剪切流场下短支链对shish-kebab晶体形成与调控的影响研究

This project, based on bimodal polyethylene as example, using SAXS/WAXD and infrared technology in Shanghai Synchrotron Radiation Facility, offline and online researches the formation mechanism of shish-kebab crystals, with varying degrees of chain entanglement, owing to coil-stretch transition and stretched entangled chains of bimodal polyethylene, in shear flow field. A series of solvable and unsolvable entangled melt system are formed by changing the content of high molecular weight component, shear temperature, shear rate, and shear time, and by finely tuning the chain entanglement through the use of high molecular weight fractions of bimodal polyethylene with different chain length and branching content, and supplemented by chitin nanocrystals. The aim of this project is reveal the effect of short branched chain on shish-kebab crystal formation, and realize the modulation of shish-kebab crystal of bimodal polyethylene with different chain entanglement by changing the chain structure and process conditions, and develop and perfect the formation mechanism of shish-kebab crystals. This project can provide the rules for the study of shish-kebab crystal as a model system, in addition it can be of service to promote the process and product performance of bimodal polyethylene material products.

本项目以双峰聚乙烯为示例聚合物，通过改变高分子量组分含量和剪切温度、剪切速率、剪切时间等工艺条件来调节其缠结体系的解缠程度，并通过选用高分子量组分具有不同支链长度和支链含量的双峰聚乙烯、并辅以甲壳素纳米晶的作用，微调链缠结形成系列不同缠结程度的熔体体系，利用上海光源的SAXS/WAXD以及红外联用测试平台，离线及在线深入系统研究剪切流场下可解缠结和不可解缠结两种不同链缠结条件的双峰聚乙烯shish-kebab晶体的coil-stretch转变机理和拉伸网络机理，揭示短支链对shish-kebab晶体形成的影响规律，实现链结构和工艺条件对具有不同链缠结的双峰聚乙烯的shish-kebab晶体形成的调控，以发展和完善shish-kebab晶体形成的机理。此项目可以作为一类模型体系为shish-kebab晶体的研究提供规律，其研究结果也可以应用于双峰聚乙烯材料制品的工艺改进和产品性能提升。

Shish-kebab晶体对高分子材料制品性能的提高有着重要意义，因此研究shish-kebab晶体的形成与调控机理十分重要。本项目以双峰聚乙烯为示例高分子，通过改变高分子量组分含量和剪切温度、剪切速率等工艺条件来调节其缠结体系的解缠程度，并通过选用高分子量组分具有不同短支链长度（乙基和丁基）和短支链含量的系列双峰聚乙烯，形成系列不同缠结程度的熔体体系，主要利用同步辐射SAXS/WAXD联用测试平台，离线及在线深入系统研究了高温剪切和低温剪切两种剪切流场下的双峰聚乙烯shish晶体的coil-stretch转变机理和拉伸网络机理，揭示了短支链对shish-kebab晶体形成的影响规律，突破了shish晶体只源于其中一种形成机理的认识，实现了链结构和工艺条件对双峰聚乙烯的shish-kebab晶体形成的调控。本项目进一步将上述shish-kebab晶体形成的调控机理应用于双峰聚乙烯的加工过程，并通过加入适量甲壳素纳米晶，有效提升了双峰聚乙烯注塑制品的力学性能。在此基础上，通过保留或破坏注塑制品中的shish-kebab晶体，探索形成了高性能纳米孔和微米孔双峰聚乙烯发泡材料的制备工艺。本项目研究结果不仅作为一类模型体系发展和完善了shish-kebab晶体形成机理的本质认识，而且可以应用于双峰聚乙烯制品的工艺改进和产品性能提升。