International Wood Products Journal

The sap and heart wooden stakes of Acacia nilotica var. indica, after seasoning and castor bean (Ricinis communis) oil application for exposure to workers of the termites, Odontotermes obesus (Ramb.), were placed in soil pits in completely randomised design with three replications. In each of seasoning and oil application, per cent weight loss of the wooden stakes were recorded and statistically analysed. Minimum per cent weight loss of sap and heart wooden stakes was observed in maximum period of seasoning (100°C for 15 days in oven drying and 60 days in sun drying method) and highest concentration of castor bean oil (20%) by vacuum pressure application. These results are discussed in relation to seasoning and castor bean oil application for wood protection against subterranean termites.

In this study, the moisture resistance properties of self-bonded plywood were enhanced by thermal modification. The plywood was prepared without any adhesive, using only heat, moisture and mechanical compression. It is known that self-bonded plywood or the wood welding joints suffer from delamination under moist conditions. The results show that the moisture resistance of the joints can be enhanced, i.e. the tendency of delamination can be reduced or eliminated (almost totally) by post-manufacture thermal modification. This was most probably caused by lowered water absorption, relaxation of stored strain energy and formation of crosslinks within the lignin–hemicellulose matrix. The changes in bond integrity in moist conditions as affected by different lay-up types and initial veneer moisture contents were also evaluated. Plywood from initially wet veneers was found to have greater bond stability when soaked. This might be caused by increased crosslinks, because the lignin–hemicellulose matrix is more mobile in wet conditions.

This study determines the influence of mechanical surfacing on tensile shear strength (TSS) and wood failure percentage (WFP) of beech wood (Fagus sylvatica L.) at the wet stage according to prEN 302-1:2011 (tensile shear tests). The wood was planed, sanded and face milled, using different qualities of cutting edges and sanding grits. Roughness and wettability of the adherends were characterised, supplemented by environmental scanning electron microscopy images. The specimens were bonded by means of a one-component polyurethane adhesive and tested at the dry stage (pretreatment A1), at the wet stage (A4) and after re-drying (mA5). Results determined that the wettability and the wood structure's integrity are considered more decisive for the TSS at the wet stage than surface roughness. Planing with very dull knives caused the lowest TSS and WFP after A4 and the most subsurface damage. Face milled and sanded batches revealed the best performance. The TSS and WFP decreased significantly from A1 to A4, but recovered after mA5.

Pine tannin extract has never been used before as an adhesive for plywood. Interior and exterior grade plywood panels were prepared based on various adhesive formulations with pine tannin extract on both, hardwood and softwood veneers. The best performing formulations appeared to be those in which the pine tannin was added in a proportion of 20–35% to a phenol formaldehyde or a urea formaldehyde resin or to pMDI (4,4′-methylene diphenyl diisocyanate). Mixed adhesive formulations where a small amount of pMDI was added on top of 20% synthetic formaldehyde resin gave plywood with even better performance but with shorter pot life of the adhesive mix.

This study aimed to characterise wood discolouration of three Brazilian eucalypt species exposed to the action of natural weathering in two distinct places. To achieve this, tests were performed at an exposed outdoor site and under a forest canopy; both located in the state of Rio Grande do Sul, Brazil. Colorimetric measurements were performed every 45 days during the period of 1 year in order to obtain the parameters L*, a*, b*, C* and h*. The main results showed significant darkening in the first 4 months and subsequently increased the greyish colour. Colour variations were observed between species, field and exposure time in service.

The paper describes refinements of rapid laboratory assessment of the mechanical performance of timbers used in the marine environment as regards their resistance to indentation, impact abrasion from smooth and sharp abrasives and to dynamic impact loads when wet. Ten tropical and home-grown hardwoods, five softwoods and a wood–polymer compound were examined. Brinell hardness, dynamic hardness, abrasion resistance, and the structural integrity in high-energy multiple impact tests were determined comparatively on dry and wet specimens. A trend was shown where softwoods show a decrease in abrasion resistance with wetting, whilst hardwoods did not. In dry conditions, impact abrasion using steel balls was higher than when using sharp grit. It is suggested that when wet, water in the cells has a hydraulic energy absorbing effect.

Addition of urea to a melamine modified urea formaldehyde resin in the surface and core layer reduces significantly the formaldehyde release of the particleboards bonded therewith. Under the used boundary conditions (long press time) urea addition seems to have no noticeable negative impact on the physical–mechanical properties of the boards. The reduction of formaldehyde release due to urea addition as a scavenger can be followed by measuring the emission in the chamber according to EN 717-1, the perforator method according to EN 120 and the flask method as described in EN 717-3. The results reveal that under the used conditions a good correlation exists between the emission in the chamber and the corrected perforator values (R² = 0·865), as well as between the chamber value and the formaldehyde emission measured by the 3h-flask method (R² = 0·792) according to EN 717-3, a slightly better correlation was found between the measured flask values after 24 h and the emission in the chamber (R² = 0·869). The correlations seem to hold in the emission range between 0·06 and 0·016 ppm.

Western hemlock (Tsuga heterophylla), was dried using two different schedules with optional conditioning and seven day post-drying equalisation in a covered and climate controlled space that emulates outdoor conditions in south-central Japan from October to May. Timber quality was evaluated pre- and post-drying, and/or post-equilibration. Drying times, moisture content variation between and within timbers and internal stresses were also assessed. Data analysis revealed that conditioning and aggressive drying reduced casehardening, while milder drying resulted in less twist and diamonding. Although the control run seemed to develop less shape distortions than the treatments, it required longer drying times. With aggressive drying the kiln turnover will be quicker and the dried timber might be stored in a covered area for post-drying equalisation that will level out moisture gradients and alleviate casehardening. As a subsequent step, the timber might be planed to reduce twist, diamonding and superficial checks.