Syntheses of Flame-retardant Cellulose Esters and Their Fibers

3-(Hydroxyphenylphosphinyl)-propanoic acid (3-HPP) esters of cellulose (HPP-Cellulose) were synthesized homogeneously in ionic liquid 1-butyl-3-methylimidazoliumchloride by in situ activation. The chemical structure of the cellulose esters is characterized by FTIR and NMR. The degree of substitution was easily controlled within 0.38-1.51 by varying the molar ratio of 3-HPP/anhydroglucose unit, reaction time, and temperature. All the products showed excellent solubility in common organic solvents. The results of TGA, DTG, LOI, and cone calorimeter test show that 3-HPP has a positive influence on the thermal properties and flame retardance of cellulose. Based on the volatilized products analysis by TGA-IR, the presence of 3-HPP reduces the intensity of volatilized product and accelerates the dehydration action. Moreover, the addition of cellulose (3 wt%) is beneficial to prepare HPP-Cellulose fibers using a dry-wet spinning technique, and the blended fibers possess good mechanical properties as well as flame resistance.