流动场下茂金属等规聚丙烯γ晶的生成机理及其多层次聚集态结构调控研究

Metallocene-made isotactic polypropylene (m-iPP) exhibits better performance than the conventional Ziegler-Natta isotactic polypropylene in the areas of spinning and injection. In addition, the molecular chain structure features of m-iPP promote formation of γ-crystals. And manipulation of the crystallization kinetics and morphology of γ-crystal under the flow field are the foremost ways to tune and improve the performance of m-iPP. However, the related research is still in the primary stage. The previous study reported by the applicant found that there was an inhibiting effect on the formation of γ-crystals under the extreme (continuous and strong) shear, which is due to the molecular chain orientation. Based on this result, in this proposal, we plan to explore the critical shear strength of suppression γ-crystal formation, monitor the nucleation-growth process of γ-crystals, and reveal the mechanism of γ-crystal formation under the flow field. The relationship between the flow field and γ-crystal hierarchical structure was expected to be established, aiming to fabricate m-iPP injection products with better mechanical properties. We attempt to investigate the rules of γ-crystal formation under the simple shear flow, regulate the γ-crystal hierarchical structure, and build the relationship between γ-crystal hierarchical structure and the sample property of injection molding. The results are promising to provide valuable theory guideline and technical support for the manipulation of the structure and the performance of m-iPP.

茂金属等规聚丙烯（m-iPP）与常规齐格勒纳塔等规聚丙烯相比，在纺丝和注塑等领域表现出更优的性能。此外，m-iPP分子链结构特性易于γ晶生成，流动场下对γ晶结晶行为和形态的控制是调控和提高m-iPP性能的重要途径，但该方面的研究目前尚处初级阶段。申请人前期研究发现，极端剪切引起的m-iPP分子链取向抑制了γ晶生成。在此基础上，本项目拟通过研究抑制γ晶生成的临界剪切强度，以及流动场下γ晶成核和生长动力学，获取流动场下γ晶生成机理，然后建立流动场参数与含γ晶多层次聚集态结构的联系，并进一步调控含γ晶多层次结构的形态，从而指导实际加工成型中γ晶及其多层次结构生成，获得综合性能优异的m-iPP注塑制品。本项目拟系统研究流动场下γ晶的形成规律，对含γ晶的多层次聚集态结构进行调控，指导多层次结构在注塑制品中的实现，及建立结构与制品性能的关系，为m-iPP注塑制品的形态和性能调控提供理论依据与技术指导。

流动场对等规聚丙烯（iPP）多晶态（α,β,γ）的生成有着重要的影响，流动场诱导取向α晶会使制品强度变大，促使生成的β晶能使制品韧性提高，但流动场对γ晶生成的影响规律及γ晶与iPP制品性能的关系目前尚未明确。本研究发现，非剪切试样的α晶和γ晶在茂金属等规聚丙烯中同时出现，而剪切试样中α晶先于γ晶出现。这是由于剪切引起的分子链取向有利于α晶的生成，而取向分子链松弛才有利于γ晶的生成。而非等温结晶完成后，剪切试样中却得到了更高含量的γ晶。这完全不同于等温结晶情况，剪切对γ晶的含量表现出抑制作用。研究表明α晶和γ晶的含量是动态竞争过程，γ晶的含量不但和剪切引起的分子链取向和松弛有关，还和剪切引起的聚合物分子链的结晶温度区间密切相关。申请人获得了流动场下γ晶成核和生长动力学，获取流动场下γ晶生成机理，建立了流动场参数与含γ晶多层次聚集态结构的联系，并进一步调控含γ晶多层次结构的形态，进而在注塑成型中获取具有较高力学性能的含γ晶等规聚丙烯试样。此研究为含γ晶等规聚丙烯注塑制品的形态和性能进一步调控提供理论依据与技术指导。