Gluing Characteristics of Giant Bamboo Using Four Commercial Adhesives

The study aimed to determine the bonding performance of laminated giant bamboo[Dendrocalamus asper (Schult.) Backer] glued with four commercial adhesives (PVAc-D3, PUR, UF, PF) at different surface pairings (pith-pith, pith-skin, and skin-skin) and glue spread rates(100, 150, and 200 g/m2). Kiln-dried giant bamboo poles were ripsawn, planed, and cut to length to produce slats for lamination. Slats for surface roughness and wettability tests were sanded with 180-grit sandpaper on both skin and pith surfaces. Surface roughness of the skin and pith was measured using Mitutoyo SJ–210 Surftest unit, whereas wettability was determined via the sessile drop method. Giant bamboo slats were bonded using specific lamination parameters for each adhesive. Tensile shear tests at dry and wet conditions were performed on the laminates to determine bond strength. The results showed that the bamboo pith had a rougher texture than the skin but with insignificant contact angle differences. Moreover, PVAc-D3 and PUR gave the highest and lowest initial contact angles on both sides, respectively, with PUR maintaining the smallest values throughout the contact duration. Adhesive, surface pairing, and some interactions (adhesive x glue spread and adhesive x surface pairing) significantly affected the dry shear strength, whereas adhesive and adhesive x surface pairing influenced wet shear strength. PUR-bonded laminates had the highest dry shear strength, followed by PF, PVAc-D3, and UF. In terms of wet shear strength, only PVAc-D3 did not conform to the minimum glue bond strength requirement of more than 1 MPa and cohesive bamboo failure of at least 40% (PNS 2099:2015). Skin-skin and pith-pith surface pairing yielded the highest and lowest dry shear strengths, respectively. Increasing the amount of glue did not translate to a stronger bond. PUR, UF, and PF are feasible alternatives to PVAc-D3 in engineered bamboo production for various end-uses.