In-situ Enzymatic Saccharification Method For Recycling Waste Polyester-Cotton Textiles

With people’s pursuit of fast fashion,waste textiles have also increased year by year.This includes pre-consumer waste in the production process and post-consumer waste discarded at the end of the product’s service life.At this stage,most waste textiles are still treated by traditional chemical incineration or physical landfill,causing a series of problems such as environmental degradation and resource waste.Therefore,new technologies for recycling waste textiles and using them to prepare high value-added products are attracting attention.In this study,the raw material is waste polyester-cotton textiles.First,pretreatment with dilute sulfuric acid is used to reduce the degree of polymerization of cotton cellulose.To increase the solubility of cotton components in N-methylmorpholine oxide(NMMO).On this basis,the technical route of in situ enzymatic saccharification with NMMO coupled with cellulase was studied,and the cotton component was converted into glucose through a combination of chemical-physicalbiological methods.Through solid-liquid separation,polyester with high purity and low loss is recovered.The results show that:(1)Use dilute sulfuric acid to pretreat waste pure cotton fabrics to obtain cotton cellulose with different polymerization degrees.It was found that with the intensification of acid treatment conditions,such as increasing acid concentration,temperature,and treatment time,the degree of polymerization of cotton cellulose showed varying degrees of downward trend.Among them,the degree of polymerization of untreated cotton cellulose is 1621.After being treated with 0.4mol//L dilute sulfuric acid at 100°C for 60 minutes,the degree of polymerization decreases to 431,and its solubility in NMMO solution increases from 2wt% to 7wt%.(2)In situ enzymatic hydrolysis of acid-treated polyester-cotton textiles with NMMO coupled cellulase.Taking glucose yield as an evaluation index,the optimal conditions for enzymatic hydrolysis were obtained as follows: cotton cellulose substrate loading amount 6wt%,40FPU/g cotton cellulose,PH=5.0,55°C,180 rpm.Under these conditions for 72 hours,the cotton cellulose was converted to glucose for reuse.The glucose yield was 73.2%.The polyester was separated by filtration.The recovery rate of the polyester was 97.1%.The chemical structure and thermal properties of the recovered polyester were basically the same as those of the original polyester.There is no difference,the recovered polyester can be reused by physical or chemical methods.Compared with the enzymatic hydrolysis of untreated polyester-cotton textiles,the glucose yield is increased by about 7 times.(3)The mechanism of NMMO coupled in situ enzymatic saccharification was explored,and it was found that the important factors affecting the efficiency of enzymatic saccharification were the crystallinity and contact area of cellulose,rather than the degree of polymerization.After acid treatment and NMMO dissolving and regenerating cotton cellulose,the surface has relatively porous holes and the specific surface area is increased,which is conducive to the adsorption of cellulase to the cellulose surface in a short time.Compared with untreated cotton cellulose,the crystallinity of cellulose after acid treatment and NMMO dissolution and regeneration is reduced from 80.4% to54.2%.The increase of amorphous cellulose promotes the synergistic effect of cellulose complex enzymes,thereby improving the efficiency of enzymatic saccharification.