Extrusion of starch-acetate with mixed blowing agents

There are three consecutive processes involved in extrusion foaming: extrusion (mixing and melting), cell initiation and cell growth, and cooling. Extrusion of polysaccharidebased polymers with a single blowing agent is limited by cost, safety, and the various physicochemical requirements of the three processes in extrusion. Balancing or comprising between requirements of various processes should be maintained in the optimization process. Secondary blowing agents such as pentane, ethyl acetate, and sodium bicarbonate were used in water and ethanol-based foaming processes. The introduction of secondary blowing agents of low surface tension or, in other words, of high evaporation rate, such as pentane and ethyl acetate, increased cell density while the addition of high surface tension secondary blowing agents reduced cell density. The specific volume of foams can be increased by secondary blowing agents by increasing nuclei density, increasing solvency, and increasing the amount of vaporized blowing agent.