Reinforcement of acrylonitrile-butadiene rubber and poly(Vinyl chloride) blends by in situsilica

Abstract

Acrylonitrile-butadiene rubber (NBR) and poly(vinyl chloride) (PVC) blends were reinforced with silica by sol-gel method of tetraethoxysilane (TEOS) and ethyl polysilicate (EPS) using ethylenedimine as a catalyst. Natural rubber (NR) was used to replace part of the NBR in a 70/30 NBR/PVC blend. NBR and NR were soaked in TEOS or EPS and in an aqueous solution of the catalyst. The sol-gel reaction proceeded by the mixture of TEOS or EPS with water, EtOH and THF was also related to the degree of swelling of the rubber. The amount of TEOS or EPS added and the mass ratio of TEOS or EPS to rubber was related to the degree of swelling of the rubber. From the viewpoint of the degree of swelling and silica content of sol-gel process of the NR, the method using only water at mass ratio at 10/1 (TEOS or EPS/rubber) was found to be better than other system. For NBR, the method using only THF at mass ratio of 10/1 (TEOS or EPS/rubber) was found to be better than other systems. Ethylenediamine concentration and soaking time slightly effected the silica content in the rubber. The dispersion of the in situ silica particle was better than that of conventional silica. The in situ silica did not much inhibit the accelerated sulfur curing. Thus, it is estimated that the concentration of silanol groups on the in situ silica surface was smaller than those on the conventional silica surface. The silica-silica interaction of in situ silica seems to be weaker to result in better dispersion in the rubber matrix compared with the conventional silica. The modulus at 100% elongation, tensile strength at break and elongation at break of in situ silica-filled rubber/PVC vulcanizate were lower than those of conventional silica-filled rubber/PVC vulcanizate.