硫氰酸钠水溶液体系的聚丙烯腈溶液凝固行为

Coagulation Behavior of Polyacrylonitrile Solution in Sodium Thiocyanate Aqueous Solution System

硫氰酸钠(NaSCN)溶剂路线是国外制备高性能聚丙烯腈(PAN)基碳纤维原丝成熟的纺丝工艺路线,该技术在国内碳纤维领域尚处于发展阶段。文中采用流变仪、红外光谱研究了PAN在不同质量分数NaSCN水溶液中形成的聚合物溶液的流变性能和PAN大分子状态;溶液中NaSCN质量分数的提高,PAN溶液的黏度先减小后增大,在51%NaSCN溶液中PAN溶液的黏度最低、,用光学显微镜和X射线衍射研究了NaSCN水溶液为溶剂的PAN溶液凝固行为。研究发现,51%NaSCN溶液中,PAN大分子以最舒展状态存在,PAN分子链的31螺旋构象更多,这与溶液中硫氰酸根主要以异硫氰酸根(—N=C=S)存在有关,PAN的氰基与异硫氰酸根的—N=C形成桥键结构。随着聚合物溶液中NaSCN质量分数增加,凝固剂水在PAN溶液中的扩散速率增加,PAN溶液凝固结晶程度先增大后减小,在质量分数为51%的NaSCN水溶液中,PAN的凝固结晶规整度更优异,这与PAN以解缠伸展状态存在相关,由于流动活化能更低,PAN溶液更易发生相转变。

The preparation of high-performance PAN based carbon fiber precursor with sodium thiocyanate(NaSCN)aqueous solution as solvent abroad was a mature spinning technology,which was still in the development stage in the domestic carbon fiber field.In this paper,rheometer and FT-IR were used to study the rheology of PAN solution in NaSCN aqueous solution with different mass fractions,and the macromolecular state of PAN was speculated.The coagulation behavior of PAN solution in NaSCN aqueous solution with different mass fractions was studied by optical microscope and XRD.It is found that with the increase of NaSCN mass fraction in aqueous solution,the viscosity of PAN solution decreases first and then increases.In 51%NaSCN solution,the PAN solution has the lowest viscosity and lowest viscous flow activation energy.PAN macromolecules exist in the most extended state,and PAN molecular chains mainly exist in trinity helix conformation with a lower energy state,which is related to the maximum content of isothiocyanate(-N=C=S)in solution,the cyano group of PAN forms a bridge structure with-N=C of isothiocyanogen.With the increase of NaSCN mass fraction in PAN solution,the diffusion rate of water in PAN solution increases,but the crystallization degree of PAN solution increases first and then decreases,and the crystallization degree of PAN in 51%NaSCN aqueous solution is more excellent,which is related to the untwisting state of PAN in this NaSCN aqueous solution,because the flow activation energy is lower,PAN solution is more prone to phase transition.