Poly(ethylene terephthalate) (PET) was modified by regulating different contents of branching agent epoxy‐based multifunctional oligomer and chain extender pyromellitic dianhydride in reactive extrusion process. The modified PET with better long‐chain branched (LCB) structure boosted its rheological properties, and its enhancement of melt viscoelasticity resulted in excellent foamability in molten‐state foaming process using supercritical CO₂ as blowing agent. More importantly, the branched structures acted as crystal sites to accelerate the crystallization kinetic of LCB PET whether under atmospheric pressure or high‐pressure CO₂. The shear and elongation flow inside die further quickly induced the crystallization of LCB PET. The rapidly generated fine crystals could both introduce heterogeneous cell nucleation and suppress CO₂ escape, so the cell morphology of LCB PET in continuous extrusion foaming process exhibited a three‐fold increase in cell density and smaller uniform cell size with respect to those of other foam‐grade PET with long‐chain structure.

中文翻译：

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长链支化PET增强的结晶性使其具有良好的挤出发泡性能

聚对苯二甲酸乙二醇酯（PET）通过在反应挤出过程中调节支化剂环氧基多功能低聚物和扩链剂均苯四酸二酐的不同含量进行改性。具有更好的长链支化（LCB）结构的改性PET增强了其流变性，并且其熔体粘弹性的增强导致在使用超临界CO ₂作为发泡剂的熔融态发泡过程中出色的发泡性。更重要的是，无论是在大气压下还是在高压CO ₂下，支化结构均充当晶体位点以加速LCB PET的结晶动力学。。模具内部的剪切和伸长流动进一步迅速引起了LCB PET的结晶。快速生成的微晶既可以引入异质的细胞核，也可以抑制CO _2的逸出，因此与其他泡沫相比，连续挤出发泡过程中LCB PET的细胞形态表现出三倍的细胞密度增加和更小的均匀泡孔尺寸具有长链结构的高档PET。