Biomass-based coating from chitosan for cotton fabric with excellent flame retardancy and improved durability

Eco-friendly biomass-based coating was designed to endow cotton fabrics with durable flame retardancy through a dip-pad-dry-cure process. The coating involved phosphorylated chitosan (PCS) as intumescent flame retardant that is fixed onto the fiber surface by the co-action of electrostatic interaction and chemical grafting. Consequently, the obtained fabrics exhibit good flame retardancy and improved durability. The resultant cotton fabrics treated by 7.5 wt% of PCS solution show limiting oxygen index (LOI) of 25.7% and self-extinguished immediately after removing the igniter in the vertical flame test. Additionally, the total heat release value and heat release rate are significantly decreased by 59.4% and 88.2%, respectively, in the cone calorimeter test compared with pure cotton. A combined condensed-phase flame-retardant mechanism by forming a phosphorus-rich intumescent and gas-phase mechanism by diluting effect of the non-flammable volatiles is proposed. Moreover, enhanced washing durability is achieved even after 10 detergent laundering cycles with a LOI value of 23% due to the partial chemical grafting of PCS on cotton fibers. Meanwhile, the tensile property remained almost unchanged. Herein, this work provides a promising approach for fabricating durable flame-retardant cotton fabrics with satisfactory tensile performance and for applying to other fabric substrates.