Foam extrusion of LDPE with solid phase CO2 as blowing agent

Physical foaming usually requires special metering equipment to inject the blowing agent at high pressures. In this study, low density polyethylene (LDPE) was foamed in the extrusion process using dry ice as physical blowing agent. The blowing agent was metered in form of pellets over the hopper. To determine relevant process parameters and improve the understanding of the process a melting model is applied. The influence of the formation of a melt film and melt pool on the dissolution of the blowing agent is discussed. The theoretical considerations are validated in a design of experiment study. As a result, the efficiency of the process is especially affected by the throughput rate, granules temperature, and blowing agent concentration. Further varied parameters are the barrel temperature in the melting zone and diameter of the dry ice pellets. Fast melting and pressure build-up were shown to reduce blowing agent losses. POLYM. ENG. SCI., 55:2821–2828, 2015. © 2015 Society of Plastics Engineers

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