Bio-based phenolic resin adhesives prepared by partial replacement of phenol and formaldehyde with cardanol and 5-HMF

Conventional phenolic resins are often composed of petroleum-derived phenol and formaldehyde, which can lead to serious environmental and health hazards. In this work, a bio-based phenolic varnish resin was synthesized by partially replacing phenol and formaldehyde with cardanol and 5-hydroxymethylfurfural (HMF). When 50 wt% of phenol was replaced by cardanol, the resulting resin showed the best overall performance: its bonding strength was 7.68 MPa, free formaldehyde content was as low as 0.0015%, and free phenol content was 1.98%, which was significantly better than that of commercial adhesives (bonding strength of 0.7 MPa and free formaldehyde of 0.3%). In addition, the cured resin’s water contact angle was 88.14°, indicating its good hydrophobicity. In conclusion, our study innovatively used the synergistic impact of cardanol and HMF to provide a new and more sustainable alternative for the synthesis of more environmentally friendly adhesives with satisfied performance. In particular, the application prospects are quite promising.