Novel theoretical and computer-assisted modeling of isothermal and non-isothermal depolymerization kinetics

A novel kinetic model accounting for the observed asymptotic approach of the degree of polymerization (DP) to a limiting value significantly greater than unity on prolonged degradation is derived and applied to the solid-state degradation of cellulose (Kraft paper) and poly(acrylic acid) (PAA) under isothermal and non-isothermal conditions. Experimental data were fitted using two iterative computer algorithms: one for isothermal DP data and the other for non-isothermal DP data obtained under a linear temperature ramp. The apparent activation energy for the solid-state recombination of chain radicals was found to be low in each case and was attributed to the proximity of free radicals being facilitated by restrictions imposed by the polymer matrix. The application of the model to non-isothermal DP yielded rate parameters that could be reconciled with those obtained from isothermal analyses, suggesting the novel approach has much merit for the future study of polymer degradation.