The objective of the present work was to study the dependence of the foaming temperature window of poly(ethylene terephthalate-co-ethylene 2,5-furandicarboxylate) (PEFT) copolyesters on 2,5-furandicarboxylic acid (FDCA) content after different saturation pressures. First, the chemical structure of PEFT copolyesters was characterized, and the effect of FDCA content on the sorption of carbon dioxide (CO₂) and the crystallization behavior of PEFT copolyesters was studied. Second, the foaming of PEFT copolyesters was carried out using a batch foaming process. Third, the foaming temperature window was defined for PEFT copolyesters through identifying the lower and the upper foaming temperature boundaries. It was found that with the increase of FDCA content, the sorption of CO₂ decreased, and the melting temperature and the crystallinity of PEFT decreased. This led to the increase of the lower foaming temperature while the decrease of the upper one, thus making the foaming temperature window gradually narrowed. It is considered that the lower foaming temperature was determined by the rigidity of the macromolecular chains as well as the CO₂ sorption, while the upper one by the crystals formed in PEFT with copolymerization of FDCA units. In addition, with the increase of the saturation pressure, the lower foaming temperature of all PEFT samples decreased, and the upper foaming temperature of PEFT15%, PEFT20% and PEFT30% decreased as well, attributed to the plasticization effect of CO₂. However, the upper foaming temperature of PET, PEFT5% and PEFT10% unexpectedly increased with the saturation pressure due to the CO₂-induced crystallization. The findings in this study are very important for guiding the foaming and cell structure control, not only for PEFT copolyesters, but also for other semicrystalline copolymers.

本工作的目的是研究不同饱和压力后聚对苯二甲酸乙二醇酯-共-2,5-呋喃二甲酸乙二醇酯 (PEFT) 共聚酯的发泡温度窗口对2,5-呋喃二甲酸 (FDCA) 含量的依赖性. 首先，对PEFT共聚酯的化学结构进行了表征，研究了FDCA含量对PEFT共聚酯吸附二氧化碳（CO ₂）和结晶行为的影响。其次，PEFT共聚酯的发泡采用间歇发泡工艺进行。第三，通过确定较低和较高的发泡温度边界来定义 PEFT 共聚酯的发泡温度窗口。结果表明，随着 FDCA 含量的增加，CO ₂降低，PEFT的熔融温度和结晶度降低。这导致较低的发泡温度升高而较高的发泡温度降低，从而使发泡温度窗口逐渐变窄。认为较低的发泡温度是由大分子链的刚性以及CO ₂吸附决定的，而较高的发泡温度是由在PEFT中形成的晶体与FDCA单元的共聚决定的。此外，随着饱和压力的增加，所有PEFT样品的下发泡温度降低，PEFT15%、PEFT20%和PEFT30%的上发泡温度也降低，这归因于CO _{2的塑化作用。}. 然而，由于CO ₂诱导的结晶，PET、PEFT5%和PEFT10%的上限发泡温度出乎意料地随着饱和压力增加。本研究的发现对于指导发泡和泡孔结构控制非常重要，不仅适用于 PEFT 共聚酯，而且适用于其他半结晶共聚物。