Renewable vitamin B5 reactive N–P flame retardant endows cotton with excellent fire resistance and durability

A bio-based P–N synergistic flame retardant ammonium salt of d-Panthenol-tri (methylphosphonic acid) (ADPTMPA) was synthesized using a formaldehyde-free and solvent-free strategy for the highly efficient preparation of durable flame-retardant cotton. The ADPTMPA structure was verified by ¹H NMR, ¹³C NMR and ³¹P NMR. FT-IR test revealed successful grafting of the flame retardant onto the cotton through P–O–C covalent bonding. The morphologies and structures of pure cotton and treated cotton were characterized by SEM and XRD, and the elemental compositions of cotton samples were analyzed by EDX. Volatile pyrolysis products of treated cotton were analyzed by TG-IR. Flame retardancy and washability of treated cotton were analyzed by limiting oxygen index (LOI) and vertical flammability tests (VFT). The LOIs of 40 wt% ADPTMPA treated cotton before and after 50 laundering cycles was determined as 46.5% and 35.8%, respectively. VFT showed the treated cotton exhibited no smoldering and continuous burning. All carbon lengths of treated cottons were less than 60 mm. The heat release rate and total heat release of treated cotton were decreased by 91.34% and 58.01% compared with pure cotton, respectively. There was 29.42 wt% carbon residual remaining when the treated cotton was exposed to heat flow of 35 kw/m². The treated cotton exhibited excellent flame retardancy and washability. Additionally, the mechanical properties and whiteness of the treated cotton were well-maintained.