International Wood Products Journal

An important aspect in machine strength grading of timber is the direction of the grain and deviations from the main axis, which can cause a dramatic loss of strength. Therefore, an essential requirement of the wood industry is to find the direction of wood fibres in a fast and non-invasive way. For three decades now the use of polarised microwave radiation has been investigated, revealing the main direction of wood fibres in a non-contact and non-destructive way. The development of new small sized patch antennas now allows the detection of grain deviations on a local scale using a free microwave transmission method. This paper presents experimental results on accuracy and resolution for spruce specimens of different dimensions. Local signal variations, as well as boundary effects are discussed, particularly in view of possible industrial implementation.

Acacia auriculiformis A. Cunn. (ex Benth) is an extensively planted fast-growing species in Bangladesh. Understanding the anatomical property variation has significant importance in tree improvement and wood utilization. Radial variations of anatomical properties in 11-year-old trees were examined in this study. Vessel diameter increased gradually up to about 40–45% distance from pith and then levelled-off to bark. Fibre diameter gradually decreased toward bark, whereas fibre wall thickness showed a reverse pattern. In contrast to fibre proportion, vessel and ray proportions gradually increased from pith to bark. Cell wall proportion was nearly stable up to ∼70% distance from pith and then increased gradually to bark. Results suggest that air-dried density or compressive strength variation is mainly attributed by the fibre morphology, i.e. fibre diameter and fibre wall thickness (at 1% level). Significant variations among the trees in vessel and fibre diameters (at 1% level), and ray and axial parenchyma proportions (at 5% level) suggest the possibility of tree selection for breeding.

The effect of pure Zn²⁺ and combined Zn²⁺ and Mn²⁺ supplements on the growth and ligninolytic activity of wood-rotting basidiomycetes was studied. Based on measurements of minimum inhibitory concentration and minimum decolourisation-inhibiting concentration available from cultures of Inocutis sp., Trametes versicolor and Gloeophyllum trabeum, and a comparison of such results with those obtained in previous work for P. chrysosporium and P. atropurpurascens, metal supplements were shown to inhibit fungal physiology at concentrations within the study range. Average minimum inhibitory concentration values were consistently lower for ZnSO₄ than for ZnSO₄/MnSO₄ (2 mM Zn²⁺), demonstrating the antagonistic effect of the tested cations. Furthermore, because the ligninolytic system of P. atropurpurascens had shown a high tolerance to metals, its ligninolytic and germinative behaviour was compared with that of P. chrysosporium. Conidial germination was inhibited at 1 mM of Zn²⁺ in the two strains, whereas extracellular activity was inhibited at concentrations above 2 mM.

The aim of this study was to explore the golden ratio (Φ) based scaling relations existing between the golden ring volume, the golden measure equation (GME) and transversal dynamics of growth ring formation. Magnitudes of the golden ring volume, the golden ring cube and parameters of the GME were experimentally quantified based on X-ray densitometer data of Douglas-fir and white spruce. Thereafter, transversal dynamics of the parameter-fitted equations were analysed. The Φ (1·618) was satisfied by both species with 95% confidence. The first order derivative of the GME agreed with the transversal momentum of growth ring formation. The second order derivative was deduced to have potential in explaining transversal physiological transitions from earlywood to latewood and juvenile to mature wood. The structure and formation of growth rings are shown to be self-optimised based on Φ and this finding may explain why wood has higher strength-to-weight ratio in comparison with other materials.

Chestnut hydrolysable tannins are phenolic materials that have been considered too unreactive to compete in the phenolic resin adhesives market for exterior boards for the building industry. However, an article in 1973 describing 3 years of industrial application of chestnut hydrolysable tannins during the first oil crisis indicated that this was not the case. This previous work has been extended by using superior phenolic resins formulations and producing phenol–formaldehyde–chestnut tannin adhesives where a substitution of up to 80% of the phenol is possible with remarkably good results. The reactions involved were clarified by ¹³C NMR and MALDI–TOF mass spectrometry.

This study reports the effect of two finger profiles on the static bending parameters of Eucalyptus tereticornis samples when joined with urea formaldehyde adhesive. Two sets of finger profiles with tip thicknesses of 0·11 and 0·14 cm were used. Interestingly, the profile with the thinner tip produced weaker joints. This behaviour is attributed to the larger contribution of the tip area to the total joint area in a joint when using the thinner tipped profile. The study suggests that for a given geometry, one needs to reduce the tip area in relation to the total area encountered in a joint. This gives the manufacturer an opportunity to make not too thin and fragile tips but still making it possible to design a profile which can result in useful strength parameters. The results obtained on the effect of tip area on bending parameters were confirmed by using another adhesive.

Finger-jointing round wood segments into straight logs may provide an efficient method for converting small-diameter timber harvested during thinning operations into value-added products. Currently available applications for round wood finger joints appear to be limited. This study investigated the mechanical performance of round wood finger joints using plywood peeler cores. The effects of two joint profiles and two joint orientations on the performance of round wood finger joints were determined. The strength, stiffness and strain variation properties of round wood finger joints were evaluated and compared with those of solid joint-free round wood cores. The strength of finger-jointed round wood segments was found to be less than the strength of solid round wood cores without joints. Both joint profile and joint orientation were found to affect the strength and the strain of round wood finger joints. Finger-joint base strain increased at a greater rate than did finger-joint tip strain during bending tests.

The aim of this work is to demonstrate that Fourier transform near infrared spectroscopy, with multivariate data analysis, can be used to distinguish between preservative treated wood and non-treated wood. This technique is quick, easy to use and has the potential to be non-destructive and portable. For this research, a set of calibration models for the elements boron, chromium, copper and cadmium and the organic preservative cypermethrin have been created using principal component analysis and soft independent modelling of class analogy. The actual metal contamination levels in the wood samples were determined by induction coupled plasma-atomic emission spectroscopy. It is shown that these models can be used to classify samples of wood on the basis of the presence of these chemical substances.

The determination of surface free energy of wood is an important parameter in applications such as coating, painting and gluing. The simplest technique for that is measurement of contact angle. This technique has been used for the investigation of the effect of heat treatment of wood on the surface free energy. Two wood species – aspen and grey alder – have been treated in a range of temperatures from 140 to 180°C. With the sessile drop technique, series of contact angle data have been collected and used to determine the corresponding surface energies and changes in wettability. The most commonly used approaches, Zisman, Owens–Wendt, Wu, equation of state and acid–base theories, were applied. The results demonstrate that heat treatment affects wettability and solid surface energy, in particular, from the Owens–Wendt and Wu theories. We know that at higher treatment temperatures, the polar component of the surface energy for both wood species decreases, while the dispersive component is almost constant. The experiments have been conducted while trying to fulfil the same measuring conditions, but in any case, it was not possible to reach the thermodynamic equilibrium conditions assumed by Young's equation, due to chemical heterogeneity, surface roughness and capillarity. It is possible to improve the accuracy of results using a larger number of probe liquids.