A Proposed Model for the Decomposition of Cellulose and the Effect of Flame Retardants

摘要

A simplified model for the decomposition of cellulose is presented along with the effects of flame retardants on this model. It is supported by several specific laboratory tests. The basic hypothesis is that above 275C cellulose decomposes through the simultaneous unzipping of all the cellulose molecules, thus accounting for the constant rate of decomposition over most of the pyrolysis period. There is only one controlling reaction, namely unzipping, not competing reactions as usually postulated. The rate of decomposition is proportional to the number of molecules present which is essentially constant over most of the decomposition period. The lengths of the molecules decrease linearly with time. After the oxygen links between the glucosan units are broken during the unzipping process, the units can either be transformed into levoglucosan or participate in the char-forming process with the release of H2O, CO2, and H2. The other observed products of pyrolysis come from the decomposition of the levoglucosan. The action of the flame retardants is to increase the rate of decomposition and the amount of char produced. The rate is increased by increasing the number of molecules through the breaking of inter-ring intramolecular bonds, or by increasing the unzipping rate through the breaking of intermolecular bonds. Direct action of the flame retardant on the levoglucosan causes the increase in char produced, and thus the reduction in flammability of the volatiles released. (Author)