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Improving thermoplastic foam stability in the molten state by interfacially-adsorbed particles

Abstract:

Addition of particles of low surface energy is shown to have a strong stabilizing effect on polymer foams. We examine two high melt index polymers, polystyrene and polylactic acid, foamed by chemical blowing agent. Both polymers show extensive coalescence and collapse when held in the melt state for extended periods. Addition of 5-10 wt% PTFE particles almost completely eliminates collapse, and greatly reduces coalescence. SEM shows that particles adsorb on the inner surface of the foam cells and creates a particulate shell that protects against coalescence. This appears to be a promising route to foam polymers with poor melt strength, especially in processing operations which involve slow cooling.