全降解型原位纳米纤维化增强聚酯共混物结构调控与性能研究

Blending biodegradable polymers is a versatile and efficient approach to achieve high performance of environmental friendly materials, without sacrifice of the promising property of biodegradability. In this proposal, a method of "melt extrusion with high-elongated die - hot stretching - cold stretching" was proposed to fabricate a novel blend, named poly(L-lactide) (PLLA)/poly(butylene succinate) (PBS) in-situ nanofibrillar blend, in which PLLA nanofibrils can be tailored easily. The PLLA nanofibrils have several desirable features, such as high crystallinity, high molecular orientation, and few defects, leading to an excellent reinforcement of PBS matrix. In this system, the nanofibrils can be easily preserved during post processing with a relatively low processing temperature, leading to an obvious reinforcement of PLLA/PBS nanofibrillar blend moldings. Based on this technology, we will conduct some fundamental researches regarding flow-induced phase behavior, morphology manipulation, as well as structure-property relationship. The new understandings on flow-induced PLLA phase behaviors and the relationship between morphology and mechanical properties will be revealed. The fundamentals on the basis of the researches will be a guideline for the processing, structure, properties, and applications of PLLA/PBS in-situ nanofibrillar blends.

制备全降解型聚酯共混物为可降解高分子高性能化提供了一条方便高效灵活的途径，且不失去环境友好这一宝贵性质。本项目拟利用"高收敛口模挤出-热拉伸-冷拉伸"工艺制备左旋聚乳酸（PLLA）/聚丁二酸丁二醇酯（PBS）原位纳米纤维化增强共混物，实现PLLA纳米纤维化和调控，从而使纳米纤维具有高结晶度、高取向，以及缺陷少等优点，提高其增强效果。该过程中PLLA纳米纤维原位形成，随后选择合适的后续加工温度，可使原位纳米结构很好保持在制品中，提高制品强度。在本项目中，拟开展加工流动场下相结构演变、形态控制和性能的基础研究，获得流动场下PLLA原位纳米纤维的形态演变规律和调控方法，进而建立结构与性能的关系，提高PBS的性能，为全降解原位纳米纤维化PLLA/PBS增强共混物的"加工-结构-性能-应用"提供理论基础。

本项目为实现可降解高分子材料的高性能化，且不完全失去其可降解性，采用加工外场定构加工思路，开展了可降解聚合物多相体系的结构和性能的相关工作。首先项目通过拉伸流动场，使可降解聚酯共混物中分散相原位形成纳米纤维，获得了含PBS纳米片和含PBAT纳米纤维的PLA基薄膜材料，以及含PLA纳米纤维网络的PBS基薄膜材料，实现全降解型聚酯薄膜材料的高强度、高韧性和高阻隔性能。其次，为改善聚酯注塑制品的力学性能，我们通过剪切场诱导聚酯多相体系纤维化形成多层次取向结构，获得了仿贝壳PBS/苎麻复合材料，以及含shish-kebab多层次结构的PBS/PLA、PLA/PBS和PLA/PBAT的注塑制品，实现了同时增强增韧，例如，与普通注塑成型的纯PBS相比，注塑过程中施加剪切场的PBS/PLA（10 wt%）共混物样品的拉伸强度，拉伸模量和冲击强度分别增长了34.9%、133.2%和23.2%。最后，为解决PLA注塑制品耐热性低的问题，系统研究了剪切场对PLA晶体结构、结晶形态和耐热性能的影响，揭示了剪切场和成核剂共同作用下PLA晶体生成规律，发现了剪切场诱导PLLA/PDLA共混物SC晶，显著提高耐热性能，剪切场诱导等摩尔PLLA/PDLA共混物生成了100%SC，使制品VST达196 °C，在沸水中仍能支撑外部载荷、保持形状稳定。上述工作为全降解型聚酯制品高性能化和功能化提供加工和理论指导。