Evaluation of industrial lignins for biocomposites production

• Two Kraft lignins were precipitated from black liquors supplied by pulp and paper industry, using carbon dioxide.
• Structure and composition of lignins were determined to vary according to the plant origin and the extraction process.
• Kraft lignins are evaluated as the best samples for application in biocomposites based on polyethylene.
• Pyrolytic and Soda lignins are better adapted for resin and adhesives application or as additives in polyolefins (antioxidant, UV stabilizer or fire-retardant).

Following important market changes to the pulp and paper industry, the interest in valorization of industrial lignins has significantly increased. Recent advancements with the LignoBoost process in Europe have made the availability of Kraft lignins a realistic prospective. The objective of the present study was to identify industrial lignins that have the potential to replace a portion of polyolefins, such as polyethylenes within composites. In order to identify the best lignin candidates for applications in biomaterials, five industrial lignins were compared. Softwood and hardwood Kraft lignins were precipitated by CO2 from black liquor obtained from two Quebec pulp mills. The isolated lignins were characterized along with the commercial Kraft lignin Indulin, Soda (from wheat straw) and pyrolytic lignin obtained from pyrolysis of hardwood biomass. Elementary composition and purity of the studied lignins were determined. Phenolic contents were studied by UV-spectrophotometry, while additional structural characteristics and molecular mass distribution were analyzed by FT-IR, pyrolysis-GC–MS and by GPC. Thermal properties were determined by TGA and TMA. The results obtained confirmed that the major differences between the studied lignins were related to the plant origin and to the industrial process from which they were issued. The properties of Kraft lignins compared to the other lignins samples studied seem to be the best suited for use in biocomposites based on polyolefins. Such application of Kraft lignins could promote new pathways to the value added products based on by-products of pulp and paper industry, while simultaneously contributing to the decrease of greenhouse gases by replacing a part of petroleum origin materials by natural products.