Comparison of the effect of nano ZnO and conventional grade ZnO on the cross-linking densities of NR/BR and NR/SBR blends

In this research, the effect of nano zinc oxide (ZnO) and conventional ZnO on cross-linking densities of natural rubber (NR)/butadiene rubber (BR) and NR/styrene–butadiene rubber (SBR) blends was investigated. The cross-linking densities of blends were determined using swelling behavior technique. Blends of NR/BR and NR/SBR with various concentrations ranging from 0.5 to 5 parts per 100 g of rubber (phr) of nano ZnO and ZnO were prepared. A sheet of each compound was prepared using compression molding method and tests were carried out. The results indicated that the incorporation of nano ZnO instead of conventional rubber grade ZnO resulted in increasing the cross-linking density. The swelling test results show that the compounds containing nano ZnO absorb less solvent, since they had greater cross-link density in comparison with compounds that had conventional ZnO. Nano ZnO provides a more effective surface for the formation of accelerator–sulfur–ZnO complex. As a result, interfacial interaction increased and particles dispersed efficiently into the matrix of the polymer. The swelling ratios of NR/BR blends were increased, while the swelling ratios of NR/SBR blends were decreased by increasing the amount of nano ZnO from 3 to 5 phr.