Renewable coatings from liquefied wood: Linking epoxide structure to material properties and chemical recyclability

The heavy fraction of liquefied wood (LW) serves as a promising renewable precursor for polymeric coatings. Owing to its inherent brittleness and relatively low molecular weight, LW requires crosslinking to form durable films. Previous work demonstrates that LW is curable with bio-based glycerol diglycidyl ether (GDE), yielding wood coatings with favorable properties and recyclability. In this study, we systematically studied two additional, structurally distinct epoxides: bisphenol A diglycidyl ether (BDE), the widely used commercial aromatic standard, and poly(ethylene glycol) diglycidyl ether (PDE), which contains long, flexible aliphatic ethers. These chemical differences enable a rigorous investigation of how epoxide structure influences curing behavior, material properties, and circularity. Fourier-transform infrared spectroscopy and differential scanning calorimetry confirm successful crosslinking. Analysis of gel content, thermal stability, and nanoindentation reveals dramatic structural effects: BDE produces rigid, dense networks, increasing the glass transition temperature (Tg​) up to 83 °C (vs. LW at ∼31 °C) and maintaining approximately 50% gloss retention after 2.5 months of accelerated weathering. In contrast, PDE leads to soft films exhibiting substantial hydrogel-like swelling, with water uptake reaching 207 wt%. Recycling studies via liquefaction verify that both LW–BDE and LW–GDE coatings are chemically recyclable. The LW–PDE system, due to its low crosslink density (gel content below 12 wt%), remains soluble and is easily recovered in solution form. These results collectively demonstrate that the choice of epoxide allows for tuning the property profile of LW-based renewable coatings while fully preserving their end-of-life circularity.