Investigation of flame-retardant characteristics of natural flax coated with hydrothermally synthesized calcium borate and organic PDA

Flame-retardant behavior of flax fabric coated by calcium borate powders with clove-like and elongated morphologies was investigated by thermal analysis and cone calorimeter. PDA was used to form strong and uniform adhesion of calcium borate onto fabric. Thermal analysis showed a 20% of decrease in mass loss, while detected exothermic/endothermic peaks as a result of the degradation of fabric and PDA. Significant reductions in HRR, p-HRR, EHC and CO2 amount were observed for fabric coated by PDA and elongated calcium borate powder. PDA was carbonized at low temperatures and formed a char layer that prevented flame propagation. At the same time, calcium borate powder dilutes the flammable gases in the environment with the release of water within its body. Among the calcium borate powders, rod-like morphology showed the best flame-retardant performance.