Synthetic dyes: a barrier to circular economy within the textile industry?

Global textile waste continues to rise, with most sent to landfill. This is partly due to the current challenges of textile recycling. This review assesses the emergence of post-consumer textile-to-textile recycling techniques and explores their respective challenges, opportunities, and environmental impacts. Following a systematic selection process, this review groups 39 studies into three thematic areas based on research scope: 12 textile recycling reviews, 16 decolorization studies, and 11 life cycle assessments (LCAs) of conventional and recycled textiles. First, this paper finds that while mechanical, chemical, and biological recycling methods represent unique opportunities, each faces its own specific challenges, partly due to the presence of synthetic dyes. Second, the analysis of decolorization case studies reveals that color removal is complex, generates hazardous by-products, and releases harmful solvents and microplastics, undermining the sustainability potential of the recycling process. Although the case studies and review papers were framed around circular economy principles, these focused more on fiber quality and stripping success than on environmental performance. In contrast, the LCA case studies compared the environmental impact of conventional and recycled textiles. The results show various environmental trade-offs along the supply chain and across measurements. Although some studies establish positive environmental impacts, improvements are often small and shaped by many parameters that may limit their expansion at scale. This review concludes that synthetic dyes and finishes serve as barriers to optimizing textile-to-textile recycling, and more research is needed on the environmental impacts of the recycling process. This paper proposes addressing the dye barrier during the design stage and replacing synthetic with undyed, naturally dyed cotton and plant dye to enhance circularity within the industry. • Synthetic dyes are a barrier to textile-to-textile recycling. • Textile-to-textile recycling presents challenges due to fiber blend and dye. • Recycling may cause MPF, emissions, water depletion and toxic chemical release. • Replacing synthetic with undyed, NCC and plant-based dye can enhance circularity.