A new approach to flame‐retardant cellulosic fabrics in an environmentally safe manner

This article investigates reacting potassium salts of phosphorous‐containing acids in the presence of urea with cotton cellulose under thermosol conditions (pH 5, 185 °C) to esterify the cellulose and produce a flame‐retardant effect. Attenuated total reflectance‐Fourier‐transform infrared (ATR‐FTIR) spectroscopy confirmed chemical modification of the cotton cellulose, where only the phosphite salt formed a covalently bonded cellulose ester (confirmed by flammability tests). Urea plays a vital role; decomposing to ammonia and isocyanic acid (the reactive intermediate) and it is the isocyanic acid/phosphite anion addition compound that reacts with cellulose hydroxyl groups to form the required ester. ATR‐FTIR analysis showed that phosphate and hypophosphite salts did not react with cellulose and thus gave no flame‐resist effect. Whilst the esterification of cellulose introduces phosphorous onto the cellulose, in order to meet more severe work‐wear laundry standards it was necessary to further incorporate a nitrogen species by addition of a cationic polymer. To develop a one shot “all‐in” process the possibility of simultaneously bonding nitrogen through carbodimide chemistry is researched, with initial promising trials demonstrated. Many after‐treatments of dyed fabrics can cause colour shifts due to interactions with the chromophores. Azo dyes, for example, are particularly susceptible to attack by the formaldehyde produced during the Pyrovatex process or the reducing nature of the Proban process, both resulting in a colour change. An advantage of the novel phosphite/urea flame‐retardant system presented herein, is that the system is less aggressive which allows the possibility of using reactive dyes to produce a bright and wide shade range as the results demonstrate.