干喷湿纺聚丙烯腈初生纤维的微原纤结构形成及其致密化机理研究

Dry-jet wet spinning is an important technology to prepare polyacrylonitrile-based carbon fibers with high performance and low cost. The preparation of polyacrylonitrile precursor fibers with high quality is the prerequisite for obtaining carbon fibers with excellent performance. The densification of nascent fibers is the key to the quality of precursor fibers and carbon fibers. This project is based on the national “973” program entitled "The molecular design and fine structure controlling of ultra-high strength carbon fibers" and will focus on the formation and densification mechanism of the microfibril structure of polyacrylonitrile nascent fibers prepared by dry-jet wet spinning. The ultra-thin section and unique ultrasonic etching method combining with high resolution electron microscopy technology will be utilized to analyze the microstructure formation of the nascent fibers and the evolution law during its solidification process. The correlation between the microfibril structure of the nascent fibers, precursor fibers and carbon fibers will also be discussed. The effects of spinning preparation and solidification conditions on the structural densification and uniformity of polyacrylonitrile nascent fibers will be studied. A new microstructure model for the polyacrylonitrile nascent fibers, precursor fibers and carbon fibers will be established. The relationship between the structure of the nascent fibers and the properties of the precursor fibers will be found. The preparation process of the dry-jet wet spinning and the structure of polyacrylonitrile precursor fibers will be optimized, and then the polyacrylonitrile -based carbon fibers with high performance and low cost can be obtained.

干喷湿纺是实现聚丙烯腈基碳纤维高性能化和低成本化的重要工艺，优质的聚丙烯腈原丝是生产高性能碳纤维的前提，初生纤维微结构致密化是决定原丝和碳纤维质量的关键。本课题的提出基于前期承担国家“973”项目“超高强度型碳纤维分子设计与精细结构形态控制”的研究基础，重点对干喷湿纺聚丙烯腈初生纤维的微原纤结构形成及其致密化机理进行研究，运用科学的超薄切片和独特的超声刻蚀方法，结合高分辨电子显微技术解析聚丙烯腈初生纤维微结构形成及其凝固过程中的演变规律，探索聚丙烯腈初生纤维微原纤结构与原丝和碳纤维微原纤结构的相关性，研究不同的纺丝原液制备条件和凝固条件对干喷湿纺聚丙烯腈初生纤维结构致密化和组织均匀性的影响，建立聚丙烯腈初生纤维和原丝及碳纤维的微结构新模型，明确聚丙烯腈初生纤维结构与原丝性能间的关系，由此对干喷湿纺聚丙烯腈原丝的制备工艺和结构进行优化控制，进而研制出兼具高性能和低成本优势的聚丙烯腈基碳纤维。

本项目运用超薄切片和超声刻蚀方法，结合高分辨电子显微技术解析聚丙烯腈初生纤维微结构形成及其凝固过程中的演变规律，对干喷湿纺聚丙烯腈初生纤维的微原纤结构形成及其致密化机理进行研究。微原纤网络和片层结构是PAN初生纤维的重要结构组成，在凝固过程中，纤维细流发生相分离、凝胶化、结晶以及浓度波动等现象。致密、伸长的富聚物相凝固到微原纤中，并且微原纤交联形成网状结构。由浓度波动引起的横向结构域畴可作为片层结构的前驱体，随后片层结构紧密有序排列。同时，整个过程中伴随着结晶现象，分子链折叠形成片晶结构，并堆叠形成微原纤结构。.干喷湿法纺丝过程中不同纺丝阶段牵伸诱导PAN纤维微原纤取向过程。在凝固浴中形成的交联微原纤网状结构，被塑性拉伸，微原纤结构取向；同时纤维内部形成了横向片层结构。然后，在致密化过程中，分子链的重组显著提高纤维结晶度。最后，由于纤维经历较大的塑性变形，纤维内部形成了取向良好和排列规整的微原纤结构；同时，片晶结构以相对有序、规整的方式，堆砌在微原纤中。.通过对PAN纤维微观结构表征，研究溶液刻蚀过程和纺丝过程中PAN纤维微原纤结构的形貌变化，分别建立了PAN纤维结构模型、溶液刻蚀过程中PAN纤维结构变化模型、纺丝过程中PAN纤维原纤和片晶结构转变模型。PAN初生纤维内部呈多孔网络结构，微原纤交联形成纤维网络骨架结构。PAN原丝中微原纤沿纤维轴向取向，微原纤由折叠链片晶堆叠而成；微原纤倾向于凝聚、合并形成原纤以及原纤束。在干喷湿纺过程中，微原纤网络结构经过塑性拉伸、取向，逐渐聚集、融合形成致密、取向的原纤结构。同时，微原纤中的片晶数量增多，排列更为规整有序。