Physical properties and bonding quality of laminated veneer lumber produced with veneers peeled from small-diameter rubberwood logs

The peeling of small-diameter rubberwood logs from the current short-rotation practices undoubtedly will produce lower grade veneers compared to the veneers from conventional planting rotation. Hence, this raises the question of the properties of the produced laminated veneer lumber (LVL) from veneers peeled from small-diameter rubberwood logs using the spindleless lathe technology. Different thicknesses of rubberwood veneers was peeled from rubberwood logs with diameter less than 20 cm using a spindleless lathe. Three-layer LVLs were prepared using phenol formaldehyde (PF) adhesive and hot pressed at different temperatures. During the peeling of veneer, lathe checks as deep as 30–60% of the veneer thickness are formed. Owing to deeper lathe check on 3 mm rubberwood veneer, higher pressing temperature significantly increased the gluebond shear strength of the PF-bonded LVL. In addition, lathe check frequency was also shown to influence the bond strength. The presence of higher lathe check frequency on 2 mm veneer increased the wettability, thus facilitating optimum penetration of adhesive for stronger bonding. These findings stress the importance of measuring and considering the lathe check depth and frequency during the lamination process to get a better understanding of bonding quality in veneer-based products.

Investigating face veneer check development in decorative plywood panels: the impact of four common manufacturing factors

An optical method based on digital image correlation was used to investigate the impact of four decorative plywood manufacturing factors (core type, veneer type, adhesive type and lathe check orientation) on face veneer checking. The four core types were: combination core, medium density fibreboard, particleboard, and veneer core. The four veneer types were: peeled 0.604 mm, peeled 0.706 mm, sliced 0.508 mm, and sliced 0.564 mm. Both loose-side out and tight-side out lathe check orientations were used. The adhesive systems were urea–formaldehyde, polyvinyl acetate, and soy-protein based. 96 treatment combinations with 8 replicates were tested. All specimens were exposed to harsh but realistic drying conditions (approximately 30°C and 26% relative humidity) for 4 h during inspection. Checks were detected on 428 out of a total of 765 specimens (56%). The estimated mean check densities (area of checking per unit area) indicated some unfavourable factor combinations. All factors had some degree of interaction with one another and check development could not be attributed to a single factor examined in this study. The data were fit to a generalized linear mixed model based on Tweedie’s compound Poisson distribution. Confidence intervals were calculated via bootstrapping. The check density estimates produced by this model can be used to cautiously guide manufacturers as they decide on panel components. The broader use of the model is to highlight the complexity of the problem and guide future research in this area.

The Quality of Samama Rotary Cut Veneer

Lathe check on veneer is formed as wood response to peeling process, which is usually analyzed in green veneer. After the veneer passed through drying process, the tendency of lathe check rises due to another factor and then it properly named as veneer check. This study was carried out to analyze lathe check and veneer check of samama. The fresh 8 year old samama log was peeled with the thickness of 1.5 mm and 3.0 mm subsequently after pretreatment of boiling in 50˚C for 4 hours and no boiling treatment as the control. Several 2-centimeter wide segmentations were noted from pith to bark and the resulted veneer of each segment was analyzed to determine the quality of lathe check and veneer check. The result showed that the total of peel crack (lathe check) declined from pith toward bark. The thicker veneer produced more lathe checks than the thinner veneer. Whereas, the depth and length of lathe check showed the same tendency as the total lathe check, which showed reduction toward bark’s segmentation. Boiling pretreatment in 50˚C for 4 hours before peeling process tended to increase the quality of samama wood veneer. It was indicated by decreasing in total, length, and depth of lathe checks. Further, it was found that veneer check increased by 19.42-24.94% in comparison to the lathe check. Therefore, the result of this research can be used as consideration in veneer production process of samama including handling and drying, so the quality of the veneer is well sustained.

The influence of lathe check depth and orientation on the bond quality of phenol-formaldehyde – bonded birch plywood

During the rotary peeling of veneer for plywood or the laminated veneer lumber manufacture, checks are formed in the veneer that are as deep as 70–80% of the veneer thickness. The results of this study show that, during adhesive bond testing, deep lathe checks in birch (Betula pendula Roth.) veneer significantly reduce the shear strength and the percent wood failure of phenol-formaldehyde (PF) – bonded plywood. The results also show that specimens tested with the checks pulled open or closed can fail by different mechanisms. Dried rotary peeled birch veneers were sanded to create uniform surfaces with lathe check depths varying from 30% to 90% of veneer thickness. Then, 7-ply plywood was manufactured with a commercial PF resin. After the preparation of the test specimens, the check depth of each specimen was measured microscopically. Subsequently, bond quality was measured according to EN 314. The results show that veneer checking alone can bring EN 314 specimens to the brink of failure even with an excellent adhesive. These findings stress the importance of measuring the depth of lathe checks and considering the orientations of checks during the testing to get a better understanding of bond quality in veneer-based products.