| In recent years,as the production of oil is decreasing and the environmental pollution caused by oil is becoming more and more serious,people are paying more attention to the rich and renewable cellulose.Because of its unique strong hydrogen bond structure,the cellulose can only be dissolved in some special solvents.Viscose process is currently the most widely used method for producing cellulose fibers,but its production process can cause serious environment pollution.O ver the past decades,Ionic liquids is becoming more and more popular as a new kind of green solvent.However,the existing ionic liquids used to dissolve cellulose have some drawbacks such as high melting point,high viscosity,inefficient dissolution as well as high dissolving temperature which can lead to serious degradation of regenerated cellulose.In addition,The high costs of the ionic liquids strongly limits its application.In this paper,by using orthogonal experimental method,we studied the best dissolving process conditions of different solid content cellulose in composite solvent system.Based on the solidification mechanism of this solution system,we successfully used the high concentration cellulose solution for wet Spinning and obtained cellulose fibers with good performance.The kinetics and thermodynamics of cellulose dissolution were studied by calculating the dissolution rate constant,dissolution apparent activation entropy,dissolution apparent activation enthalpy,activation energy using the change of crystallinity and the Arrhenius equation and data fitting.The results showed that the dissolution rate constant of the composite solvent system was higher than that of the pure ionic liquid system,and the dissolution apparent activation enthalpy and the apparent activation entropy were significantly lower than that of the pure ionic liquid system.The orthogonal test was used to determine the ratio of complex solvent,dissolution temperature and dissolution time.The dissolution condition of cellulose was observed under polarizing microscope and the best dissolving conditions of cel ulose were determined.By comparing the spinnability of the spinning solution with 15% to 19%cellulose content,we found that the spinnability and mechanical properties of the spinning solution with 17% of the solid content was optimal.The solidification mechanism of the cellulose in the mixed solvent system was studied by measuring the mass transfer rate and the solidification rate.Meanwhile,the effects of coagulation temperature,coagulation concentration,time and cellulose content on the solidification process of the cellulose mass transfer rate and solidification rate were also investigated.The results indicated that the solidification rate and mass transfer rate increased with the increase of coagulation bath temperature.In addition,the solidification rate of cellulose solution regeneration process and the mass transfer rate first increased and then decreased with the increase of coagulation bath concentration.However,the solidification rate and mass transfer rate were decreased with the increase of cel ulose content.The effect of spinning conditions on the structure and properties of regenerated fiber was investigated by wet spinning of the cellulose solution with 17% cellulose content.The optimum spinning conditions of our study were described as below:coagulation bath was composed of 20% DMSO and 80% H2 O,the coagulation bath temperature was 25 ?,the coagulation stretching ratio was 1.05 times,the first water bath draft ratio was 1.3 times,the temperature of the first water bath was 60 ?,the second water bath draft ratio was 1.28 times,and the temperature of the secondary water bath was 80 ?.The cellulose fibers obtained under the optimum conditio ns were compact,smooth and nearly elliptical in cross section.The highest breaking strength of the fibers can reach to 2.23 CN / dtex,the elongation was 9.01%;The degree of crystallinity was 54.35% and the orientation factor was 0.863. |
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