Sustainable bio-phenol-hydroxymethylfurfural resins using phenolated de-polymerized hydrolysis lignin and their application in bio-composites

• Bio-phenolic compounds from hydrolysis lignin (HL) were produced by phenolation.
• The Mw of HL was reduced from ∼20,000 g/mol to 1500 g/mol at low temperature.
• HL was valorized for 50 wt.% phenol substitution in phenolic resins synthesis.
• A high yield of bio-phenol HMF resins was obtained, with high Mw of 9030 g/mol.
• Harden resins are stable at 300 °C and their composites present high Tg (272 °C).

In this study a bio-based novolac resin, bio-phenol-hydroxymethylfurfural (BPHMF) resin, was prepared using a hydrolysis lignin (HL) as bio-phenol to partially substitute phenol and using glucose as a precursor for HMF. To enhance the chemical reactivity of the hydrolysis lignin with very high molecular weight, the HL was first degraded to de-polymerized hydrolysis lignin (DHL) followed by phenolation. BPHMF resin was then synthesized by resinification reaction between the phenolated DHL and HMF in-situ derived from glucose under pressure in the presence of Lewis acid catalysts, at an 85% yield. The resin was curable with 15 wt.% hexamethylenetetramine (HMTA) and the crosslinkage of the resin could also be strengthened by the functional groups in the DHL structure. Thermal/curing behaviors of the BPHMF-HMTA systems were studied using differential scanning calorimetry (DSC), peaking at 152 °C. The cured BPHMF resin demonstrated excellent thermal/thermomechanical properties, owing to the addition of HL, e.g., thermally stable up to 315 °C. The BPHMF-fiberglass thermoset composite demonstrated a high glass transition temperature (272 °C), and tensile strength (89 MPa) comparable to other phenolic composites.