Preparation of "green" composites by the sol-gel process:: In situ silica filled natural rubber

Green composites with different amounts of in situ silica nano-particles were prepared by a sol-gel reaction of tetraethoxysilane (TEOS) in natural rubber (NR). The control of swelling degree of TEOS in NR and concentration of n-butylamine in water was useful to change the amount of generated in situ silica in the uncured NR matrix. In situ silica up to 42 parts per hundred rubber by weight (phr) was successfully filled in the NR matrix. The particle size of in situ silica became larger with the increase of silica content from ca. 10 nm to ca. 40 nm for 10 phr - 40 phr loadings in the NR matrix, respectively. Even when the amount of in situ silica content was high, the dispersion of in situ silica particles was more homogeneous than that of commercial silica (VN-3). The reinforcement effect of the in situ silica for NR vulcanizates increased with increasing the in situ silica content.