Thermooxidative degradation of polyoxymethylene homo- and copolymer nanocomposites with hydroxyapatite: Kinetic and thermoanalytical study

In this paper thermooxidative degradation process of polyoxymethylene homo- and copolymer (POM)/hydroxyapatite nanocomposites has been studied. Kinetic analysis by Friedman, Ozawa-Flynn-Wall and multiple non-linear regression methods, as well as thermoanalytical studies using TG-MS and TG-FTIR method, were performed. TG results show that thermal stability of POM matrix significantly decreases with an increase of HAp nanoparticles concentration. The presence of higher HAp concentration changes mechanism of POM degradation, including its kinetics, which was demonstrated by a change of kinetic model from autocatalytic to phase-boundary or nth order reaction one. Hyphenated TG-MS and TG-FTIR data show that the main degradation product in the presence of higher amounts of HAp is formaldehyde, and formation of other degradation products - typical for POM thermoxidative degradation - is considerably diminished. Finally, mechanism of POM degradation in the presence of stoichiometric hydroxyapatite has been postulated.