A phosphoric acid and urea-based PIN compound provided an effective PIN FR for the cellulose-derived fibre lyocell. Lyocell is a lightweight, soft, wrinkle-resistant fibre produced by processing cellulose fibres from wood or bamboo, but it is highly flammable. A novel PIN FR was synthesised by combining in water ethanolamine, glyoxal, phosphoric acid and urea at c. 170°C. This PIN FR was then reacted onto lyocell by soaking in aqueous solution with dicyandiamide as a catalyst, resulting in P-O-C covalent bonding, in this study to a weight gain of c. 15 % dry matter. This resulted in an increase in LOI from 18 (untreated lyocell) to 44, which fell back to 34 after 30 laundering cycles. The treated lyocell could not be ignited in cone calorimeter tests. The treated lyocell showed only slightly deteriorated mechanical properties (c. 15% loss in tensile strength and elongation at break). The authors conclude that this novel PIN FR provides a durable and effective PIN flam retardancy solution for lyocell.
“Synthesis of an effective halogen-free flame retardant rich in phosphorus and nitrogen for lyocell fabric”, Y. Guo et al., Cellulose (2021) 28:7355–7372 https://doi.org/10.1007/s10570-021-03975-8