Cell structure-tunable PEFT copolyester foams prepared via conducting a prior cold crystallization

The slow melt crystallization behavior of the new bio-based poly(ethylene terephthalate-co-ethylene 2,5-furandicarboxylate) (PEFT) copolyester makes its foaming a big challenge, thus severely hindering the exploration of its applications in the foam field. To address this issue, the objective of this study was to fabricate cell structure-tunable PEFT foams via a regulating approach of cold crystallization prior to batch foaming. First, cold crystallization via thermal annealing at a fixed temperature of 110 °C was carried out for poly(ethylene terephthalate) (PET), PEFT5%, PEFT10% and PEFT15% to investigate its effect on the foaming behavior. Second, cold crystallization at various temperatures was performed to investigate its effect on the cell structure. Third, the cell structure variation of the foams with the crystallinity was studied. Fourth, the thermal insulation of the foams was studied. It is found that with the increase in the crystallinity for all samples, the cell size decreases, the cell density increases, and the expansion ratio first increases and then decreases. Hence, the rule of cell structure variation with the crystallinity is proposed and cell structure-tunable PEFT foams are thus fabricated. In addition, microcellular PET and PEFT foams are prepared via controlling the thermal annealing temperature. Moreover, it is found that PEFT foams show comparable thermal insulation with PET foams of similar expansion ratio. Therefore, this study has made great contribution for fabricating cell structure-tunable PEFT foams and developing potential applications through improving foaming behavior via applying cold crystallization as an effective regulating approach.