Effects of resin rheology on the extrusion foaming characteristics of PET

Extrusion foaming by injection of inert gases (carbon dioxide, nitrogen, argon) in the polymer melt is increasingly finding applications for a wide variety of resins, competing with chemical blowing agents, volatile organic compounds or microcellular foaming. The molecular weight and molecular weight distribution of the resin affect its rheological characteristics (shear and elongational viscosity, melt elasticity, melt strength), its process characteristics and control cell size and stability of the resulting foam. In the present work, a variety of PET resins (including virgin materials, recycled and post-reactor modified) having different rheological characteristics were foamed by direct carbon dioxide injection and through the use of chemical blowing agents. Foamability as related to density and cell size and distribution was evaluated and correlated with rheological characteristics of the particular resin, process conditions and type of blowing agent.