Modification Of Phenolic Resin Adhesives And Performance Characterization

Phenol formaldehyde (PF) resin has excellent adhesion performance and weathering resistance, but its low curing speed, non-renewable raw material, and other shortcoming limit its application.. In this study, metal compound catalysts, such as Na2CC>3, (CH3COO)2Zn, Ba(OH)2, and LiOH, were employed to synthesize PF resin possessing high performance, and synthesis mechanism was proposed by the measurement and analysis of PF resin. Pretreatment of depolymerizing tannin macromolecule into flavonoid monomer and the ring opening of furan in furfural structure was employed to increase reactive efficiency to synthesize the tannin-formaldehyde-furfural (TFFu) resin. Chemical structure, curing properties, rheology, thermal stability, and other properties of TFFu resin were characterized. Blending adhesives for plywood was produced by depolymerized tannin and PF resin, and its performance was characterized. The main conclusions of this study were as follow:(1) Metal compounds catalyst could effectively accelerate PF resin, and the catalysts could be ranked as Na2CO3>(CH3COO)2Zn> Ba(OH)2> LiOH. The quantitative 13C NMR analysis showed that the (CH3COO)2Zn and Na2CO3 catalysts could significantly promote the reaction activity of the phenol ortho position, and favor the condensation reaction of ortho methylol or direct formaldehyde toward the phenol ortho position exclusively. The (CH3COO)2Zn-accelerated resin showed a faster contact angle change rate, which represents a better wettability on the wood surface, which indicated that it had more content of methylol. The four peaks in the DTG curve and higher weight residue of TG data indicated that (CH3COO)2Zn has a different accelerating mechanism to others, and improves the thermal stability of PF resin.(2) The pretreatment of depolymerizing tannin macromolecule into flavonoid monomer and the ring opening of furan in furfural structure improved the reaction efficiency to synthesize the TFFu resins. The free formaldehyde content of TFFu dramatically decreased from 5.57% to 1.77% when the substitution ratio of formaldehyde by furfural reached 10%. The substation of formaldehyde by furfural made TFFu resin internal structure become more compact and smooth, and has better thermal stability.(3) Blending adhesives for plywood was produced by depolymerized tannin and PF resin. Depolymerized tannin could perfectly dissolve into the system of PF resin. When the substitution rate of PF resin by depolymerized tannin reached 30%, the blending adhesives had excellent coating usability. The bonding strength of plywood decreased as the increase of substitution rate.