Development of polymeric foams from recycled polyethylene and recycled gypsum

The extrusion foaming of recycled polyethylene through different foaming agents has been studied. Cellular structures were obtained in a single screw extruder with different grades of polyethylene (low and high density), using recycled gypsum and a commercial foaming agent (azodicarbonamide). Differential scanning calorimetry and thermogravimetric analysis were used to characterize the transition temperatures of the polyethylenes used, and the dissociation temperature of the foaming agents. The effect of processing conditions on the density of extrudates was studied. The pressure developed during extrusion and the residence time in the die was shown to influence the final density and cellular structure of foamed polyethylene. The results indicate that a higher polymer viscosity corresponds a lower density of the foamed product. The formation of the gaseous phase should take place at temperatures immediately higher than the melting temperature range of the polymer, in order to allow complete dissociation of the foaming agent in highly viscous molten polymer.