Thermochemical conversion of wood in levulinic acid and application in the preparation of wood coatings

In this work, levulinic acid (LLA) was used as a new bio-based solvent for solvolysis liquefaction of wood under mild conditions (temperature 160 ± 5 °C and atmospheric pressure). The liquefaction of sugar maple ( Acer saccharum Marsh.) wood at a high rate (up to 93%) was obtained under these conditions. The liquefied product was divided into water-insoluble (WILW) and water-soluble (LArF) fractions. LArFs were mixtures of low-molecular weight compounds including unreacted LLA and furfuryl alcohol, as shown by electrospray ionization-mass spectrometry (ESI–MS) analysis. WILW has shown a high acid number (205–211 mg KOH/g) and a low hydroxyl number (< 23 mg KOH/g), which is in contrast with the conventional hydroxylated liquefied products reported in the literature so far. WILW was cured with LArF, a glycerol-liquefied wood, hexamine, and methylene diphenyl diisocyanate for the preparation of wood coatings. Cured coatings showed good pull-off adhesion strengths to the surface of beech wood, resistance to water, and low ΔE* color change when exposed to ultra-violet (UV) light. Liquefying wood in LLA provides a reactive product containing carboxylic acid groups that could be used to produce cleaner, petroleum-free materials.