Properties and morphology of nanocomposites based on styrenic polymers. Part I: Styrene-acrylonitrile copolymers

For polymer/organoclay nanocomposites formed by melt processing, interactions between the polymer, montmorillonite surface, and surfactant determine any thermodynamic driving force for dispersion of the clay in the polymer. Interactions between poly(styrene-co-acrylonitrile) (SAN) and a single organoclay were probed by varying the SAN copolymer composition. Sample preparation was accomplished by melt processing on a microcompounder followed by injection molding. The level of mechanical reinforcement was observed to increase with acrylonitrile content. Digital analyses of TEM photomicrographs of core samples suggest an optimum in the aspect ratio of the particles at ∼38 wt% acrylonitrile; montmorillonite particles are much longer and thicker for the PS-based composites indicting poor exfoliation compared to the SAN-based composites. The melt viscosity of the SAN copolymers used in this work increased with AN content; experiments showed that varying melt viscosity independent of AN content can account for some improvement in reinforcement.