Effect of synthesized lignin-based flame retardant liquid on the flame retardancy and mechanical properties of cotton textiles

The flammability of cotton (Gossypium hirsutum) is a significant concern for technical applications, prompting ongoing research into solutions to mitigate this risk. Traditional flame-retardant methods utilizing acid-based approaches are complex and can negatively affect the mechanical properties of textiles. To address these challenges, this study focuses on developing a liquid bio-based flame retardant (LBF) utilizing a lignin-silica-based liquid (LSL) extracted from rice husk (RH) (Oryza sativa ssp. japonica) and 9, 10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). A one-pot dip-coating technique is utilized to treat cotton with the LSL, and the flammability and mechanical properties of the treated cotton are subsequently tested. Fourier-transform infrared spectroscopy (FTIR) confirms the covalent bond formation of the LSL with DOPO and the hydrogen bond formation of the LBF with cotton. Scanning electron microscopy (SEM) confirms the uniformity of the coating. The experimental results demonstrate that the treated cotton exhibits self-extinguishing behavior during a vertical burning test (VBT), with a 78% reduction in peak heat release and a 65% reduction in total heat released during pyrolysis combustion flow calorimetry. Surprisingly, the treatment also improves the tensile behavior of the cotton by 21.7% and thermal stability by producing a protective char layer that accounted for 36.9% of the final residue. This study provides a promising approach for improving the flame resistance and mechanical strength of cotton for technical applications.