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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 App | |
