Improving properties of phenol- lignin- glyoxal resin as a wood adhesive by an epoxy resin

Abstract

The aim of this work was to improve the properties of plywood panels bonded with phenol- lignin-glyoxal (PLG) resin by the addition of an epoxy resin. For this reason, various contents (3, 5 and 7% on resin solids) of an epoxy resin were added to the prepared PLG resin. The structural, thermal and physicochemical properties of the resins prepared as well as the water absorption and dry and wet shear strength of the plywood panels bonded with them were measured according to standard methods. The results showed that the addition of an epoxy resin not only shortens the gel time but also increases the viscosity, density and solids content of the PLG resin. FTIR analysis indicated that an epoxy resin can chemically react with functional groups of the PLG resin. Differential scanning calorimetry (DSC) showed that the addition of the epoxy decreased the curing temperature of the PLG resin. The panels bonded with PLG resins modified by epoxies yielded lower water absorption and thickness swelling when compared to those bonded with the pure PLG resin. The dry and wet tensile shear strength of plywood panels bonded with PLG resins indicated that mechanical properties could be significantly improved by increasing the percentage of the epoxy resin added. Finally, it can be noted that the physical and mechanical properties of the green panels bonded with the epoxy-modified PLG resin are comparable to that of phenol–formaldehyde (PF) resin wood adhesives.