Flame‐Retardant Cellulose‐Chitosan Blend Fibers Based on Phytic Acid‐Derived Phosphorylated Ureido‐Chitosan

ABSTRACT

The synthesis of a biobased flame‐retardant additive for cellulose prepared from phytic acid‐derivatized chitosan for the preparation of flame‐retardant cellulose fibers and fabrics is reported. Phosphorylated ureido‐chitosan (PUC) with a nitrogen and phosphorus content of 9.5 and 3.1 wt.%, respectively, was prepared in quantitative yield by reacting chitosan with phytic acid and urea. A soluble form of PUC, i.e., PUC‐S with an only slightly decreased phosphorus content of 1.9 wt.%, was obtained via acid hydrolysis. Blend fibers were dry‐jet wet spun from a 3:1 mixture of cellulose and PUC‐S in the ionic liquid 1‐ethyl‐3‐methylimidazolium octanoate ([EMIM] ⁺ [Oct] ⁻ ), had a phosphorus content of 0.46 wt.% and allowed for the fabrication of knitted fabrics. No significant changes in the structure of cellulose were determined by wide‐angle X‐ray scattering upon mixing with PUC‐S. Accordingly, the mechanical properties of the cellulose/PUC‐S blend fibers did not differ significantly from those of pure cellulose fibers. Cellulose/PUC‐S fabrics showed good char formation with a residual mass of 42.9% at 600°C and a substantially improved limiting oxygen index (LOI) of up to 26.0% as compared to 18.4% for fabrics prepared from pure cellulose.