International Wood Products Journal

This study quantified the spatial distribution of moisture content and basic density within Cryptomeria japonica branches using near-infrared (NIR) hyperspectral imaging and multivariate data analysis techniques. The hyperspectral data for wood disk samples were acquired using a Compovision NIR Composition Imaging System (Sumitomo Electric Industries, Ltd., Yokohama, Japan) with a spectral range of 913–2519 nm. The calibration models for prediction of moisture content and basic density were developed using partial least squares (PLS) regression analysis. The PLS model for moisture content and basic density showed good predictive performance with coefficients of determination 0·82 (RMSEP = 12·4%) and 0·84 (RMSEP = 28·0 kg m⁻³) respectively. The spatial distribution of predicted moisture content clearly detected the low moisture white zone surrounding the heartwood. The high density compression wood could be also visualised with the NIR hyperspectral imaging technique. The results presented here provide useful information for development of a novel log sorting method.

The aim of this work was to study the bondability of birch (Betula verrucosa Ehrh.) veneer subjected to different surface treatments (chemical treatment, short term thermo-mechanical densification, and combination of these two processes) using phenol-formaldehyde (PF) resin with the aim of improving bonding during the production of plywood. Four chemical agents (hydrogen peroxide, aluminium potassium sulphate, potassium carbonate, and potassium permanganate) were used for chemical treatment of the veneer surface. The veneer samples were thermo-mechanically densified between heated plates of a laboratory press. The results revealed that short term thermo-mechanical densification and combined chemical and thermo-mechanical pre-treatment of the veneer surface prior to the resin application reduced the glue spread (a 33% reduction) and improved the bondability of the veneer. The obtained shear strength values for all of the studied treatments exceeded the standard requirements (1·0 MPa), and the properties of the plywood samples satisfied the European standard EN 314-2.

The objective of this study was to investigate the influence of the earlywood and latewood of different annual rings of kiln dried Japanese larch wood upon the water vapour sorption properties. Samples of earlywood and latewood from different lateral positions in the tree at 1·5 m height were exposed to water vapour over a range of different relative humidities to obtain sorption isotherms. A difference was found between the behaviour of the earlywood and latewood and this became more pronounced as the distance from the pith increased. The results indicated that there was residual water trapped in the cell wall of the latewood of the more recent annual rings after the first drying curve was completed. However, when the latewood was exposed to a second sorption cycle much of the residual trapped water was no longer present. Nonetheless, there were still differences in the EMC between the earlywood and latewood.

Emission of volatile organic compounds (VOC) from wood during processing to pellets – significance of wood extractives. Cellulose, hemicelluloses and lignin are the main components of the cell wall in wood. Moreover, wood contains different amounts of extractives, depending on the wood species. Extractives in softwoods play an important role during processing of wood to different wood products. This work studies the influence of storage on the change of extractives as well as on the emission of monoterpenes (primary emission) and aliphatic aldehydes, as degradation products of fats and fatty acids (secondary emission). In case of pine wood storage for 2 days at 80°C proved to be more efficient in the reduction of emissions of terpenes and aldehydes than 4 weeks at 40°C. Quantitative differences between pine (Pinus sylvestris) and spruce (Picea abies) wood chips in the emission were evaluated and discussed. Pinewood emits about 10 times higher amounts of terpenes and aldehydes than spruce wood. The results indicate that the intense of change in primary and secondary emissions due to storage depends on the wood species as well as on the boundary conditions under which storage is carried out. In general, storage at high temperature (80°C) is much more effective than at low temperature (40°C). The results also reveal that removal of wood extractives from pine wood by extraction with ethanol-cyclohexane or treatment with sodium hydroxide decreases the emission of primary and secondary volatile organic compounds drastically. Nevertheless, after such treatments minute amounts of volatile organic compounds are still detectable.

The effect of nano-copper oxide treatment on the colour change and loss of droplet contact angle on the sapwood of eastern cottonwood (Populus deltoides) after 180 days of natural weathering was investigated. Small clear samples were prepared, and vacuum impregnated with an aqueous suspension of nano-copper oxide at concentrations of 0·5, 1 and 1·5% nano copper. Treatment with nano-copper oxide decreased colour changes and loss of contact angle due to weathering. Colour change and contact angle loss decreased with increasing retentions of nano-copper oxide.

Research was conducted to evaluate the decking performance of northeastern United States wood species treated with copper based preservatives. Decking specimens were treated with one of four wood preservatives and exposed near Madison, Wisconsin. Specimens were evaluated for biological attack and dimensional stability. After 10 years, none of the preservative treated specimens had fungal decay. All of the untreated Southern Pine specimens were severely decayed within 5 years, but untreated specimens of other species were much slower to decay. Surface mold was most commonly observed on untreated specimens, but was also sometimes present on preservative treated wood. Warp and checking were greatest in red maple and least in eastern white pine. Although all wood species/preservative combinations were decay resistant, concerns with appearance and dimensional stability may make red maple and balsam fir less desirable for use as decking. Eastern white pine appears to be the northeastern species most suitable for use in decking.

Emission of volatile organic compounds (VOCs) from medium density fibreboards (MDF) containing different proportions of softwoods (SW) and hardwoods (HW) was evaluated. The results reveal that decreasing the proportion of HW in MDF elevates the emission of terpenes and aliphatic aldehydes. The pulping method (TMP, CTMP) seems to have no significant influence on the emission of terpenes or aldehydes from MDF. On using the TMP process, the emission of acetic acid elevates remarkably with increasing the amount of HW in the boards. Compared with the TMP process, the CTMP process leads to a decrease of acetic acid emission at 40°C with more than 15% at 35% HW content of the boards and 40% at 65% HW content.

Growth characteristics and wood properties were investigated for 26-year-old Eucalyptus alba trees grown in Ambon, Indonesia. The mean stem diameter and tree height were 27·9 cm and 19·5 m, respectively. In addition, the mean stress-wave velocity (SWV) of trees and basic density (BD) of outer wood (2 cm from the bark) were 3·23 km s^− 1 and 0·67 g cm^− 3, respectively. The mean BD of outer wood was almost the same in fast-growing and medium-growing trees. No significant correlations were found between stem diameter and SWV of trees and BD of outer wood. Based on the results, trees with faster-growing characteristics of E. alba do not always have the lower wood properties. Radial profiles in relation to relative distance from pith to bark were almost the same among three growth categories, suggesting that xylem maturation in E. alba might depend on cambial age.

Laminated veneer products (LVPs) consist of veneers bonded together with an adhesive into a predetermined shape. Deviation from the intended shape is a problem for both manufacturers and customers of the final products. The shape stability of LVP depends on a variety of material and process parameters, and this review identifies several important factors that influence shape stability, the purpose being to find ways of decreasing distortion and improving shape stability so that product quality can be improved.

The review ends to the following statements:

The fibre orientation of the veneer strongly influences the shape stability of LVP. The products can show considerable distortion (particularly twist) if the fibre orientation of the veneer is oriented in an unsuitable way in the assembly before moulding.

The effect of fibre orientation on shape stability can be very small directly after moulding, but it can increase considerably when the moulded product is subjected to a change in moisture content (MC). In general, a change in moisture leads to distortion. Moisture changes alone, however, result in a controlled distortion.

The orientation of the loose and tight sides of the veneers in LVP affects the shape stability.

An asymmetrical construction, coupled with different levels of moisture in the different veneers in an assembly before moulding, will result in poor shape stability of the product.

The choice of wood species affects shape stability. Beech shows more distortion and poorer shape stability than birch.

Based on existing knowledge to produce shape-stable LVP, the veneers should be conditioned to uniform MC and sorted with regard to fibre orientation and loose or tight side of the veneer before bonding. End-user climates should govern the veneers’ MC and added moisture from the adhesive during the process. Straight grain veneers and symmetry should always be sought.

This review reveals several areas that need to be further clarified in order to achieve shape-stable LVP, for example the influence of adhesive, the distribution of pressure, temperature, stresses and strains during moulding and the development of numerical methods to better predict the final shape.