Synthesis, characterisation and properties of clay and silica based rubber nanocomposites

Abstract

Rubbers are high molecular weight polymeric materials, which possess very low interchain attraction, low glass transition temperature and predominantly amorphous nature with low green strength. Fillers like carbon black and silica are frequently added to rubbers in order to improve the mechanical properties of the composites. In recent years, more attention has been paid towards polymer nanocomposites, where the dimension of the inorganic fillers is of the order of nanometre (1–100 nm) and which impart better physicomechanical properties as compared with conventional composites. This chapter is a compendium of the authors' work on clay and silica filled nanocomposites based on various rubbers. Rubber–clay nanocomposites have been prepared by modification of the naturally occurring Na montmorillonite clay followed by mixing with rubber in solution. Intercalation and/or exfoliation of the clay layers, which depends on a number of factors, has been observed in styrene–butadiene rubber (SBR), acrylonitrile–butadiene rubber (NBR), polybutadiene rubber (BR), brominated polyisobutylene–co-paramethylstyrene (BIMS), ethylene–octene copolymers and thermoplastic elastomers. Predominant intercalation is observed with modified clays in the case of in situ nanocomposites from acrylic monomers. The average dimension (i.e. the width) of the clay layers ranges from 10 to 60 nm in the hybrid nanocomposites, as observed by transmission electron microscopy, scanning electron microscopy and atomic force microscopy studies. Significant improvement in mechanical, dynamic mechanical and barrier properties has been obtained with these clay filled rubber nanocomposites even at very low filler concentration. Sol–gel technique generating in situ silica from the sequential hydrolysis and condensation reactions of tetraethoxysilane (TEOS) has been adopted to synthesise transparent rubber–silica hybrid nanocomposites from polar rubbers like acrylic rubber (ACM) and epoxidised natural rubber (ENR). The sol–gel reaction parameters such as concentration of TEOS, solvents, TEOS/H2O mole ratio, pH value and temperature have profound effects on the morphology of the dispersed silica phase and hence their interaction with the matrix. These factors are crucial in determining various properties like mechanical, dynamic mechanical, rheological and thermal behaviour of the resultant nanocomposites. Some interesting observations have also been recorded in the case of in situ synthesised acrylic copolymer–terpolymer/silica hybrid nanocomposites.