Mechanical properties of silane-treated silica particle-filled polyisoprene composites: Influence of the alkoxy group mixing ratio in silane coupling agent containing mercapto group

摘要

Spherical silica particles were treated with a mixture of silane coupling agents with mercapto functional groups and dialkoxy or trialkoxy groups. The surface coverage, which indicates the number of layers covering the silica surface, was in the range from 1.6 to 6.0. The molecular mobility of the treated layer was analyzed with 1H-NMR spectroscopy. The silane chain became more flexible with increasing dialkoxy structures in the mixture and with increasing surface coverage. The stress-strain behavior was measured for a composite consisting of the treated silica and vulcanized polyisoprene rubber (PIR). There was no influence of the dialkoxy and trialkoxy mixing ratio for near monolayer coverage. In the case of the pure dialkoxy and low trialkoxy contents, a higher stress was observed at the same strain for surface coverages of 2.4-3.8. However, a longer length flexible silane chain, that is, with a surface coverage of 6.0, was disadvantageous for the reinforcement effect. The results of pulse NMR analysis of the unextracted PIR on the particle surface and swelling test indicate that the reinforcement effect was strongly affected both by entanglement and the crosslinking reaction between the silane chain and PIR at the interfacial region.