Effect of loading and particle size of rubber powder vulcanizate on physical properties of natural rubber compound

The cure characteristics, rheological property, and some mechanical properties of natural rubber (NR) compounds containing different sizes of rubber powder vulcanizates were investigated with varying the contents of powder from 0 to 40 phr. Five different sizes of rubber powders were selected to see the effect of particle size. A typical reclaimed rubber powder was also used to see the reclaiming effect. The average particle size of rubber powders ranged from 70 to 2000 μm. In the cure characteristics, as the powder content increased, the maximum torque, cure initiation time, and optimum cure time decreased, while minimum torque increased. As the powder content increased, the Mooney viscosity and the shear viscosity of the compounds increased linearly, whereas the die swell decreased. The tensile strength at break and resilience decreased considerably, while tan δ and heat build-up increased with the increased powder content, and the effect was greatly enhanced for larger particles of rubber powders.