含微交联分子链网络的聚乙烯流动诱导互连串晶研究

The mechanical properties of polymer are enhanced by flow-induced shish-kebab. At present, the main approach to promote the formation of shish-kebab is to add small amount of high molecular weight component into polymer matrix, besides exerting shear or elongational flow during the freezing of melt. The aim to add high molecular weight component is to increase the entanglement of molecule chains, and slow the process of relaxation after flow-induced orientation, thus the primary nuclei easily form. However, it is still possible to disentangle for the type of entanglement between linear molecular chains, hence the effect to promote formation of shish-kebab is limited and there is no shish-kebab appearing in the core region of product. In this program, slightly crosslinked polyethylene network is added into polyethylene to promote formation of shish-kebab by taking advantage of its slow relaxation process. The result of earlier stage shows that shish-kebabs form in the core layer of oscillation injection molding after adding 3% slightly crosslinked polyethylene (radiation dose is 5kGy) into polyethylene matrix. In the meantime, the proportion of shish-kebab is markedly enhanced, thus the mechanical properties is notably increased too. It suggests that the slightly crosslinked network is certainly effective to promote formation of shish-kebab. The idea and result have never been reported before. We want to study the crystallization process of polyethylene containing slightly crosslinked polyethylene network in situ by synchrotron radiation and Linkam shear cell. Finally, it is hoped to reveal the relationship of structure and properties after testing the mechanical properties and characterizing the morphology of oscillation injection product.

流动诱导的串晶(shish-kebab）赋予了聚合物优异的力学性能。目前，促进串晶形成的方法除了在熔体冻结过程中提供剪切或拉伸流场外，就是添加少量长链分子，其原理是增加分子链间的缠结，使缠结网络在流动取向后松驰较慢，故易于形成shish晶核。然而，这种缠结在流动场还是存在解缠的可能，故促进串晶形成的作用有限，且制品芯层不会生成串晶。本项目提出利用微交联网络松驰较慢的特性，将其加入聚乙烯中以促进串晶形成。从前期研究成果看，将3%的微交联聚乙烯（辐照剂量5kGy）加入聚乙烯基体后，其振动注塑样品的芯层也生成了串晶，使串晶比例大幅度提高，力学性能也得到显著增强，这说明微交联网络确实起到了促进串晶生成的作用，这是从来没有报道过的。本项目拟利用同步辐射和剪切热台在线跟踪研究含微交联网络的聚乙烯流动诱导结晶过程，最后利用振动注塑技术成型样条，通过测试力学性能和结构表征揭示其形态、结构与性能之间的关系。

本项目围绕聚合物分子结构以及加工外场对聚合物流动诱导结晶影响这一基础科学问题开展研究，主要采用同步辐射检测装置表征聚合物的晶体形态结构，利用取得的研究成果指导实际加工过程中聚合物的结构与性能调控，从而弄清聚合物“加工-结构-性能”的关系，从基本原理到实际工程方案设计为制备高性能聚合物制品和扩展其应用打下了良好基础，顺利完成了项目预定的研究目标。此项目对以下四个方面开展了研究：①不同聚乙烯分子网络结构对流动诱导聚乙烯基体中shish-kebab形成以及制品力学性能影响的机理和相关基础科学问题；②利用自制压力-剪切仪开创性地研究了压力场下流动诱导等规聚丙烯的结晶行为，揭示了压力对等规聚丙烯在流动下结晶的影响规律；③利用等规聚丙烯在流动场下形成的晶体网络增强无规聚丙烯，从而使无规聚丙烯得到高效高性能化利用；④受限条件下低维度纳米粒子（碳纳米管）诱导等规聚丙烯结晶的相关研究，揭示了碳纳米管对等规聚丙烯结晶的多重影响，比如阻碍分子链运动、加速成核等。研究成果共发表SCI收录期刊论文6篇。