مجله صنایع چوب و کاغذ ایران
سال پنجم شماره 2 (پاییز و زمستان 1393)

In this research، biodegradation behaviors of cellulose nanocrystals-poly vinyl alcohol nanocomposites were investigated. Nanocomposite films with different filler loading levels (3، 6، 9 and 12% by wt) were developed by solvent casting method. The effect of cellulose nanocrystals on the biodegradation behaviors of nanocomposite films was studied. Water absorption and water solubility tests were performed by immersing specimens into distilled water. The characteristic parameter of diffusion coefficient and maximum moisture content were determined from the obtained water absorption curves. The water absorption behavior of the nanocomposites was found to follow a Fickian behavior. The maximum water absorption and diffusion coefficients were decreased by increasing the cellulose nanocrystals contents، however the water solubility decrease. The biodegradability of the films was investigated by immersing specimens into cellulase enzymatic solution as well as by burial in soil. The results showed that adding cellulose nanocrystals increase the weight loss of specimens in enzymatic solution but decrease it in soil media. The limited biodegradability of specimens in soil media attributed to development of strong interactions with solid substrates that inhibit the accessibility of functional groups. Specimens with the low degree of hydrolysis underwent extensive biodegradation in both enzymatic and soil media، whilst specimens with the high degree of hydrolysis showed recalcitrance to biodegradation under those conditions.

In this study، the effect of nanoclay particles content on the mechanical properties of wood flour-polypropylene composites was investigated using Dynamic Mechanic Thermal Analysis (DMTA). To meet this objective، wood flour was mixed with polypropylene at 60 % by weight fiber loading. The concentration was varied as 0، 3 and 5 per hundred compounds (phc) for nanoclay. The amount of coupling agent (PP-g-MA) was fixed at 2 phc for all formulations. The samples were made by melt compounding and injection molding. Static mechanical tests including bending and tensile were performed. DMTA test in the range of -60 to 120 0C with 5 0C/min temperature rate and 1 Hz frequency was done. The morphology of the nanocomposites has been examined by using x-ray diffraction and transmission electron microscopy. Results indicated that the mechanical strength and storage modulus of samples increases with increase of nanoclay up to 3 phc and then decreases with 5 phc nanoclay addition. Also، the alpha and beta transition in samples transmitted to higher temperatures with addition of nanoclay. The morphological studies with XRD and TEM revealed that nanoclay distributed as intercalation structure in polymer matrix.

The study aimed at predicting bending moment resistance plywood of screw (coarse and fine threads) joints using regression models. Thickness of the member was 19mm and compared with medium density fiberboard (MDF) and particleboard with 18mm thicknesses. Two types of screws including coarse and fine thread drywall screw with nominal diameters of 6، 8 and 10mm and 3. 5، 4 and 5 cm length respectively and sheet metal screw with diameters of 8 and 10 and length of 4 cm were used. The results of the study have shown that bending moment resistance of screw was increased by increasing of screws diameter and penetrating depth. Screw Length was found to have a larger influence on bending moment resistance than screw diameter. Bending moment resistance with coarse thread drywall screws was higher than those of fine thread drywall screws. The highest bending moment resistance (71. 76 N. m) was observed in joints made with coarse screw which were 5 mm in diameter and 28 mm in depth of penetration. The lowest bending moment resistance (12. 08 N. m) was observed in joints having fine screw with 3. 5 mm diameter and 9 mm penetrations. Furthermore، bending moment resistance in plywood was higher than those of medium density fiberboard (MDF) and particleboard. Finally، it has been found that the ultimate bending moment resistance of plywood joint can be predicted following formula Wc = 0. 189×D0. 726×P0. 577 for coarse thread drywall screws and Wf = 0. 086×D0. 942×P0. 704 for fine ones according to diameter and penetrating depth. The analysis of variance of the experimental and predicted data showed that the developed models provide a fair approximation of actual experimental measurements.

The goal of this study was to investigate bending moment resistance of doweled joint with plywood members. Joint members were out of 11-ply hardwood plywood (Hornbeam، Beech and Alder) that were 19 mm in thickness. Dowels were fabricated out of Beech and Hornbeam species. Their diameters (6، 8 and 10 mm) and depths of penetration (9، 13 and 17 mm) in joint members were chosen variables in this experiment. Results have shown that bending moment resistance، increases with increase of dowel’s diameter and its penetration depth. Joints made with dowels of Beech had higher resistance than dowels of Beech ones. Highest bending moment resistance (44. 29 N. m) were observed in joint made with dowels of Beech which were 10 mm in diameter and their depth of penetration was 17 mm. Lowest bending moment resistance (12. 08 N. m) was observed in joints having Hornbeam dowels with 6 mm diameter and 9 mm penetrations

The goal of this study was to investigate effects of wood species (Beech and Fir)، number of connectors (1 and 2)، size of biscuit (10 and 20) and type of adhesives (Polyvinyl acetate (PVAc)، polyurethane (PU) and urea-formaldehyde (UF)) on bending moment resistance of joints fabricated with biscuit. Results have shown that member of joint، number of connector، size of biscuit and type of adhesive had significant effect on the bending moment resistance. Bending moment resistance of joints made of Beech wood were stronger than joints made of Fir ones. Bending moment resistance has increased، with the increase of size and number of biscuit. Performance of joints with PU adhesive had better than PVA and UF. Highest bending moment resistance were obtained from joints glued with PU adhesive، size of biscuit 20 and 2 connectors. The results also indicated that joints made with biscuit and glued with PU had higher resistance than wooden dowel joints.

Since human creation up to now، wood has been discussed as an important organic material، therefore its maintain and optimum usage is a considerable problem. From one hand، with due attention to condition of forest in Iran، using fast growing specie Paulownia provides new way in wood industries. But from other hand، this specie with low density has low strength. One of the suggested ways to increase density of this wood is its impregnation by resin and to compress it. In this research it is tried to increase the penetrability and impregnation of Paulownia by using urea formaldehyde resin at first pretreatment and then compression should be done. In order to perform this process، two variables pretreatment and compression percent were defined that each of them had two levels. The pretreatment was performed by NaCl and NaOH and 40، 50% compression. Totally، 72 samples were prepared and after producing the compressed wood، the absorption percent and mechanical properties were evaluated which included compression parallel to grain، modulus of rupture، modulus of elasticity in bending and impact strength. The results showed that the provided mechanical properties and pretreatments samples with NaCl had most values of these properties in 40 and 50% compression levels.

This research was conducted to investigate the effect of Tin oxide nanoparticles and heat treatment on decay resistance and physical properties of beech wood. Biological and physical test samples were prepared according to EN-113 and ASTM-D4446-05 standards respectively. Samples were classified into 4 groups: control، impregnation with Tin oxide nanoparticles، heat treatment and nano-heat treatment. Impregnation with Tin oxide nano at 5000ppm concentration was carried out in the cylinder according to Bethell method. Then، samples were heated at 140، 160 and 185˚C for 2 and 4 hours. According to results، decay resistance improved with increasing time and temperature of heat treatment. Least weight loss showed 46. 39% reduction in nano-heat samples treated at 180˚C for 4 hours in comparison with control at highest weight loss. Nano-heat treated samples demonstrated the maximum amount of water absorption without significant difference with control and nanoparticles treated samples. Increase in heat treatment temperature reduced water absorption so that it is revealed 47. 8% reduction in heat treated samples at 180°C for 4h after 24h immersion in water. In nano-heat treated samples at 180˚C for 2h was measured least volume swelling. Volume swelling in nano-treated samples decreased 8. 7 and 22. 76% after 2 and 24 h immersion in comparison with the control samples respectively.

Surface properties of cellulosic fibers can be modified by Layer-by-Layer (LbL) technique. Cotton fibers are one of important non-wood and industrial cellulosic resources in the world. Cotton linters is produced as a by-product accompany with cotton fibers which is used as a significant cellulosic sources in paper industry for producing durable paper. In this research، the influence of alternate adsorption of cationic chitosan and anionic Nanosilica on modification of fiber surface of cotton linter was investigated. The adsorption of materials on cellulosic fibers was analyzed via electrolyte titration. Experiments were conducted at pH≈3-4 for formation of cationic layer and pH≈9-10 for formation of anionic layer applying stirring rate of about 750rpm، for15 minute deposition time to construct 1 to 3 layers. Hand sheets of about 60 g/ m2 basis weight were made form modified pulp fibers prepared by multilayering of chitosan and nanosilica، then their structural properties and bonding ability were evaluated. Bonding ability of fibers was improved by polyelectrolyte multilayering (PEM) on the surface of cotton linter fibers which was visualized by Field Emission Scanning Electron Microscopy (FESEM). The results showed that apparent density and also bonding ability was improved in the treated fibers because of the increased electrostatic attraction between polycation and anion sites existed on the fiber surface. Apparant density of paper was improved remarkably compared to the untreated fibers. Tensile index of the sheet was increased about 16% with consecutive adsorption onto the cotton linter fibers compared to untreated fibers. Formation index of paper was slightly deteriorated after polyelectrolytes multilayering.

Large part of wooden relics is located in open air spaces under weathering exposure. Conservation of the relics has a great importance due to their cultural values. Application of linseed oil in conservation backs to centuries ago. Today، it is used as a traditional treatment of wooden relics extensively. Regarding to importance of historical wooden relics، there is a need for detail study of traditional treatments. Therefore، conservative properties of linseed oil treatment on white poplar wood (Populus alba L.) was studied under weathering exposure. Firstly، linseed oil absorption of the wood samples was measured and its leaching was evaluated according to BS EN 84:1997. Treated wood samples were artificially weathered regarding to ASTM 2565-99. After 300 and 800 hours weathering، samples were analyzed by Colorimeter، FTIR spectroscopy and Scanning electron microscopy. Results showed that linseed oil treatment has a good resistance against leaching but causes to serious aesthetical changes which were continued during weathering process. FTIR data were indicated structural degradation of treated samples after weathering. The degradation was clarified as rupture and cracks of cell walls and vessel pits in SEM images of wood surface. Results signified inappropriate effects of linseed oil for conservation of wood in open air spaces.

Furniture industry is one of the most important employment and wealth productive industries، and also one major category in developing countries. This study aimed on determining the effective indices on export development of office furniture throughout the analytical hierarchy process (AHP) and also by group decision. For this، imports and exports of office furniture were determined through visiting the custom office of Islamic Republic of Iran. By then، after initial studies، furniture industry and relevant experts were interviewed to recognize the effective indices on export development، and specified indices were categorized on six main groups and forty-eight sub-index. After receiving the comments of experts، degree of importance of indices and sub-indices determined thereby Expert Choice software. Results showed that raw material and product has been chosen among the major indices. Among the 48 influential sub-indices also product designing، guaranty and costumer services، quality control، custom tariffs، and strategic marketing had highest value-weighted priorities in export development of office furniture، respectively. Regarding to government’s policies and decisions in wood raw materials extent، monetary and banking system and marketing infrastructures، to maintain the productivity competitiveness of Iran’s furniture industry in first step، and to achieve to the export markets in second step، full cooperation of government with furniture industry is necessary provision for participating of this industry in global markets.

An experimental investigation was conducted to evaluate the effect of elevated temperatures، ranging from room temperature to 80oC، on mechanical characteristics of a commercial bagasse fiber/polypropylene composite. The test results were used to determine the temperature dependencies of the mechanical properties of the studied composite material at temperatures up to 80°C in order to develop temperature adjustment factors for the use in structural applications. The results have shown that as temperature increases، the material become more ductile due to increased plastic deformation gets lower stiffness and fails at higher strains. The resulted adjustment factors were different for each loading mode and the results also have indicated that the influence of elevated temperatures on values of modulus was higher than that on strengths.