Rigid Foam Extrusion of Polyvinylchloride – Effects of Blowing Agent and Plasticizer

Abstract The effects of blowing agent and plasticizer on foaming characteristics of polyvinylchloride (PVC) were investigated, using a short cylindrical die. Of two blowing agents tested, azodicarbonamide (ADCA) exhibited a wider leverage of volumetric flow rate for processability while sodium bicarbonate (SBC) showed a wider temperature leverage. The mixed use of two blowing agents gave a better control for extrudate density, product color and processability. Of three nucleating agents, two acidic ones, citric acid and boric acid, enhanced uniformity of cells and efficiency of the blowing agents slightly. It was observed that dioctyl phthalate (DOP), used as plasticizer, tended to migrate toward the surface of the die wall, giving rise to smooth surface layer of the extruded profile foam. A possibility exists to produce profile foams having smooth skin, by controlling the type of blowing agent and processing conditions.