High-value transformation of waste cotton textiles into flame-retardant regenerated cellulose film

Large quantities of waste cotton textiles currently remain underutilized in high-value applications, leading to significant resource waste. To address this challenge, this study proposes and validates a full-process conversion strategy for transforming waste cotton into functional films. Waste cotton fabrics were first decolorized and pulped to obtain cotton pulp, which was then phosphorylated to introduce flame-retardant functional groups, yielding phosphorylated cellulose carbamate (PCC). The resulting intermediate was dissolved in a low-temperature alkali-urea system and regenerated in a sulfuric acid coagulation bath, successfully producing regenerated phosphorylated cellulose carbamate films (RPCCF). The as-prepared RPCCF exhibited self-extinguishing behavior in both vertical and horizontal burning tests, with a limiting oxygen index (LOI) of 32.8%. Compared with unmodified cellulose, the RPCCF showed an 84.95% reduction in peak heat release rate (PHRR) and an 83.84% reduction in total heat release (THR). In addition, the film achieved a maximum tensile strength of 36.2 ± 2.2 MPa. This work provides a viable technical route for converting low-value waste textile resources into novel functional materials with high economic value, advanced technical content, and environmental benefits.