NR Composites Research Articles

Influence of the cure systems on long time thermal aging behaviors of NR composites

NR composites with different curing systems were aged thermally at 60, 70, 80, and 90 °C for 2–185 days in a convection oven, and the changes in the crosslink density were investigated as a function of the accelerated thermal aging. The overall crosslink densities increased with increasing aging time irrespective of the aging temperatures and curing systems. The changes in crosslink density were enhanced by increasing the aging temperature. The degree of the increased crosslink density was in the following order: “the conventional cure system > the semi-EV system > the EV system”. For short term thermal aging, the change in crosslink density with the aging time was complicated, particularly for low temperature aging. The activation energies of the change in crosslink density with thermal aging using the conventional and semi-EV cure systems increased and then remained relatively constant with increasing aging time, whereas that of the specimen with an EV cure system tended to increase linearly. The experimental results were explained by the dissociation of the existing polysulfidic linkages and the formation of new crosslinks through the crosslinking-related chemicals remaining in the sample.

Processing and Material Characteristics of a Carbon‐Nanotube‐Reinforced Natural Rubber

AbstractCNT/NR composites were fabricated based on a CNT treatment using an acid bath followed by ball‐milling with HRH bonding systems. Thermal properties, vulcanization characteristics and mechanical properties of the CNT/NR composites were characterized. Compared to CB, the incorporation of CNTs into NR was faster and the energy consumption was less. The over‐curing reversion of CNT/NR composites was alleviated. After acid treatment and ball‐milling, the dispersion of CNTs in the rubber matrix and the interaction between CNTs and the matrix was improved. The performance of the CNT/reinforced NR composites was enhanced by the incorporation of the treated CNTs as compared to neat NR and CB/NR composites.magnified image

Influence of thermal aging on pyrolysis pattern of carbon black-filled NR composite

NR composites were aged at 60 oC for 10 to 185 days and the aged samples were pyrolyzed using pyrolysis-GC/MS. Isoprene, toluene, xylene, 1,4-dimethyl-4-vinylcyclohexene, and 1-methyl-4-(1-methylethenyl)-cyclohexene were detected as the major pyrolysis products. The 1,4-dimethyl-4-vinylcyclohexene and 1-methyl-4-(1-methylethenyl)-cyclohexene are the isoprene dimer species. Peak intensity ratio of the isoprene dimers/isoprene decreased until 100 days of the aging time and then slightly increased. The decreased trend of the isoprene dimers/isoprene ratio before 100 days of the aging time was due to the increased crosslink density by thermal aging. The slightly increased ratio after 100 days of the aging time might be due to the distribution of the free chain length between crosslink points.

Structure and properties of strain‐induced crystallization rubber–clay nanocomposites by co‐coagulating the rubber latex and clay aqueous suspension

AbstractNatural rubber (NR)–clay (clay is montmorillonite) and chloroprene rubber (CR)–clay nanocomposites were prepared by co‐coagulating the rubber latex and clay aqueous suspension. Transmission electron microscopy showed that the layers of clay were dispersed in the NR matrix at a nano level, and the aspect ratio (width/thickness) of the platelet inclusions was reduced and clay layers aligned more orderly during the compounding operation on an open mill. However, X‐ray diffraction indicated that there were some nonexfoliated clay layers in the NR matrix. Stress–strain curves showed that the moduli of NR were significantly improved with the increase of the amount of clay. At the same time, the clay layers inhibited the crystallization of NR on stretch, especially clay content of more than 10 phr. Compared with the carbon‐black‐filled NR composites, NR–clay nanocomposites exhibited high hardness, high modulus, high tear strength, and excellent antiaging and gas barrier properties. Similar to NR–clay nanocomposites, CR–clay nanocomposites also exhibited high hardness, high modulus, and high tear strength. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 318–323, 2005

Rheological Effect of Zinc Surfactant on the TESPT-Silica Mixture in NR and S-SBR Compounds

Abstract The effects of zinc surfactant (ZB) on the TESPT (bis(triethoxy-silylpropyl)tetrasulfide)-silica mixture in NR (isoprene rubber) and S-SBR (solution butadiene-co-styrene rubber) were investigated, and their processability, dynamic, mechanical, heat build-up, blowout properties, and silica dispersion characteristics were compared. In the NR composite, the addition of ZB increased the reversion resistance time, tensile modulus, and blowout time and lowered the viscosity, heat build up, and tanδ values. In the S-SBR composite, the addition of ZB increased the heat build up, and tanδ values and lowered the reversion resistance time, tensile modulus, blowout time, viscosity, and tanδ values of the compound. Over all, in the NR compounds, addition of the ZB significantly increased the processability and mechanical property; however, in the S-SBR compounds, it increased the processability but it was not effective in improving mechanical property.

Influence of static and cyclic compression on the electrical conductivity of FEF black‐loaded rubbers

It was found that the electrical conductivity of fast extrusion furnace black-loaded rubber vulcanizates (SBR, NR, BR, NBR, IIR) is most pressure sensitive for the SBR and NR composites and exhibits a slight dependence upon the number of compression cycles. In addition, the temperature coefficient of conductivity for SBR shows a weak dependence upon the stress amplitude and the number of compression cycles

Electrical Conductivity and ESR Studies of Carbon-Black-Loaded Natural Rubber

Abstract The results of electrical conductivity and electron spin resonance (ESR) measurements on NR with four types of carbon black filler were reported. Two forms of space change limited current (SCLC) were identified, indicative of different electron trap energies, depending on the type of carbon black filler. Such SCLC behavior, with steep trap-filling regions on the current-voltage curves, is indicative of trap-dominated transport in the polymer regions of carbon-black—NR composites. Discrete shallow traps are evident for two of the compositions; deeper, exponentially distributed traps for two others. ESR spectra of the composites are very pronounced, with lineshape also depending on the type of carbon black used. Observed g-values are close to that of the free electron, and don't vary with carbon black type or temperature. Linewidths narrow and increase in intensity with increasing amount of carbon black, with no detectable g-value shift, indicative of exchange narrowing from nonorbital electrons. T...

Short Silk Fiber Reinforced Natural Rubber Composites

Abstract (1) The resorcinol-hexa-silica bonding system is essential for NR-silk fiber systems. (2) Mechanical anisotropy is observable only at higher fiber loadings (20 phr and above) in NR-silk fiber systems. (3) In composites containing a sufficient amount of bonding agents and fibers for tensile anisotropy to be observed, tensile failure occurs by both fiber breakage and debonding. (4) Addition of silk fiber to NR causes (a) increase in hardness, (b) reduction in resilience and elongation at break, (c) increase in heat buildup and set, and (d) increase in tear resistance. (5) The aging resistance of silk fiber-reinforced NR composites is excellent only beyond a fiber loading of 20 phr. (6) Mill shrinkage and green strength of NR improve, while Mooney viscosity and scorch time increase with the addition of silk fiber to NR.