Elucidating the adhesion mechanism, bond-line thickness, and resin penetration of waste cooking oil-Based polyurethane adhesives in plywood

초록

The adhesion performance of waste cooking oil (WCO) - based polyurethane adhesives (Bio-PUA) in plywood was investigated. The WCO-based polyol was formulated at four different formulations of WCO and polyol, namely 1:4, 2:3, 3:2, and 4:1. The bond-line characteristics were analyzed using digital microscopy and Raman spectroscopy. At the same time, the physical and mechanical properties of the plywood were assessed in accordance with JAS No. 233:2003 standards. The fracture lines were filled with adhesive, and this was more pronounced in Bio-PUA with a low WCO content. Bubbles were observed in the bond line of untreated Bio-PUA, and the vessels in all samples were partially filled with adhesive. A strong peak in the Raman spectra at 1610 cm-1 confirmed effective urethane bond formation within both the bond line and the vessels. Quantitatively, Bio-PUA with lower WCO content achieved thicker bond lines but did not facilitate deep adhesive penetration. Adhesive distribution has a significant influence on plywood density and mechanical performance. Increased bond-line thickness improved panel density, while excessive penetration may reduce density without enhancing strength. Tensile shear strength in untreated Bio-PUA correlated strongly with both thickness (positive) and penetration depth (negative), whereas heat-treated Bio-PUA showed more consistent performance with no significant correlations.

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