Stepwise Grafting of Ammonium Vinylphosphonate and PNIPAM onto Cotton for Flame Retardancy and Thermal-Moisture Management

Abstract

This study proposes a stepwise grafting strategy to simultaneously impart flame retardancy and intelligent thermal-moisture management to cotton fabrics, addressing both their inherent flammability and the comfort degradation typically associated with conventional flame-retardant treatments. First, ammonium vinylphosphonate (AVP) was covalently anchored onto cotton fabrics via P–O–C linkages through a Dicyandiamide-catalyzed pad-dry-cure finishing process, establishing a flame-retardant system. Subsequently, the introduced vinyl groups served as reactive sites for surface-initiated polymerization of a temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) layer, forming a dynamic thermo-regulable architecture. Systematic evaluation reveals that the resulting fabric (Cotton/AVP-PNIPAM) exhibits substantially enhanced flame retardancy, with the limiting oxygen index increasing from 18.1% to 34.0%, whereas the peak heat release rate and total heat release decrease by 91.6% and 46.8%, respectively. Concurrently, the surface-grafted PNIPAM imparts temperature-dependent functionality, transitioning from a hydrophilic, expanded state below 32 °C to a hydrophobic, contracted state above 32 °C, thereby enabling intelligent thermal-moisture regulation characterized by low-temperature insulation and high-temperature cooling. By overcoming the inherent trade-off between flame retardancy and wearing comfort through precise chemical functionalization, this work provides a design paradigm for next-generation high-performance textiles.