Thermal degradation kinetics and lifetime of high-density polyethylene/poly (l-lactic acid) blends

In this work, a kinetic study on the thermal degradation of films prepared from high-density polyethylene (HDPE), poly(l-lactic acid) (PLLA) and their blends is presented. Activation energy (E-a), order of reaction (n) and frequency factor (ln (A)) were studied through thermogravimetric analysis (TGA) over a temperature range of 25-600 degrees C at four heating rates, that is, 5, 10, 15, and 20 degrees C min(-1). The TGA data were used to predict the thermal stability of the film samples, comparing the kinetic parameters obtained by three model-free isoconversional techniques and estimating the lifetime of the films. The value of E-a for neat HDPE was found to be much higher than that for PLLA, but for HDPE/PLLA blends, it was nearer to that of HDPE. An increase in E-a of 80/20 (HDPE/PLLA) blends was noticed with the addition of compatibilizer, maleic anhydride-grafted HDPE. Overall, the thermal kinetics of the polymer samples depends on fractions of their constituents, heating rates and calculation technique used. It was proved, through lifetime estimation method, that the lifetime of neat HDPE decreases by addition of PLLA. With increase in temperature, the lifetime of all samples decreased exponentially. Scanning electron microscopy studies verified that HDPE and PLLA interfaces became fairly compatible by adding the compatibilizer.