The blend ratio of SBR/SMR L was varied from 0 to
100% whereas the resin content was increased from 40 to 120 phr in the
adhesive formulation. The viscosity was determined by a HAAKE rotary
viscometer. The loop tack and peel strength of paper/polyethylene
terephthalate film were measured using a Lloyd adhesion tester operating
at 30cm/min. The adhesive viscosity decreases with % SBR but
increases with resin loading. Loop
tack of adhesive indicates a maximum value at 20% SBR for all resin
loadings, whereas the peel strength exhibits maximum value at 40%
SBR. An observation is attributed to the optimum wettability of
adhesive on the substrate where formation of mechanical interlocking
occurs.
Natural
rubber filled SiC and B4C ceramic composites as a new NTC thermistors and
piezoresistive sensor materials
Z.
Todorova, N. Dishovsky, R. Dimitrov, F. El-Tantawy, N. A. Aal, A.
Al-Hajry, M. Bououdina
Polymer
Composites, 29(1), 109-118 (2008)
Conductive
SiC and B4C were homogeneously dispersed in an insulating natural rubber
(NR) matrix in order to prepare a novel electrically conductive composite
for NTC thermistor and piezoresistive sensor. The composites were
investigated for their morphology, crosslink density, volume fraction of
rubber, and interparticle distance among conductive phases. The influence
of the filler concentrations on the mechanical properties such as modulus
of elasticity, hardness and elongation at break were studied. Effects of
B4C and SiC concentrations on the volume resistivity of NR based
composites were investigated. Temperature dependencies of volume
resistivity were also measured to examine the possible application of the
composites to polymer linear negative temperature (NTC) thermistors. The
thermal stability of the composites was examined by means of resistivity
temperature and pressure hysteresis cycle for practical application. In
parallel, the conduction mechanism of conductivity of the composites was
interpreted in terms of the computed the activation and hopping energy.
The results of mechanical properties and thermal stability of NR
composites showed that the composites can be utilized for fabricating
various electronic devices as NTC thermistors and piezoresistive
sensor.
Effect
of foaming temperature and rubber grades on properties of natural rubber
foams
Z. M.
Ariff, Z. Zakaria, L. H. Tay, S. Y. Lee
Journal
of Applied Polymer Science, 107 (4), 2531-2538 (2008)
Effects
of foaming temperature and grade of dry natural rubber on the morphology
and mechanical properties of natural rubber (NR) foams were
evaluated. Three different grades of NR; ENR-25, SMR-L, and SMR-10;
and three different foaming temperatures; 140, 150, and 160 oC
were studied. The NR foams were prepared using sodium bicarbonate as the
chemical blowing agent, and were expanded using conventional compression
molding technique via a heat transfer foaming process. Their relative
foam density, density of crosslinking, cell size, compression stress, and
compression set were investigated. It was found that increase in foaming
temperature resulted in lower relative density, larger cell size, and a
slight decrease of crosslink density. The highest foam density
resulted in the highest compression stress. ENR-25 foam was found to have
the highest compression stress among the produced foams. The results
showed that the foaming temperature and rubber grades have a strong
influence on the morphology, physical, and mechanical properties of the
rubber foams.
Breathable
film from reactive processing of LLDPE/NR blends with ENR and maleic
anhydride
P.
Tasanatanachai, N. Singsat, A. M. Jamieson, R. Magaraphan
International
Polymer Processing, 23 (2), 146-151 (2008)
Blends
of linear-low density polyethylene, natural rubber, and epoxidized
natural rubber with a small content of maleic anhydride as a reactive
coagent were prepared via reactive blending and processing to yield the
high oxygen permeability film, so-called breathable film. The
breathable films have the foam-like structure which was created by the
reaction between the functional groups during the extrusion. Oxygen
permeability of the blended films can be controlled by the blend
composition, screw speed, and draw ratio during the chill-roll casting
step. The good breathablility and the outstanding UV screening with a
small transparency trade-off made the films suitable to be used in
agricultural applications to enhance the growing and production of
various.
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Health and Environmental Issues
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Review and the latest update of N-nitrosamines
in the rubber industry; the regulated, the potentially regulated. And
compounding to eliminate nitrosamine formation
L.C. Goss Jr., S. Monthey and H.-M.
Issel Rhein Chemie Corporation. Rubber Chemistry and Technology. Vol.7,
pg 541-552.
For several years, Germany
has led the effort to eliminate the use of common nitrosamines in the
rubber industry. Their TRGS 522(Nov 95) allows no more than 2.5 µg/m3
emission of nitrosamines between vulcanization and warehousing.
Additionally, major U.S. Automobile manufacturers have issued stringent
requirements with regards to the use of nitrosamines. One company has
issued a restricted standard that prohibits the use of nitrosamines in
excess of the 0.1% threshold value of the part’s total weight. With
over 300 nitrosamines listed as either known or suspected carcinogens,
safety continuous to drive the elimination of nitrosamines in the rubber
industry. Therefore, this is a review of nitrosamine regulations,
identification of nitrosamines, how they are formed, and the latest in
compounding essentials to produce non-nitrosamines generating compounds.
Gerüche aus NK – Bestimmung chemischer
Bestandteile (Detection of chemical components that cause mal-odour from
Natural Rubber)
V. Hoven, K. Rattanakaran, Y. Tanaka,
GAK 12/2004, p. 783-790
Indicates that by-products of non-rubber components cause mal-odour due
to microbial breakdown during storage or thermal degradation during
processing.
Latex
allergy: Two educational cases
L.
Baker, J. O. Hourihane
Pediatric
Allergy and Immunology, 19 (6), 477-481 (2008)
Health
care workers and children with complex medical and surgical conditions
that require multiple surgical interventions are subjected to natural
rubber latex (NRL) allergy. To identify the high risk groups such
as spina bifida (SB), primary and secondary prophylaxes are effective
measures. With proper attention to prevention and secondary prophylaxis
in the highest risk groups, the numbers of paediatric SB patients with
NRL allergy will continue to decrease.
An
assessment of the endotoxin contents of Natural Rubber latex medical
gloves
A.
Ikram, M. Y. Amir-Hashim
Journal
of Rubber research, 11 (1), 29-35 (2008)
The
endotoxin levels of Malaysian Natural Rubber (NR) latex medical gloves
were determined by a kinetic turbidimetric Limulus Amoebocyte Lysate
(LAL) assay. Based on the results from 39 pairs of sterilised
surgical gloves and 21 pairs of non-sterilised examination gloves from
various brands, the endotoxin concentrations was found in a range from
3.2 to 114.1 EU/glove pair for surgical gloves and from <8.4 to 9,632
EU/glove pair for the examination gloves. It was found that 72% of
surgical gloves, had endotoxin activity below the specified FDA standard
of 20 EU/device, while only 38% of the non-sterilised examination gloves
had values below the specified level. However, this study found no
correlation between endotoxin concentrations and the presence of glove
powders.
Latex
allergy: new insights to explain different sensitization profiles in
different risk groups
C.
Peixinho, P. Tavares-Ratado, M. R. Tomas, L. Taborda-Barata, C. T.
Tomaz
British
Journal of Dermatology, 159 (1), 132-136 (2008)
Differences
in latex allergen sensitization profiles have been described between
children subjected to repetitive surgical interventions and health care
workers (HCW). 'Major' allergens for patients with spina bifida are Hev b
1, 3 and 7, while for HCW, 'major' allergens are Hev b 2, 5, 6.01 and 13.
The aim of this work is to investigate latex allergen profiles on
internal and external surfaces of natural rubber latex gloves. Eighty-two
samples of commonly used surgical gloves were used for analysis. Specific
allergen levels of Hev b 1, 3, 5 and 6.02 on both surfaces of the gloves
were quantified using an enzyme immunometric assay. Differences in
allergen levels were observed between internal and external surfaces of
all glove types. Concentrations of Hev b 1 and Hev b 3 were significantly
higher on external surfaces, while internal surfaces had higher allergen
levels of Hev b 5 and Hev b 6.02.
Latex
allergy: a model for therapy
J. M.
Rolland, R. E. O'Hehir
Clinical
and Experimental Allergy, 38 (6), 898-912 (2008)
High-risk
groups to natural rubber latex allergy include latex glove users, spina
bifida patients and others with multiple surgical procedures. Following
the significant advances in the identification and characterization of
common aeroallergens, latex allergy was become an excellent model of
therapy. Awareness
of latex allergy and modes of sensitization enabled epidemiological
studies to inform allergen avoidance initiatives, substantially reducing
inadvertent exposure in major hospitals in Western countries. Spina
bifida is often identified in utero or soon after birth, allowing
vigorous latex allergen avoidance with enhanced efficacy of primary
prevention. Identification
of allergenic components of latex products, with generation of monoclonal
antibodies and recombinant allergens, allowed sequence determination and
mapping of T cell and B cell epitopes. Together, these reagents and data
facilitated improved diagnostics and investigation of novel-specific
therapeutics. Potential hypoallergenic latex preparations identified
include modified non-IgE-reactive allergen molecules and short T cell
epitope peptides. The co-administration of adjunct therapies such as
anti-IgE or corticosteroids and of appropriate adjuvants for induction of
regulatory T cell response offers promise for clinically effective, safe
latex-specific vaccines.
Sensitivity
and specificity of different skin prick tests with latex extracts in
pediatric patients with suspected natural rubber latex allergy - A cohort
study
R.
Bernardini, N. Pucci, C. Azzari, E. Novembre, M. De Martino, M.
Milani
Pediatric
Allergy and Immunology, 19 (4), 315-318 (2008)
Since
there are no direct clinical comparisons between sensitivity and
specificity of different latex extracts in patients with clinically
confirmed latex allergy, the objective of this study was therefore to
evaluate sensitivity and specificity of non-ammoniated or ammoniated Skin
prick tests (SPT) of latex extracts in children with a clinical history
suggestive of NRL allergy. The Forty-two subjects (age 4-15 yr)
with suspected clinical signs of NRL allergy were evaluated. SPT for
latex were performed with three different SPT solutions; two of non-ammoniated
NRL extracts and one of an ammoniated extract. No difference between the three products was
observed regarding diagnostic specificity. This study shows that
diagnostic sensitivity of different latex extract for SPT could differ.
Ammoniated latex extract shows a higher sensitivity in comparison
with non-ammoniated products. The diagnostic of
suspected NRL allergy shall consider this different
sensitivity.
Epidemiology
of latex allergy in healthcare workers
F. L.
Filon, R. Cerchi
Medicina
Dellavoro, 99 (2), 108-112 (2008)
Prevalence
and incidence of latex sensitisation and symptoms in health care workers
was evaluated based on an analysis using the reported data from the
scientific literature and from the follow-up study in health care workers
in Trieste Hospitals carrying on since 1999. It was found that
latex allergy and sensitization, evaluated by skin prick test, are
significantly higher in health care workers respect to the general
population with symptoms, such as urticaria, rhinoconjunctivis and
asthma, ranging between 4 and 5.6%. The reduction of symptoms and
incidence sensitisations can be achieved after the changeover to a
powder-free environment and the avoidance of unnecessary glove use.
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