| With the advancement of economy and the improvement of people’s living standards,the demand for textile raw materials has increased and the use cycle of textiles has shortened,resulting in the accumulation of waste textiles.Among them,cotton fiber,as an important textile raw material,accounts for a high proportion.China produces more than 30 million tons of waste textiles each year,most of them are burned and landfilled as ordinary solid waste,waste cotton textiles are mainly burned or landfilled as ordinary solid waste,leading to environmental and land pollution as well as waste of resources.If waste cotton textiles can be effectively recycled and reused,it can reduce environmental pollution,and can also help relieve the high demand on textile raw materials.The main component of cotton is cellulose,so the recycling of waste cotton textiles is also the recycling of cellulose resources.Phosphoric acid,as an efficient and economic solvent for cellulose,can solubilize cellulose of high degree of polymerization(DP)in high concentrations.Besides,phosphoric acid is easily available,low cost and recyclable.Therefore,this work uses phosphoric acid as the solvent to dissolve waste cotton textiles followed by regeneration in water to obtain different forms of cellulosic materials,to enable high value-added utilization of waste cotton textiles.In the first part,the dissolution of cotton fabrics in different phosphoric acid concentration(77%,81% and 85%)and temperature(0℃,20℃ and 30℃)was mainly investigated.It was found that the phosphoric acid concentration was 85%,the temperature was 30°C and the cotton fiber content was 1wt%,complete dissolution was achieved in 30 min.Polyester-cotton blended fabrics(40/60)were treated with phosphoric acid under these conditions to separate cellulose and polyester(PET).The separation products were characterized.The results show that the original structural properties of polyester were not changed by phosphoric acid treatment,and its recovery rate is as high as 97%,demonstrating complete separation of cellulose and polyester.In the second part,cellulose solution in phosphoric acid was regenerated in water,followed by high-pressure homogenization to prepare regenerated cellulose suspension,then freeze-dried to obtain regenerated cellulose.The FTIR and X-ray diffraction of the regenerated cellulose showed that they remain unchanged chemically but transform from cellulose Ⅰ to cellulose Ⅱ,with decreased crystallinity,compared with original cotton fabrics.TEM micrograph results that the regenerated cellulose is less than 100 nm in diameter and a few microns in length,qualifying to be categorized as nanocellulose.The regenerated cellulose suspension shows "gel-like" fluid behavior,thixotropic and shear thinning rheological properties,and has a promising application as a rheological additive for aqueous coatings.In addition,regenerated cellulose films(RCF)were also prepared based on the phosphoric acid dissolution regeneration process,and the effects of regeneration conditions and cellulose content on RCF properties were investigated.Optimum performance was achieved using water as the regeneration bath and using a solution containing 6wt% cellulose.Mechanical properties and transmittance tests showed that RCF has a flat and uniform surface,dense structure,good tensile strength(up to 169 MPa)and high transparency(optical transmittance above 78%),and has great potential as packaging material. |
