Thermal degradation studies of cellulose phosphates and cellulose thiophosphates

Abstract

The thermal degradation of cellulose, cellulose phosphates, and cellulose thiophosphates was studied by differential thermal analysis, dynamic thermogravimetry, and derivative thermogravimetry from ambient temperature up to 75OOC. Various thermodynamic parameters for different stages of thermal degradation of cellulose and its derivatives have been obtained following the methods of Broido, and Freeman and Carroll. Infrared spectra of thermally degraded samples were obtained. The data were analyzed in an effort to obtain more information concerning the flame-retardant mechanisms of cellulose phosphates and cellulose thiophosphates. Lower values of decomposition temperatures and activation energies of decomposition and higher char yields of cellulose phosphates as compared to cellulose lead to the conclusion that cellulose phosphorus esters are good flame retardants, and this property is retained even when these esters were subjected to ion exchange by Na+ and K+ ions. However, with the introduction of sulphur atoms, there was some decrease in this property.und Kf -1onen ausgesetzt werden. Durch die Einfuhrung von Schwefelatomen macht sich jedoch eine AbschwPchung der flammhemmenden Wirkung bemerkbar.Cellulose, one of the major textile materials, is intrinsically flammable. Flaming combustion by definition is a gas-phase reaction. In the flaming combustion of cellulose, cellulose first breaks down into smaller volatile fuel compounds, which then volatilize, mix with air, and burn. Laevoglucosan has been seen to be the primary volatile fuel compound'*2 formed during combustion of cellulose. However, cellulose can be rendered flame resistant with the application of proper condensed phase-active flame retardants, which generally alter the mechanism of degradation of cellulose in a way that the formation of laevoglucosan and other flammable volatile gases is minimized and, correspondingly, char formation is increased3. In the present case, cellulose has been treated with various phosphorylating agents to obtain certain flame-retardant compounds. Studies on thermal degradation of these samples have been concentrated on decomposition temperatures, obtained by DTA curves, physical changes such as weight loss, char yield, etc. and thermodynamic parameters such as energy of activation, entropy of activation, free energy of activation, etc., obtained by TG curves. Experimental SamplesThe following samples of cellulose, cellulose phosphates, and cellulose thiophosphates were selected for the present work.Sample (i): cellulose (from Schleicher and Schull, Dassel, West Germany) dried to constant weight i. vac. over P4010 at 60 "C; sample (ii): cellulose phosphate, prepared4 by treating cellulose (3.24 g; 0.02 mol of anhydroglucose units) with phosphorus oxychloride (9.20 g; 0.06 mol) in pyridine at 115 "C for 2 h. The product was washed with water, filtered, and dried first in air and then i.vac. over P4010; sample (iii): cellulose ammonium phosphate, prepared by treating cellulose (4.86 g; 0.03 mol of anhydroglucose units) wit...

Thermal degradation of cellulose and cellulose esters

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