Separation And Recycling Of Waste Cotton/polyester Blended Fabrics Under Hydrothermal Condition

Recycling and utilization of waste resources is an important part of ecological civilization construction.In recent years,with the improvement of living standards,textile fiber consumption has increased rapidly.Tens of millions of discarded textiles produced every year is regarded as garbage to landfill or incineration,resulting in great ecological environmental pressure and waste of resources.The proportion of waste cotton/polyester blended fabric in waste textiles is more than 50%.However,due to the special nature of the blended structure,the cotton and polyester components cannot be separated effectively.At present,most waste blended fabrics are mainly recycled by physical method and prepared as low value-added felt and filler directly,which can not really realize the waste cotton fabric of high value-added recovery and reuse.Hydrothermal method,used water as reaction medium,is widely used in research because of its safety and small damage to environment and equipment.The subcritical water has the characteristics of acid-alkali catalyst and organic solvent because of the ionization of the sub-critical condition and the increase of the ion product constant.Therefore,the micro-acid catalyst can promote the rapid reaction of hydrolysis,making hydrolysis of the cotton fiber while polyester in the stable state,which provides the feasibility for the separation of the waste cotton/polyester blended fabrics.In this paper,the separation of waste polyester/cotton blended fabrics and the reuse of the recycled products were studied by hydrothermal method.First,with pure cotton and pure polyester as raw materials,the hydrolysis mechanism of cotton fiber in subcritical water and the thermal stability of polyester were studied.Moreover,the degradation reaction of cotton fiber in acidic subcritical water and the thermal stability of polyester fiber was discussed,thus the critical point of selective hydrolysis of polyester and cotton fiber in the same hydrothermal system was explored.Further,using waste polyester/cotton blended fabrics as raw materials and polyester recovery rate,cellulose powder yield,and reducing sugar yield as indicators to study the effects of hydrothermal temperature,reaction time,and hydrochloric acid concentration on the separation process.The product was characterized and analyzed to determine the optimum process conditions for the separation of polyester and cotton.Second,the optimum cycle times of hydrolysis solution were discussed.The mechanical properties of polyester fiber before and after cyclic hydrolysis,the yield of cellulose powder,whiteness and reducing sugar concentration were used as indices to determine the hydrolysis efficiency of waste cotton/polyester blended fabrics and the optimum cycle times of hydrolysis solution were determined.When the glucose in the hydrolysis solution reaches a certain concentration,the carbon microspheres are prepared by hydrothermal carbonation.Finally,in order to improve the solubility of cellulose powder,the main hydrolysis products of waste cotton fiber were treated with alkaline and etherification,and the effect of the alkali etherification process on the properties of carboxymethyl cellulose sodium was investigated with the substitution degree and viscosity as the index.The results show that:(1)In the subcritical environment,the cotton/polyester blended fabrics can be selectively hydrolyzed to achieve effective separation of it.Under the hydrothermal conditions of hydrochloric acid quality fraction 1.5%,hydrothermal temperature 150 ? and reaction time 3 h,the waste cotton/polyester blended fabrics has a selective hydrolysis.Under the condition,the structure and physicochemical properties of polyester fiber have no obvious change,still maintain the fiber-like,the recovery rate can reach more than 90%,and the fracture strength can reach 2.95 cN/dtex,the molecular weight,strength and the fiber morphology were basically unchanged.At the same time,the cotton fiber was hydrolyzed to cellulose powder or oligosaccharide,and the powder formed by the cotton fiber hydrolysis was still the cellulose ?.(2)The hydrolysis liquid can be recycled,the best circulation number is 5 times.After hydrolysis 5 times,the glucose content in hydrolysis liquid was more than 70%,and the yield and whiteness of cellulose powder were still good.The hydrolysis liquid after recycling was used for hydrothermal carbonation,and the carbon microspheres with homogeneous shape and carbon content reached 74.99% were prepared.(3)The best reaction conditions for the modification of cellulose powder are: the alkali temperature 40 ?,45 min,the etherification temperature is 60 ?,100 min,the dosage of sodium chloroacetate is 4 g,the concentration of chloroacetic acid is 30%,the isopropyl alcohol is selected as etherification agent,and the viscosity of carboxymethyl cellulose sodium is 450~550 mPas.The yield of the product is 75%,the degree of substitution is 1.0~1.8,and the water solubility of carboxymethyl cellulose is good.