Ultrasonic welding of wood veneers

Creating wood joints usually requires glue or staples. These items are detrimental for the end-of-life of wood products, decreasing their potential recyclability, reusability, and biodegradability. Ultrasonic welding is a processing method to assemble thermoplastic polymers, allowing the creation of joints without adhesive. Wood is composed of amorphous lignins and hemicelluloses that could, under the right conditions of heat and pressure, act as a glue to bind wood pieces together. Thus, the scope of this proof-of-concept study is to investigate the use of ultrasonic welding to assemble veneer wood for packaging applications. Wood pieces were assembled using an ultrasonic welder while screening a large range of materials and processing conditions. Mechanical performances were assessed by measuring the shear strength of wood joints. Results showed that veneer wood can be assembled using ultrasonic welding, leading to a higher resistance than stapled joints. However, the procedure is highly sensitive to wood properties, as the acoustic energy tends to be easily focused by its internal structure. It decreases the reproducibility of the welding procedure and increases the dispersion of joint properties. Achieving a better energy focus is nonetheless possible using appropriate conditions. Overall results are encouraging for further industrial development.