Thermal degradation behaviour of isotactic polypropylene blended with lignin

The influence of lignin on the thermal degradation of isotactic polypropylene, investigated by thermogravimetric analysis, is reported in this article. Polypropylene blends containing 5 and 15 wt% of lignin were prepared by mixing the components in a screw mixer. An increase of the thermal degradation temperature of the blends was observed as a function of lignin content, in both oxidative and non-oxidative conditions. The increase is noticeably marked for the experiments carried out in air atmosphere, where the interactions between the polypropylene and the lignin lead to the formation of a protective surface able to reduce the oxygen diffusion towards the polymer bulk. Morphological analyses were carried out by optical and electronic microscopy, to evaluate the degree of dispersion of the lignin in the polypropylene matrix. X-ray techniques were employed to study the influence of lignin on the structure of the blended polypropylene.