جستجوی مقالات مرتبط با کلیدواژه « ویژگی های فیزیکی و مکانیکی » در نشریات گروه « جنگلداری »

The aim of this study was to compare nanolignin and ionic liquid (IL)-treated lignin as new compatibilizers in Wood-Plastic Composites (WPC). For this purpose, lignin was extracted from black liquor and modified with [Emim][OAc]. Then, the modified lignin was used as a compatibilizer in the WPC.  Nanolignin was prepared by an acidic method, and its performance was compared to that of ionic-liquid-treated lignin as a compatibilizer in the composites. Nanolignin and ionic liquid-modified lignin at the same levels (1, 3, and 5 wt%) were added to the wood flour and polypropylene mixture, and WPCs were manufactured using the hot press method. In the next step, all physical and mechanical properties of the prepared panels were analyzed using standard methods. FTIR analysis indicated that modification of lignin by an ionic liquid can change some chemical bonds and even produce new bonds.  However, the chemical structures of the virgin lignin and nanolignin were similar. The physical and mechanical properties of the prepared composites indicated that the addition of both forms of lignin significantly increased the dimensional stability, bending properties (flexural modulus and flexural strength), and impact strength of the composites. Based on the findings of this research, IL-treated lignin exhibited better physical and mechanical results as a coupling agent in wood plastic composites compared to nanolignin; thus, the composites with 5 wt% have the highest mechanical strength and dimensional stability among all lignin-containing samples.

Todays, environmental problems of synthetic adhesives such as formaldehyde emission danger for human health cause to consider bio adhesives for wood based composites production by researchers and industries. Human health problems and formaldehyde emission from wood-based composites are some of the major drawbacks of the traditional synthetic adhesives such as urea formaldehyde resins. There have been many attempts to decrease formaldehyde emission and replace urea formaldehyde resins with bio-based adhesives for wood-based composites. Recently, researchers were developed bio based adhesives for wood based product manufacturing with acceptable physical and mechanical properties. These adhesives are totally environment-friendly and they have no gas emission. In this research, feasibility of replacing soy based adhesives by urea formaldehyde resin for plywood manufacturing was investigated.

Soy flour and soy protein combined with two types of different hydrolysable tannin and condensed tannin namely chestnut tannin and mimosa tannin by 5 wt% (as cross-linker agents) to produce different soy adhesives. Some properties of soy adhesives were evaluated by thermo-mechanical analyzer and differential scanning calorimetry. The adhesives were tested dynamically by thermomechanical analysis (TMA) on a Mettler 40 apparatus. Thermal transition properties of modified and unmodified soy flour samples were measured with an INNUO DSC 500-B instrument. Also, three ply plywood specimens with Populus deltoides plies were manufactured and their mechanical strength (shear strength) and delamination properties were investigated.

The results obtained from thermo mechanical analysis showed that addition of tannins to soy based adhesives cause to decrease in their gelation time and temperature. Also, results of differential scanning calorimetry analysis showed a decrease in the denaturation temperature of soy protein by tannins addition. The results of plywood mechanical test showed an increase in the shear strength of specimens which prepared with improved-soy based adhesive by tannins as crosslinking agents. Their shear strength were evaluated higher than European standards, EN-314-2, and manufactured plywood by urea formaldehyde resin. Delamination test based on ANSI HPV- HP1 standard, also, showed the lower cyclic water resistance of all types of plywood which manufactured by soy based adhesives without crosslinking agents and, urea formaldehyde resin even indoor condition. But, addition of tannins as crosslinking agent to soy based adhesives, successfully, increased their delamination resistance for indoor and outdoor applications

Based on obtained results, soy adhesives because of acceptable physical and mechanical properties according to EN-314-2, have good potential to replace urea formaldehyde resin for plywood manufacturing.

Sizing of paperboard has a distinctive position in packaging grade paperboard material. Optimization of sizing by alum-rosin at neutral pH in 4 layered paperboard (330 g/m2) wereevaluated in this study to find the optimum ratio of alum- rosin loading in the process. fixed amount of 1% cationic dispersed rosin together with alum as a fixing agent at 5 different levels of 1, 1.5, 2, 3, and 4% (based on OD weight of pulp) were used. Water absorption of top and back layers of the sized paperboard (Cobb test) and the paperboard strength and surface properties weredetermined. According to the results performance of rosin sizing system was improved by increasing the loading of alumledand led to a decrease in water absorption at top and back layers of the paperboard. Also, regarding to the unique improving features of alum in retention, bonding ability and charge neutralization of pulp ingredients, the strength properties such as ply bond, tensile and bending stiffness were improved, too. The results revealed that strength properties of cardboard are more affected by alum and rosin consumption levels than alum to rosin ratio and the best ratio of alum-rosin at the neutral pH, revealed as 2:1.

In this study , the physical and mechanical properties of polypropylene composites reinforced with bagasse alkaline-Sulfite-Anthraquinone, Soda-Anthraqouinone, Monoethanolamine-Anthraquinone chemical pulps and mechanical pulp (CMP) known as Pulp-Plastic Compostes (PPC) were investigated and the results were compared among PPCs and with polypropylene composites reinforced with bagasse flour known as Wood-Plastic Composite (WPC) . The ratio of the matrix (polypropylene) to reinforcement agent (pulp) was 50/50. The results showed that elastic modulus, tensile strength, bending strength and impact strengths of the produced composites were influenced by the pulping processes significantly. Furthermore, the composites which contained chemical pulps had higher strength and dimensional stability as well as less water absorption than that of containing mechanical pulp. In comparison to WPCs , the water absorption and dimensional stability of PPCs decreased and increased, respectively. Generally, the results showed very superior physical and mechanical properties in pulp - plastic composites than flour bagasse- plastic composites.

Influences of temperature as well as holding time on physical and mechanical properties of Fir wood were studied in this work during the oleothermal wood modification. Wood samples were cut and treated oleothermally in the soybean oil at 200 and 230°C for the holding time of 1، 3 and 5 hours. Weights and the dimensions were measured before and after treatment. Bending strengths، water absorption and swelling، dry density and the impact load resistance (un-notched) were determined in the samples. Results revealed that the oleothermal treatment of wood had no significant effects on the density. Dimensions and the weights were reduced significantly in the treated wood. There was more reduction in the radial dimension than that of the tangential one. It means that wood was collapsed in this direction after treatment. Reductions in the water and moisture absorption as well as the swelling were determined in the samples. Bending tests revealed reduction in moduli of the elasticity and the rupture. There was no significant change in the impact load resistance of the treated samples.

The effect of fiber surface modification on physical and mechanical properties of Kraft pulp was studied with and without Chitosan. First, the amount of carboxyl groups of Kraft pulp at different addition levels (0, 2, 3, 4 and 6%) of hydrogen peroxide was determined by means of methylene blue test. Then, the samples containing the highest carboxyl groups were treated at pH=8.5 with Chitosan at 0.75% addition level (based on oven dry pulp). Results showed that individual surface modification of fibers increased the strength properties of paper. It was also indicated that alone application of Chitosan can act as a dry strength agent due to its ability to produce Hydrogen, Ionic and Covalent bonding. Also, surface modification of fibers by H2O2 lead to increase of Carboxyl groups followed by increasing anionic charge with together with Chitosan formed a dual system. The effect of Chitosan on apparent density, tensile index and burst index of Kraft paper were significant and on the tear index of paper was not significant. In the current study, the best results obtained at level of 3% hydrogen peroxide.

Fiberboard is one of the widely used wood-based panels for inside the building. In this study، the possible use of Basilit (BH3O3) or Boric acid with two concentrations levels، 3% and 5% for high density fiberboards (HDF) was investigated. Fire resistance properties including weight loss، the development of the flame height and physical and mechanical properties of the samples were determined. The results showed that the samples treated with 3 % Basilit had less weight loss than the samples treated with 5 % Basilit and control. In the case of the physical and mechanical properties، the samples treated with 3 % Basilit had lowest water absorption and thickness swelling and had the highest bending strength.

Influence of the oleothermal treatment as one of the thermal wood modification techniques on physical and mechanical properties of beech wood was studied in the current research work. For this purpose, beech wood samples were cut with sizes of 20×20×20 mm (r×t×l) to determine the physical properties and samples with sizes of 20×20×140 mm (r×t×l) to determine the mechanical properties. The samples were treated in sunflower oil at temperatures of 200, 230 and 260 °C for 30 minutes. The wood samples were soaked in water to determine the water absorption as well as the swelling properties. Bending strength as well as the impact load resistance was determined in the treated and untreated samples. Results revealed that the Oleothermal treatment of the wood reduced the water absorption as well as the swelling in beech wood, significantly. Treatment of the beech wood in sunflower oil enhanced the water repellence effect (WRE) and the anti-swelling effects (ASE). It was also revealed that mechanical properties (bending strength as well as the impact load resistance) were reduced by increase of the treatment temperature.

In this study, layering technique effect of particleboard with poplar particles on physical and mechanical properties was evaluated. To attain this purpose, surface layer particles type (poplar and industrial), resin content (8 and 10 percent) and press time (4 and 5 minutes) were selected as variable factors. The properties that were investigated consisted of Modulus of rapture, Modulus of elasticity, Shear strength and Thickness swelling in 24 hours. Results showed that using poplar particles in surface of panels significantly increased physical and mechanical properties of boards. The press time had the most particular effect on shear strength. With increasing press time, this strength was increased. In other hand, resin amount increasing in surface layer from 8 to 10 percent improved all of the properties. Finally, to obtain high physical and mechanical properties and efficiency, application of poplar particles in surface layers, using of 8% resin content and 4 minutes for press time was found as the best condition.

In order to investigate the potential of two agricultural residues (cotton and corn stalks), laboratory MDF boards were produced using fibers generated applying ten minutes steaming at 175 ºC, defibrated with 25 centimeters single disc refiner. Three press temperatures (170, 180 and 190 ºC) were used. For board pressing. Boards after conditioning at 65% RH and 21 ºC and then test samples were prepared according to relevant EN standard. All tests were performed according to relevant EN standard methods and then analyzed. The results indicate that the strength (MOR and MOE) of boards produced from corn stalks is almost 25% higher than those from cotton stalks. However no significant difference was observed for internal bonds of boards. Thickness swelling of MDF boards from corn stalks was lower than cotton stalks. Comparing the results with the strength of boards produced from beech wood showed the similarity between corn stalks and beech wood, but the strength of MDF boards from cotton stalks was lower than those produced from beech wood. Our results fulfill the minimum EN requirement.

In this research، manufacturing of fiberboard (HDF) and treated fiberboard from creosote treated solid wood was studied. Recycled fibers were generated by pretreatment of creosote treated wood chips with sodium hydroxide and fiberized under normal environmental condition. These fibers were blended with 0، 15، 30، 45 and 100 percent by weight of virgin fiber; generated from untreated wood under high vapor pressure condition. Then fiber mixtures were treated with creosote (free of high molecular weight PAH components) and creosote free runoff obtained from both fiber generation processes، to form wet fiber mats. All fiber mats were completely dried and hot pressed to produce 3mm (d: 1g/cm3) nominal thickness hardboards. Next، physical and mechanical properties of creosote treated and untreated fiberboards were evaluated. The results showed that creosote treated fiberboards had better physical properties with minor water absorption (<17%) and thickness swelling (<11%) after 24 hours submersion in water while FTIR test indicated that creosote components were not absorbed chemically by wood ingredients. On the other hand، creosote free fiberboards presented better mechanical properties so that adding only 45% of virgin fibers resulted in similar properties to those of 100% virgin fiber samples.