Abstract: The use of CO₂ for substituting volatile organic compounds in polymer processing, i.e., supercritical CO₂-assisted polymer processing, has attracted increasing attention in recent years. Dissolution of CO₂ in polymer could swell, plasticize and deliver small molecules into the polymer matrixes. Consequently, the structure and morphology of the polymer would change, as well as the fundamental properties, including polymer crystallization, interfacial tension between polymer and gas, and rheology of CO₂/polymers melt.CO₂-induced changes in these properties could be used to realize the supercritical CO₂-assisted polymer processing, e.g., CO₂-assisted polymer grafting, CO₂-assisted penetrating of small molecules into polymer and CO₂-assisted polymer foaming.Several cases from the authors' laboratory are presented for elucidating how to use the changes to manipulate the CO₂-assisted polymer processing.The cases include CO₂-induced crystallization of isotactic polypropylene and syndiotactic polypropylene, CO₂-induced crystal phase transition of isotactic poly-1-butene, and how to use CO₂-induced crystallization to manipulate melt strength of three linear polymers, i.e., isotactic polypropylene, poly(lactic acid)and poly(ethylene terephthalate), to prepare the polymer foams with different structures.

Key words: supercritical CO₂, polymer processing, crystallization, foam, solution, diffusion

摘要： 近年来,以超临界CO₂替代聚合物加工过程中大量使用的有机溶剂实现超临界CO₂辅助聚合物加工过程已引起人们越来越多的关注。CO₂在聚合物中的溶解扩散可导致其结构和形态的变化,能够溶胀增塑聚合物并且将溶解于其中的小分子物质携带输运到聚合物基体中,进而影响聚合物的结晶及晶型转变行为,聚合物/CO₂体系界面张力以及聚合物/CO₂体系流变行为等基本物性的变化。利用聚合物基本物性的变化可实现CO₂辅助聚合物接枝反应,CO₂辅助聚合物渗透小分子物质以及CO₂辅助聚合物发泡等超临界CO₂辅助聚合物加工过程的应用。结合本研究室的实例,探讨了CO₂作用下等规聚丙烯和间规聚丙烯的结晶行为以及一种多晶型聚合物——等规聚丁烯-1的晶型转变行为;探讨了利用CO₂对等规聚丙烯、聚乳酸和聚酯三种典型的低熔体强度结晶聚合物具有的不同诱导结晶作用,调控聚合物的结晶行为,使其具备发泡所需的熔体强度,制备了具有不同结构特征的发泡聚合物材料。

关键词: 超临界CO₂, 聚合物加工, 结晶, 发泡, 溶解, 扩散