IMPACT OF FILLER DISTRIBUTION ON VISCOELASTIC RESPONSE OF ELASTOMER BLENDS

ABSTRACT Heterogeneity of microstructure is a key factor for dynamic-mechanical behavior of materials. For rubber, mostly development of domains consisting of different polymer types allow us to design high-tech materials. Such polymer blend systems can combine rubber-specific benefits of decisive significance for application performance. Generally, fillers like carbon black or silica are used to enhance ultimate properties, like tensile strength or wear resistance. In polymer blends, distribution of filler particles toward domains of various composition defines the quality of the material used. An already proven model for determining filler distribution based on experimental measurements was optimized and applied for the blend system made of natural rubber and styrene butadiene rubber, whose blend ratio, filler content, and type were varied systematically in fine steps. The model focuses on temperature function of loss modulus at glass transition, of which heterogeneous blend systems have two separated at different temperatures. The modulus contribution occurring in the temperature range between these was previously interpreted as a small layer between domains of different types called interphase, which is preferentially enriched with filler before other phases and therefore has very high filler loads. However, investigations using atomic force microscopy have shown no concentration of filler particles at phase boundaries but decreasing domain size in areas of high filler concentration. Fining of phase morphology due to filler particles indicates compatibility improvement of both polymers, so that the filler acts as a compatibilizer. The influence of the filler on miscibility is tremendous. With high filler loads in silica-filled blend systems, instead of two separate glass transitions a single, very wide, plateau-like glass transition occurs.