Extrusion of Linear Polypropylene-Clay Nanocomposite Foams

This work presents new results on using organoclay with an appropriate polymeric compatibilizer as rheology-modifying additives for extrusion foaming of a linear polypropylene (PP), which by itself does not display strain hardening in extensional flow of the melt. The uniaxial melt-extensional viscosity behavior of several nanocomposites prepared with varying ratio of bound maleic anhydride to clay as well as varying compatibilizer molecular weight was investigated. A chemical-blowing agent was used at a fixed concentration for foaming these nanocomposites in a single-screw extruder. Among nanocomposites with similar levels of clay dispersion or intercalation, the ones that displayed significant strain hardening in the melt state along with slower crystallization led to extruded PP nanocomposite foams with smaller cell sizes and greater cell density by reducing cell coalescence. This was achieved with as little as 3 wt% organoclay and a high-molecular weight PP-g-MA compatibilizer in linear PR POLYM. ENG. SCI., 51:1749-1756,2011. (C) 2011 Society of Plastics Engineers