The invention provides a counter-rotating extrusion system for processing foam material. The system is designed to introduce a physical blowing agent into the extruder, thoroughly disperse the blowing agent within the polymer melt and, preferably, to maintain relatively high pressures downstream from the point of blowing agent introduction. High quality polymeric foams, including microcellular foams, can be produced using the extrusion system. The system is particularly suitable for the production of foams using shear sensitive and degradable materials, such as PVC.
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