The rheological properties of conventional PET resins are not particularly suitable for low density extrusion forming with physical blowing agents, and as a result modified resins with higher melt viscosity and elasticity are often used. In this work, parameters affecting the monolayer flat sheet extrusion of foams having variable densities (from about 1.2 to 0.2 g/cc) are presented. Unmodified and chemically modified resins with different melt viscoelastic properties are used. The effects of variables such as type and concentration of atmospheric gases, resin rheology and choice of process conditions are related to product characteristics, including density, crystallinity and thermoformability.
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