热塑性聚醚酯弹性体硬段含量对其超临界CO2发泡行为的影响

Effect of hard segment content on microcellular foaming process of thermoplastic polyether ester elastomer using supercritical CO2 as blowing agent

研究了以聚对苯二甲酸丙二醇酯(PBT)为硬段,聚四氢呋喃醚(PTMG)为软段的热塑性聚醚酯弹性体(TPEE)在超临界CO2作用下的固态发泡行为,考察了硬段含量的差异对结晶行为,CO2在TPEE中溶解度及扩散行为,以及固态发泡行为的影响。发现硬段含量的差异对TPEE结晶行为影响尤为显著,当硬段含量由29%上升到65%时,其熔点从162.6℃上升至201.9℃,且结晶度由20%上升到40%。结晶的存在抑制了CO2在基体内的溶解度且阻碍了其在基体内的扩散。由不同硬段的TPEE中CO2溶解度和扩散过程的变化可知,CO2更倾向于溶解在TPEE软区内,而由结晶为主构成的硬区中CO2溶解量较低。通过研究高压CO2环境下的TPEE等温结晶过程发现,经扩散进入TPEE软区内的CO2可以提升TPEE链段运动能力,诱导未结晶链段通过规整堆叠而结晶。在CO2压力15 MPa经快速降压发泡聚醚酯弹性体,发现随着硬段含量的增加,其温度发泡窗口向高温区移动,当硬段含量为29%时,发泡温度区间为50~160℃,平均孔径4.6~16.5μm,泡孔密度8.1×10^7~7.5×10^8cells/cm^3,发泡倍率1.1~5.8;当硬段含量为65%时,发泡温度区间为165~195℃,平均孔径1.8~6.8μm,泡孔密度2.6×10^8~1.1×10^11cells/cm^3,发泡倍率1.0~4.2。

Solid-state foaming process of TPEE composed of poly(tetra methylene glycol)(PTMG)"soft"blocks and poly(butylene terephthalate)(PBT)"hard"blocks using supercritical CO2(scCO2)as the blowing agent was investigated.Plastic foams with average cell diameter of 2-17μm and expansion ratio of 1-6 folds were prepared from TPEE.Three kinds of TPEE copolymers with different block ratio were used to investigate the influence of hard segment content on foaming behavior.The CO2 dissolved into soft segments(PTMG)and hard segments(PBT)were carefully characterized by sorption process,meanwhile the gas diffusion coefficient was fitted from the Fick’s diffusion law.The results show that the solubility and diffusivity of CO2 in soft segments(PTMG)is significantly higher than that in hard segments(PBT).When the hard segment content rose from 29%to 65%,the melting point rose from 162.6℃to 201.9℃with a crystallinity rising from 20%to 40%.TPEE copolymers were foamed in a high-pressure chamber by using scCO2.The effect of temperature and block ratio on the cell morphology was investigated.It was found that the content of hard segment had great influence on the solid-state foaming process.With higher hard segment content,the processing window was broadened and shifted to higher temperature.