高性能PVA纤维成型机理及结构控制

The research on high performance PVA fibers is very important to enrich the high performance fiber products of our country, which have been widely used in many fields, such as national defence, modern aircraft manufacturing,transportation, petroleum industry, new energy resource, and information industry.In this project, we choose the high molecular weight PVA with low branching degree, a soft chain polar polymer, as a model polymer for studying the basic scientific problems dealing with the process of the high performance fibers. The initial orientation of molecular chains and the hydrogen bond network of the spinning dope in gelation under the coexistence of shear flow and temperature are investigated by means of in-situ two dimensions X-ray scattering technique, rheometer with the precise control of temperature and shear rate, and FT-IR instrument. The molecular chain orientation, nucleation of crystals, crystallization kinetics and morphology of PVA as-spun fibers in drawing process are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), sonic orientation detector, optical and polarized microscope, and scanning electron microscope. The relationship between the double diffusion and phase separation kinetics of spinning dope in coagulation bath and the molecular chain conformation, crystallization, orientation and deficiency of as-spun fibers is studied in detail. Combined the results of the formation of highly oriented molecular chains and regular crystal structure in drawing and thermal setting, we try to reveal the inherent relationship of process-structure-property of high performance PVA fibers. The outcome of this project will be the foundation for producing the high performance PVA and other soft chain polar polymers.

开展高性能PVA纤维的研究对丰富我国高性能纤维的品种，为国防军工、现代航空业、交通运输、石油化工、新能源、信息产业等领域提供必须的高性能纤维有十分重要的意义。本项目将围绕极性柔性链聚合物PVA高性能化的基础科学问题开展研究。采用2维X射线在线检测装备，表征纺丝原液在凝胶化转变过程中在不同温度场、剪切场下的预有序与分子取向及其初生纤维在拉伸应力场中分子取向、结晶过程的成核与晶体生长动力学，深入研究基于高分子量、低支化度PVA纺丝溶液凝胶化转变过程中双扩散及相分离动力学与PVA初生纤维分子链构象和结晶、取向、缺陷等聚集态结构形成的内在联系，结合拉伸、热定型过程中高取向度、规整结晶结构的形成规律研究，弄清PVA高性能化过程中加工-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PVA纤维和扩展其应用打下良好基础。

为了得到高强高模聚乙烯醇纤维，本研究项目从PVA纺丝原料的分子结构、纺丝原液的组成及其凝胶化行为、凝胶纺丝工艺条件、纤维热拉伸条件等方面入手，研究了高强高模PVA纤维的成型机理和结构控制。重点探索了高分子量低支化度、不同间规度PVA的合成以及不同条件（分子结构、溶液状态、溶剂、温度、浓度等）下PVA纺丝原液的凝胶化转变过程。我们还将凝胶化过程与PVA初生纤维的形成相联系，研究了初生纤维分子链构象和结晶、取向、缺陷等聚集态结构形成与纺丝原液、凝胶纺丝加工条件之间的内在联系。再结合高倍热拉伸、热定型过程中高取向度、规整结晶结构的形成规律，弄清了PVA高性能化过程中加工条件-结构-性能三者之间的关系。研究发现，降低聚合反应温度和控制自加速效可以得到高线性低支化度的聚乙烯醇。第二单体三甲基叔丁醇的引入可以实现对PVA的间规度的调控，当引发剂KPS与单体的物质的量比为1/1200，单体摩尔比为(VAc:VPi) 3:7，反应温度为12℃，可得到聚合度5180、间规度59.30%的PVA。同时，随着间规度的增加，PVA溶液的凝胶化转变能力得到提高。通过对比不同浓度和温度下PVA溶液的流变性能，确定了凝胶纺丝原液的最佳浓度和加工温度。并且在纺丝原液中添加适量的水，有利于分子链的解缠结，促进纺丝原液的凝胶化转变能力，进而增强初生纤维的可拉伸性和最终的力学性能。除此之外，具有适当缠结结构和结晶结构的初生纤维，在热拉伸之后具有出色的力学性能。通过对PVA凝胶纺丝成型工艺条件进行探讨，得知随着空气层高度的增加，初生纤维的取向度先减小后增大，且初生纤维结构变得逐渐完善。同时，凝胶态拉伸V2/V1对初生纤维的拉伸性能以及最终的力学性能影响最大，具有最高拉伸倍数的初生纤维应具有适中的取向度。最后，对纤维然拉伸过程中结构与性能的研究发现，结晶度并不是影响纤维力学性能的唯一因素，纤维的力学性能很大程度上依赖于非晶区取向度。