Research On The Technology Of Preparation Of Regenerated Pulp From Waste Cotton Textiles By Hydrogen Peroxide-caustic Soda Process

With the continuous growth of the population,the rapid development of the economy and the rapid rise of the fast fashion market,the demand for textile products in countries around the world continues and rapidly increases.This fast-changing fashion cycle and excessive consumption concepts have resulted in the repeated generation of a large number of waste cotton textiles.At present,the recycling of waste cotton textiles in most countries is still in the initial stage of simple,direct and extensive landfilling,incineration,and crushing.It not only wastes a lot of valuable resources,but also causes great pollution and damage to the environment.If it is made into waste cotton pulp and used in the preparation of Lyocell fiber by chemical recycling method,a regenerated fiber product with high added value can be produced,which not only realizes the closed-loop recycling of cotton fiber,but also has great significance for reducing environmental pollution.In this paper,waste towels and old jeans are used as experimental raw materials,and waste cotton pulp with good performance is prepared by cooking pulping and bleaching processes.According to the test method of pulp for viscose fiber,the polymerization degree,whiteness and alpha-cellulose content of the prepared cotton pulp were measured.And the basic performance parameters such as microscopic morphology,crystallinity,metal ion content,chemical group and so on were tested and characterized by SEM,XRD,ICP-OES and FTIR.The experimental results are as follows:Research on the cooking and pulping process of waste cotton textiles: Based on the alkaline pulping process,the addition of hydrogen peroxide has a significant effect on the depolymerization of cotton fibers,but when the amount of hydrogen peroxide is higher than 1 wt%,the degree of polymerization decreases excessively and the whiteness increases less.The research on cooking technology shows that the polymerization degree of pulp can be reduced by increasing the cooking temperature,increasing the alkali concentration and prolonging the cooking time.Among them,the effect of cooking temperature on the degree of polymerization is the most obvious.Increasing the alkali concentration can increase the content of methyl fiber in the pulp,and prolonging the cooking time can improve the whiteness of the pulp.Based on the above experimental results,the cooking and pulping process parameters suitable for waste towels were determined as follows: cooking temperature is 160℃,cooking time is 120 min,NaOH concentration is 40g/L,the obtained regenerated pulp had a degree of polymerization of 662,a whiteness of78.2%ISO,and the content of alpha-cellulose of 96.3%.The process parameters suitable for old jeans are: cooking temperature is 140℃,cooking time is 120 min,NaOH concentration is 30g/L,the obtained regenerated pulp had a degree of polymerization of 623,a whiteness of 76.3%ISO,and the content of alpha-cellulose of 93.4%.Research on bleaching process of waste cotton pulp: Hydrogen peroxide is used as bleaching agent,sodium silicate is added to provide an alkaline environment,and EDTA is added as chelating agent to remove metal ions.For hydrogen peroxide,when the dosage of hydrogen peroxide is 6 wt%,the pulp whiteness is obviously improved,but further increasing the dosage will cause the pulp polymerization degree to decrease too much.When the EDTA content was 0.5 wt%,the iron ion content in the pulp of waste towels and old jeans decreased by 65.6% and 79.9%,respectively.Research on bleaching process shows that by increasing the bleaching temperature and prolonging the bleaching time,the pulp whiteness will be further improved,but at the same time,the degree of polymerization will also be reduced,which has a certain regulatory effect on the degree of polymerization.Based on the above experimental results,the bleaching process parameters suitable for pulping waste towels were determined as follows: the bleaching temperature is 90°C,the bleaching time is 90 min,the polymerization degree of the obtained pulp is 574,the whiteness is88.7%ISO,and the alpha-cellulose content is 96.2% and the content of Fe is 8.58 ppm.The bleaching process parameters suitable for the pulp of old jeans are: bleaching temperature is 80 ℃,bleaching time is 80 min,the polymerization degree of the obtained pulp is 568,the whiteness is 87.1%ISO,and the content of alpha-cellulose is 93.2% and the content of Fe is 9.08 ppm.