Biobased Polyurethane Coatings with High Biomass Content: Tailored Properties by Lignin Selection

New biobased polyurethane (PU) coatings with high lignin content were developed and characterized in this work. These materials were based on a α,ω-diisocyanate monomer (1,4-bis(4-isocyanato-2-methoxyphenoxy)butane, VA-NCO) obtained from lignin-derived vanillic acid and its further cross-linking reaction with three different nonchemically modified technical lignins obtained from different pulping processes, namely, mild acetone organosolv, kraft, and soda. After determining the optimal VA-NCO/lignin mass ratio for each type of lignin, an in-depth characterization of the obtained PU coatings highlighted their high biomass content, effective cross-linking, improved thermal stability, hydrophobic character, good adhesion performance on different types of substrates, and tunable mechanical response. These properties were found to be well-correlated to the chemical-physical features of the parent lignins used (namely, molecular weight, glass transition temperature, distribution of phenylpropane subunits, and -OH content), thereby suggesting the possibility to predictively tailor the characteristics of such biobased PU coatings by lignin selection. The results of this study demonstrate that the reaction of a lignin-derived biobased diisocyanate with different chemically unmodified technical lignins represents an interesting pathway for the production of thermosetting PU coatings with a high biomass content that can find application as high-performance biobased materials alternative to traditional petroleum-based platforms.