Bio-based polyurethane coatings with high biomass content: tailored properties by lignin selection

New bio-based 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 crosslinking reaction with three different non-chemically-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 crosslinking, 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 c...