International Wood Products Journal

The effect of different parameters on the surface discolouration (yellow stain and kiln brown stain) and thermal discolouration of Pinus elliottii during kiln drying was investigated. Boards were dried with different kiln schedules and discolouration was assessed at different depth levels from the surface of each board. The discolouration data were analysed using notched boxplots, multivariate analysis of variance and canonical variate analysis biplots. Thermal and surface discolouration were distinguishable by the distribution of colour data point plots in the CIE-L*a*b* colour system. Thermal discolouration was less intense and less varied than surface discolouration. The greatest degree of thermal discolouration occurred in one of the higher temperature (T_db≥90°C during first drying phase) schedules that was run for an excessively long period due to low air velocity. Discolouration progressively decreased as the boards were planed to a greater depth. Higher temperature schedules yielded 77.5-82.5% discoloured replicates at the 2 mm depth level. Lower temperature (T_db≤71°C during first drying phase) schedules yielded no discoloured wood at the surface or at the centre of the boards.

The transition from sapwood to heartwood is characterised by several changes including increasing acidity. On the basis of the strong correlation, which has been established between strength reduction and wood acidity during heat treatment, the differences in the response of heartwood and sapwood strength properties were investigated. Heartwood and sapwood samples obtained from one board of Scots pine (Pinus sylvestris) were heat-treated and their strength properties compared. There was 15.8% and 3.3% reduction in modulus of elasticity in the heartwood and sapwood respectively while the loss in modulus of rupture is 32.9% and 15.6% in the heartwood and sapwood respectively. The lower reductions in the strength properties in the sapwood compared to the heartwood indicate that the former is less amenable to heat treatment than the latter. This is probably due to the higher acidity of the former, which could have resulted in higher degree of degradation, higher cellulose crystallinity and consequently higher strength reduction. Therefore the effects of heat treatment on wood especially the strength properties depends on the proportions of heartwood and sapwood.

Thermal treatment in soy oil medium is one of the techniques used as a substitute for chemical treatment in wood preservation. However, the effects of this technique vary from one species to another and hence the need to investigate the response of individual species to it. Thermal treatment of air-dried Nigerian-grown Albizzia zygia and Funtumia elastica wood was carried out in a vessel containing soy oil at a temperature of 220°C for 2hours. This was followed by the determination of hygroscopy and swelling by water soaking method; surface energy by the sessile drop contact angle method; pH and buffer capacity by the cold extraction method. The process of soy oil thermal treatment resulted in significant reductions in hygroscopy, swelling properties and pH in both species with accompanying increase in buffer acid and alkaline buffer capacity. The surface energy which is an indication of wettability was reduced in Albizzia zygia but increased in Funtumia elastica. The reductions in hygroscopy and pH are indications of cellulose degradation during the heat treatment process leading to build up of acid formation. The reduction in hygroscopic behaviour indicates potential for stability in wood-water relationship especially when the material will be used in a continuously-changing ambient environment. The reduction in surface energy in Albizzia zygia implies that soy-oil-thermally modified wood from this species will have reduced interfacial attractions with most chemical adhesives. On the other hand, the increase in surface energy in Funtumia elastica shows possibility of improvement in the level of interfacial attractions between wood (substrates) and adhesives. The reduction in pH in both species is expected to have a two-way effect; a benefit through reduction in adhesive curing time and an adverse effect through expected reduction in strength properties.

Wood biscuit joints are commonly used to join particleboard and medium density fibreboard (MDF) panels. This paper describes the mechanical characteristics of biscuit joints. Specifically, the moment of resistance and bending stiffness of biscuit joints are evaluated. Centre to centre spacing between the biscuit holes, edge distances between the centres and the corresponding edge of board, the type of loading as compression and tension loads, the type of composite materials, and glue effects are taken into consideration. The experimental results indicate that gluing of the face and butt members significantly affect joint strength. The maximum bending moment for particleboard joints was 5.74 Nm under tension and 6.0 Nm under compression. These values were 5.39 Nm and 4.69 Nm, respectively for MDF joints. In addition, the experimental results also indicate that biscuit joints in particleboard panels are stronger than those in MDF panels. The former tensile strength was 7.4% and the compression strength was 29.9% higher than the latter. However, the biscuit joints in MDF panels were found to be stiffer than those in particleboard panels by an average of 11%. The on-centre spacing between biscuits had insignificant effects on the joint tensile and compressive strengths of the joints. This discovery is useful for the manufacturing industries where fewer biscuits can be used and time and cost can be saved. Finally, the experimental results suggest that the bending strength of glued and unglued joints is inversely related to the spacing between the centres of the biscuit holes and the edge distance between the holes and the board edge.

Radial and axial variation in specific gravity and certain anatomical properties were investigated in twenty year old plantation grown Eucalyptus citriodora Hook. Specific gravity and certain anatomical properties varied significantly in both directions. Average specific gravity ranged from 0.666 to 0.711 pith outwards and 0.762 to 0.728 base upwards; average fibre length ranged from 1062 μm to 1301 μm and 1211 μm to 1166 μm in radial and axial directions respectively. Similarly vessel diameter showed a range of 112 μm to 151 μm radially and 118 μm to 141 μm axially; vessel element length ranged from 405 μm to 505 μm in radial direction and 428 μm to 461 μm in axial direction. Although the fibre diameter, fibre lumen diameter and wall thickness showed significant variation, the differences in their values were found to be minor. Maximization of parameters was taking place after 75% of radial distance for specific gravity and fibre length. Based on general features, physical properties and anatomical structure, the wood can be used in furniture and handicraft industries.

A series of machining experiments on the oil-palm empty fruit bunch (OPEFB) particleboard were carried out using a CNC router, to evaluate the tool wearing properties of the composite in comparison with a standard wood-material particleboard. A single-fluted tungsten-carbide router bit (12 mm dia., 18 000 rpm), with a rake angle of 15° was used in this experiment, in which the depth of cut was 1.5 mm and feed speed was 4.5 m/min. The router bit machined the edge of the board, moving along the full length before returning to repeat the cycle. The tool was examined for the extent of wear after complete failure had occurred. The result found that the wear pattern was similar in the oil-palm based particleboard and the wood-based particleboard, but the former is twice more abrasive compared to the latter. Microscopic examination of the cutter edge reveal a greater incidence of micro-fracture when cutting the oil-palm based particleboard, indicating the presence of hard impurities in the composite. From an economic perspective, the tooling cost for machining oil-palm based particleboard is estimated to be twice of the cost for machining wood-based particleboard. This study shows that the machining properties of oil-palm based particleboard will be a primary concern, if it is to find widespread application as a potential substitute for wood-based particleboard.

Development trend of Iranian particleboard industry is not satisfactory. Effective indicators in non-development of the industry were divided into five major groups, i.e. by economic, raw material and product, social, technical and man power, rules and regulation plus 23 subsections. After obtaining the two-by-two comparisons of the mentioned criteria and subsections from the experts in the industry, their weighting values were calculated using the analytical hierarchy process (AHP) while group decision making were conducted using Expert Choice software. The results of this study showed that inconsistency ratio for all average comparison matrices are smaller than 0.1 and the overall inconsistency ratio is 0.02. Therefore, the judgments in current study have high consistency. Moreover, the results indicated that among 23 effective sub-criteria in non development of the industry, the following sub-criteria had the highest priority respectively: Lack of raw material, non-expert elements, lower production quality, changing of management, long decision making process and ancient technology. Feasible solutions have been suggested to develop of the industry.

The classification systems used by wood flooring enterprises in Greece has been investigated, using a questionnaire. After 56 answers, the results showed that there are deviations in grades and in the criteria currently used to classify wood flooring. There were reported very different grading systems, adopting from three to more than six grading categories. The majority (40 %) adopted five grading categories, but there were also enterprises using main (three or four) and also a number of subcategories. Deviations were also observed among the producers who claim to apply the same criteria and different trade names may be used for the same or similar qualities. Although there are difficulties, it is imperative that common national standard is accepted or conformation with the European standards. Evaluators should be trained to the same standard, in order to achieve this goal.