Influence of Partial Replacement of Conventional Zinc Oxide with Nano-Zinc Oxide on Latex Processing and Properties

This work was conducted to investigate the activity of nanosized zinc oxides in carboxylated nitrile elastomer (XNBR) and natural rubber (NR) under the vulcanization process. Zinc oxide (ZnO) nanoparticles were synthesized by using the sol-gel method and calcination method. Nano-ZnO-substituted NR and XNBR vulcanizates were prepared by varying the loading level of nano-ZnO from 10 phr to 20 phr, 30 phr, 40 phr and 50 phr added to NR and XNBR. The testing specimens of the prepared nano-ZnO-added NR and XNBR vulcanizates were produced through the dipping and drying process. The samples were cut to the required size and standard before being subjected to the tensile test, scanning electron microscopy analysis, and colloidal stability test. ZnO nanoparticles, acting as a curing activator in both NR and XNBR, were found to be more uniformly dispersed in the rubber matrix in comparison with the conventional rubber grade ZnO, as evident from scanning electron microscopy. The tensile strength of NR was observed to be significantly improved as the amount of ZnO nanoparticles was gradually increased up to 50 phr. This indicates that the ZnO nanoparticles can be used as curing activator in NR. For the samples of XNBR, it was also found that further increasing of nano-ZnO amount up to 30 phr significantly improved the tensile strength of XNBR samples. However, subsequent increment of the nano-ZnO amount up to 50 phr did not improve the tensile properties. There was an increase in elongation at break of XNBR vulcanizate with ZnO nanoparticles added. The XNBR vulcanizate showed an optimum performance at 30 phr, which gave the vulcanizates the optimum tensile strength and elongation at break. Meanwhile, for the NR vulcanizate, the addition of 50 phr nano-ZnO was found to provide the optimum effect in term of tensile strength and elongation at break.