Clay-dispersed nanocomposite of poly(styrene-co-acrylonitrile) copolymer (SAN): Processing and mechanical properties

Abstract

Hybrids of clay and poly(styrene-co-acrylonitrile) copolymer (SAN) were prepared by simple melt mixing. Clay was modified with an ammonium salt of stearylamine before mixing in order to facilitate the intercalation and/or exfoliation of the clay. Two different mixing devices, an internal mixer and a lab scale twin screw extruder, were used to investigate the effect of processing conditions. It was expected that the maximum shear rate in the twin screw extruder is higher than that in the internal mixer at the same rotation speed because it is inversely proportional to the smallest gap height. Processing time was controlled by changing the number of mixing cycles in the twin screw extruder and the mixing time in the internal mixer. The degree of exfoliation of organoclay in the hybrids was investigated by using an optical microscope, a transmission electron microscope, and an X-ray diffractometer. It was found that SAN can be easily intercalated between the silicate layers at a processing temperature of 180 degrees C, and the twin screw extruder is more efficient in breaking down the clay particles into nano-scale building blocks rather than the internal mixer. Although the stiffness-reinforcing effect of the modified clay is observed in either case, the tensile moduli of the hybrids prepared with the twin screw extruder are higher than those from the internal mixer. The fact that the strengths of clay/SAN hybrids are lower than that of neat SAN may be discussed in terms of the size and shape of clay particles distributed in the hybrids.