Much effort has been invested in developing methods for
producing small molecules from lignin as a way to source feedstock
chemicals from renewable sources. Significant progress is being made, and
methods for deconstructing lignin are producing good yields of small,
mononuclear aromatic products?sufficient amounts to enable studies of the
potential use of these compounds as replacements for compounds currently
produced from petroleum. To investigate the use of lignin products in
epoxies, we begin with aromatic acids that can be produced from lignin, treat
them with epichlorohydrin to make glycidyl ethers, and investigate the
thermal and mechanical properties of cured mixtures of these compounds
with a commercial epoxy resin (EPON 826) and an anhydride curing agent
(NMA). While most of the lignin-modified epoxy polymers exhibit good
physical and thermal properties, the polymer prepared from p-hydroxybenzoic
acid (compound 6) has a higher glass-transition temperature (Tg = 159 °C) than do thermosets made with other ligninderived materials, such as vanillic acid diglycidyl ether (compound 4) and matches the Tg of cured samples of the commercial EPON-826/NMA epoxy system. This is significant, as p-hydroxybenzoic acid is readily available by simple hydrolysis of several different lignins and functions as a drop-in replacement for 50% of the BPA-based material in this commercial system without significant degradation of material properties. The use of lignin-derived small molecules in high-value systems such as epoxies may help improve the economics of biorefineries.