Effect of curcumin on thermal degradation of poly(glycolic acid) and poly (ε-caprolactone) blends

The influence of curcumin on the thermal stability and degradation kinetics of poly(glycolic acid) (PGA), poly epsilon-caprolactone (PCL) and their blend has been investigated in detail using thermogravimetric analysis. A 50/50 ratio was chosen for the blend and the effect caused by the addition of different percentages of curcumin (CUR) was evaluated. The thermogravimetric analysis was carried out under an atmosphere of inert nitrogen, operating in a dynamic regime at six different heating rates between 3 and 30 degrees C/min. The results obtained from the degradation on a blend of PCL and PGA concluded that CUR hardly affects to the decomposition of PCL but instead, it significantly influences the stability of PGA. To observe this effect in detail, a more complete degradation study was carried out for the system formed by PGA incorporating 5% of the drug. The activation energy could be determined accurately using Kissinger and isoconversional methods like KAS and Friedman, without previously assuming a reaction model. Coats-Redfern method and generalized master curves were adopted to determine the optimal mechanism of degradation. Results showed a F1 model as suitable mechanism able to describe the degradation process of PGA with curcumin in a range of conversions between 20 and 60 %. Incorporation of CUR did not change the degradation mechanism of PGA but had a dramatic effect on the activation energy that was significantly lowered.