Sistema Regional de Información
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In the classical approach, cutting forces and cutting power in sawing processes of orthotropic materials such as wood are generally calculated on the basis of the specific cutting resistance kc (cutting force per unit area of cut). For every type of sawing kinematics (frame saws, band saws and circular sawing machines) different empirical values of specific cutting resistance kc have to be applied. It should be emphasised that sources in the scientific literature and handbooks do not provide any information about wood provenance, nor about cutting conditions in which cutting resistance had been determined. In analyses of sawing processes in which the offcut is formed by shear, Atkins’s ideas that all cutting forms a branch of elastoplastic fracture mechanics can be applied. Thanks to this modern approach it was possible to reveal, using experimental results data of fracture toughness and shear yield stresses of Polish pine (Pinus sylvestris), the significant effect of the raw material provenance (source of wood) on cutting power. In the common model for circular sawing machine kinematics, which is similar to metal milling, the sum of all uncut chip thicknesses of the all the teeth simultaneously engaged represented the mean uncut chip thickness. In this work predictions of the newly-developed model for the circular sawing machine are presented. In the model, beside uncut chip thicknesses changes, appropriate changes in shear yield stress and toughness with tooth/grain orientation have been taken into account. The conducted analyses have demonstrated that values of RMS of cutting power obtained with the new developed model are slightly larger than experimental values. On the other hand computed values of cutting power with the use of the mean uncut chip thicknesses in the model are a bit lower from the empirical one.

In the previous years, black locust wood (Robinia pseudoacacia) has been participating in the European subsidizing programme of tree species cultivation, aiming in the establishing of new plantations in many European countries, therefore large quantities of this species is going to be harvested in the forthcoming years and the examination of its properties would be very crucial for future utilization. In the present research, the bondability of black locust wood is examined using two different adhesives, Polyvinyl acetate and Polyurethane and two different pressure levels. Beech wood is also included in the research for comparative reasons. According to the results, the shear bond strength of black locust wood was found to be satisfying, especially in the presence of Polyvinyl acetate adhesive and the less intensive pressure used during the specimens’ construction, although it was found lower compared to beech wood, referring both to Polyvinyl acetate and Polyurethane adhesive.

Furniture is the general name given for the portable equipment used in various human activities such as seating, working and relaxing. They can be a product of design and is considered a form of decorative art. They can widely be manufactured with different adhesives. Biodegradable and biobased adhesives which have no toxic compounds and non-dangerous elements have been selected since the furniture is generally benefited in interior locations. Meanwhile, polyvinyl acetate (PVAc) is a thermoplastic polymer which is widely used in the furniture industry. In this study, tension and bending strength of the furniture joints bonded with polyvinyl acetate adhesives filled with nano-TiO2 and nano-SiO2 were investigated. Three materials; oak (Quercus robur) wood, beech (Fagus orientalis) wood and plywood made with beech veneers were selected, and the joints were prepared by mortise and tenon joints. The results showed that the maximum value for the tension strength and bending strength were obtained to beech wood and oak wood in 2% addition of nano-SiO2 fillers. The minimum values for the tension and bending strength nano-SiO2 were found to plywood and 4% loading.

Effects of tensile and compression loading on the overall strength of two miter frame corner joints, namely V-nail and dovetail joints, with and without adhesive were studied for medium-density fiberboard and particleboard. Two sizes of V-nails were chosen, sizes 7 and 10. Tensile and compression load-carrying capacity values were measured on the internal and external corners of the joints. Results showed that both wood-composites had greater load-carrying capacities for compression stress in comparison to tensile stress. Medium-density fiberboard demonstrated higher strength compared to particleboard specimens because of its higher compactness of fibers and more integrity in the composite matrix. Application of adhesive resulted in a significant increase in the strength of all joints and both composites. The increase in medium-density fiberboard was significantly higher in comparison to particleboard because lower permeability in medium-density fiberboard did not let adhesive to be uselessly penetrated into the texture. In particleboard specimens, however, adhesive penetrated into the voids and spaces in the composite, and the adhesive line was weakened between the surfaces of the composite bodies. It was concluded that V-nails are recommended for craftsmen in case adhesive is used. However, dovetail joints provide higher strength if the production process necessitates not to use adhesive in joints.

In this study, wood polymer composites were manufactured using insect damaged Eastern Black Sea Fir (A. Nordmanniana) wood as filler. The effects of wood type (sound vs insect damaged) and presence of coupling agent (0% vs 3%) on the flexural, tensile, impact, thermal and morphological properties of the wood polymer composites were investigated. The mechanical property values of the wood polymer composites specimens decreased when insect damaged wood was used as filler than sound wood, except for the impact strength values. Flexural, tensile and impact strength values, insect damaged wood filled with coupling agent composites provided higher values compared to sound wood filled without coupling agent composites. However, addition of maleic anhydride-graftedpolyethylene coupling agent into polymeric matrix improved both sound and insect damaged filled composite properties. Thermogravimetric analysis analysis showed two main decomposition peaks for polymer composites. Compared to unfilled high-density polyethylene, addition of both sound and insect damaged wood reduced decomposition peak but increased the residue due to the charring of the wood. The results of differential scanning calorimeter analysis showed that addition of sound or insect damaged wood in polymer matrix increase the crystallinity compared the unfilled high-density polyethylene due to the nucleating effect of the filler. Among the composite maleic anhydride-graftedpolyethylene modified composites provided higher crystallinity than unmodified ones.

This paper presents a modeling of an instrumental indirect solar wood dryer less expensive functioning in a Cameroonian climate applied to the climate of Yaoundé. The dryer is easy to build and electric energy is only used for the fan. Applications are done on Iroko wood (Chlorophora excelsa), a tropical wood 50mm thick most utilized in Africa. A satisfactory agreement between experimental and numerical results was found. Influences of thickness, wood initial water content and airflow rate were studied.

In this work Eucalyptus grandis and Dipteryx odorata were submitted to photodegradation by ultraviolet radiation. The effect of ultraviolet radiation irradiation on the color change and chemical composition of each wood flour were evaluated. The samples were submitted to a total of 500h of artificial weathering using condensation stages and ultraviolet radiation B irradiation cycles. The changes in wood flour color were monitored by spectrocolorimetry, while the changes in wood chemical composition were evaluated by Fourier transform infrared spectroscopy. Both species showed changes in color with increased exposure time to artificial weathering. For both wood species the variation in color change was considered very appreciable after 500h. The Eucalyptus grandis specie showed appreciable color change after 120h, while for Dipteryx odorata specie the color change is appreciable only after 240h. The Fourier transform infrared spectroscopy results showed that lignin was strongly degrades by ultraviolet radiation radiation in both species. However, Dipteryx odorata was more resistant to photodegradation than Eucalyptus grandis, probably due to lower lignin content in this wood. The results clearly indicated that for the wood species studied the rate of weathering is influenced by wood species.

A method to estimate the surface moisture content below the fibre saturation point that is a function of the surface temperature, wet- and dry bulb temperatures, equilibrium moisture content, and fibre saturation point was evaluated. The method is based on the premise that the surface temperature is solely influenced by the surface moisture content and the climate that the surface is exposed to. The prediction model contends that the surface moisture content is equal to the fibre saturation point when the surface temperature is equal to the wet bulb temperature, and equal to the equilibrium moisture content when the surface temperature is equal to the dry bulb temperature, with a linear interpolation between those two points. The model thus predicts that the average moisture content of a thin piece of veneer can be predicted with fairly good accuracy. Also, when drying boards in a fast changing climate, e.g. fan reversals in industrial kilns, the surface temperature and surface moisture content should change as abruptly as the climate does. Additionally, the surface moisture content should correlate to the known drying phases, with a consistently high surface moisture content during the capillary phase when the wet line is close to the surface, and a quickly decreasing surface moisture content when the wet line moves into the wood during the transition to the diffusion phase. The prediction model was tested in these three scenarios and the results suggest that the basic premise is reasonable, and that the method is useful for surface moisture content estimation.

The thermal behavior of lignins from softwood and hardwood species has been investigated using thermogravimetry and differential scanning calorimetry. Klason Lignin from Pinus taeda and Klason lignin from Eucalyptus grandis were studied. The differential scanning calorimetry results showed that both Klason lignins studied presented similar glass transition temperature. Thermogravimetric results showed that the lignin degradation occurs in three stages. The Klason lignin of Pinus taeda is more thermally stable than Eucalyptus grandis, probably because of the higher thermal stability of the guaiacyl units in softwood lignin. The degradation of both lignins initiate by a diffusion process. However when the conversion values are higher than 0,1 the lignin degradation mechanism is a complex procedure and involves the degradation of a highly condensed aromatic structure formed at the previous degradation stages.

El Gynerium sagittatum es una gramínea que presenta gran adaptabilidad ecológica lo cual la hace una fuente lignocelulósica ideal para la fabricación de tableros aglomerados sin aditivos sintéticos. Se evalúa el efecto de la presión de prensado y de la adición de lignina kraft purificada sobre las propiedades fisicomecánicas de tableros de fibras de Gynerium sagittatum de alta densidad. La materia prima es pretratada en un reactor de steam explosion a severidad 4,1 y la temperatura de prensado se fija en 217°C. Se varia la presión de prensado entre 2 y 15 MPa. Se determina que la presión de prensado más apropiada para obtener tableros de buena calidad es 2 MPa obteniendo valores para el módulo de elasticidad de 6000 MPa, módulo de ruptura de 47 MPa, enlace interno de 1,50 MPa, absorción de agua durante 24 horas de 25% e hinchamiento en espesor durante 24 horas del 15%. Partiendo de estas condiciones de operación, se evalúa la inclusión de lignina entre 0 y 30%. Se determina que el aumento de lignina no afecta significativamente el desempeño mecánico de los tableros, pero sí su estabilidad dimensional, dando como resultado una absorción de agua durante 24 horas de 19% e hinchamiento en espesor durante 24 horas del 8,5%, a un valor óptimo de 20% de inclusión de lignina. Gynerium sagittatum is a grass that has great ecological adaptability, which makes it an ideal lignocellulosic source for the manufacture of fiberboards. The effects of pressing pressure and the addition of kraft lignin on the physicomechanical properties of high density fiberboards of Gynerium sagittatum are evaluated. The raw material is pretreated in a steam explosion reactor at severity 4,1. The pressing temperature is set at 217°C. The pressing pressure is varied between 2 and 15 MPa. The most appropriate pressing pressure to obtain a good quality boards is 2 MPa. The values of properties at optimal conditions are: modulus of elasticity 6000 MPa, modulus of rupture 47 MPa, internal bond 1,50 MPa 24 h water absorption 25% and 24 h thickness swelling 15%. Based on these operating conditions, the inclusion of lignin between 0 and 30% is evaluated. The addition of lignin does not significantly affect the mechanical performance of the fiberboards but improve its dimensional stability. The obtained values for 24 h water absorption and 24 h thickness swelling are 19% and 8,5% respectively, at a 20% of lignin addition.   PDF XML