Thermal and spectroscopic studies on flame‐retardant cotton cellulose modified with THPC‐urea‐ADP and its transition metal complexes

Abstract

AbstractCotton cellulose has been treated with tetrakis(hydroxymethyl)phosphonium chloride (THPC), urea and small amounts of ammonium dihydrogen orthophosphate (ADP) to impart flame retardancy. Complexes of cell‐THPC‐urea‐ADP with transition metals such as chromium, manganese, iron, cobalt, nickel, copper and zinc have been characterized by reflectance UV‐visible spectra. The samples were subjected to differential thermal analysis and thermogravimetry from ambient temperature to 700°C in air to study their thermal behaviour. From the resulting data, various kinetic parameters for different stages of thermal degradation were obtained following the method of Broido. For the decomposition of cellulose and flame‐retardant celluloses, the activation energy was found to increase from 242 to 322kJ mol−1, the entropy of activation from 140 to 307 JK−1 mol−1 and the char yield from 2.5 to 31%. The free energy of activation for decomposition of cellulose and its derivatives was almost the same, viz. 148–162 kJ mol−1, indicating that the basic steps in the decomposition of cellulose and its derivatives are the same. The IR spectra of the thermally degraded residues of cell‐THPC‐urea‐ADP and its metal complexes indicate that dehydration takes place and a compound containing the carbonyl group is formed. The electron paramagnetic resonance signals indicate the formation of trapped and stable free radicals in the thermal degradation of cellulose and its derivatives.