Abstract:

Significance As a result of improved wealtiness of consumers and the change in consumption concept, and the amount of waste textiles generated has increased year by year. Cotton is the most important natural fiber, the average annual waste is huge, the development of high-value reuse technology of waste cotton textiles, the establishment of waste cotton textile cleaning and recycling system has important economic value. Strengthening the basic research of cellulose dissolution mechanism and development a new cellulose solvent system with high efficiency, economy and environmental protection, further optimizing the recycling process of waste cotton fibers, have been priary driving force for establishing and improving the recycling system of waste cotton textiles. Opening up different comprehensive utilization channels of waste cotton textiles has an important positive role in promoting resource conservation, environmental protection and carbon emission reduction, and the development and application of biomass materials.

Progress Cellulose cannot be directly spun into fiber by melting method, hence dissolution is the premise and key to high-value processing and utilization. However, it is challenging to achieve the dissolution of cotton fibers due to its high crystallinity, high molecular weight, complex aggregate structure, and insoluble in water and ordinary organic solvents. Therefore, researchers have been constantly exploring and researching cellulose solvents. The cuprammonium method and viscose method are conventional processes for the production of regenerated cellulose fibers. However, because the production process of the two involves a large amount of harmful chemicals causing serious environmental pollution, the use of these methods in industrial production has been gradually reduced. Some new cellulose solvent systems, including alkali/urea systems, lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) systems, N-methylmorpholine-N-oxide (NMMO) systems, ionic liquids have been reported. In addition, based on various solvent systems, many important results have been achieved in the research on the graded recycling of waste cotton fibers through mechanical, physical and chemical methods. A variety of regenerated cellulose and their derivative products have been produced with excellent performance and application values, for example, regenerated cellulose fiber, regenerated yarn, regenerated cellulose film, aerogel, hydrogel have a very wide range of application prospects.

Conclusion and Prospect The conventional cellulose dissolution systems have many problems such as poor solubility, high cost, cumbersome recycling process, and environmental pollution. Compared with conventional cellulose solvent systems, the development of new solvent systems such as alkali/urea and NaOH/thiourea, ionic liquids, and DES provide possibilities for green processing of cellulose and high-value recycling. However, these systems still have problems such as high cost, harsh dissolution conditions and limited solubility, and it is still difficult to achieve efficient dissolution of cotton fibers. In order to obtain comprehensive utilization, cotton fiber can be processed into corresponding recycled products from the level of fiber structure, aggregate structure and molecular structure, through mechanical opening, dissolution and regeneration and chemical degradation and graded utilization. Although many important progress and outstanding results have been achieved in the research of cellulose recycling, the existing solvent system and recovery technology still face challenge in general in achieving efficient and clean reuse of waste cotton fiber. It is still necessary to further explore more cost-competitive and technically competitive cotton fiber recycling schemes. Breaking through the bottleneck problem and directly improving the comprehensive utilization rate are of positive significance to help the construction of ecological civilization and the achievement of the ″dual carbon goal″, and accelerate the construction of a resource recycling industrial system and a waste material recycling system.

Key words: waste cotton fiber, cellulose, dissolution mechanism, solvent system, recycling