Expansion of polystyrene using water as the blowing agent

The expansion of polystyrene using water as the blowing agent has been investigated. Hydrophilic particles are dispersed in styrene before the suspension polymerization. During this polymerization the necessary amount of water is absorbed and/or adsorbed by these additives. The different additives used in this work are ordinary corn starch and high-amylose starch, zeolite A and Y, and SiO2. Factors that influence the density and the morphology of the expanded product are the type of additive, the additive and water content, the polymerization conditions, and the expansion procedure. High frequency electric field heating and hot air have been used for the expansion. The lowest density is obtained with high frequency electric field heating.