Boric Acid Influence on Ammonium Phytate Finish for Eco-Efficient Flame Retardancy of Cuprammonium Fabrics

Cuprammonium fabric is a regenerated cellulose fiber known for its silk-like luster appearance. However, due to its cellulose-based composition, the fabric is inherently flammable, limiting its application in many other areas. Therefore, the objective of this study was to evaluate two water-based finishes to improve fire performance: (i) APA, generated in situ from phytic acid and urea (ammonium phytate), and (ii) PAB, obtained by reacting boric acid with phytic acid and subsequently with urea. Compared to untreated fabric, APA- and PAB-treated samples exhibited self-extinguishing behavior and formed char layers during vertical flame tests, with char lengths of 35 mm and 33 mm, respectively, at a concentration of 400 g/L. Furthermore, thermogravimetric analysis in nitrogen showed an increase in char yield at 700 °C, from 0.23% (untreated) to 39.54% (APA) and 40.63% (PAB), indicating condensed-phase action (acid-catalyzed dehydration/char formation). Although the results demonstrated that the PAB-treated samples had no washing resistance, they exhibited better tear resistance and whiteness index compared to the APA-treated samples. Overall, the results show that both phosphate and nitrogen systems (with and without boron) significantly enhance the fire resistance of cuprammonium fabric by promoting protective char, while also revealing trade-offs in durability and appearance that require further improvement.