Effect of Adhesives on Bonding Performance of Softwood and Hardwood Plywood

Abstract

In this study, the effects of adhesives on the bonding performance of both southern yellow pine (SYP) and red maple plywood were investigated. Phenol–formaldehyde (PF), polymeric diphenylmethane diisocyanate (pMDI), phenol–resorcinol–formaldehyde (PRF), and polyurethane (PUR) were evaluated. This allowed us to understand the difference between thermosetting and cold-setting adhesives, as well as phenolic and isocyanate ones. Three-ply plywoods were fabricated using red maple veneers (Acer rubrum) for hardwood plywood specimens and using SYP (Pinus spp.) for softwood plywood specimens. The bonding was evaluated using lap shear and cyclic tests. According to ASTM D906, approximately 40 specimens per adhesive per species were subjected to a lap shear test to determine their shear strength. Wood failure of the shear specimens was evaluated visually and using an image processing software, ImageJ. In accordance with the American National Standards Institute for Hardwood and Decorative Plywood/Hardwood Plywood and Veneer Association (ANSI/HPVA HP-1 2020), 12 specimens per adhesive per species were tested for delamination. These specimens underwent three cycles of soaking in water for 4 hours followed by drying for 19 hours. The findings of this study indicated that the isocyanate-based adhesives produced superior bonding, particularly PUR for red maple and pMDI for SYP. PF resin could potentially substitute for these isocyanate-based adhesives, as the observed difference was not statistically significant.

Citation

Belaidi, Dalila; Lamichhane, Aadarsha; Pradhan, Suman; Mohammadabadi, Mostafa; Shmulsky, Rubin; Wang, Xiping. 2025. Effect of Adhesives on Bonding Performance of Softwood and Hardwood Plywood. Forest Products Journal. 75(1): 16-25. https://doi.org/10.13073/FPJ-D-24-00044.