ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
An investigation of the thermal decomposition of natural cellulose is described, in which the rate of the reaction was determined by the rate of evolution of gas in vacuo in the temperature range 100-250°C. Two states of the material could be distinguished with respect to thermal decomposition behavior, the “initial” state and a state produced by protracted heating which is described as the “stable” state. In the initial state the rate of evolution of CO is given by k = 2.8 × 109 exp {-34.0 × 103 RT}, in the stable state by k = 1.0 × 1011 exp {-39.4 × 103/RT}, where k is expressed in moles of CO per mole of cellobiose per second, R is the gas constant, and T the absolute temperature in degrees Kelvin. The composition of the gas evolved in the initial state is given by xH2O:yCO2:1CO, where x is observed as a range of values fairly close to 3, and y to 1, depending upon the stage of the reaction. In the stable state the composition of the gas evolved is about 10H2O:2.5CO2:1CO; these ratios remain within rather close limits (about 10%) in observations made over a considerable range of conditions. The ratio 2.8 × 109/1.0 × 1011 may be interpreted, on the basis of simplifying assumptions, to represent the fraction of the structure which decomposes with the lower activation energy (i.e., 34.0 kcal./mole). This fraction may be regarded as a measure of the concentration of some secondary aspect of the structure of the material which may be described as internal surfaces, a micellar structure, or the endgroups of long-chain molecules. Because of the stability of the value 39.4 kcal./mole with respect to protracted heating and to variations in secondary composition, this value is regarded as the activation energy for the thermal decomposition of the α-cellulose present in natural cellulose. At all temperatures natural cellulose decomposes at rates given by the first of the above equations for the initial stage and by the second equation for later stages of the reaction. (There are, of course, intermediate states between the extremes represented by these equations.) The effect of partial thermal decomposition of natural cellulose on its physical properties, such as water adsorption, can be studied as a function of the degree of thermal decomposition as measured by the rates given by these equations. The “endpoint” in the drying of cellulosic materials can also be determined from the thermal decomposition data. Water removed after this point has been reached does not result in increased dryness of the material, but is a measure of the progress of the thermal decomposition reaction.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1962.1205816640
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