Korean scientists have developed a new form of chemical sorting of textiles which can be applied to separate polyester from textile waste that are disposed of in a mixed and contaminated form.
- A unique chemical compound, which selectively disrupts the chemical interaction between polyester and the dye used for its colour, has been used for the separation.
- The research team has also developed a new chemical recycling technology that consumes less energy than conventional methods to convert polyester into valuable monomers, which can be repeatedly used for the synthesis of polymer materials.
- The process has been developed by a research team at the Korea Research Institute of Chemical Technology (KRICT).
- Their study has been published in the journal ACS Sustainable Chemistry & Engineering.
- The technology has been licensed to Renew System Co Ltd. Multidisciplinary R&D teams are now working closely to build multi-scale facilities for the chemical recycling of clothing waste.
- A demonstration plant will be ready by the end of 2024 and commercial operation with an annual capacity of 10,000 tonnes is planned for 2025.
The Problem at Hand: Synthetic fibres are a big threat to the environment and human health because, similar to other plastics, those are not biodegradable.
- Due to its low cost and durability, polyester is the most widely used synthetic fibre on the planet, accounting for more than half of all fabrics annually produced.
- In practice, crude textile waste is not suitable for reuse or recycling because it is mixed with different fabric materials, coloured by different dyes, and contaminated by various other impurities.
- Sorting it into homogeneous materials, therefore, is necessary to make the waste recyclable by a chemical or mechanical method.
What They Did: The KRICT research team adopted an inexpensive and non-toxic biodegradable compound to chemically discriminate polyester from a mixture of waste fabrics.
- When the compound is applied to textiles, colourants only present in polyester are completely extracted while no significant changes occur in other materials.
- As a consequence, clean polyester can be separated from the mixture of coloured fabrics.
- The method can be applied to select polyester from an uncoloured fabric mixture as well.
- When uncoloured fabric comes into contact with the waste colourants extracted from the sorting process, only polyester accepts the colourants while the other materials remain unchanged.
- As a consequence, the fabrics containing only polyester can be separated from mixed fabric waste in an inexpensive, accurate, and facile manner.
- The sorted polyester can then be used as clean feedstock for chemical recycling because the sorting method eliminates most organic impurities including intractable dyes.
Chemical Sorting: Chemical recycling, which converts polymer waste into the original building blocks, has the potential to achieve circularity in recycling of polyester waste whereas mechanical recycling can be used to produce only low-quality material.
- In conventional chemical recycling, a high reaction temperature of above 200 degrees is required to completely decompose polyester.
- Furthermore, energy-intensive purification steps are also inevitable in most commercial applications to obtain a high-quality monomer product.
- The KRICT research team has developed a low-temperature glycolysis reaction system to convert chemically sorted waste polyester into pure bis(2-hydroxyethyl) terepthalate, which is an important building block monomer to produce new polymers.
- Monomer compounds obtained from the chemical recycling have a quality equivalent to that derived from petroleum.
- Since the same compound as that used in "chemical sorting" functions as an additive to lower the energy barrier of depolymerisation, the reaction system can be easily and economically integrated with the chemical sorting technology for applications involving plastic or textile recycling where there is high demand for good product quality.
Recycling Issues: Post-consumer clothes, made up of various materials with unknown compositions, are often discarded. They commonly comprise a variety of textiles such as cotton, wool, polyester, acrylic, nylon, elastane, and other blended fibres. Recycling cannot be achieved without sorting them into individual materials because of their incompatible chemical and physical properties.
- Industrially, the separation of individual materials from waste fabrics is accomplished by manual sorting, largely depending on human labour. This method has low accuracy and is unreliable and in turn fails to collect homogeneous materials, which is often critical for further steps of recycling.
- Recently, studies to develop an automatic sorting machine employ hyperspectral imaging technologies to acquire structural information of individual fabric targets. However, the sorting system still remains far from commercialisation, mainly due to technical and economic barriers.
What They Said:
Recently, the garment industry has utilised transparent and clean post-consumer PET bottles to produce recycled polyester clothes. However, this method is not sustainable because the material cannot be repeatedly recycled. In contrast, our current technology would not be limited by the complexity of the constituent materials or the initial level of impurity in the waste. Whether the targeted materials are derived from petroleum directly or recycled from waste, the technology can repeatedly process most post-consumer textile streams. Thus, it will help reduce waste in landfills and substantially achieve a circular economy in the plastic and textile industries."
— Joungmo Cho
Scientist
Korea Research Institute of Chemical Technology
