In-situ detection of phosphorus-containing gas phase species at steady-state pyrolysis of flame retardant coated cotton

This work presents a novel experimental approach for investigating the gas-phase activity of flame retardants on textiles and provides initial results for pristine and DOPO (C₁₂H₉O₂P)-coated cotton fabrics. Steady-state pyrolysis was achieved by continuously moving fresh, unpyrolyzed textile into a locally fixed pyrolysis zone, maintaining a consistent degree of pyrolysis. The textile was pyrolyzed using a hot argon flow at temperatures ranging from 200 to 700 °C. Validation of chemical steady-state conditions was first carried out by analyzing the surface composition of the textile as a function of position using ATR-FTIR spectroscopy. After confirming these conditions, pyrolytic gases were analyzed via electron impact mass spectrometry at an ionization energy of 18 eV. The first system investigated was pristine cotton, where temperature-dependent quantities of selected hydrocarbons were analyzed and compared with literature data. The results indicate that the novel setup yields promising results, as expected pyrolysis products were successfully detected. The first heterogeneous flame retardant textile system analyzed was DOPO/cotton. Temperature dependent profiles of key hydrocarbons were recorded, and their potential influence on the gas-phase mechanism was discussed. To further assess the validity of the proposed mechanism, comparisons were made with literature-reported mechanisms of DOPO derivatives applied to cotton, revealing certain similarities. Additionally, phosphorus-containing species were detected under specific conditions, providing evidence of limited gas-phase activity. Finally, based on the experimental data, the effectiveness of DOPO as a flame retardant for cotton was evaluated. The results suggest that DOPO exhibits limited gas-phase activity in this system, emphasizing the need for alternative phosphorus-based FRs with enhanced efficiency.