Formaldehyde-free flame retardant finishing of silk using a hydroxyl-functional organophosphorus oligomer

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Flame retardancy is a desirable property for silk textiles, and it becomes necessity when silk textiles are for interior decorative use in building with public access. However, the flame retardant finishing technology available for silk has significant limitations. In this research, we studied the use of the combination of a hydroxyl-functional organophosphorus oligomer (HFPO) and 1,2,3,4-butanetetracarboxylic acid (BTCA) as a formaldehyde-free flame retardant finishing system for silk. When BTCA is applied to silk, most of BTCA reacts with the hydroxyl group on silk by single ester linkage. In the presence of HFPO, BTCA is able to bond HFPO onto silk by either a BTCA “bridge” between silk and HFPO or a BTCA–HFPO–BTCA cross-linkage between two silk protein molecules. We evaluated the flammability and physical properties of the silk fabric treated with HFPO and BTCA. The treated silk fabric demonstrated a high level of flame retardancy with modest loss in fabric tensile strength. The treated silk passed the vertical flammability test after 15 hand wash (HW) cycles. Increasing the HFPO concentration from 20% to 30% does not show significant improvement in the flame retardant performance of the treated silk. The thermal analysis data demonstrated that HFPO reduces silk's initial thermal decomposition temperature and promotes char formation.