Study On The Preparation Of Recycled Pulp And Corresponding Lyocell Fiber From Waste Ployester/Cotton Blended Fabric

Our country's waste textiles have a huge output and low recycling rate.Most of them are incinerated and landfilled,causing environmental pollution and waste of resources.Polyester-cotton blended fabrics are the most common textiles.For the recycling of waste polyester-cotton blended fabrics,they are mainly recycled to low-value products such as carpets and mops through simple physical and mechanical treatment.Therefore,the development of high-efficiency chemical regeneration technology for waste polyester-cotton blended fabrics and the preparation of high value-added fiber raw materials are of great significance for improving resource utilization and reducing environmental pollution.However,the polyester-cotton blend structure restricts its chemical recycling.Therefore,relevant separation and recycling technologies have become the research focus of high-value polyester-cotton recycling.In this paper,waste polyester-cotton blended fabric was used as raw material,and the separation of polyester-cotton and the preparation of dissolving pulp by caustic soda method were combined for the first time.The hydrolysis removal process of polyester during caustic soda cooking was studied by orthogonal test method.And the regulation process of cotton fiber polymerization degree was researched.Then the demetallization and bleaching process of the cotton fibers separated by the optimal cooking process were studied.Finally,the Lyocell process spinning verification was carried out on the 100%waste polyester-cotton recycled pulp,and the structure and properties of Lyoce ll fibers and raw pulp were compared.The main findings of this paper are as follows:Firstly,the caustic soda cooking and separation process of waste polyester-cotton blended fabrics was studied by orthogonal test method,and the influence of the cooking temperature,the amount of alkali and the holding time on the separation of polyester-cotton and cotton fibers polymerization degree were obtained.With the increase of the cooking temperature,the increase of the amount of alkali and the prolongation of the holding time,the polyester fiber is depolymerized from partial depolymerization and thinned to completely hydrolyzed and removed,and the polymerization degree of the cotton fiber gradually decreases.From the analysis of the range of the orthogonal test,it can be seen that the primary and secondary order of the influence on the degree of polymerization of the cotton fiber is:temperature>alkali consumption>holding time.Since the degree of polymerization of cotton fibers obtained by the cooking process in the orthogonal experiment is still higher than the index,the optimal cooking process that can achieve the target degree of polymerization(500?600)was obtained through a single-factor strengthening experiment(increasing the amount of alkali):the cooking temperature is 165°C,the amount of alkali is 40 wt%,and the holding time was 150 min.The degree of polymerization of the cotton fiber obtained under this process is about 590.Secondly,the research on pulping and bleaching process of polyester-cotton cooking and separating cotton fiber was carried out,and the change of iron ion content in pulp during pulping was also investigated.The results show that compared with the beater,the amount of iron ions introduced in the refiner treatment method is significantly reduced.Deionization of the refined cotton fiber can reduce the iron ion content to 16.8 ppm,which is close to the iron ion content index(5 ppm).If the cotton fiber obtained by cooking and separating polyester-cotton is directly deionized(without beating/refiner treatment),the iron ion content can be reduced t o 7.6 ppm.The bleaching process of deionized cotton fiber was further explored,and the effects of bleaching time and H ₂O₂dosage on pulp whiteness and polymerization degree were studied.The optimal bleaching process was obtained:the dosage of Na ₂Si O₃ was 2wt%,the dosage of Mg SO ₄ was0.05wt%,the dosage of fatty alcohol polyvinyl ether was 0.1wt%,the pulp consistency was 10wt%,the temperature was 90?,the dosage of H₂O₂ was 1wt%,and the bleaching time was 70 min.The pulp obtained by the preferred process had a brightness of 91.1%and a degree of polymerization of 578.Finally,Lyocell spinning was explored by recycling dissolving pulp from waste polyester-cotton blended fabrics.The research shows that polyester-cotton regenerated pulp 1^#(DP=578)with suitable polymerization degree ha d the same good spinnability as the imported raw wood pulp(DP=634)and the domestic raw cotton pulp(DP=555).With the increase of spinning speed(90 to 110 m/min),the fineness of Lyocell fibers gradually decreased,and the breaking strength,degree of orientation and crystallinity gradually increased.Under the spinning conditions investigated in this paper(sp inning speed is 90to 110 m/min),the breaking strength of Lyocell fiber obtained from 100%polyester-cotton regenerated pulp 1^#is equivalent to that of raw pulp,and both can meet the requirements of superior Lyocell fiber(fineness 0.90?2.20 dtex,stren gth?3.60 c N/dtex).In addition,the degree of polymerization of polyester-cotton recycled pulp also has a significant effect on its spinnability and the mechanical properties of Lyocell.The fiber strength decreases with the decrease of the degree of polym erization,and the spinnability of the polyester-cotton regenerated pulp(regenerated pulp 3#,DP=300)with a low degree of polymerization also deteriorates significantly.In this paper,a green and high-value utilization method for waste polyester-cotton blended fabrics was developed.First,the effective separation of polyester and cotton fibers was realized by the caustic soda cooking process.Then,using separated cotton fiber as raw material,through pulping,deionization and bleaching treatment,regenerated pulp was prepared.Further,Lyocell fiber was spun from the pulp,and its performance was comparable to that of the Lyocell fiber prepared from raw pulp.Relevant research is of great significance to the green and sustainable development of the textile industry,and is expected to promote the transformation of the comprehensive utilization of waste textiles to green environmental protection and high-value utilization.