Development of a Bead Foam from an Engineering Polymer with Addition of Chain Extender: Expanded Polybutylene Terephthalate

In this work, the development of a bead foam from the engineering polymer polybutylene terephthalate (PBT) in a continuous process is described. The polymer was chemically modified by means of multifunctional epoxy chain extender (CE) to improve the rheological properties, the foaming behavior, and the fusion of the beads. Shear experiments indicated the formation of branched structures as a result of the chemical modification. Viscosity and melt strength were increased due to the chain extender. Also, strain hardening was observed for PBT modified with CE. It was shown that modified PBT has enhanced foaming behavior; namely, a higher expansion and more homogeneous and finer cell morphology were achieved. For the first time, expanded polybutylene terephthalate bead foams (E-PBT) were produced and welded in a steam chest molding process. The parts from steam chest molded beads showed a density down to 170 kg/m3. An optimum concentration of chain extender in terms of expansion and welding behavior was identified as 1 wt %.