نشریه تحقیقات منابع طبیعی تجدید شونده
سال چهارم شماره 3 (پیاپی 13، پاییز 1392)

In this study, two dimensional mathematic models were developed for predicting wood temperature at different depth and density of wood during heating process. Fractional differential equations were applied for development of the model. For evaluating effect of wood density on heat transfer, Beech wood (Fagus orientalis) and poplar wood (Populous deltoides) with densities of 0. 67 g cm-3 and 0. 43 g cm-3 and moisture content of 12% was applied. Holes of 5 mm diameter were made on the board specific distances to measure the temperature using thermocouple. Good agreement was found between model predictions and experimental data. Heat loss from edges of wood block under effect of environmental conditions was identified by model. However, model has to be modified for increasing its accuracy. It had high ability for temperature prediction at different depth of wood during heating by increase of model accuracy, it can be used for wood drying and heat treatment applications.

In this study, effect of veneer on flexural creep behavior of medium density fiberboard (MDF) was investigated. MDF panels were prepared from Pars Neopan industries with 760 kgm-3 density, layered and then laminated with natural and melamine veneers. Their creep behavior was compared to MDF unlaminated as control treatment. For evaluating maximum bending load in static flexural test, samples were cut from panels according to ASTM D 1037 with dimensions of 370×50×16 mm. Then, the flexural creep tests at 20% and 40% of the maximum bending load was applied to the sample prepared. Results showed that levels of stress are effective on all creep parameters, but showed less effect on relative creep. Also, creep parameters of layered MDF were indicated less than laminated and unlaminated MDF.

In this research, influences of defects in end to end and face to face joints have been investigated. 21 poplar specimens and 42 beech specimens with different type of joints (end to end face to face) have been used. Polyvinyl acetate adhesive applied and bending vibration tests have been carried out to perform elastic properties of specimens. No significant differences were observed comparing elastic modulus and acoustical coefficient of defective joints and solid beams, while the adhesion defect in this joint increased the damping factor and decreased the acoustic conversion efficiency. The results also indicate that defect in end to end joints has significant impact on the elastic modulus, acoustical coefficient, damping factor and acoustic conversion efficiency. Totally, variation on acoustic conversion efficiency as an effectively factor could be used for detection and extent of the defects in end to end and face to face joints before use and at service time.

This research has been to study the effect of lignocellulosic wastes (rice husk ash [Pozollan] and rice straw) on properties of wood-cement composite. Accordingly, some boards using rice straw, mixture of poplar wood and rice straw, and cement (Portland type2) were prepared. Rice husk ash was also used as pozollan in 3 levels of 0, 2% and 4% by weight. For evaluation of applied properties, bending strength, modulus of elasticity, shear strength, water uptake and thickness swelling were done in accordance with ISO-16983 and DIN-68763 standards. The results showed that, while lignocellulosic material switched from rice straw to mixture of poplar and rice straw, mechanical properties were improved, but physical properties were increased. In addition, the highest bending strength, modulus of elasticity, shear strength, and lowest water uptake and thickness swelling was obtained in 4% pozzolan treatment.

The present study is conducted to measure longitudinal growth stress and strain in the trees observed in the west part of Mazandaran region and also to compare the current phenomena in two tree species of Acer spp and Quercus Castaneifolia. The selected species are generally grown in the forests located in the highest point of the west part of Chalous River, i.e. southwest corner of Chalous city. Employing the single-hole method proposed by CIRAD, a French research center, the growth stresses index was determined according to the longitudinal growth residual strain value along the stem. The findings suggest that the stress and strain levels in these species are highly influenced by various features such as the age and diameter of the tree, the wood type (the reaction wood), the surface slope, and the wind. Moreover, as Acer spp and Quercus Castaneifolia are both extremely sensitive to the environmental elements, their recorded stress and strain values are relatively high that is clearly evident in the corresponding longitudinal growth residual strain. The average measured longitudinal strain in Acer spp and Quercus Castaneifolia were equal to 76 micron and 82 micron, respectively.

 In this study, the effect of different values of peroxide in three levels 3%, 4%, 5% and sodium hydroxide in two levels 2%, 3%, on bleaching of tobacco stalks (Nicotiana tabacum L.’PVH 19') soda pulp was investigated. Tobacco stalks were soda pulped using 22% alkali at 170°C for 100 min. Produced pulp had 36.2% yield and kappa number of 77. Bleaching process was included two stages of chelating and alkali peroxide bleaching. Results indicated that brightness increased and kappa number decreased by increasing sodium hydroxide and hydrogen peroxide level. The data related to 3% caustic soda and 5% peroxide treatment without chelating stage indicated that initial chelating stage significantly affected on the brightness, kappa number and yield of the bleached pulp, and this treatment had the lowest brightness and the highest kappa number and yield among the treatments. Finally, 3% caustic soda-5% peroxide treatment with initial chelating stage had the highest brightness (40.99%) and the lowest yield (40.10%), was selected as the best treatment.