Cellulose depolymerization, thermal

Mechanism. No single mechanism explains the action of all fire retardants, so they probably work through a combination of several mechanisms. The mechanisms of fire retardants in wood involve a complex series of simultaneous reactions whose products may affect subsequent reactions. Pyrolysis of cellulose involves dehydration, depolymerization, decarbonylation, decomposition of smaller compounds, condensation, and other reactions. These pyrolysis reactions occur both in the solid phase and vapor phase. Addition of fire retardants will alter the reactions however, this alteration will depend on the additives, the material, and the thermal-physical environment. The presence of oxygen adds subsequent and competitive oxidation reactions to the above series. These oxidative reactions can take place in both the solid and vapor phases. Evidence indicates that most fire retardants reduce combustible volatiles production and limit combustion to the solid phase. The best retardants also inhibit solid-phase oxidation to effectively remove the fuel from the fire. 

Konkin [50] divides the chemical processes undergone in the transition of cellulose to carbon fiber into four groups heterolytic depolymerization, dehydration, homolytic depolymerization and a more thorough thermal deeomposition. Since the initial pyrolytic reactions are heterolytic, the eourse of pyrolysis and the evolved products can be substantially changed by the addition of acidie or alkaline catalysts [51]. 

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