Rice husk ash is mainly composed of silica and carbon black remaining from incomplete combustion. Both silica and carbon black have long been recognized as the main reinforcing fillers used in the rubber industry to enhance certain properties of rubber vulcanizates, such as modulus and tensile strength. In this study, two grades of rice husk ash (low-and high-carbon contents) were used as filler in natural rubber.Comparison was made of the reinforcing effect between rice husk ashes and other commercial fillers such as talcum, china clay, calcium carbonate, silica, and carbon black. Fourier transform infrared spectroscopy (FTIR) analysis was employed to study the presence of functional groups on the ash surface. The effect of silane coupling agent, bis(3-triethoxysilylpropyl)tetrasulfane (Si-69), on the properties of ash-filled vulcanizates was also investigated. It was found that both grades of rice husk ash provide inferior mechanical properties (tensile strength, modulus, hardness, abrasion resistance, and tear strength) in comparison with reinforcing fillers such as silica and carbon black. However, the mechanical properties of the vulcanizates filled with rice husk ash are comparable to those filled with inert fillers. The addition of silane-coupling agent has little effect on the properties of the ash-filled vulcanizates. This is simply due to the lack of silanol groups on the ash surface.

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Abstract. The effect of blend ratio on properties of chloroprene rubber/natural rubber (CR/NR) blends was investigated. In addition to the mechanical properties, attention was also given to the resistance to thermal aging, oil and ozone of the blends. Silica was selected as a reinforcing filler in this study due to its unique characteristic to interact with CR. The results reveal that, due to the better filler dispersion and the greater crosslink density, the silica-filled CR possesses lower compound viscosity and better mechanical properties, compared to the silica-filled NR. The aging properties, oil and ozone resistance of the silica-filled CR are also significantly better than those of the silica-filled NR. The mechanical properties and the resistance to degradation of the silica-filled CR/NR blends are mainly governed by the blend morphology. It is found that good mechanical properties in association with adequately high resistance to degradation from thermal aging and oil are obtained when CR remains the matrix in the blends. Even though the ozone cracks are found in all blends, a thorough look at the results reveals that considerable improvement in ozone resistance is achieved with increasing CR content.

Influence of silanization temperature on properties of silica‐filled solution polymerized styrene butadiene rubber was investigated. Two types of silica, i.e., highly dispersible silica (HDSi) and conventional silica (CSi), were compared. Results show that the increased silanization temperature leads to the enhanced rubber–filler interaction, filler dispersion, and cross‐link density giving rise to the improvement in vulcanizate properties such as modulus, heat build‐up (HBU), and dynamic set, as well as tire performance, e.g., wet grip (WG), rolling resistance (RR), and abrasion resistance. Great care, however, must be taken to avoid the scorching phenomenon during the mixing process at too high temperature. Taken as a whole, the balanced properties are found at the silanization temperature of 140°C. Surprisingly, HDSi provides insignificant differences in degree of filler dispersion, WG, and RR, compared to CSi, despite its claimed greater dispersability. Probably, the relatively long mixing time used in this experiment may override the influence of silica type. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43342.

Blends of 75/25 chloroprene rubber(CR)/ natural rubber (NR) filled with various loadings of precipitated silica were prepared and their processability and mechanical properties as well as their resistance to thermal aging and oil were determined. The blend morphology was also studied using the atomic force microscopy technique. The results reveal that the mixing energy and the Mooney viscosity of the compound are increased continuously with increasing silica loading. It is also found that both scorch and optimum curing times are shortened while the total crosslink density is increased with increasing silica loading. The positive effect on cure could be explained by the chemical reaction between the allylic chlorine atom of CR and the silanol group on silica surface. The tensile strength, modulus, and hardness of the blend vulcanizate are noticeably improved while the compression set at elevated temperature is impaired with increasing silica loading. The results also reveal that both thermal aging resistance and oil resistance of the blend vulcanizates, as represented by the relative properties, are enhanced with the addition of silica. The resistance enhancement is believed to arise from the combination of the dilution effect, the increased crosslink density and also the reduction of NR dispersed phase size.

Properties of natural rubber (NR) filled with various fillers, i.e., furnace black (N330), conductive carbon black (XE2-B), and carbon nanotube (CNT) were investigated. Both untreated and sonicated carbon nanotubes were used and designated as U-CNT and S-CNT, respectively. The filler content was varied from 0 to 8 phr. Regardless of the filler type, the increase in the filler content not only results in increased compound viscosity, reduced cure time, and enhanced cross-link density but also leads to the increase in the modulus and hardness of the vulcanizates. For N330 and XE2-B, the tensile strength increases continuously with increasing filler content. However, for both U-CNT and S-CNT, the tensile strength tends to increase with increasing filler content up to 2 phr and decreases noticeably afterward. At any given filler content, the CNTs give the vulcanizates with the highest values of electrical and thermal conductivities, storage modulus, and tan δ, followed by XE2-B and N330, respectively. Results also elucidate that the sonication of CNT without the presence of surfactant prior to mixing could not improve the degree of CNT dispersion, leading to insignificant difference in properties of the U-CNT-filled and S-CNT-filled vulcanizates. C