A novel boron–nitrogen intumescent flame retardant coating on cotton with improved washing durability

A series of boron–nitrogen polymers (PEIPAs) were synthesized to provide a green alternative for flame retardant finishing on cotton fabrics. An organic boron compound, phenylboronic acid (PA) was successfully bonded to the branched polyethylenimine, which was confirmed by 1H NMR and FTIR analysis. Thermogravimetric analysis showed that the polymer with molar ratio 1:1 of ethylenimine:PA (PEIPA 1:1), presented the optimal thermal-oxidative stability. PEIPA 1:1 was easily applied on cotton fabrics through a simple dipping method with high uptake in acetone medium. The fabric with 33.8 wt% add-on got self-extinguishing ability. SEM analysis on the char morphology of the treated fabrics revealed the fire protection by the coating through intumescent flame retardant mechanism. TGIR analysis showed the coated fabric has significant reduction in the flammable volatiles production. Further improvement of the coating washing durability was achieved by a novel formaldehyde-free cross-linking treatment. The new washing stable coating achieved LOI values 29.6 and 23.2% before and after repeated launderings respectively with 30 wt% add-on. Cone calorimetry analysis showed that the total heat releases of PEIPA 1:1 treated sample and cross-linked sample (PEIPA 3:1/NeoFR treated) were decreased by 30.3 and 45.5% respectively. Smoke analysis revealed that the treated fabrics have significant decrease in CO2/CO ratio, indicating an effective flame inhibition in gas phase. The novel coatings, simple to synthesize and easy to apply with low waste, are suitable alternative to toxic halogenated flame retardants for cellulosic products.