Dispersing organoclay in polystyrene melts: Roles of stress and diffusion

Abstract

Organoclay was dispersed in polystyrene of five different relative molecular mass by melt blending. Melt rheology was used to screen the resulting nanocomposite samples for a plateau in the elastic modulus G′. Presence of this plateau behavior indicates a solid-like network in the blend, brought about by dispersion of the organoclay. Using the values of the G′ plateaus for the PS blends, a percolation theory was tested for the nanocomposites and two solvent/organoclay blends. Lowering the blending temperature to take advantage of high mixing viscosity and subsequent high mixing stress allowed for stronger networks to be formed than when processing conditions favored increased diffusion. A constant viscosity mixing study shows that the relative molecular mass is the most prominent variable affecting dispersion in PS nanocomposites and has reaffirmed the importance of stress over diffusion. By applying high stress to 18 kg/mol PS with 1% organoclay, we were able to disperse the clay to an aspect ratio of 60. Several master batching methods and PS-NH2 compatibilizer were also considered.