Effects of zinc oxide particle shape on properties of a prevulcanized latex

Abstract

From a zinc precursor of zinc nitrate hexahydrate and a precipitating agent of sodium hydroxide, zinc oxide (ZnO) was hydrothermally synthesized. Using different formulations and different reaction conditions of time and temperature, the obtained ZnO presented two different morphologies: short prism-like, and flower-like. X-ray diffraction data confirmed the wurtzite structure of the obtained ZnO. The short prism ZnO presented a higher specific surface area than the flower-like and the conventional forms. The synthesized ZnO was then compounded with natural rubber (NR) latex at loading contents of 0.1–0.6 phr and NR with conventional ZnO (CZnO) at 1 phr which was used for comparison. The tensile and tear strength of all vulcanizates increased with increased loadings of ZnO, except the vulcanizate containing flower-like ZnO. NR vulcanized films containing short prism ZnO at 0.4 phr showed the highest mechanical properties and they were higher than those of the film containing CZnO at 1 phr. Modulus of all samples tended to increase with increasing content of the synthesized ZnO and it was comparable with the modulus of the sample contained CZnO. NR films containing either short prism or flower-like ZnO showed nearly the same elongation-at-break. The cross-link density of short prism ZnO-incorporated NR was higher than NR comprising flower-like ZnO and CZnO. Furthermore, the aging properties of films containing synthesized ZnO were comparable with the properties of rubber films containing CZnO. Hence, 0.4 phr short prism ZnO was the optimum content for the preparation of prevulcanized latex.