Study On Dissolution And Regeneration Of Colored Waste Cotton Fabric

Under the trend of sustainable development of resources,recycling processing and reusing of textiles are becoming more powerful,meanwhile the cotton fabric account for the majority of discarded textiles,so the recycling of waste cotton textiles is more widely concerned.Compared with traditional landfill or incineration treatment,solvent dissolution recovery has higher green recycling value,some new green solvents are environmentally friendly and have the advantages of simple process and solvent recovery,but most of the current research is limited to colorless fabric.However,colored waste cotton fabrics need to be stripped,which has great damage to the fabric structure and affects the reuse performance.the regenerated products still need to obtain color through dyeing processing.In addition,the process is cumbersome,consumes a lot of water and energy,also pollutes the environment.Waste cotton fabrics tend to have higher degree of polymerization,but difficult to good dissolved in solvent and form a uniform solution,therefore colored cotton fabric as raw material,after pretreatment by using green solvent dissolved preparation of non-ferrous products directly,that can shorten the recycling process of colored waste cotton fabric,save energy,reduce consumption,quite conform to the development trend of green and recyclable.The main research contents are as follows:（1）Taking colored cotton fabric as raw material,the effects of H₂SO₄and NaOH pretreatment concentration,temperature and time on the degree of polymerization,color strength and crystallinity of colored cotton fabric were investigated,It was found that the degree of polymerization of cellulose decreased significantly under acidic conditions,while the glycosidic bond was relatively stable under alkaline conditions,and the degree of polymerization could not be reduced in a short time even if the concentration of lye was increased..At the same time,the color retention of H₂SO₄pretreated fabric is higher than that of NaOH pretreated fabric.High concentration NaOH pretreatment can also reduce the degree of polymerization in a short time,but in this way,the crystalline structure of cellulose was destroyed and the crystallinity decreases obviously,which is not suitable for the pretreatment conditions in this paper.Considering the structure and color strength of cotton fabric after pretreatment,colored cotton fabric samples with different degree of polymerization and small degree of decolorization were obtained by pretreatment with low concentration H₂SO₄（0.5wt%）at high temperature（70℃）and different time（1 h,2 h,3 h）.（2）Colored cellulose films were successfully prepared by dissolving colored cotton fabrics with different degree of polymerization in[Bmim]Cl/DMSO system,NMMO/H₂O system and NaOH/urea/H₂O system respectively.It was found that cellulose was dispersed in NMMO/H₂O,swelled in NaOH/urea/H₂O and[Bmim]Cl/DMSO by polarized light observation.The dissolution rates of cellulose in the three systems are as follows:NaOH/urea/H₂O>[Bmim]Cl/DMSO>NMMO/H₂O.At the same time,with the increase of polymerization degree,the solubility decreases,and the cellulose with higher polymerization degree（DP1111,DP911）could not dissolve in the NaOH/urea/H₂O system to form a uniform and stable mucus.By comparing the structure and properties of the regenerated membranes,it was found that the three systems were non-derivatization solvents of cellulose,and the crystal type changed from cellulose I to II.Within the experimental range,the regenerated membrane of[Bmim]Cl/DMSO system had higher polymerization degree,smooth surface,uniform,and relatively optimal fracture strength.The color retention degree of the three system regenerated membrane was:NaOH/urea/H₂O>[Bmim]Cl/DMSO>NMMO/H₂O.（3）Colored cellulose with the same degree of polymerization（DP557）was used as the raw material to dissolve in the three systems.Rheological tests showed that all the solutions were shear thinning pseudoplastic fluids.The zero-shear viscosity,relaxation time,structural viscosity index,activation energy and modulus of NaOH/urea/H₂O system and NMMO/H₂O system were higher than those of[Bmim]Cl/DMSO system,which proved that[Bmim]Cl/DMSO/cellulose solution had good fluidity.The temperature stability of NaOH/urea/H₂O/cellulose solution showed that irreversible gelation occurs,and[Bmim]Cl/DMSO/cellulose solution had high stability.[Bmim]Cl/DMSO was used as solvent to dissolve colored cellulose with different degree of polymerization（DP1111,DP911,DP557）.By comparing the rheological properties,it was found that increasing degree of polymerization would reduce the fluidity of the solution,and increasing temperature would help to improve the problem of excessive viscosity.