Relationship between thermal conductivity and adhesive distribution of phenol-formaldehyde visualized with x-ray computed tomography on sugi (Cryptomeria japonica D.Don) heartwood plywood

Abstract

The relationship of transverse thermal conductivity of non-resin region and resin-rich region in softwood plywood with various relative resin thicknesses in lumen of softwood has been determined theoritically. Futhermore, Interest in influence of adhesive penetration on adhesive bond performance and adhesive behavior has been evident by using microscopy technique and X-ray apparatus for several decades. Therefore, the relationship between thermal conductivity and adhesive distribution on softwood plywood product is needed to reveal as the development of material properties by visualizing X-ray CT apparatus. Micro Focus X-ray Computed Tomography (X-ray CT) was used to analyse the adhesive distribution of sugi heartwood plywood for different amount of glue spreading rates which were applied on the veneer surface. Four plywood samples (5-ply) were produced by spreading the phenol-formaldehyde resin adhesive on the veneer surface (dimension 450 mm× 450 mm× 3.81 mm) as much 0, 75, 150, and 225 g/m2 of glue spreading rates. All the veneer samples were conditioned 30 days under 20°C and 65% RH before plywood manufacturing. The veneer samples were dried at 60 temperature 60°C for 24 hours before pressing by cold press apparatus, the plywood samples were pressed (1 MPa) for 20 minutes and hot press apparatus at 125°C for 19 minutes. The analysis of thermal conductivity apparatus followed standards are JIS A 1412 and ASTM- C518. The plywood samples (dimension 200 mm× 200 mm ×thickness mm) in air dried condition were put on among plates of thermal conductivity apparatus for 40 minutes for each sample to obtain the thermal conductivity values. The results seemed to indicate that the thermal conductivity increases with increasing amount of glue spreading rates. By visualizing with the X-ray CT was revealed that the largest amount of glue spreading rate (225 g/m2) had the highest distribution of PF adhesive penetrated within the lathe checks of veneer sheet compared to 150, 75, and 0 g/m2. Furthermore, increasing of the adhesive distribution into the lathe checks of veneer increased the plywood density. According to the results, we suggested that the X-ray CT images analysis was powerful to reveal the relationship between the thermal conductivity and the adhesive distribution.