Development of new bio-based lignin polyurethane coatings

Lignin is considered one of the most promising biomass feedstocks due to its abundance, its renewable character and its global availability. Lignin is mainly generated as a co-product during the pulping process for cellulose isolation in the papermaking industry and it is mostly used as low-cost fuel for energy production in these installations. Nowadays, in spite of its huge potential as polymeric precursor and the set-up of different fractionation methods, the industrial use of lignin is limited because of its very complex and bulky structure, its high heterogeneity and its intrinsic recalcitrance. Therefore up to now, only few lignin applications for the production of high-added value materials have been developed.1,2 In this context, new polyurethane (PU)-based coatings with a high biomass content (over 85 wt.%) and diverse properties are presented in this work. This approach relies on the use of lignin in two different ways. On one hand, the -OH moieties naturally present in the lignin structure allowed its exploitation as polyol without the requirement of any chemical modification. On the other hand, lignin could be used to produce smaller bioderived units with a higher chemical potential, like vanillic acid, which can be transformed into an aromatic α-ω diisocyanate.3 Hence, by combining these two approaches, a variety of PU-coatings were produced from different types of lignin (namely organosolv, kraft and soda). The complete characterization of these high-biomass-content lignin-derived PU coatings highlighted an excellent film forming ability, solvent resistance, hydrophobic character, high adhesion on different substrates and tunable thermal properties thanks to their structural and reactive differences. The obtained results demonstrate the technical viability of exploiting lignin in two different ways (i.e., as precursor of smaller-reactive units and as macromolecular building block) to achieve materials with very promising tailored properties. [1] Allegretti, C.; Fontanay, S.; Krauke, Y.; Luebbert, M.; Strini, A.; Troquet, J.; Turri, S.; Griffini, G.; D’Arrigo, P. ACS Sust Chem Eng 2018, 6, 9056. [2] Allegretti, C.; Fontanay, S.; Rischka, K.; Strini, A.; Troquet, J.; Turri, S.; Griffini, G.; D’Arrigo P. ACS Omega 2019. [3] Griffini, G; Passoni, V.; Suriano, R.; Levi, M.; Turri, S. ACS Sust Chem Eng 2015, 3, 1145.