COMPARISON OF RUBBER REINFORCEMENT USING VARIOUS SURFACE-MODIFIED PRECIPITATED SILICAS

The reinforcement of a natural rubber compound by various surface-modi fied precipitated silicas was compared. Compound physical properties w ere determined for two silicas differing in surface area and were used as controls to evaluate these silicas after surface modification by u sing either a bifunctional organosilane coupling agent (gamma-mercapto propyl-trimethoxysilane) or a new surface modification process. This n ew process is based on the in situ polymerization of organic monomers solubilized inside surfactant bilayers that are adsorbed onto the sili ca surface to afford silicas modified with styrene-butadiene and styre ne-isoprene copolymers. Both surface modification processes afford mat erials that dramatically increase the compound cure rate, thereby sign ificantly reducing T-90 cure times, while also improving tensile prope rties, tear strength, abrasion resistance, and compression set of the cured compound. The silane-modified silica gives a higher flex-crackin g resistance than do the silicas modified by the in situ polymerizatio n of organic monomers, whereas these latter silicas significantly incr ease rebound resilience and offer greater overall improvements in rubb er compound performance. The rubber compound physical properties obtai ned using the modified, higher surface area Hi-Sil(R) 255 silica are g enerally improved relative to those obtained using the modified Hi-Sil (R) 233 silica. (C) 1996 John Wiley & Sons, Inc.