Sheet Extrusion of Foamed Polyethylene Terephthalate, 1998 Polymers, Laminations & Coatings Conference Proceedings

Extrusion foaming of thermoplastics by injection of inert gases in the polymer melt or through chemical blowing agents is increasingly finding applications competing with processes employing volatile organic compounds, (VOC’s), and halocarbons. (CFC’s and HCFC’s). Expanding semicrystalline polyesters such as polyethylene terephthalate (PET) is a relatively new and increasingly active area presenting several challenges since the rheological properties of PET at processing temperatures are not particularly conducive to foaming. In this paper parameters affecting the flat sheet estrusion of single layer foams and co-extruded ABA layered structures, where the core B is foamed PET. are examined: intended potential applications are in thermoforming and lamination. Criteria for producing high density (0.7 g/cc) or low density (less than 0.3 g/cc) foams based on resin melt viscosity and melt strength, type of chemical blowing agent and inert gas. and process conditions are discussed.