压力场下流动诱导等规聚丙烯结晶研究

Study on flow-induced crystallization of polymer has received wide attention, but most have been carried out under normal pressure. Practical processing operations involve pressure and flow fields as well, so research results obtained under normal pressure is limited to guide practical processing. The reason that flow-induced crystallization under pressure is seldom studied is due to the high requirements to equipment, such as dynamic sealing. The applicant successfully designed and manufactured a pressure-shearing device by designing self-sealing structure to solve the dynamic sealing problem. The initial results of study on iPP show that there are big differences between flow-induced crystallization under certain pressure and atmospheric pressure. For example, some oriented spherulites are generated and some lamellae with high melting point (almost 180 ºC) are obtained within a short time. Therefore, we will study the flow-induced crystallization behavior of iPP under pressure in order to explore the condition window of generating different kind of iPP crystals and oriented lamellae, such as shish-kebab, to reveal the law that pressure and flow fields affect crystallization of iPP, and to plot the phase diagram of iPP crystalline type. Through this research, one can more easily understand the mechanism of iPP congregated structure formation under practical processing fields. The results can also afford theoretical and experimental evidences for tailoring crystalline structure and morphology of iPP and guiding practical processing.

流动诱导聚合物结晶研究一直以来受到广泛关注，但其研究结果基本上都是在常压下获得的。实际加工中不仅普遍存在流动场，还有压力场，因此，常压下取得的研究成果对实际加工的指导作用受限。压力下流动诱导聚合物结晶研究较少的难点是对设备的要求高（如动密封）。申请人前期采用自密封结构解决了动密封问题，成功设计并搭建了压力-剪切仪，并初步研究了压力下流动诱导等规聚丙烯（iPP）结晶，发现与常压下流动诱导结晶存在很大区别，如形成了取向球晶、短时间内可生成熔点高达180ºC的晶体。本项目拟进一步研究压力下流动诱导iPP的晶体结构与形态，探索iPP晶型（α、β和γ晶）和取向晶体（如串晶）在压力-流动场下生成的临界窗口条件，以及晶体形态演变规律，绘制几种晶型的生成相图。研究结果可深入理解iPP在实际加工场下凝聚态结构形成机理，为调控iPP制品形态结构、指导实际加工过程提供理论基础和实验依据。

加工外场对结晶聚合物的结构与性能有很大影响，而目前由于设备限制对聚合物在压力和流动场共同作用下的结晶行为研究很少，因此我们在基金委的资助下设计了压力-剪切仪，并对等规聚丙烯（iPP）的结晶行为开展了以下研究：（1）压力场下流动诱导iPP结晶研究；（2）异相成核（添加β成核剂）iPP在压力和流动场下形成β-iPP的窗口。并利用资助经费对聚乳酸（PLA）和聚偏氟乙烯（PVDF）的结晶行为开展了扩展研究：（1）压力场和流动场共同诱导PLA结晶研究；（2）流动场及离子-偶极相互作用对高压下PVDF结晶行为影响。.在iPP结晶方面取得了以下研究成果：.（1）明确了iPP在压力场下流动诱导β晶的临界条件。通过研究iPP在不同压力和剪切速率条件下的结晶规律，绘制了在加工外场下形成β晶的相图。.（2）揭示iPP在压力场下流动诱导γ晶与流动场强度之间的依赖关系，获得形成γ晶的条件窗口，绘制在加工外场下形成γ晶的相图，为实际成型加工中iPP晶体结构调控提供理论依据。.（3）建立压力场、流动场与iPP晶体形态（取向晶体、片晶厚度、长周期等）的对应关系，确立了形成取向晶体形成的临界条件（流动比功和剪切速率），探索了流动场下压力对流动比功的影响规律，实现了对iPP晶体形态的可调控，可指导iPP实际加工过程。