Zinc Oxide Nanoparticles as an Activator for Natural Rubber Latex

This work focuses on the study the effect of ZnO nanoparticles on the vulcanizate properties of natural rubber (NR) latex films. Zinc oxide nanoparticles were synthesized by a simple and an efficient wet chemical method. The Powder X-ray Diffraction (PXRD) characterization confirmed the successful synthesis of pure ZnO and the average particle size was found to be 50 – 100 nm as indicated by particle size analysis. ZnO nanoparticles thus prepared were surface modified with oleic acid as a capping agent and the modification was carried out under ultrasound sonication in order to provide mechanical forces to separate nanoparticles leading to an efficient surface reaction. The existence of organic layer was confirmed by the Fourier Transform Infrared (FT-IR) spectra. The oleic acid modified ZnO nanoparticles were then introduced into natural rubber centrifuged latex. The mechanical properties and swelling characteristics of the films were compared with those prepared using conventional ZnO particles (particle size ~ 800 nm and concentration 0.25 phr). The experiment was carried out with varying particle sizes of synthesized ZnO particles (30 nm, 50 nm, 500 nm) and by adding varying concentrations of ZnO nanoparticles with an average particle size of 30 nm (0.25 – 0.06 phr). A significant improvement in strength characteristics was observed for the films prepared with 0.25 and 0.125 phr of oleic acid modified ZnO nanoparticles whilst those of the films prepared using 0.06 phr were almost comparable with that of the conventional films. The swelling characteristics in toluene were significantly reduced in the films prepared with ZnO nanoparticles corroborating the improved cross linking density as observed from the improvement of reinforcement of NR latex vulcanizates. It can be thus concluded that the increase in the available surface area of ZnO nanoparticles increases the efficiency of vulcanization, while modification with oleic acid increases the compatibility between rubber matrix and the inorganic fillers which led to an increase in the degree of cross linking. The study therefore significantly contributes to reduce the ZnO concentration in latex compound formulation in the latex industry.