Assessment of phenolic resin as a curing agent for silica-filled natural rubber composites

Silica-reinforced natural rubber composites cured with sulfur and phenolic resin were prepared in this study. The properties were monitored through the rheological characteristics, mechanical strength, and dynamic mechanical analysis of the composites. Maximum torque and torque difference increased with silica loading in all cases, but the composites cured with phenolic resin showed greater changes. The composites cured with the phenolic resin also showed greater swelling resistance, crosslink density, stress at different strains, and tensile strength compared to composites with the sulfur system. The highest tensile strength was observed at 30 phr silica loading, with about 38% improvement for phenolic resin and about 6% for sulfur systems compared to their unfilled controls. Hydrogen bonding or condensation reactions possibly took place between phenolic resin and silica filler in the phenolic cured composites, whereas such interactions were absent in the cases with the sulfur system. This was confirmed by monitoring the silica aggregation and Payne effect. Although the phenolic resin is considered the second-choice system for silica-reinforced natural rubber composites. However, this study has demonstrated their performance as a system of choice for silica-based rubber composites.