Fiber Processing With Ionic Liquid As Solvent

Some fiber materials include strong polar bonds that can only be dissolved in strong polar solvents,or strong acid or alkali,which brings enormous pressure on environmental protection.Ionic liquids have been recognized as green solvents in the cleaner producing process,and attracted widespread interest in the scientific field and industry with its unique structure and excellent properties.The formation thermodynamics and dynamics of polyacrylonitrile and cellulose with ionic liquid as solvent were investigated in detail.The spinning experiment was carried out as the foundation for clean processing of fiber.First of all,the polymer/ionic liquids/coagulator ternary phase equilibrium was studied.For polymer system,it is assumed that phase transition caused by crystal does not appear during the solidification process.Therefore,critical content of each group can be gotten when the phase separation happens in the low concentration solution using turbidity titration method.Then the ternary phase diagram of polymer/ionic liquids/coagulator can be drawn by turbidity correlation equation for full concentration.H₂O is good coagulator for the forming process of PAN/[BMIM]Cl system.Phase separation is easier to happen when[BMIM]Cl was used as solvent compared with DMF(Dimethylformamide) and DMSO(Dimethyl Sulfoxide).Then the diffusion dynamics of Cellulose/[BMIM]Cl/H₂O system compared with PAN/[BMIM]Cl/H₂O system was studied.It can be found that the diffusion speed of solvent and nonsolvent in Cellulose/[BMIM]Cl/H₂O system is much lower than which in PAN/[BMIM]Cl/H₂O system.Based on Fick's second law and mass transfer model of solvent and coagulator,the diffusion coefficient of solvent and coagulator was calculated.The diffusion coefficient D_[BMIM]Cl) and D_H2O increased with coagulator bath concentration and temperature,decreased with spinning solution concentration. Both D_[BMIM]Cl and D_H2O were in the order of 10^-10 cm²/sec for Cellulose/[BMIM] Cl/H₂O system.For PAN/[BMIM]Cl/H₂O system,D_[BMIM]Cl and D_H2O were only in the order of 10^-8 cm²/sec.Finally,the dry-wet spinning of PAN/[BMIM]Cl system was conducted.The polyacrylonitrile fiber with high intensity,high degree of orientation and smooth surface can be obtained.The chemical structure of PAN has not changed after spinning.The nascent fiber has obvious shell-core structure.The higher of the draw ratio is,the thicker of the shell and thinner of core layer.With the draw ratio increases, the orientation and mechanical properties increase first and then decrease.With the draw ratio of 3.5,degree of orientation is at the maximum,and the tenacity is up to 4.0CN/dtex.