Toward a Greener Bioeconomy: Synthesis and Characterization of Lignin-Polylactide Copolymers

In the modern world, plastics have become indispensable. Due to their properties, they are used for a wide variety of applications ranging from packaging materials to textiles and medical technology. The vast majority of these plastics are made from finite fossil feedstocks that will need to be replaced in the long term to meet consumer demands in the future. Intensive research is being conducted into alternative bio-based feedstocks to replace petroleum-based plastics with more environmentally friendly variants. This includes polylactide, a polyester derived from lactic acid, which is mainly used as packaging material. In this work, star-shaped copolymers consisting of polylactide and OrganoCat lignin with varying lignin loadings are synthesized using a "grafting-from" approach directly from the lactide melt using a zinc-based guanidine catalyst. This method proves to be efficient and copolymers can be produced after 30 min to three hours with high lactide conversions. Kinetic studies are performed to investigate the influence of different lignin loadings on the polymerization rate and 31P NMR experiments are used to analyze the functionalization of the lignin. Thermal analysis reveals an increase of the glass transition temperature and a higher thermal decomposition temperature with increasing lignin content. Herein, lignin-PLA copolymers with lignin loadings ranging between 10 and 50 wt% are synthesized using a zinc guanidine complex as catalyst. High-purity lignin is isolated from beech wood using the recently developed OrganoCat process. The resulting polymers are characterized with different analytical methods and kinetic investigations reveal full lactide conversions after 20 min to three hours.image (c) 2023 WILEY-VCH GmbH