Abstract
To improve the water resistance of tannin adhesives, bio-sourced furfuryl alcohol was used to react with trace formaldehyde to synthesize hydroxymethylated furfuryl alcohol as a modifier for tannin adhesives. The bonding performance of tannin-hydroxymethylated furfuryl alcohol(T-PFA) with different pH values, amount of formaldehyde addition and mass ratio of tannin to furfuryl alcohol were studied by preparing laboratory three-layer plywood and evaluating their shear strength. At the same time, resorcinol and 5-hydroxymethylfurfural (HMF) were used as model compounds to prepare resorcinol-HMF resins and then were analyzed by means of electrospray ionization mass spectrometry(ESI-MS), nuclear magnetic resonance carbon(13C NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy, which aimed to explain their reaction mechanisms more clearly. The results showed that resorcinol could react with hydroxymethylfurfural and produce a branched macromolecular structure, thus demonstrating the feasibility of preparing wood adhesives with hydroxymethyl furfuryl alcohol modified tannins. In addition, plywood test results indicated that a T-PFA adhesive shows a good bonding performance and water resistance with a shear strength as high as 0.80 MPa after soaking in boiling water for 3h, which satisfied the requirements of Chinese National Standards GB/T 9846-2015(≥0.7 MPa).
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