Functionalization of silk fabric using phytate urea salt for durable flame retardant performance

Bio-based phytic acid represents a promising approach to endow textile with effective flame retardancy due to its eco-friendliness and high P content, but it suffers from poor washing durability on textile. In the present study, the reactive phytate urea salt (PUS) was synthesized using phytic acid and urea, and it was applied as durable intumescent flame retardant (FR) agent to improve the flame retardancy of silk fabric via pad-dry-cure technique. The chemical structure of PUS and its potential cross-linking action with silk fiber were studied, the thermal resistance, smoke/heat emission ability, flame retardancy and functional mechanism of modified silk were investigated. The PUS modification imparted good FR ability to silk fabric and significantly inhibited the smoke and heat emission of silk. The modified silk sample possessed the low char length of about 6 cm and the high LOI value of 34.2%. The modified silk fabric had the self-extinguishing ability after 35 home washings, which should be assigned to the covalent bonding of PUS on silk. Besides, the FR modification also showed little influence on the handle and mechanical performance of silk fabric. The char residue analyses suggested an intumescent FR mechanism for the modified silk. The synthesized PUS shows great possibility to act as durable and formaldehyde-free FR agent for enhancing the fire safety of silk fabric.