Enhancement of fire insulation performance for aramid non-woven fabric via chitosan/M(OH)(OCH₃) (M=Co, Ni)/sodium hexametaphosphate nano-composite coating

With the complexity of fire scenarios and the increasing risk of fire, there was an urgent need for high-performance fire-resistant insulation fibers to be better developed in the market to protect firefighting and rescue personnel. In this work, we used layer-by-layer self-assembly technique to alternately coat food-grade sodium hexametaphosphate and biomass chitosan mixed with two-dimensional nanomaterials M(OH)(OCH₃) (M=Co, Ni) on the surface of aramid nonwoven fabric (ANF), and prepared novel ANF composite materials. The results show that after heating from room temperature to 800 ℃ in air, the char yield of the 15BL coated sample (CMP/ANF-Ⅲ) increases from 1.59% (pure ANF) to 20.55%, significantly enhancing its thermal stability. CMP/ANF-Ⅲ exhibits lower peak heat release rate (PHRR) and total heat release (THR), which are 48.90% and 58.57% lower than ANF, demonstrating a significantly improvement in flame retardancy. In the vertical flame test, the damaged length of CMP/ANF-Ⅲ reduces to 2.4 cm (while that of the pure ANF is 9.0 cm). In the fire resistance and insulation test, pure ANF burns through in 12 s, while CMP/ANF-Ⅲ remains unharmed for 120 s, and the backside temperature greatly drops to 335 ℃ (while the pure ANF is over 500 ℃). The analysis of residual char reveals that CMP/ANF-III generates a dense char layer after combustion, effectively blocking the spread of flame and thermal convection with the matrix, thereby improving the flame retardancy and thermal insulation properties of non-woven fabric. Gas phase product analysis shows that CMP/ANF-III can release non-combustible gases such as CO₂, H₂O, NH₃, etc. at lower temperatures, performing a gas phase flame retardant function. The ANF nanocomposite material developed in this work supports the development of a new generation of highly efficient fire-resistant and thermal protective clothing.