Composites made of epoxy resins are high strength, yet lightweight alternatives to traditional metal components used in automotive, wind, and electronics industries. Traditionally, epoxy resins are produced from petroleum-derived bisphenol A (BPA), which is epoxidized and cured with an amine or anhydride hardener. Unfortunately, BPA-based epoxy resins are derived from a non-sustainable resource and are not easily recycled, and BPA itself is a known endocrine disruptor. Lignin, a polyphenolic component of biomass, offers potential as a more sustainable and less toxic replacement for BPA in epoxy resins. Here we present the use of syringic acid, a product of the catalytic oxidative depolymerization of lignin, as a precursor for producing biobased epoxy resins. Syringic acid was epoxidized and the structure was determined via nuclear magnetic resonance spectroscopy. We observed the presence of a side product of the epoxidation reaction that contains an extra hydroxyl group on the aromatic ring. The amount of this side product increased with increasing reaction time. We have examined the curing chemistry of epoxidized syringic acid with an anhydride curing agent and studied the properties of the cured resins. This study, in combination with previously published work, has helped us understand how the chemical structure of the lignin-derived monomer impacts epoxy resin properties, which in turn can help produce targeted epoxy resins with superior properties to petroleum-derived resins.

Sustainable epoxy resins derived from syringic acid

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