Manufacturing flame-resistant lyocell fibre from flame-resistant cotton waste fabrics through optimized pulping process

This research investigates the use of flame-resistant (FR) cotton waste to produce regenerated cellulose fibres via the lyocell process. The study employed an FR fabric used in coveralls. Cellulose pulp was prepared using acid hydrolysis and chelation to regulate cellulose degree of polymerization (DP) and remove metal ions. The hydrolysis process was optimized by varying sulfuric acid concentration, temperature, and treatment duration, which reduced the transition metal content close to the recommended limit for the lyocell process and brought the degree of polymerization within the spinning range. Different chelating agents were also explored to reduce metal content while preserving cellulose quality. The resulting pulps were dispersed in a 50% N-methylmorpholine-N-oxide (NMMO)-water solution, followed by controlled water evaporation, yielding a final dope composition of 83% NMMO, 3% pulp, and 14% water by weight. Fibres were spun via dry-jet wet spinning using a microreactor and a water-containing graduated cylinder. Although surface roughness was observed, the extruded fibres exhibited uniform morphology and flexibility. Phosphorus content was retained for FR performance. The results show for the first time that FR cotton waste is a viable feedstock for the production of permanently FR lyocell fibre, offering significant potential for performance retention in circular textile manufacturing.