Thermal stability of phosphorylated cellulose modified with various transition metals

Abstract

Complexes of cellulose phosphate with transition metals such as chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, molybdenum, silver, cadmium and mercury have been characterized by reflectance UV-visible spectra. The thermal behaviour of cellulose and the metal complexes of cellulose phosphate in air has been studied by differential thermal analysis and thermogravimetry from ambient temperature to 750°C. From the resulting data, various thermodynamic parameters for different stages of thermal degradation can be obtained following the method of Broido. The activation energies for decomposition of cellulose and metal complexes of cellulose phosphatewere found to kJ mol −1. Pyrolysis-mass spectrometric studies of metal complexes of cellulose phosphate using soft ionization modes such as field ionization and field desorption give very low abundances of volatile products in the spectra compared with the yields with untreated cellulose. The IR and reflectance UV-visible spectra of the pyrolysis residues of metal complexes of cellulose phosphate indicate that dehydration takes place and the metal complexes are stable up to 250°C. At higher temperatures, a compound containing carbonyl groups is formed. A mechanism for the thermal degradation of metal complexes of cellulose phosphate is proposed which explains the generation of reduced amounts of smoke. Scanning electron microscopic studies of cellulose phosphate and its transition metal complexes showed that the fibrillar sites have mostly reacted and throw light on the morphological changes of treated cellulose in the thermal degradation range. The observed effects are of interest with respect to the flame-proofing of cellulose.