Reinforcement of natural rubber and methyl methacrylate grafted natural rubber films by in situ silica

Abstract

The objective of this research was to prepare thin rubber films from natural rubber (NR) grafted with methyl methacrylate (MMA) and reinforced by in situ generated silica. The MMA grafting was carried out using cumene hydroperoxide/ tetraethylene pentamine (CHPO/TEPA) redox system as an initiator pair. The latex contained particles having a core-shell structure, where the core consisted of NR and the shell layer was formed by PMMA, as revealed by transmission electron microscopy (TEM) analysis. The grafted NR latex was then mixed with tetraethoxysilane (TEOS), a precursor of silica. In the latex state, TEOS was discovered embedded in the MMA shell surrounding the NR particles. The silane was converted to silica particles by sol-gel process that was induced during film vulcanizing at 80C. The influences of NR:MMA weight ratio on the surface morphology of the composites were investigated by scanning electron microscopic (SEM) and atomic force microscopic (AFM) methods. With the presence of grafted MMA, the silica tends to slightly aggregate, but remained dispersed throughout the entire NR matrix. It was also found that increasing weight ratio of MMA in the rubber resulted in an increase of root-mean-square roughness of the surface and led to a reduction of the film tackiness. The presence of both grafted MMA and silica particles led to slight increases in modulus at 500% elongation and tensile strength, but decreases elongation at break of the composite film.