Sustainable mechanical recycling of cotton textile waste: impact of structure based feedstock optimisation on fibre length outcomes and closed-loop recovery

Closed-loop recycling is critical for establishing a circular economy, diverting textile waste from landfill and reducing the environmental impacts of the textile industry. Although mechanical recycling is an established route for textile waste, severe fibre fragmentation limits the use of recovered material in high value yarn spinning applications. Using a controlled, laboratory mechanical recycling process, this study establishes a novel structural hierarchy to maximise fibre length outcomes from textile waste feedstocks. Thirteen bespoke 100 % cotton fabrics were produced to systematically isolate the impacts of fibre type, yarn spinning configuration, yarn count and fabric construction on the ease of fabric opening and spinnable fibre yield. The manual Fibre Array method (ASTM D1440) was utilised for fibre length distribution measurements to overcome the optical detection limits associated with Fibrogram based methods, capturing the true short fibre content of mechanically recycled material and providing a detailed assessment of the recoverable length-based value. It was demonstrated that fabric interlacing density was the primary predictor of mechanical opening efficiency, displaying a strong negative correlation (r = -0.94) with the degree of fabric opening in woven structures. Conversely, single jersey knits exhibited the highest opening resistance and significantly reduced fibre length retention. Extra Long Staple Fibres, combed yarns, coarser yarn counts and ring spun configurations enhanced fibre length outcomes under these testing conditions, with up to 70 % of the recovered fibre mass from low-interlacement weaves retaining sufficient length (> 12.7 mm) for staple yarn spinning. By elucidating the impact of structural variables on end-of-life recovery, this study provides actionable Design for Recycling principles and valuable insights to aid the development of structure-based automated textile sorting systems, ultimately facilitating the transition toward high value fibre-to-fibre circularity.