Clean polyester can be separated from mixed waste cloth by chemical fractionation and converted to the original monomer.
The apparel industry accounts for 10% of global carbon emissions. Annual production of textiles will reach 113 million tons* in 2021, and demand is increasing year by year. However, nearly 90% of post-consumer textile waste is disposed of by incineration or landfill. Among these forms of waste, synthetic fibers, like other plastics, are not biodegradable and pose a major threat to the environment and human health. Due to its low cost and durability, polyester is the most widely used synthetic fiber on the planet, accounting for more than half of the fabrics produced annually. Comprehensive recycling of polyester is therefore an important challenge for environmental sustainability and the health of future generations.
In practice, raw textile waste is mixed with various textile materials, colored with various dyes and contaminated with various other impurities, making it unsuitable for reuse or recycling. In order to be able to recycle waste by chemical or mechanical means, it must be sorted into homogeneous materials. To this end, a research team (PI: Dr. Joungmo Cho) at the Korea Research Institute of Chemical Technology (KRICT) has developed a new chemical technology called ‘chemical sorting’. This technology is applied to separate polyester from textile waste that is disposed of in mixed and contaminated form. The process uses a unique compound in the separation that selectively disrupts the chemical interaction between the polyester and the dyes used in its colors. The research team also developed a new chemical recycling technology that consumes less energy than traditional methods to convert polyester into valuable monomers* that can be used repeatedly in the synthesis of polymer materials.
*Monomers: single-molecule substances can react with other monomer molecules to form polymers through chemical bonding
Used clothing made up of various materials of unknown composition is often discarded. They are typically composed of various fabrics such as cotton, wool, polyester, acrylic, nylon, elastane, and other blended fibres. Due to the conflicting chemical and physical properties, recycling is not possible without separating the individual materials. Industrially, the separation of individual materials from fabrics is done primarily by hand, relying on human labor. This method is inaccurate, unreliable, and fails to collect homogeneous material, which is often important for further steps in recycling. Recently, there has been an active research effort to develop an automatic sorting machine that uses hyperspectral imaging techniques to obtain structural information of individual cloth targets. However, sorting systems are still far from commercialization, mainly due to technical and economic barriers.
The KRICT research team employed an inexpensive, non-toxic, biodegradable compound to chemically identify polyester from a mixture of waste fabrics. When applying compounds to textiles. The colorants present only in polyester are completely extracted, and there are no significant changes in other materials. As a result, the clean polyester can be separated from the colored fabric mixture. This method is also applicable for selecting polyester from uncolored fabric mixtures. When the waste colorant from the sorting process touches the uncolored fabric, only the polyester accepts the colorant and the other materials remain unchanged. As a result, fabrics containing only polyester can be separated from mixed fabric waste in an inexpensive, accurate and easy manner. The resulting sorted polyester can be used as a clean raw material for chemical recycling, as the sorting method excludes most organic impurities, including persistent dyes.
Chemical recycling, which converts polymer waste into its original building blocks, has the potential to achieve circularity in polyester waste recycling, whereas mechanical recycling can be used to produce only low-quality materials. In the conventional chemical recycling method, the reaction temperature is as high as 200°C or higher, which is necessary to completely decompose the polyester. In addition, energy-intensive purification steps are also inevitable in most commercial applications in order to obtain high-quality monomer products.
The KRICT research team developed a cryogenic glycolytic reaction system for converting chemically screened waste polyesters into pure bis(2-hydroxyethyl) terephthalate, a key building block monomer for generating new polymers. developed. Monomer compounds obtained through chemical recycling have the same quality as those derived from petroleum. Since the same compounds used in “chemical sorting” act as additives that lower the energy barrier for depolymerization, the reaction system can easily and easily be combined with chemical sorting techniques for applications involving high-demand plastic or fiber recycling. Can be economically integrated. for good product quality.
Dr Cho said: However, this method is not sustainable as the material cannot be recycled repeatedly. In contrast, our current technology is not limited by the complexity of the materials of construction or the initial level of impurities in the waste. This technology can be repeated for most spent fiber streams, regardless of It therefore helps reduce landfill waste and virtually achieve a circular economy in the plastics and textiles industry. ”
Chemical recycling technology is licensed to Renew System Co., Ltd. (Korea). An interdisciplinary R&D team is now working closely together to build a multi-scale facility for the chemical recycling of used clothing. We plan to complete the demonstration plant by the end of 2024 and start commercial operation with an annual production capacity of 10,000 tons in 2025.
Original: KRICT has developed a breakthrough technology that realizes closed-loop recycling of textile waste
Than: Korea Institute of Chemical Technology
