De-polymerization of industrial lignins to improve the thermo-oxidative stability of polyolefins

De-polymerized lignins with greatly reduced molecular weight (< 1700 g/mol based on GPC-UV) and increased reactivity were prepared from two types of technical lignin, kraft and hydrolysis, using a proprietary de-polymerization technique. The resulting de-polymerized kraft and hydrolysis lignins (DKL and DHL) have increased aromatic hydroxyl content and decreased aliphatic content, and thus decreased total hydroxyl content and decreased polarity compared to the original lignins. Both types of de-polymerized lignin tested showed significant improvement in the thermo-oxidative stability of the polyolefins as measured by oxidation induction time, activation energy, initial degradation temperature and maximum degradation temperature. The de-polymerized lignins had up to five times more antioxidant activity than the crude lignins as a result of their higher phenolic content, improved hydrophobicity, and lower molecular weight. De-polymerized KL (DKL) had the strongest antioxidant effects, followed by de-polymerized HL (DHL), KL and HL: this correlates with their phenolic content. Mechanical tests show that incorporating de-polymerized lignins did not degrade the mechanical properties of the polymers. These properties are to be investigated further.