مجله تحقیقات علوم چوب و کاغذ ایران
سال بیست و هفتم شماره 4 (پیاپی 41، زمستان 1391)

In addition to genetic features, wood anatomy is affected by environmental factors. Soil erosion is among the environmental factors which greatly affect anatomical features of tree root wood. In this study, the effects of soil erosion on the anatomical properties of the root wood of Juniperus excelsa - an Iranian indigenous softwood with high longevity- inside the soil and exposed was investigated. The anatomical properties of roots and wood from trees selected from both from the inside of the soil and exposed were examined using micro-sections. Results showed that root wood under the soil contained one row of late-wood and as the root is exposed from the soil, the lumen thickness in both early-wood and late-wood decreased and appeared that the cells are thicker and the late-wood portion is increased. In the exposed roots, the axial parenchyma contains larger quantities of black color inclusions. By exposing of roots out of the soil, the thickness of bark of the exposed portion decreased and the thickness of phloem and periderm in exposed root was not as wide as in normal roots

In this study, the possibility of using spectrophotometery and CIELAB technique to detect reaction woods in poplar tension wood and spruce compression wood was examined. Thus, two sample trees of spruce (Picea abies) and poplar (Populous nigra) containing reaction wood were felled in a forest belonging to ENGREF (the National Engineering School of Forestry close to Nancy in France). Then lightness (L*) and reflectance (R) parameters in reaction wood and normal wood both in green and dry conditions were measured. The results showed that in the green condition, the spruce compression wood had less lightness than the normal wood and the lightness of compression wood increased as a result of drying. The difference between the lightness and reflectance parameters of the two types of reaction woods and those of their corresponding normal woods was statistically significant in the green condition. Consequently, it can be concluded that the macroscopical detection of reaction wood is easier in the green condition than in the dry samples.

The effect of nanoclay particles addition to composite mixture on mechanical properties of HDPE/ wheat straw powder was studied. The composite compound was prepared using 35% wheat straw as reinforcement, 63% high-density polyethylene (HDPE) and 2% MAPP as coupling agent and different amounts of nanoclay (1%, 2% and 3%) were used. The composite compound was made using a counter-rotating twin-screw extruder and test specimens prepared by injection molding. Results showed that at higher dosages of nanoclay particles, the flexural strength and tensile strength increased. However, the addition of nanoclay particles has led to the decreased impact strength.

The influence of different contents (0, 5 and 10% W/W) of silica and poplar wood powder (30, 40 and 50% W/W of total weight of composite) on strength properties of polypropylene/wood powder/silica composite was evaluated. Various compositions of the composite was melt mixed using two screw counter rotating extruder, followed by cooling and granulizing. Composite granules were injected into test samples. The results of strength properties measurements revealed that almost all strength values were improved. At higher content of silica, the MOR increased from 47.9 to 53.3 MPa, flexural MOE from 2625 to 4517 MPa and MOE in tensile increased from initial value of 4525MPa (without silica) to 6884MPa (10% silica in composite). Marginal increase in tensile strength and Izod impact strength was observed, and the hardness of the composite was improved from 66 to 73.77 shoreD. At higher silica content, the density of the composite was higher, as expected

The lateral shear strength of tree piece elit sliding joints in MDF were measured and compared with fixed joints. L-shape joints were made as defined in ASTM D1761 using two MDF members with the dimensions of 20X20 mm. Test specimen were made in 5 replications and a total of 80 specimens were tested. The fixed joints used were wooden rough dowel joint with the diameter of either 8 or 10 mm covered with PVA glue, screw fasteners with the length of either 40 or 50 mm and the wooden biscuit fasteners no.10 covered with PVA glue. The sliding joints were selected as elit joints, elit joints reinforced with 8 and 10 mm dowels, metallic sliding joints with notch and without notch reinforced with glue free 8 or 10 mm dowel joints. Laminated and raw MDF boards were used to identify the impact of lamination. The results showed that in corner joints, the strength of the sliding notched joints were superior to sliding joints without notch. The strength of angular sliding elit joints with 10 mm dowel was more than the strength of fixed elit joint with 8 mm dowel and elit without dowel. The strength of fixed dowel joint without glue was higher than similar joint with 8 mm dowel. The strength of 50 mm screw joint in unlaminated MDF was more than 40 mm screw and similar MDF. The highest strength was measured using sliding joint in corner joint configuration using notched 10 mm doubles. However, in fixed joints, 10 mm dowel showed the highest strength. As the results indicate, sliding notched joints with 8 mm dowel joints (191.61 N) and fixed joints with 10 mm dowel (135.14 N) were the superior joints.

Influence of nanoclay addition on the strength properties of HDPE/ Wheat straw powder composite was investigated. Composite compounds were produced using 73% HDPE, 25% wheat straw powder and 2% MAPE and three dosages of nanoclay (1, 2, and 3% of composite compound weight). First, HDPE and nanoclay was melt- mixed and after cooling, the extrudate was milled to fine granules. These granules were then melt compounded with pre-weighted amount of wheat straw powder and MAPE followed by injection molding to produce test specimens. The flexural, tensile and impact strength were measured. Results showed that addition of nanoclay to the composite improved flexural strength and modulus, tensile strength and modulus. However the notched Izod strength was reduced.

Effect of increasing urea additions to urea-formaldehyde adhesive on physical and mechanical properties of poplar wood particleboard was investigated. Four levels of urea (0, 4.1, 8.2, 16% based on the solid content of adhesive) and two hot pressing times (170 and 180° C) were investigated. Boards with the density of 0.63 gr. /cm3 and 10% adhesive were prepared. Mechanical properties including modulus of rupture (MOR), internal bond (IB) and physical properties including water absorption and thickness swelling were measured. Results showed that the urea addition to urea formaldehyde adhesive improved the mechanical strengths of the board and reduced the water absorption and thickness swelling. Also, the impact of press temperature on mechanical and physical properties of boards was significant and the boards produced applying 170° C press temperature was superior.

Tannins are the most desirable natural, and renewable phenol compound obtained from plan. The phenolic nature of tannins causes this material to react with formaldehyde and form tannin-formaldehyde resins. Wheat straw and forest residues were used for the manufacture of particleboard (with a ratio of about 50 to 50 percent) using tannin formaldehyde based resin. Either 10 or 20% (based on the dry weight of the phenol formaldehyde resin was added to 35% formaldehyde solution to make the glue. Particleboards were prepared at two thicknesses of 10 and 16 mm and then the properties of the boards including bending strength, modulus of elasticity, internal bonding, thickness swelling and water absorption were measured. The results showed that the strength properties of the fabricated boards from combined particles were lower than those from wood particles only. Also, increasing the tannin dosage to phenol formaldehyde resin led to the increased internal bonding, swelling and water absorption (2 and 24 hours) of the boards

Ammodendron persicum (locally called Divdal) is a less- known woody species of the Zirkooh-Qhaen in the east of Iran. In this study, for the first time wood of this desert species was studied from different physical and anatomical aspects. Three selected logs were used for the study of wood properties. Results showed that Ammodendron wood is a ring -porous hardwood and all parts of its cross section have long rays that are visible with naked eye. In the study of physical properties of Ammodendron wood, the apparent and the dry density were determined as 1.125 and 0.92 g/cm3, respectively that classify this wood in the very dense category.

Effect of nail length (32, 42, 48 mm), the nail number (2 and 3) and the kind of particleboard and MDF on tensile strength and bending moment of the joint were investigated. The member dimension of 10*15*1.6 cm was selected in L–shaped joint manufacture and the adhesive was not used in the production of the joints. Using 4 replications, a total of 96 samples of L shaped joints were fabricated. Bending and tensile strength of the joints was measured. Results showed that the interaction of variables; nail penetration length, nails number and the material of the joint were not statistically significant on tensile and bending. The length and number of the nails increased the strength. Joints produced with MDF and the penetration length of 48 mm and 3 nails showed the greatest flexural strength and the joints produced with MDF and the penetration length of 42 mm and 3 nails showed the greatest tensile strength

This paper presents a new approach to forest wood production and stand productivity through dendroecology and analysis of the annual tree rings of forest broadleaves species. Based on this approach, samples were collected from different heights of the trees and the circumferential growth and wood production under the growth conditions were determined and the impact of probable competition was investigated. The application of tree dendrochronological method is also considered. The results of this study as part of a comprehensive work showed that in the Caspian forest region, this method can be used for such evaluation for more than last five years. A minimum three tree species namely oriental beech (Fagus orientalis Lipsky), oak (Quercus castaneaefolia C. A. Mey.) and hornbeam (Carpinus betulus L.) in three different elevations along the transect line (profile line) from low (400 m), medium (900 m) and high elevation (1250 m) in Astara, Gilan region were selected. Various behaviors of tree species and their responses to climate changes have been recorded in different elevations.

To investigate the effects of acetylation and antioxidant on discoloration and the contact angle of weathered composite, composite samples were manufactured using poplar wood flour and high density polyethylene. The samples were exposed to natural weathering for the duration of 6 months. The results showed that acetylation can relatively reduce the discoloration of weathered sample compared to the untreated control sample. Antioxidant did not impose any influence on color change but could partly prevent destruction of plastic. It should be mentioned that acetylating process increased surface contact angle before weathering, but it could not protect the sample surface against photo degradation. The contact angle of all samples was lowered to zero at the end of weathering period.

In order to evaluate the durability of commercial wood species of alder and hornbeam exposed to coastal water, the logs were cut into lumbers. Then after the reduction of moisture content, the lumbers were converted to special marine samples. The wood blocks were impregnated by CCA (Chrome- Cupper-Arsenic) using Betel impregnation method. Then treated and untreated wood samples were installed in one meter depth of water at seaside of Amirabad port, for 3, 6, 9 and 12 months periods. The result of the observations showed that, the staining fungi and balanus were able to colonize on the surface of control samples. However, treated specimens were only occupied by balanus and with increasing time (3 to 12 months) balanus presence were prevalent. The numerical result showed that untreated alder samples after one year were faced with 3.5% weight loss and treated samples not only had no weight losses but also increased in weight by12.21%. In the case of hornbeam, the result indicated that the weight loss of control was 2.7% while, in the case of treated samples was 7.9%. Also there were no sign of staining fungi on surfaces of treated samples of both wood species. As a consequence, treated woods could be safely used for many operations in the Caspian sea water.

The goal of this study was to investigate bending moment resistance of L-shaped screwed corner joints constructed of plywood members. The thickness of plywood members was nominal 19 mm that were compared with medium density fiberboard (MDF) and particleboard with 18 mm thicknesses. Effects of thread screws (coarse and fine), screw diameter (3.5, 4 and 5 mm), and penetration depth (9, 15 and 28) on bending moment capacity of joints under diagonal tension were investigated. Test results indicated that a screw corner joint becomes stronger as either screw diameter or screw length is increased. Screw length was found to have a greater effect on moment capacity than the diameter. The highest bending moment resistance was observed for joints made with coarse screw which were 5 mm in diameter and 28 mm depth of penetration. The lowest bending moment resistance was observed in joints having fine screw, with 3.5 mm diameter and 9 mm penetrations. Results also showed that bending moment resistance with coarse thread drywall screws was higher than those of the fine thread drywall screws. Bending moment resistance of joints made of plywood was higher than those of joints made of medium density fiberboard (MDF) and particleboard.

Effects of moisture content of four wood species (beech, elm, alder and spruce) on adhesion strength of clear paints (nitrocellulose lacquers and acid catalyst lacquers) were investigated. Boards (550×110×12 mm in dimensions) were cut from sapwood in tangential surfaces and air dried for one month according to wood drying procedures. Then, for pre-conditioning to reach the moisture content of 8%, 12% and 15%, the samples were separately placed in three conditioning chambers. Then the finish was applied and strength tests were performed. Results revealed that for acid catalyst lacquers, the highest bonding strength (5.14 MPa) was attributed to elm wood with 8% moister content and the lowest bonding strength (1.99 MPa) was observed in spruce wood having 15% moisture content with nitrocellulose lacquers application.