Experimental design to determine the manufacturing parameters of a green-glued plywood panel

The objective of this research was to investigate the technical feasibility of producing plywood by green-gluing technology. 2.5 mm thick rotary cut veneers obtained from steamed maritime pine (Pinus pinaster Ait.) logs were used. Plywood was manufactured under vacuum with veneers in a wet state. Five-layer plywood panels were produced using a one-component polyurethane adhesive to evaluate the effects of two parameters, the wood moisture content and the amount of adhesive, on the mechanical properties of plywood. First, a full factorial experimental design was realised to study the bond performance. Shear tests were carried out in order to determine the bond quality and failure type. It was observed that the values of plywood panels’ shear strength depend more on the wood moisture content than on the amount of adhesive applied. A model representing the shear strength of the panels according to the manufacturing parameters was established by using statistical analyses. Another part of this study focused on microscopic observations of the bondline in order to get information about the joint morphology and the degree of adhesive penetration into the wood structure. Results suggested that definite proportions of water (moisture content between 30 and 60 %) and adhesive have to be present on wood surface when gluing to create efficient bonds. These analyses were followed by the panel’s characterisation in flexure to validate the process.