Over the last few decades, fashion trends have rapidly changed, and the demand for following the latest fashion trends has led to fast fashion, namely, inexpensive trendy clothing produced rapidly by mass-market retailers in response to the latest trends. Many fast fashion brands produce tremendous amounts of new products every week, encouraging overconsumption. The overconsumption of clothing has generated millions of tons of post-industrial or post-consumer textile waste worldwide.
The Environmental Impact of Textile Waste
Textiles in municipal solid waste (MSW) mainly constitute discarded clothing or other items, such as carpets, footwear, sheets, and towels. According to the United States Environmental Protection Agency (U.S. EPA), approximately 17 million tons of textile waste were discarded in landfills in 2018 in the US (US EPA, 2020). The US EPA also estimates that textile waste accounts for nearly 5% of all landfill spaces in the US.
Landfilling textile waste causes environmental issues such as the formation of greenhouse gases upon decomposition and contamination of groundwater (Dissanayake et al., 2018). Some types of textiles (e.g., synthetic textiles) require >200 years to decompose in landfills (Gupta et al., 2019). In addition to generating tremendous amounts of textile waste, synthetic textile fibers are manufactured using fossil fuel resources (e.g., natural gas and crude oil) as feedstock. The production, consumption, and post-industrial waste handling of synthetic textile fibers not only results in greenhouse gas emissions but also releases microplastics (EEA, 2021). Therefore, the textile waste disposal strategy has changed from a landfill-based solution to a recycling-based solution.
Upcycling as a Sustainable Solution
Upcycling is a type of recycling process that converts lower-value substances into higher-value products. Thermochemical conversion processes are a techno-economically feasible option for treating low-value carbonaceous feedstocks (Ha et al., 2019; Kim et al., 2019a; Seo et al., 2022). Among those, pyrolysis, thermal decomposition of carbonaceous components in the absence of oxygen (thus avoiding combustion), has gained increasing attention as a sustainable waste upcycling process (Wan Mahari et al., 2021).
Recently, pyrolysis has been widely studied to transform waste materials into value-added products (e.g., hydrogen gas (Park et al., 2021), gaseous fuels (Foong et al., 2021), aromatic compounds (Lee et al., 2021b), commodity chemicals (Kim et al., 2021), engineered carbon materials (Foong et al., 2020), hydrocarbons (Ryu et al., 2020), and catalysts (Lee et al., 2020)). In addition, pyrolysis of plastic waste results in lower net greenhouse gas emissions than other plastic recycling methods such as incineration and gasification (Devasahayam et al., 2019; Hwang et al., 2020). Pyrolysis is an effective process for the treatment of heterogeneous and complex waste materials (Lee et al., 2021a) and a representative waste-to-energy process (Lee et al., 2023).
Given that textile waste has a diverse nature (e.g., synthetic and natural fibers), pyrolysis is a promising upcycling option for textile waste. For example, pyrolysis has been proven to be fairly successful in recovering nylon monomers from textile waste containing nylon (e.g., carpet waste) with a high yield (Bockhorn et al., 2001). A pyrolysis process has been suggested as a waste-to-energy method to transform textile waste into combustible gas (Kwon et al., 2021). Therefore, pyrolysis is regarded as a promising technology for the upcycling of textile wastes.
Overview of Pyrolysis Processes for Textile Waste
This review aims to support the creation of sustainable upcycling pathways for textile waste. From this perspective, we provide a systematic overview of the pyrolysis processes applied to various types of textile waste. Studies on the pyrolysis of textile waste using thermogravimetric analysis (TGA) (e.g., thermal degradation kinetics) were excluded in this review because most of them do not provide detailed information on the characteristics and properties of pyrolytic products (Akyürek, 2019; Sun et al., 2021; Wen et al., 2017; Wu et al., 2017).
The types and reactor designs that have been applied for the pyrolysis of textile waste are explored, followed by a summary and comparison of the various pyrolysis processes used to upcycle textile waste. The economic aspects of the pyrolysis process for upcycling textile waste were assessed. The challenges faced by upcycling of the textile waste using pyrolysis are discussed, and recommendations for future research are presented.
Conclusion
In conclusion, the fast-paced fashion industry and overconsumption of clothing have resulted in significant amounts of textile waste. Landfilling textile waste is not a sustainable solution due to its environmental impact. Upcycling through pyrolysis offers a promising alternative for the sustainable management of textile waste. Pyrolysis has been proven effective in transforming textile waste into valuable products and reducing greenhouse gas emissions. Further research and development in pyrolysis processes for textile waste upcycling are needed to optimize efficiency and economic viability. By promoting the upcycling of textile waste, we can contribute to a more sustainable and circular fashion industry.