A facile and durable flame retardant approach for silk fabric through Kabachnik-Fields reaction

Highlights: • Flame retardant silk textile was fabricated through Kabachnik-Fields reaction. • The modified silk textile had durable flame retardant effect. • The flame retarding activity served as intumscent charring mechanism. • This study offers an effective and durable strategy to reduce fire risks of silk textile. This study facilely developed the durable flame retardant (FR) silk fabric by bonding phosphonate groups to silk fiber through Pudovik addition of diethyl phosphite onto Schiff base aldehyde-amine intermediate, namely Kabachnik-Fields reaction. The cross-linking mechanism between FR agent and silk fiber, the thermal resistance, FR ability and durability, and FR mechanism of the modified silk were studied. The modified silk had increased thermal resistance. The modified silk fabric with diethyl phosphite over 13.8 g/L had the self-extinguishing ability and obtained the char length of lower than 11.0 cm and LOI value of higher than 27.4 %, suggesting high FR ability of the modified silk. The modified silk also reached self-extinction after 15 robust launderings, which should be attributed to the covalent cross-linking of phosphonate groups onto silk fiber. The char residue analyses suggested a condensed charring FR mechanism for the modified silk. The Pudovik addition of diethyl phosphite onto silk macromolecular participated Schiff base intermediate shows great possibility to act as effective and durable FR strategy for silk textile.