Tailoring of polyesters for bead foams with enhanced thermal resistivity and investigation of structure-property-relationships during expansion and fusion

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The main goal of the proposed project is to scientifically explain and understand the complex effects that are happening during the expansion and fusion of bead foams from the engineering polymer polybutylene terephthalate (PBT). These PBT bead foams (E-PBT) are newly developed and possess a higher heat stability compared to the established bead foams from polystyrene (EPS, approx. 80 °C) and polypropylene (EPP, approx. 110 °C). A good foaming with an even morphology and welding of E-PBT is currently only possible with an epoxy chain extender (CE). However, this CE induces changes in the polymer chains and thereby also the rheological behavior is different leading to different expansion. By now, it is not possible to explain the welding behavior of E-PBT due to the complex reactions of the CE. So far, no deeper correlation of the molecular structure and the foaming/welding behavior was found. Therefore, PBT with systematically varied structures (linear, branched, cross-linked etc.) will be made and investigated regarding their rheological behavior (elongational, shear and melt strength). Foaming will be carried out firstly in a lab scale with an autoclave to determine the expansion behavior. Based on these result the most promising systems will be bead foamed on a larger scale. The fusion of E-PBT differs significantly from the established bead foams and is yet not understood. Here, the main focus will be the surface investigation to explain the effects during the fusion in the steam chest moulding machine. By modifying the polymer and consequently the beads surface it would be possible to influence the welding performance.