Expandable polystyrene (EPS) and expanded polypropylene (EPP) dominate the bead foam market. As the low thermal performance of EPS and EPP limits application at elevated temperatures novel solutions such as expanded polybutylene terephthalate (E-PBT) are gaining importance. To produce parts, individual beads are typically molded by hot steam. While molding of EPP is well-understood and related to two distinct melting temperatures, the mechanisms of E-PBT are different. E-PBT shows only one melting peak and can surprisingly only be molded when adding chain extender (CE). This publication therefore aims to understand the impact of thermal properties of E-PBT on its molding behavior. Detailed differential scanning calorimetry was performed on neat and chain extended E-PBT. The incorporation of CE remarkably reduces the crystallization and re-crystallization rate. As a consequence, the time available for inter diffusion of chains across neighboring beads increases and facilitates crystallization across the bead interface. For E-PBT bead foams, it is concluded that sufficient time for polymer inter diffusion during molding is crucial and requires adjusted crystallization kinetics.
Since January 2021, Prof. Dr.-Ing. Holger Ruckdaeschel is full professor for Polymer Engineering at University of Bayreuth. Based on his strong academic background, he became member of various institutes in recent time, for instance the Bavarian Polymer Institute. He is also well-connected to multiple companies and industries. Before becoming professor, he has been working at BASF for 13 years. In his current role, he is connecting material, technology and application. His primary material research areas are resins & composites, polymer foams, functional thermoplastics and integrative as well as additive manufacturing. He integrates the aspects of digitalization and sustainability into research to develop a modern approach for polymer science & engineering.
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