Polyurethane Coatings Based on Chemically Unmodified Fractionated Lignin

Abstract

New lignin-based thermoset polyurethane (PU) coatings with high lignin content are presented in this work. These materials were obtained by extracting a sol fraction from a raw kraft lignin sample with the bioderived solvent 2methyltetrahydrofuran (MeTHF), and subsequently directly cross-linking the MeTHF-soluble lignin fraction with a toluene diisocyanate (TDI)-based polyisocyanate at different weight ratios. A thorough characterization of the PU materials highlighted their improved thermal stability, better film forming ability and higher hydrophobic character compared with the un-cross-linked lignin precursor. Additionally, force− distance curve measurements by atomic force microscopy were employed to determine the elastic modulus of the PU materials. Finally, the lignin-based PU materials were found to exhibit high adhesion on different substrates, including glass, wood and metals. The results of this study demonstrate that the direct reaction of chemically unmodified fractionated lignin with polyisocyanates represents an interesting strategy for the development of lignin-based thermoset PU systems that may find application in the field of high-performance biobased coatings and adhesives.

Comparing chemical composition and lignin structure of Miscanthus x giganteus and Miscanthus nagara harvested in autumn and spring and separated into stems and leaves

“…17,18 As a polyphenolic substance, lignin gained rising interest as substitute for fossil-based diols/polyols in polyurethane synthesis. [19][20][21][22][23] However, valorization of extracted lignin is still restricted to a few commercial products, mainly due to missing procedures for fast and reliable analysis of the highly complex 3D structure consisting of three randomly crosslinked monolignol units p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) (Fig. 1).…”

Lignin nanoparticles by ultrasonication and their incorporation in waterborne polymer nanocomposites

“…To this end, different fractionation approaches (pH‐induced precipitation, membrane‐assisted ultrafiltration, and solvent extraction) have been used to improve the miscibility of lignin in common solvents while better controlling its chemical, structural, and physical properties . In addition, highly specific chemical functionalization reactions have been applied to lignin to improve its reactivity, add functionalities to its structure, and allow easier incorporation as reactive material into bio‐based thermoplastic and thermosetting polymers, including polyurethanes, (PUs) polyesters, phenolics, and epoxies …”

Antimicrobial Activity of Lignin-Derived Polyurethane Coatings Prepared from Unmodified and Demethylated Lignins

“…Typically, the presence of a double bond in α, β positions of the side chain and a methyl group in the γ position grants the phenolic fragments with the most potency against microorganisms. However, none of the hitherto published studies included the investigation of the antibacterial activity of lignin when included in polymeric matrices.Unmodified lignin is widely studied as a component for polymer production with a focus on phenol-formaldehyde resins and polyurethanes (PUs) [25], where lignin is used as polyol substitute due to the high amount of hydroxyl groups resulting in high crosslinking densities and variable mechanical properties [26][27][28]. In previous studies, lignin-derived polyurethane coatings have been prepared using Kraft lignin isolated at room temperature from aqueous media (black liquor) at different pH values [29].…”

“…Unmodified lignin is widely studied as a component for polymer production with a focus on phenol-formaldehyde resins and polyurethanes (PUs) [25], where lignin is used as polyol substitute due to the high amount of hydroxyl groups resulting in high crosslinking densities and variable mechanical properties [26][27][28]. In previous studies, lignin-derived polyurethane coatings have been prepared using Kraft lignin isolated at room temperature from aqueous media (black liquor) at different pH values [29].…”