China is a large country in the production and application of chemical fibers in the world. In 2019, the total output of chemical fibers in China was 58.27 million tons, including 47.51 million tons of polyester, accounting for 81.5% of the total output of chemical fibers. The waste pollution problem associated with the huge output is also increasingly serious. Therefore, the development of recycling chemical fiber is an important way to realize the sustainable development of China's chemical fiber industry and even the textile industry. The following will take recycled polyester as an example.

Production technology of recycled polyester fiber

At present, recycled polyester raw materials mainly come from waste polyester bottle chips, sheets, films and polyester blocks and waste silk in the production of polyester and polyester.

Waste polyester bottle piece

The preparation methods of recycled polyester fiber can be divided into physical method, chemical method and physical-chemical method according to the regeneration principle.

Physical method

The physical method refers to the regeneration method that the waste polyester material is directly melt spun as raw material after sorting, cleaning and drying.

Chemical method

Chemical method refers to the process of depolymerizing waste polyester materials into polymerized monomers or polymerized intermediates by chemical reaction, and then conducting regeneration polymerization and melt spinning after purification and separation. At present, the chemical recovery technologies in the market include glycolysis, methanol decomposition and alkaline hydrolysis.

Physicochemical method

The physicochemical method is a recycled chemical fiber prepared by crushing and cleaning polyester waste (waste bottle chips) and thickening during spinning. The physicochemical method combines the advantages of physical and chemical recovery.

Advantages and disadvantages of physical and chemical methods

Relatively speaking, physical method is the dominant polyester regeneration method at present because of its simple production technology, short process flow and low production cost. More than 70% ~ 80% of the production capacity of regenerated polyester fiber is recovered by physical method. However, the physical recycling method is mainly one-way recycling. Even the food grade bottle to bottle recycling technology can not realize the complete closed-loop recycling of pet at present; Due to the unstable dyeing property, the recycled polyester fiber is mainly used as some non clothing fabrics and home textile fabrics, such as filling fibers, clothing linings, home textiles, glue sprayed cotton, packing belts, non-woven fabrics and industrial fabrics; As it belongs to open-loop recycling, with the increase of processing times, the intrinsic viscosity, molecular weight distribution and impurity content of polyester fiber will continue to change, and finally it will not be able to use physical methods for recycling.

In recent years, the chemical method has shown an increasing trend through the innovation of equipment and process. Its main advantage is that it can realize the complete recycling of waste polyester; Low requirements for sorting and cleaning of waste polyester. The raw material of chemical method can be waste silk or even polyester in clothing. In the sense of recycling, chemical method is more beneficial to solve the problem of clothing waste. With the increase of functional requirements of polyester products in the market, the use of non single polyester materials has increased rapidly. It is very difficult to recycle these products by physical method. Only chemical method can solve these technical problems.

Relevant cases

Taiwan Far East New Century Company glycolysis pet through chemical glycolysis to produce oligomer BHET. After the glycolysis process, the oligomer is fine filtered and then re polymerized into pet; And then regenerated pet is spun into fibers.

Chemical recovery of waste PET bottles by glycolysis process

Since 2002, teiren began to produce recycled polyester products on a large scale by chemical method. The glycolysis (ethylene glycol) / alcoholysis (methanol) ester exchange combined PET recycling process developed by teiren is a commercial chemical process with the highest DMT monomer recovery rate, the highest purity and the most stable quality.

Combined process flow of glycolysis (ethylene glycol) / alcoholysis (methanol) and transesterification of teiren company

Ethylene glycol depolymerization is another major chemical recycling method for pet. At present, Japanese Teijin company, Goodyear, DuPont, Hoechst and Taiwan far east textile company have realized the operation of commercial devices, and the process conditions are basically mature.

In 2013, Zhejiang Jiaren new materials Co., Ltd. adopted the chemical method of emperor (glycolysis / alcoholysis ester exchange combined PET recycling process) to produce recycled polyester.

Liquid phase viscosity increasing homogenization and chain expansion technology is a physicochemical process technology that appears in the production of recycled polyester fiber in China. It is said that products with physical performance indexes close to or even higher than that of original polyester fiber can be produced by this technology. In addition, physicochemical process technology also includes micro alcoholysis and alcoholysis re polymerization technology. Since 2008, Ningbo Dafa has been engaged in the research and development of recycled polyester fiber, and has continuously upgraded its technology from liquid-phase viscosity increasing, quenching and tempering viscosity increasing, micro alcoholysis quenching and tempering viscosity increasing; In addition, longfu technology, Yangzhou Tianfu and Youcai environmental protection enterprises have also adopted the physical and chemical process to produce recycled polyester.