新型复合溶剂对纤维素高效溶解机理及其纺丝过程中凝聚态调控研究

As the most abundant carbon resource, cellulose is the sustainable raw material for chemical fiber, but the conventional production of viscose fiber with carbon disulfide as solvent causes serious pollution, low efficiency and large power consuming. Therefore, the recent research all over the word focuses on the green solvent of cellulose with high efficient. In the previous study, we found that the solubility of cellulose can reach 30% in the complex solvent of common solvent and little ionic liquid (IL), which is obviously higher than that in pure IL. So far, this complex solvent shows the best dissolving ability for cellulose and can be developed as a new solvent system of cellulose fiber with independent intellectual property in China, but the efficient dissolution mechanism of the complex solvent remains unclear. The project will investigate the microstructure evolution of solvent and solute in the complex system (the interaction between the components of complex solvent and the interaction between the complex solvent and cellulose, especially the hydrogen bonding including the dissociation and association of hydrogen bonds) and the dissolution kinetics to reveal the dissolution mechanism and the contribution of solvent components to cellulose dissociation. Furthermore, the bidifussion and phase separation of highly concentrated cellulose spinning dope will be investigated. during spinning and solidification, synchrotron radiation light source will be used to study the condensed state structural evolution and its relation to the properties of cellulose fiber, which may provide the theoretic foundation for the development of a novel complex solvent of cellulose and a new green process with high efficient of cellulose fiber.

纤维素是最丰富的碳资源，是化学纤维的可持续原料，但现有粘胶纤维生产使用二硫化碳污染大、效率低、能耗高，所以研发高效绿色的纤维素新溶剂成为世界各国的研究热点。我们前期研究发现普通溶剂与少量离子液体形成的复合溶剂对纤维素溶解度可高达30%，明显优于纯离子液体，是至今为止溶解度最高的纤维素溶剂，可望成为具有中国知识产权的纤维素纤维新溶剂体系，但是其高效溶解机理尚不明确。本项目拟研究该新型复合体系中溶剂和溶质多重微观结构演变规律（复合溶剂各组分之间及其与纤维素之间的相互作用，特别是氢键作用及其离解与缔合等）和溶解动力学，揭示复合溶剂溶解机理及其各组分对溶解纤维素的贡献与影响规律。并进一步研究高浓度纤维素纺丝液在凝固浴中的双扩散及相分离，利用同步辐射光源技术研究纺丝凝固过程中多级凝聚态结构演变规律及其与纤维素纤维性能的关系，为开发纤维素新型复合溶剂及纤维素纤维高效绿色制备新路线提供理论支撑。

我国是粘胶纤维的生产大国，但是随着环境意识的日益增强，粘胶纤维生产企业的排放标准已经不能适应，相继停产、搬迁或原地改造，可见急需大力发展纤维素纤维的清洁生产新工艺。将离子液体作为新型纤维素溶剂应用于纤维素纤维的生产具有巨大的潜力，但是离子液体存在成本高、粘度大、溶解效率低、溶解温度高等问题。.该项目围绕纤维素纤维高效绿色制备过程中关键科学问题及其关键技术，开展了高浓度纺丝液制备及溶解机理、新型纤维素纤维成型及结构调控等系统研究， 建立了纤维素在离子液体/非质子溶剂复合溶剂中的结构演变表征方法，确定最佳极性非质子溶剂种类及最佳添加比例，并对纤维素/离子液体/极性非质子溶剂纺丝原液的流变特性及流变行为进行系统分析，研究剪切速率、温度以及溶剂混合比例等对纺丝原液表观粘度、非牛顿指数、结构粘度指数及粘流活化能等的影响，从而为该高粘度流体纺丝提供理论依据。与纯离子液体相比，纤维素在复合溶剂中的溶解度从10wt%提高到25wt%，溶解温度从120℃升高到40-80℃，溶解时间从2h缩短至5min-0.5h，不仅提高了生产效率，也抑制了纤维素的降解，溶剂成本降低70%，纺丝液粘度降低80%，降低了能耗和设备要求，凝固浴组成简单，方便溶剂的回收。采用干喷湿法纺丝制备纤维素纤维，根据纤维素纤维力学性能和凝聚态结构两方面系统研究纺丝工艺，得到最佳纺丝条件为：气隙长度2.5 cm，凝固浴组分30%DMSO/70%H2O，凝固浴温度35℃，喷头拉伸比1.9倍，一级水浴牵伸比1.7倍，一级水浴温度60℃，二级水浴牵伸比1.1倍，二级水浴温度85℃，纤维素纤维的断裂强度2.9 cN/dtex，断裂伸长率8%，达到粘胶纤维的水平。.本项目是在离子液体法纤维素纤维基础上的创新发展，是纤维素纤维制备全新的技术。采用少量离子液体与大量廉价的非质子溶剂共混制备成纤维素的复合溶剂体系，显著降低了生产成本，对我国纤维行业的可持续发展有着重大的意义。