Study On Dissolving And Spinning Process Of Cellulose And Polvacrylonitrile In Ionic Liquids

Ionic liquids are a series of organic salts with the melting points below100℃. Due to their nonvolatility, controllable physical properties, stable chemical properties, ionic liquids have attracted widespread attentions in recent years. For the good solubility of cellulose and other macromolecules in ionic liquids, the preparation of cellulose and other functional fibers became possible.In this work, based on the controllable structure and properties of ionic liquids, the solubility, regeneration and spinnability of cellulose and polyacrylonitrile in some imidazolium based ionic liquids were compared and investigated. By utilizing thermal platform polarizing microscopy, scanning electron microscopy, birefringence, wide angle X-ray diffraction, small angle X-ray scattering, thermogravimetric analysis, wet friction, fineness and tensile tester, the process and mechanism of dissolving and spinning of cellulose and polyacrylonitrile in ionic liquids were examined. Then the regeneratied cellulose fibers with good fibrillation resistance and the cellulose-modified PAN fibers with improved moisture absorption and wearing comfort were firstly prepared, the wet spun cellulose fibers with good mechanical properties, the PAN-modified cellulose fibers with improved fibrillation resistance, were prepared.From systematic research, the following conclusions about the solubility, regeneration and spinnability of cellulose, PAN and their mixture in ionic liquids were drawn:1. Ionic liquids with the cellulose dissolving temperatures from low to high in sequence are1-ethyl-3-methylimidazolium acetate([EMIM]Ac)<1-butyl-3-methylimidazolium acetate ([BMIM]Ac)<1-allyl-3-methylimidazolium chloride ([AMIM]C1)<1-ethyl-3-methylimidazolium chloride ([EMIM]C1)<1-butyl-3-methylimidazolium chloride ([BMIM]C1)<1-benzyl-3-methyl-imidazolium chloride ([BzMIM]Cl), while the solubility reduced in turn,1-ethyl-3-methylimidazolium bromide ([EMIM]Br) can only swell cellulose. Mixed DMSO decreased the viscosity and increased the permeability of ionic liquids, which effectively lowered the dissolving temperature and increased the dissolving speeds of cellulose. All the regenerated cellulose membranes were smooth, condense and transparent, whereas the regenerated PAN membranes were hard and brittle. Hydrolysis of some-CN happened when PAN were dissolved in [EMIM]Ac. The bidiflusion became slow, the quantity and the diameters of the voids decreased as the viscosity of ionic liquids increased. There exists some compatibility between cellulose and PAN. Film formability of PAN can be enhanced by adding a small amount of cellulose.2. Smooth and dense cellulose fibers were regenerated by wet spinning of cellulose/[EMIM]Ac solution(12wt%), whose maximum tenacity reached2.88cN/dtex; the high concentration and the increased draw ratio helped to improve the crystallization, orientation and mechanical properties of cellulose fibers. Both the increments of extrusion and draw speeds made cellulose fibers easy to fibrillate. The increase of coagulation bath temperature accelerates the speeds of bidifrusion and coagulation, which made the structure of cellulose fibers more inhomogeneous, whereas the effects of the increasing concentration of coagulation bath were reverse.3. Dense and silky cellulose fibers with good fibrillation resistance were firstly regenerated by dry-wet spinning of cellulose/[EMIM] Ac solution. For cellulose with lower degree of polymerization (DP), the break of spin line could be explained by capillary wave mechanism; for cellulose with higher DP, the break of spin line could be explained by cohesive mechanism. High DP and low concentration help to spin cellulose fibers with low fineness and high tenacity, while low DP help to prepare spinning solution with high concentration, drawability and spinning speeds, which are meaningful to increase the spinning efficiency. Water added during the preparation of spinning solution had little effects on the spinning speeds and break draw ratios, but disturbed the orientation and structure formation of cellulose. With the increment of water content, the tenacity of fibers decreased. For the solution with low DP cellulose, the better drawability dominated the formation of structure and properties, then the effects of water content tended to vanish. Fibers from low DP cellulose had smaller voids and narrower voids distribution.The lateral blow did harm to the spinning stability and the mechanical properties of obtained cellulose fibers. When the residence time corresponded to the relaxation time of the spin line, the fibers with the maximum tenacity can be obtained. The shrinkage and break elongation of the regenerated fibers increased with the residence time. Although the tenacity of the fibers spun at low spinning speeds are not high, the wet friction time and the fibrillation resistance were greatly improved.4. By dry-wet spinning of cellulose/[BMIM]Cl solution, the tenacity of the regenerated cellulose fibers reached4.81cN/dtex. The proper extrusion speeds and length of gap correlate with the relaxation time of the solution, which is effected by the viscosity and the spinning temperature of the solution. With the increment of DP, the tenacity and wet friction time increased. The mean length and the mean radius of voids were about20Qnm and25nm respectively, the orientation distribution of voids were in the scope of9-23°, both of which varied with extrusion speeds, draw ratios and spinning temperature. With draw ratios increasing, the tenacity of the regenerated cellulose fibers increased, whereas the wet friction time and fibrillation resistance decreased.5. The dry-wet spinning process of PAN-modified cellulose fibers is similar to that of pure cellulose fibers. By adding PAN, the wet friction time of regenerated cellulose fibers increased markedly, especially for that from low DP cellulose, but not obvious even harmful for that spun from high DP cellulose at low draw ratios.6. As to the dry-wet spinning process of cellulose-modified PAN fibers, with the increase of temperature, the spinning speeds and draw ratios in the gap increased, which promote the increase of tenacity and modulus of the fibers and the decrease of fineness. The plastic deformation can improve the mechanical properties of the fibers. Under the same total draw ratio, the fibers with larger plastic deformation draw ratio had higher tenacity and modulus.The cross sections of the cellulose-modified PAN fibers are circular, while the lateral surfaces have some grooves along the axial direction, no obvious holes can be observed. By adding small amounts of cellulose, the tenacity of PAN fibers increased; with the further addition of cellulose, phase separation appeared and the tenacity of fibers decreased. With the increase of cellulose added, the moisture absorption increased. The moisture regains of the5%and20%cellulose-modified PAN fibers were3.20～3.67and4.06～4.33times of the pure PAN fibers.