Improving properties of phenol- lignin- glyoxal resin as a wood adhesive by an epoxy resin
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ORIGINAL
Improving properties of phenol‑ lignin‑ glyoxal resin as a wood adhesive by an epoxy resin Hamed Younesi‑ Kordkheili1 · Antonio Pizzi2 Received: 22 March 2020 / Accepted: 3 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
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.
1 Introduction Nowadays, phenol–formaldehyde (PF) resin adhesives are used for several types of wood-based panels such as plywood, oriented strand board (OSB) and particleboard panels especially for exterior applications. PF resins provide high strength and resistance to moisture preventing delamination and giving excellent temperature stability to wood-based panels (Pizzi 1993). However, PF resins present a relatively slow curing rate when compared to other commercial thermosetting adhesives. In addition, both phenol and formaldehyde are toxic. Therefore, several investigations have been carried out to overcome the defects of PF resins or to find a new formulation of wood adhesive of a higher quality than
* Hamed Younesi‑ Kordkheili [email protected] Antonio Pizzi antonio.pizzi@univ‑lorraine.fr 1
Department of Wood and Paper Sciences, Faculty of Natural Resources, Semnan University, Semnan, Iran
LERMAB, University of Lorraine, Epinal, France
2
PF resins for bonding exterior panels (Chen et al 2020; Moubarik et al 2009). In a previous work, a phenol-lignin-glyoxal (PLG) resin as a much less toxic wood adhesive has been developed to bond wood panels instead of PF resins (Younesi-Kordkheili and Pizzi 2019). Lignin is much cheaper than phenol, and glyoxal has a much lower toxicity than formaldehyde
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