Novel Reduced Density Materials by Solid-State Extrusion: Proof-of-Concept Experiments*

Abstract

The feasibility of extruding polymer in a solid phase encapsulated in a lower melting point polymer in a low-temperature extrusion process is demonstrated. Such solid-state extrusion has been accomplished in two different resin systems, using different mechanisms. The first system is based on rigid PVC pellets coated with a plasticizer and dusted with highly plasticized PVC powder. Here, PVC pellets, pre-foamed in a batch solid-state microcellular process, were extruded in a way that preserved the microcellular structure of the individual pellet. In the second system hollow pellets were co-extruded using polystyrene as the core material and encapsulating it with polyethylene and polyethylene methacrylate co-polymer (EMA). During extrusion, the softer, lower melting polyolefins carried the polystyrene through the extruder in the solid-state. The unique feature in both examples is that the polymer to preserved in the solid phase is not melted inside the extruder barrel.