Sulfur-free polymeric flame retardants enabling low-heat and low-smoke release in regenerated cellulose fibers

Regenerated cellulose fibers are highly flammable, necessitating the application of flame retardants to reduce their fire hazard. In this study, a sulfur-free polymeric flame retardant (PPSPB) was employed to enhance the flame retardancy of viscose fibers (VF), while addressing the smoke release concern associated with commercial organophosphorus flame retardants. PPSPB stayed stability against hydrolysis and agglomeration in water, thereby meeting the strict requirement of viscose spinning. PPSPB presented good compatibility with VF and a low migration tendency from VF, enabling VF to maintain high whiteness, superior moisture absorption, good mechanical properties, and exceptional washing fastness. VF/PPSPB 20 , containing 20 wt% PPSPB, achieved a limiting oxygen value of 29.5 % and presented a sharp reduction in the heat release with a moderate smoke release in cone calorimetry tests. PPSPB showed dominant condensed-phase flame-retardant mechanisms via promoting cellulose dehydration and enhancing char formation. It also presented vapor-phase flame-retardant activities through facilitating the generation of nonflammable gaseous products. This work opens a feasible approach for producing flame-retardant regenerated cellulose fibers using polymeric flame retardants.