مجله تحقیقات علوم چوب و کاغذ ایران
سال بیست و هشتم شماره 2 (پیاپی 43، تابستان 1392)

With respect to the effects of undesirable formaldehyde exposure to human health and to the environment, emission level of this gas from wood composite product was measured in order to introduce a practical method for evaluating the amount of its emission from glued wood products. In this regard, particleboards panels were prepared from Haloxylon persicum using particles with three different moisture gradients using urea-formaldehyde adhesive. Formaldehyde emissions were evaluated using desiccators’ method according to ASTM D 5582-00.The results showed that the emission declines as the moisture gradient increases. The emission values were determined as 8.946 ppm, 6.312 ppm and 4.172 ppm for the particleboards with moisture gradients of 0, 2 and 4 percent, respectively. Increasing moisture gradient from 0 to 2 percent resulted in 29 percent and increasing moisture gradient from 2 to 4 percent resulted in 34 percent lower formaldehyde emissions, respectively. In addition, comparing the measured values with standard values showed that these particleboards should be only used in outdoor application rather than indoors.

During the recent years due to the innovative trends taking place in the production, packaging and shipping of furniture, world trade of the products has increased drastically. This issue together with some given weaknesses in manufacturing and marketing domestic wooden has resulted in significant growth in furniture imports to Iran. To achieve efficient and economic imports, it is critical to understand market preferences and factors involved in selecting foreign goods for domestic products. In order to investigate the reasons for the expansion of the import quantities, the standardized questionnaires (certified by professionals and academic staff in four groups: Economics, Environmental, Technical and Technological, and Consumption) are provided using documentary and survey methods to investigate effective indices on importing wooden furniture to Iran and the reasons behind. These main indices of imports are rated by three

Likert spectrum, Duncan Test, and relative importance ratio of each index. We applied Likert spectrum on the whole statistical population and results indicated that Environment index ranked first followed by Consumption, Technical and Technological, and Economics indexes, respectively. Duncan test shows Economics index has the first rank, Environment index holds the second place. Technical and Technological index are in the same place as Consumption index and according to the test there is no significant differences between them. On the other hand, using the relative importance ratio method we classified related occupations into 4 groups: producers, vendors/ distributers, importers, and consumers. We employed third method to see how these four groups evaluate the importance of each index. Results are as follows: Producers believe that Environment index is in the first place and then Economics, Technical and Technological, and finally Consumption index. Vendors/Distributors believe Consumption, Technical and Technological, Economics, and Environment index is the sequence. Importers believe that Consumption index is in the main priority and then Technical and Technological, Economics, and Environment hold next places.

In this study, the possibility of using chick-pea straw residues for manufacturing three-layer particleboards was studied. The amounts of chick-pea straw in mixture with industrial particles were (% 25:75),(% 40:60),(% 55:45) respectively. Urea formaldehyde (100%) and Melamin urea formaldehyde at different ratios of MF / UF were used as binders. The resin were applied at two levels of (% 8,10) in core and two levels of (% 10,12) in surface layers, based on oven dried weight of particles. Mechanical and physical properties of boards (Modulus of rupture, Modulus of elasticity, internal bonding and thickness swelling and water absorption after 2, 24 hours soaking in water) were measured and data were analyzed, statistically. The results indicated that increase of chick-pea straw lead to incnement of bending strength and modulus of elasticity. Also the increase of resin content and use of melamin urea formaldehyde resin caused to improve mechanical and physical properties. In general, the use of chick-pea straw in mixture with industrial particles up to 55%, and resin content of (10,12%) in core and surface layers, resulted in producing boards with appropriate mechanical properties which are suitable for interior uses.

Detection, detect of damage in scarf joint and finger joint using the various in dynamic shear modulus values and correlation coefficient factor of the beech wood specimens were investigated. Forty two Samples were selected in accordance with international standard No. 3129. The Scarf and finger joints created with three different glue coverage rates in samples and then free-free flexural vibration test were performed. The results showed that defects changed the dynamic shear modulus values in both joints; however it is not possible to realize the amount of defects from these variations, whereas, the changes in correlation coefficient factor were useful to detect the amount of defects in both joints.

In the present study, fire-retardant properties of nano-wollastonite in fir wood (Abies alba) was studied. Water absorption and volume swelling of the specimens were also measured. Specimens were prepared according to ISO 11925 standard specifications to measure the fire-retarding properties, and ASTM D4446 -2002 standard to measure physical properties. Impregnation of wood specimens with nano-wollastonite was carried out at four consumption levels of 4, 6/3, 10 and 12%, using Bethel method (full-cell process). Five fire-retarding properties were measured; weight loss (%), ignition point (s), duration of flame after removing the burner (s), duration of glow after removing the burner (s), and carbonization area (%). The results showed that fire-retarding properties increased with the NW-content. Furthermore, the treated wood specimens showed higher dimensional stability.

This study provides an investigation of particleboard manufacture using tannin-urea formaldehyde adhesive. Test board samples were made with regard to various replacement percentage of tannin–urea (levels of 0, 10, 20 and 30%) and press time (12 and 15 min) and their properties were determined. Achieved data were analyzed according to two sides factorial plan. The results showed that with replacement of 10% urea formaldehyde adhesive by tannin-formaldehyde at both 12 and 15 min pressing times, thickness swelling (after 2 and 24 hours immersion in water) was decreased while internal bonding increased. There were no significant effect on modulus of rupture and modulus of elasticity values. In general, the results of present research showed that replacing the UF resin at lower levels of tannin is suitable as adhesive to manufacture particleboard so that with replacement ratio of 90:10, the moisture properties of boards were very close to permissible those of the exterior wood uses.

Wheat straw particle boards were produced using a mixture of wheat straw and cotton bolls with Urea formaldehyde resin and its properties were reinforced with nanoclay. Cotton bolls and wheat straw particles were mixed at the ratio of 40:60, 60:40 and 80:20percents, respectively. Nanoclay was used at two levels of 0 and 2 percents based on oven dried weight of resin. Control samples were made of wheat straw particle. Mechanical and physical properties (modulus of rupture, modulus of elasticity, internal bonding, water absorption and thickness swelling after 2 and 24h soaking in water) of the produced boards were measured. The results revealed an increase in cotton bolls in the mixture particles, leads to an increment of the bending strength, modulus of rupture and modulus of elasticity of the boards. The results also indicated that water absorption and thickness swelling after 2 and 24h immersion in water decreased with increase in nano clay and cotton bolls percents.

Coupling agents in wood fiber reinforced plastic composites play an important role in improving compatibility and adhesion between polar wood fiber and non-polar polymer matrices by forming bridges of chemical bonds between the fiber and the matrix. Maleated polyethylene (MAPE) and diisocyanate (HMDI) are the two most common coupling agents which are subject to evaluation, singly and in mixture. Polypropylene and wood fibers were compounded with Maleated polyethylene (MAPE) and diisocyanate (HMDI) in concentration of 2% and 4% in solitary form and mixture form (HMDI %2 + MAPE %2) into pellets using a counter-rotating twin-screw extruder and mechanical test specimens were prepared by injection molding. The result showed that adding 4% MAPE and 2% HMDI individually lead to increment of flexural and tensile strength of the composites. Also adding (%2HMDI + %2MAPE) caused an increase of flexural, tensile and in particular the impact strength.

The aim of this study was to investigate the factors affecting surface quality of paulownia wood during milling by advanced computer numerical control (CNC) machine. For this aim wood logs converted to proper sizes (2.5 x 10 x 15 cm) and then air dried. The variable of this study were spindle speed of machine (10000 and 18000 rpm), feeding rate (6 and 12 m/min), cutting depth (1and 5 mm), cutting method (down and up-milling) and cutting pattern (tangential and radial). Roughness of cut specimens edge were evaluated by profilometer method according to ISO 13565 standard. For evaluation of surface quality Abbott group parameters (Rpk, Rk, Rvk) were used. Degree of effective of the parameters was evaluated by fractional factorial design as completely random design at confidence level of 95%. The result showed that spindle speed, cutting method and feed rate are influencing factors on surface quality of milled specimens and their effect was significant. With increasing spindle speed and decreasing feeding rate the roughness decreased and surface quality improved. In up-milling cutting method, degree of roughness was higher and consequently surface quality was inferior. Cutting method in comparison to other factors had the high influence on surface quality. The rest variable did not have independent influence on surface quality at 95% confidence level.

The objective of this study was to manufacture water resistant kenaf stalk particleboard. Twenty seven boards were produced using 170 °C steam treated kenaf particles, 30 and 60 minute treatment time and three resin types include urea-formaldehyde, melamine-formaldehyde and a mixture of fifty percent each. Physical and mechanical properties were measured and the results by factorial model based on a completely randomized design. Results showed that boards made of treated particles with 60 minute treatment time and Urea Formaldehyde resin had the highest bending strength. Modulus of elasticity (MOE) improved with an increase in treatment time. The strongest Modulus of elasticity (MOE) was achieved with the boards bonded with urea-melamine-formaldehyde resin. Moreover, with increasing treatment time from 30 to 60 minutes internal bond strength (IB) reduced. Thickness swelling and water absorption of the boards was significantly improved with increasing treatment time.

This research was carried out with the aim of determining dielectric properties of bagasse unbleached soda pulp, long fiber kraft pulp and a mixture of both (20% kraft + 80% bagasse soda).The hand-sheets with 60 g/m2 basis weight were made after adjusting the freeness of pulps at levels of 200 ± 25 ml and 400± 25 ml and dried under mild condition around zero moisture content. Then the impregnation processes were carried out with mineral oil under vacuum at certain temperature. Finally the dielectric properties of impregnated papers including capacitance, insulation resistance, dielectric constant, and loss tangent were measured. The results showed that the refining give rise to enhance the dielectric properties in particular capacitance value. The dielectric properties of oil impregnated paper also increased. According to the preliminary results, unbleached soda bagasse pulp and its mixture with kraft pulp (20% Kraft -80% bagasse soda) found to be the suitable alternative with respect of dielectric applications for replacing kraft pulp, providing successful performance of the aging test.

Native starch has relatively suitable characteristics including biodegradable properties, being widely used as an adhesive in the corrugated carton manufacturing companies. Corn starch is currently used in the companies for producing adhesives. In this study, fines of NSSC pulp as natural additive and ammonium persulfate as chemical oxidative additive were used to improve the adhesion properties of corn starch. Fine was added at three levels of 5%, 10%, and 15% (based on oven-dry weight of starch) and ammonium persulfate similarly was mixed at 5 levels of 0.1, 0.2, 0.3, 0.4 and 0.5 grams. Addition of fine was lead to increasing adhesion strength (PAT) of the corrugating board to the amount of 25%, 35% and 43% respectively. This improvement could be due to increasing the number and strength of hydrogen bonding of fiber layers (corrugating and liner paper) and value of solid content. Addition of ammonium persulfate revealed that the method applied similar to mixing fine had no desirable results and the other methods should be used.

In this study the effect of alkaline pretreatment with 1% NaOH on physical, optical and mechanical properties and refining of NSSC (Neutral Sulfite Semi Chemical) wheat straw pulp were investigated. The wheat straw (Zagros Sp.) was obtained from croplands Golestan province. Splinted wheat straw was pretreated with 1% NaOH(on the basis of OD weight) at 70 degrees for 30 minutes. The main pulping was performed at 160 ˚C with the fixed ratio of 5:1 Na2S03 and NaOH. After pulping defibration was done by lab-refiner to 380±25ml (CSF) and total yield and changes in Kappa was determined. Hand sheets of 60 gr. /m² were made on the basis of TAPPI standard and physical, optical and mechanical properties determined. The results show that alkaline pre-treatment has a significant effect in increasing of physical, optical and mechanical properties. Calculating primary freeness of pulps indicates that by increasing chemical compounds and NaOH, freeness decreases and that by increasing chemical compounds paper density increases, whereas yield, caliper and bulk decrease.

The objective of this study was to investigate utilization of pomegranate pruning residues as the core layer of the three layer particleboard. The percentage of the pomegranate residues varied as 100, 65 and 35% in the core layer of the eucalypt particleboard and three resin levels of 8, 10 and 12 % (based on the weight of the wood particles) were applied in the core layer. Resin dosage in the surface layer was kept at 12 %. The strength and physical properties were measured and analyzed applying factorial model based on completely randomized design. The results revealed that if 65% pomegranate residues are used in the core layer, the modulus of rupture and modulus of elasticity were the highest and the combined effect of both variables on the properties were statistically significant. The highest value of the modulus of rupture and modulus of elasticity obtained in the case of 10% resin in the core layer and 100% pomegranate residues followed by 8% resin in the core layer and 65% pomegranate residues. The combined effect of both variables on internal bonding of the boards was statistically significant and the highest internal bonding was reached if 8% resin and 65% pomegranate residues were used in the core layer. The effect of resin dosage on thickness swelling after 24 hours immersion in water was statistically significant. The results indicated that pomegranate tree pruning could be used for the particleboard manufacturing.