Effects of de-polymerized lignin content on thermo-oxidative and thermal stability of polyethylene

This study demonstrated de-polymerized lignins to be cost-effective bio-substitutes for commercial antioxidant in plastics. In this work, effects of addition amounts of de-polymerized kraft lignin (DKL) and de-polymerized hydrolysis lignin (DHL) in polyethylene (PE) on its thermo-oxidative and thermal stability were investigated in air and N-2 atmosphere, respectively. Due to the difference in the solubility characteristics of DKL and DHL in PE, the oxidation induction time and activation energy for thermo-oxidative degradation of the PE blend leveled off after 2.5 wt% addition of DKL content but increased in an almost linear manner with increase of DHL content. The results also revealed that the addition of 2.5 wt% of DKL or 5 wt% of DHL attained the same level of antioxidant activity as the addition of 0.5 wt% of Irganox 1010. In addition, PE without and with addition of 2.5 wt% of DKL were comparatively investigated by thermogravimetry analysis (TGA) analysis in air and N-2 atmosphere (pyrolysis) and by Fourier Transform Infrared Spectroscopy (FT-IR), and the results showed that the addition of 2.5 wt% of DKL enhanced the thermo-oxidative and thermal stability of PE in both thermo-oxidative degradation and pyrolysis processes at above 400 degrees C.