Solvent-Free Synthesis of a Phosphorus-Based Flame Retardant with π–π Conjugation for Enhancing the Durability of Cotton Fabrics
Hejun Li, Jieyu Wei, Tian Li, Yonghua Lu, Mengxiao Liang, Hao Zhou, Qing Jing, Guangxian Zhang
Abstract
Preparing durable flame-retardant cotton fabrics via straightforward and green methods is crucial for sustainable development. A novel halogen-free and formaldehyde-free durable flame retardant (EPDDPA) for cotton fabrics was synthesized by a solvent-free synthesis method, with ethyl acetoacetate and phosphorus pentoxide as raw materials. The results demonstrated that EPDDPA-treated cotton fabrics exhibited excellent flame retardancy and remarkable durability. For fabrics treated with 30 wt % EPDDPA, the limiting oxygen index value reached as high as 57.6% and remained at 49.8% even after 50 laundering cycles. The results of thermogravimetric analysis, cone calorimetry tests, coupled thermogravimetric-infrared analysis, vertical flammability tests, and LOI tests demonstrated that EPDDPA promoted dehydration and char formation of cotton fabrics. This suggested a condensed-phase mechanism of EPDDPA. The π–π conjugation effect in EPDDPA reduced the polarity of the P(═O)–O–C covalent bond formed by grafting with cotton fabrics and significantly enhanced its stability. The peak heat release rate and total heat release of EPDDPA-treated cotton decreased by 90.9 and 20.1%, respectively. Additionally, the strength, whiteness, and air permeability of the treated fabrics were well maintained, while the softness was improved. This work provides a straightforward and green method for manufacturing durable flame-retardant cotton fabrics.