Suitability evaluation of various phosphorus-based flame retardants for waste cotton fibers

Numerous industries generate substantial quantities of waste cotton fibers as byproducts; however, their potential applications are restricted by their inherent fire hazard. In sectors such as construction, residual cotton fibers can be employed as insulation materials and other building components, and their efficacy can be improved by enhancing their flame retardancy. Recycling waste cotton fibers is a cost-effective solution that promotes recycling and conserves resources. This study investigates the efficacy of four phosphorus-based flame retardants for enhancing the flame retardancy of waste cotton fibers: ammonium phosphate monobasic (AP-1), ammonium phosphate dibasic (AP-2), ammonium polyphosphate (APP), and tris(2-chloropropyl) phosphate. Calorimetry, which objectively assesses flame retardancy performance by measuring the heat release rate during combustion, is used as the primary analytical method. Further, cone and bomb calorimeters are employed to acquire more comprehensive and stable calorimetry data. The calorimetry analysis results indicate that AP-1 exhibited a superior flame-retardant performance. AP-2 and APP formed significant char residues, exhibiting superior adhesion to cotton fibers and effective action on combustion gases, as confirmed via thermogravimetric analysis and scanning electron microscopy with energy-dispersive X-ray spectrometry. Char formation is another important mechanism; however, the overall effectiveness of flame retardants is significantly affected by their interaction with fiber materials and their behavior during combustion. AP-1 is the most effective flame retardant for waste cotton fibers and displays thermal stability and flame suppression effects. This study demonstrates the flame-retardant effect through precise calorimetry analysis data and suggests the possibility of recycling waste cotton fibers into high-value-added products.

Graphical abstract

The essential indicator of how quickly a material releases heat (HRR) showed significantly lower values for the AP-1-treated fibers compared to those of other samples. This reduction indicates that the flame-retardant treatment effectively slows the combustion rate and contributes to better flame retardancy. THR indicates the total amount of energy released during combustion, further supporting the research findings.