Technical Feasibility of Citric Acid as a Bio-Adhesive for Production of Densified Laminated Veneer Lumber

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Abstract

Laminated Veneer Lumber (LVL) is an engineered wood product widely used for structural purposes, typically manufactured using thin wood veneers bonded with synthetic resins. The potential of citric acid (CA) as a sustainable bio-adhesive has been demonstrated since 2012. This study evaluated the technical feasibility of CA for producing densified LVL panels using wood from Brazilian Pinus taeda plantation trees. Three adhesive treatments were compared: pure CA (T1), a hybrid CA and melamine-urea-formaldehyde (MUF) system (T2), and pure MUF (T3). The pressing schedule was designed to aim at the simultaneous consolidation and densification of the panels. X-ray densitometry confirmed the formation of high-density peaks at the glue lines. Results showed that all treatments significantly exceeded the 1.0 MPa shear strength requirement of EN 314-2. Although MUF-bonded panels (T3) achieved the highest mechanical performance, CA-bonded panels (T1) and the hybrid system (T2) met structural requirements, demonstrating the effectiveness of the densification process in enhancing the performance of bio-based adhesives. However, densification resulted in lower dimensional stability. It is concluded that CA is a viable, renewable alternative for structural wood bonding, providing effective adhesion suitable for engineered wood products.

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