Poly(styrene-co-acrylonitrile)/montmorillonite organoclay mixtures: a model system for ABS nanocomposites

Dispersion of clay particles in acrylonitrile-butadiene-styrene (ABS) and styrene-acrylonitrile copolymer (SAN) nanocomposites with montmorillonite (MMT) have been compared to assess whether ABS/MMT nanocomposite behavior can be adequately modeled using the simpler SAN/MMT system. Electron microscopy photomicrographs show that clay particles in ABS/MMT composites reside in the SAN matrix phase and accumulate at the rubber particle surfaces. In mixtures of four organoclays with the two polymers, WAXS (wide angle X-ray scattering) peak height and shift in gallery height was the same for a given organoclay. Aspect ratios determined through image analysis were also the same in each polymer. Modulus enhancement as measured by an exfoliation efficiency index showed the same patterns for each organoclay in the two matrices, but the ABS/MMT composites had consistently lower efficiencies than in SAN/MMT composites. This trend is expected to be due to the variations in orientation of clay particles in ABS/MMT composites at the rubber particle surface. In summary, SAN/MMT composites represent a good model system for ABS/MMT.