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

Abstract

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.

A Review of the Sustainable Approaches in the Production of Bio-based Polyurethanes and Their Applications in the Adhesive Field

“…However, on this substrate the adhesive mobility into the substrate porous is strongly influenced by wood moisture, owing to the side reaction occurring between NCO groups with water (free or bound) instead of with substrate reacting sites. Therefore, Bastani et al [234] thermally modified Scots wood pine to control its moisture content, while Lavalette et al [235] revealed the greater influence of moisture content on the ultimate shear strength than the amount of one-component polyurethane adhesive in the production of green-glued plywood. Hence, the considerable influence of water contact is apparent, although it can also be extended to curing and storage steps as shown by Chattopadhyay et al [236] or Asahara et al [217] when analyzing the curing kinetics under moisture conditions.…”

Analysis of drying stresses in green-glued plywood of Bete (Mansonia Altissima) specie

“…However, a different specimen geometry was used because preliminary tests showed that the rupture occurred in the jaws of the standard specimen. More precisely, we used a "dumbbell" specimen [8], reinforced by wooden heels at the jaws, in order to ensure the rupture in the useful part of the sample. It was cut, respectively, in the parallel and perpendicular directions of the fibers in order to obtain the elasticity modulus in those two principal directions.…”

“…It was spread on the plies by using a notched squeegee so that the glue was evenly distributed. 3-ply plywood panels were manufactured by using the vacuum process technique [7,8]. The plies were oriented according to two arrangements options.…”

“…At the industrial level, this technique may allow some energy savings and reduce the degradation of the material integrity of veneers during handling. Lavalette [8] has shown that the product from the vacuum drying of green-glued plywood processing, meets the standard requirements for shear stress according to EN 314-1 [9]. But, she showed some superficial cracks probably due to the stresses induced by the gradient of moisture and anisotropic shrinkage.…”

LCA (Life Cycle Assessment) of EVP – engineering veneer product: plywood glued using a vacuum moulding technology from green veneers

“…When the vacuum is activated, a differential pressure is created between the inside and the outside of the bagging film that forces the plywood against the mould. Moreover, the glue migrates through the wood cells (Lavalette et al, 2016). Moulded plywood technology was initiated by the boating and aviation industries at the beginning of the 20th century.…”