مجله تحقیقات علوم چوب و کاغذ ایران
سال سی و هفتم شماره 2 (پیاپی 79، تابستان 1401)

This study investigated the bending and shear strength of hybrid cross-laminated timber (CLT) manufactured from beech (Fagus orientalis) and poplar (Populus deltoides) wood using experimental and finite element methods. The CLT panels were manufactured at various span to depth ratios 6, 10, 15, 20 and 25 with width of 30 cm and thickness of 2 cm in both major and minor directions. Then, the bending and shear strength of CLTs were measured using three-point bending test according to ASTM test methods. The results indicated that with the increase of span to depth ratio of the beam from 6 to 25, the averages modulus of elasticity (MOE) and modulus of rupture (MOR) values were increased in both major and minor directions. On the contrary, the averages shear modulus ( ) values of specimens in both directions were decreased.  Moreover, the results of finite elements showed that the amounts of stress distributions and their locations were different in major and minor directions of the beam. In the major direction, the surface layers were primarily contributed load-carrying capacity of CLT panels, while in the minor direction the middle layer played the most significant role for load-carrying capacity. In this research, it was resulted that specimens with span to depth ratio greater than 15 based on ASTM D198 can be used for calculating MOE and MOR of CLT panels. Furthermore, due to existence of lower difference than 10% between experimental and numerical results, modules of elasticity of CLTs were predictable according to finite element method

In this research, the effect of adding waste tire particles on physical and mechanical properties of oriented strand boards (OSB) produced from poplar wood strands was investigated. Constant factors of this research are: Poplar wood strands (Populus deltoides), phenol formaldehyde resin (8 percent for the strands and 10 percent for waste tire on dry weight basis), three layer OSB (25 percent on either top and bottom layers and 50 percent core layer), boards with a thickness of 16 mm, dimensions of 40×40 cm with a nominal density of 0.75 g/cm3.Variable factors are: mixing ratio of waste tire particles to poplar strands at the four levels of 0:100, 5:95, 10:90, 15:85 and particle size of waste tire in three different sizes of 8, 18 and 45 mesh. The physical and mechanical properties of the boards were measured as defined in relevant European standards test methods EN 300. The results showed that changes in the amount and size of waste tire particles have a significant effect on the physical and mechanical properties of OSB panels. Increasing the ratio of waste tire particles decreased the mechanical properties and inversely improved the thickness swelling of the panels. The minimum value of mechanical strength was observed in panels made of 15% waste tire particles and 45 mesh particles. In general, OSB containing waste tire particles can meet the requirements of the EN 300 standard.

In this study, the effect of walnut shell and charcoal flour on the applied characteristics of the resulting plastic composites was investigated. For this purpose, walnut shell and charcoal flour in three levels of 20, 30 and 40% were mixed with high density polyethylene using Brabender internal mixer during the melt mixing process, then standard test samples were made by injection molding method. Mechanical properties including tensile and flexural strength, tensile and flexural modulus and impact strength were measured. Physical properties including water absorption and thickness swelling after 24 hours immersion were evaluated and scanning electron microscopy images were also examined. The results showed that the flexural strength and impact strength of the wood plastic composite containing 40% walnut shell flour were higher than the samples containing 40% charcoal flour. Also, by increasing the walnut shell and charcoal flour from 20 to 30%, the flexural strength increased by 3.3% and 6.1%, respectively, and by increasing the walnut shell and charcoal flour from 20 to 40%, the flexural modulus increased by 51.9% and 63.8%, respectively. Other results of mechanical strength indicate that with increasing walnut shell charcoal from 20 to 40%, tensile strength and modulus increased to 22.9 and 109.7%, respectively, and with increasing walnut shell and charcoal flour from 20 to 40%, the impact strength decreased by 6.6 and 5.4%, respectively. The results of physical properties showed that with increasing walnut shell and charcoal flour from 20 to 40%, water absorption for 24 hours decreased by 19.2 and 8.4%, respectively, and thickness swelling by 24 hours decreased by 53.6 and 46.7%, respectively.

In this study, the mechanical properties of kenaf cement composite were investigated using different amounts of kenaf particles (mixture of kenaf core and bark and kenaf core particles). Kenaf-cement composites were manufactured at different levels (10, 15 and 20%) of different kenaf particles. Also, Portland cement and calcium chloride (as cement accelerating additive) were used in this research. Calcium chloride and water were mixed well and then kenaf particles were added to the mixture. At next stage, cement was added to the prepared mixture and all component were mixed well. Prepared mixture was molded to the wooden mold and kenaf cement composites were produced. The results obtained from mechanical evaluation of kenaf-cement composites showed the highest bending strength in 10% kenaf bark-cement composites. Also results revealed that highest modulus of elasticity of 10% kenaf core-cement products were obtained. The results of this research revealed the potential of kenaf particles as reinforcement in cement composite production.

The aim of this study was the identification and comparison of organic chemical compounds in wood and bark of hornbeam and ironwood trees. For this purpose, the samples were chosen randomly from heartwood and bark of hornbeam and ironwood trees in Nowshahr's forest region. Then, flour and ash were prepared from heartwood and bark of hornbeam and ironwood trees separately by TAPPI test methods. Then extractives were separated from wood flours by acetone and extractives residue was transferred to glass vial and BSTFA reactive agent was added. Then samples were injected to the GC/MS device for analysis. Identification of compounds was done by retention time of each compound, calculation of Quats index and Adams table. The result of GC-MS showed that there were 19 and 25 compounds in wood and bark of hornbeam tree, that Octa-methyl-Cyclotetrasiloxan and bis (2-ethylhexyl) phthalate were the important and common components in wood and bark of hornbeam. There were  66 and 18 components identified  in wood and bark of ironwood tree that decanese, tetradecanese, hexadecanese, 1,2-benzenedicarboxylic acid and bis (2-ethylhexyl)phthalate were important and common components in bark of ironwood. These compounds can be very important in durability and consumption of wood and bark of hornbeam and ironwood trees. Comparison of chromatograms showed that bis (2-ethylhexyl) phthalate exists as a common components in heartwood and bark of hornbeam and ironwood trees.

Regeneration of cellulose by direct solvent dissolution essentially involves the pretreatment of cellulose with a solvent for swelling the cellulose chains and weakening the cellulose molecules bonds. Aqueous solutions based on sodium hydroxide (NaOH) are low cost, non-volatile, non-toxic, environmentally friendly cellulosic solvent with fast dissolution power at low temperatures. The mechanism of cellulose dissolution in this solvent is not yet fully understood because there are parameters such as temperature, crystallization and degree of cellulose polymerization that affect the solubility of cellulose in the NaOH / urea system. Therefore, this study investigated the effect of kappa factor changes in chlorine dioxide bleaching on the dissolution of OCC recycled pulp on chemical compounds (lignin and hemicellulose) and the degree of polymerization. The results showed that with further reduction of lignin, the dissolution of pulp decreases and this reduction in dissolution is more severe in lignin levels below 3% (reduction from 44% to about 37% dissolution). It seems that during the bleaching process and part of lignin and hemicellulose removal, a part of cellulose with low degree of polymerization is also removed and the average polymerization of the remaining cellulose increases which is more resistant to the phenomenon of pulp dissolution. With increasing kappa factor (to 0.2 and 0.3), there was no significant change in dissolution and hemicellulose. In general, it seems that lignin and the degree of polymerization are not only the effective factors in OCC pulp dissolving and hemicellulose content also can be effective.

The purpose of this study was to identify the factors affecting the production companies in the laminate flooring industry in terms of competitiveness using nonparametric tests. The statistical population of this research includes experts and specialists in two areas of competitiveness and structure of the laminate flooring industry; managers in companies producing and importing this product and customers of laminate flooring. The sampling method was randomly classified. The Cochran formula was used to determine the sample size. In order to determine the effective indicators while studying the available sources and using the Porter model, as a basic model and after conducting the necessary studies and factor analysis, the conceptual model of the research was designed in form of three main criteria including environmental factors, intra-organizational factors and factors creating perceptual value as well as 9 sub-criteria. After conducting the necessary studies, preparing a researcher-made questionnaire and data factor analysis, the conceptual research model was designed and by conducting a field research and analyzing the results using student's t-test and Friedman test, the relationship between laminate flooring competitiveness with 3 criteria and 9 sub-criteria was examined. The reliability of the data was confirmed by Cronbach's alpha method. The mean of all studied indices was evaluated as moderate based on the results of descriptive statistics. Based on the results of the t-test, environmental factors, intra-organizational factors and factors creating perceptual value have a more than average role on competitiveness. Also, based on Friedman test, prioritization of indicators was obtained respectively based on environmental factors, factors creating perceptual value and intra-organizational factors.