Thermal studies on C-6 substituted cellulose and its subsequent phosphorylated products in air

Abstract

The thermal behaviour of cellulose and its primary and, subsequently, secondary substituted derivatives, namely, cellulose tosylate, cellulose tritylate and phosphate, of these compounds in air was studied by differential thermal analysis and dynamic thermogravimetry from ambient temperature to 800°C. The various reactions involved, namely, dehydration, detosylation, detritylation, dephosphorylation, dehydrohalogenation, oxidative decomposition and oxidation of charred residue, have been discussed. The data obtained from TG were utilized to obtain various thermodynamic parameters of different stages of thermal degradation using the method of Broido. The values of activation energies for the oxidative decomposition of cellulose, cellulose tosylate, tritylate, phosphate, phosphate of cellulose tosylate and phosphate of cellulose tritylate were determined and are 238, 177, 109,103, 204 and 134 kJ mol −1, respectively. A new band at 900 cm −1 in the IR spectra of secondary substituted phosphoryl derivatives indicates the formation of a polypyrophosphate compound which forms a glassy surface over burning cellulosics, thus hindering the diffusion of volatile products. As a result, the large char yields obtained in the case of secondary substituted phosphoryl derivatives show that these compounds are effective flame retardants.