Thermal-oxidative Degradation of PGA, PLLA, and Random Binary PLLA-PGA Copolymers

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Dimerization process is essential for producing copolymers. The features of dimerization process like thermal-oxidative degradation should be well known to reach maximum efficiency and a superior reactor design. Also, the degradation mechanism of biodegradable polymers is important during sterilization processes. Thermal-oxidative degradation of PGA, PLLA, and their binary copolymers was investigated under isothermal heating as well as dynamic heating. All the samples were prepared by a polycondensation process and were characterized by TG, DTG, DSC, and HNMR analyses. Activation energy under dynamic heating was obtained by using Friedman plot. A new three stage mechanism, namely random, transition, and specific stages is proposed for dynamic heating degradation. Isothermal heating investigation is conducted under an inert atmosphere, and frequency factor and activation energy were achieved. It was found that the activation energy under isothermal heating is generally higher than that under dynamic heating. It was found that the rate of degradation increases significantly with an increase in temperature. The effects of pressure on the degradation rate were studied in different atmospheres with various oxygen partial pressures. Pressure effect was correlated by a second order polynomial in terms of total pressure. The obtained activation energies under isothermal heating were in good agreement with those reported by others. The complete kinetic scheme suitable for reactor design for the thermal-oxidative degradation of the samples was reported. Finally, the optimal operational conditions for the dimerization process were reported.