结晶聚合物部分熔融熔体有序结构及在流场中的演变

Usually, polymer is produced using melt-based standard methods of polymer processing. By partial melting, ordered melt including bundles of partially ordered chain segments can be generated from initial crystalline structure. Flow-induced evolution of ordered structure has an important influence on the rheological behavior and crystallization behavior of polymer. In this project, the evolution and mechanism of the later stage of the melting process (disappearing of lamellae stack structure) and evolution of ordered structure under flow at constant temperature are investigated by in situ small/wide-angle X-ray scattering (SAXS/ WAXS) and in situ Fourier transform infrared spectroscopy (FTIR). The relationship between the ordered structures, flow field, rheological behavior and the crystalline structure is established by the study of the rheological and crystallization behavior of the ordered melts. The characterization and flow-induced evolution of pre-ordered structure is a fundamental and still incompletely resolved problem in polymer physics which is distinctly different from the study of shear-induced ordered. The research of this project can not only enrich the understanding of melting of polymer and flow-induced crystallization, but also provide a novel new idea in understanding the relationship between the rheological behavior and final properties.

聚合物制品一般都是通过熔融加工成型。在熔融过程中，部分保留原有的晶体结构，可以得到含有局部有序大分子集团（有序结构）的有序熔体。熔体中有序结构及在流场中的演变对材料的流变行为和结晶行为有着重要影响。本项目拟采用小角/广角X射线散射和傅里叶变换红外等手段，原位表征结晶聚合物熔融过程中片晶消失后熔体有序结构及在等温流动过程中的演变，揭示其演变规律和机制；通过研究有序熔体的流变和结晶行为，建立熔体有序结构、流场和流变行为、结晶形态结构之间的关系。结晶聚合物部分熔融熔体有序结构及在流场中的演变不同于流动诱导结晶中流动诱导无序熔体形成有序结构及其在流动停止后的演变，是高分子物理的新问题，其研究不仅可以丰富和发展聚合物熔融和流动诱导结晶研究，还可以为通过加工调控材料流变行为和制品结晶形态结构及性能提供新思路，具有重要的理论和应用价值。

将结晶聚合物加热至名义熔点和平衡熔点之间的温度，部分保留原有的晶体结构，可以得到有序熔体。熔体中有序结构及其在流场中的演变对材料的流变行为和结晶行为有着重要影响。本项目采用广角/小角X射线散射原位表征了等规聚丙烯和聚丁烯-1等温熔融过程，揭示了片晶消失后纳米晶体尺寸的演变机制。研究表明，在高分子结晶结构熔融后期存在从片层体系向稀薄粒子体系的转变。片晶的熔融过程被重新分为三个阶段：低温下薄片晶的熔融，片晶的非均匀增厚与孔洞化以及后期纳米晶体的熔融。基于对高分子晶体熔融的新认识，在聚丁烯体系中通过将部分晶型转变样品选择性熔融，研究了聚丁烯-1晶型II向晶型I转变的成核机制。进一步，通过研究有序熔体的流变和结晶行为，建立了熔体有序结构、流场和流变行为、结晶形态结构之间的关系。本项目的研究丰富和发展了聚合物熔融和流动诱导结晶研究，为通过加工调控材料流变行为和制品结晶形态结构及性能提供了新思路，具有重要的理论和应用价值。