热-机械外场条件下的聚酰胺薄膜形变机理研究

Due to its superior mechanical and barrier properties, biaxial oriented polyamide (BOPA) film is an excellent solution to packing films, of which the quality is substantially determined by processing. Between the two most popular processing methods, sequential stretching is debated for heterogeneity of mechanical property in different directions, while simultaneous stretching suffers from the low thermal stability. Structure acquired by the biaxial stretching process is a result of the integrated effect of the thermal-mechanical external field during different processing steps which is coupled with various dynamics of hierarchical structures in semicrystalline polymers. Besides, the existence of hydrogen bonding in polyamide makes the thing even more complicated. Therefore, exploring the globally optimized processing window is impossible to achieve by the commonly-used trial and error method. In this project, in-situ synchrotron radiation X-ray scattering is combined with the home-made biaxial stretching device, tracking the structure evolutions of crystal, morphology transition (i.e. fibrillation, cavitation), as well as the stress-strain relationship. Based on these data, the diagrams of the crystalline phase and morphologies can be plotted. And the deformation mechanism of the microstructure can be correlated with macro-mechanical phenomena. This project can provide quantified in-situ structural parameters to guide the processing, which can be taken as the fundamental data for the development of bio-based nylon film, i.e. nylon 56.

双向拉伸聚酰胺薄膜（BOPA）具有优良的阻隔性和力学性能，是新一代包装膜材料的代表，其产品质量很大程度上取决于加工工艺。主流的BOPA加工中，异步法会出现破膜、力学性能均衡性差的现象，而同步法往往热稳定性能不足。由于拉伸过程是多步骤热-机械外场历史作用的叠加，同时体系涉及到多尺度结构转变的动力学耦合，加之氢键相关相行为的干扰，摸索最优加工外场窗口非常困难。本项目拟结合同步辐射X射线散射与团队研发的双向拉伸装置，原位采集单向非受限、单向受限和双向同步拉伸这三种典型工业外场模式下的宏观力学行为、晶型转变、晶体取向、球晶-纤维晶转变、孔洞化等关键结构演化动力学信息。基于以上数据，绘制加工参数空间内的晶型和形态结构相图，构建微观结构演化规律与宏观力学行为的关系，为BOPA薄膜加工工艺和产品性能优化提供理论指导，推进新型生物基尼龙双向拉伸薄膜的工业化生产。

含氢键高分子（如尼龙）由于氢键的存在使其高分子链的排列、取向等与其他高分子材料存在差别，其中的强氢键相互作用赋予其优异的耐热性能和力学性能等，使其应用广泛，但同时也限制了其加工方式。高分子材料加工大多涉及到拉伸形变过程，拉伸过程中晶体的形变和相变等非平衡结构演化对高分子材料性能有着很重要的影响。拉伸形变过程对于含氢键半晶高分子的加工也是极其重要的步骤。同时，由于氢键结构的特殊性，温度成为其加工过程的一个重要参数。 本项目中，我们选用了应用比较广泛的含氢键半晶高分子——脂肪族聚酰胺作为主要研究对象。通过同步辐射原位实验、傅里叶红外光谱等技术，我们揭示了聚酰胺（PA46）在多维拉伸外场-温度作用下的多尺度结构演化规律，着重探讨了氢键对PA46在热机械外场作用下晶体的形变与相变的作用，并得到了PA46在应变-温度和应力-温度二维空间的平衡相图。针对另一种常用聚酰胺——聚酰胺6（PA6）,对其在热-机械外场条件下（温度、拉伸）的晶型演化做出研究。我们通过自制双辊拉伸流变仪与原位同步辐射WAXS技术联用，跟踪了PA6在单一外场（温度）和多外场作用下（温度+拉伸）的相变行为。半晶高分子的过渡层的形貌变化对材料的各项机械性能有着结尾重要的影响。同时，我们利用新研制的同步辐射原位双拉装置，对PA46进行原位研究，并取得了初步的进展。