Comparacion de diferentes tecnicas de secado de madera aserrada de Pinus radiata D. Don en funcion de su efectividad

174 p.En el presente estudio se compararon las tecnologías de secado convencional y acelerado, evaluando su efecto sobre la calidad de las piezas de madera de Pinus radiata D.Don sometidas a estas técnicas que son ampliamente usadas hoy en día por la industria de la madera. La calidad de las piezas una vez secadas se evaluó cuantificando sus potenciales defectos como son los alabeos y grietas; y además la homogeneidad del contenido de humedad final de las piezas de madera sometidas a este proceso. La arqueadura, torcedura y contenido de humedad final respondieron de manera diferencial a ambas tecnologías existiendo una significativa interacción entre los efectos tecnología y ubicación dentro del horno de secado. En encorvadura solo se presentaron diferencias significativas a nivel de ubicación. No se observó acanaladura. En grietas superficiales y terminales no existieron diferencias significativas a nivel de tecnología ni en las distintas ubicaciones. La arqueadura en secado convencional presentó el máximo porcentaje de piezas con un 23,89% entre 2,91 y 5,60 mm y en secado acelerado fue de un 36,11% entre 2,81 y 5,60 mm. La encorvadura en secado convencional alcanzó un máximo porcentaje de piezas de 37,78% y en secado acelerado un 39,44%, ambos entre los rangos 3,51 y 5,10 mm y; 3,41 y 5,10 mm respectivamente. Para torcedura los máximos porcentajes estuvieron, para secado convencional que fue de un 23,33%, entre el rango 3,01 y 4,50 mm y para secado acelerado un 28,33% entre el rango 1,51 y 3,00 mm. Las piezas que presentaron grietas superficiales alcanzaron un porcentaje de 24,44% y para secado acelerado fue un 26,11%. En las grietas terminales este porcentaje fue de un 10,56% y un 6,67% para secado acelerado. En contenido de humedad final para secado convencional el mayor número de piezas, que fue de un 42,78%, estuvo entre un 10,20% y 11,50% y para secado acelerado el mayor porcentaje de piezas fue de un 36,11% entre el 7,7% y 9,2%

Use of agave durangensis bagasse fibers in the production of wood-based medium density fiberboard (MDF)

There is an increasing interest in using non-wood lignocellulosic materials for the production of wood-based medium density fiberboard (MDF). Agave durangensis Gentry bagasse is a waste product produced in large quantities in the mezcal industry. This study evaluated the incorporation of A. durangensis bagasse fibers (ADBF) to elaborate MDF wood-based panels. Three types of panels with different ratios (wood fibers: bagasse fibers) were investigated. The ratios evaluated were 100:0, 90:10, and 70:30. The density profiles, water absorption, and thickness swell of the panels were determined, as well as the modulus of elasticity (MOE), modulus of rupture (MOR), and internal bond (IB), according to the ASTM D1037-06a standard. The results were compared to the ANSI A208.2-2016 standard. The effect of the addition of ADBF on the properties of the panels was analyzed. Density profiles were comparable among the three types of panels, while water absorption, thickness swelling, MOE, MOR, and IB were similar between panels with ratios of 100:0 and 90:10. Panels with 10% and 30% of ADBF meet the minimum ANSI requirements for quality grade 115. It is feasible to use up to 30% of ADBF in the manufacture of wood-based MDF panels

Détermination des phénomènes de transfert dans les ébauches de fibres de bois

Dans la fabrication de panneaux de fibres, le pressage à chaud est une étape fondamentale, car elle a une haute influence sur la performance du panneau fini. La modélisation du pressage permet de prédire les principales variables qui ont un effet direct sur le développement du profil de masse volumique selon l’épaisseur pendant le pressage, soit la température, la teneur en humidité et la pression de la vapeur. L’interaction des mécanismes de transfert chaleur- masse ainsi que le changement des conditions internes de l’ébauche de fibres rend souvent leur étude complexe. Établir et bien caractériser les relations entre les propriétés physiques de l’ébauche de fibres pendant le pressage permet d’acroître la précision des prédictions faites par les modèles mathématiques. Ce projet de recherche a été consacré à l’étude des phénomènes de transfert de la chaleur et de la masse dans les ébauches de fibres de bois. Ainsi, la perméabilité au gaz, la conductivité thermique et la porosité ont été déterminées à cinq niveaux de masse volumique pour trois différentes tailles des fibres afin d’évaluer la relation entre ces propriétés et le niveau de densité locale de l’ébauche de fibres durant le pressage. En plus, l’effet de la taille des fibres sur les propriétés déjà mentionnées a été d’ailleurs évalué. La perméabilité au gaz a été déterminée à quatre niveaux de pression d’entrée : 50 kPa, 100 kPa, 150 kPa et 200 kPa sur d’échantillons conditionnés à 65% d’humidité relative et une température de 21°C. Le débit d’air à travers l’épaisseur de l’échantillon a montré de glissement moléculaire. La conductivité thermique a été mesurée par la méthode du steadystate thermal resistance, en utilisant un gradient de 1,6°C mm-1 sur d’échantillons avec une teneur en humidité de 7,6% (s=0,3). La porosité a été calculée par analyse d’image de coupes minces par la méthode du contraste de la couleur noir et blanc. Cette méthode utilise des images obtenues à partir de coupes minces extraites de panneaux de fibres fabriqués sans profil de masse volumique selon l’épaisseur. La perméabilité au gaz, la conductivité thermique et la porosité obtenues dans ce travail de recherche ont été entre 2,16 x10-13 et 5,96 x10-12 m2; 0,05 et 0,15 W m-1 K-1 et 0,44 et 0,93 respectivement, dans un intervalle de masse volumique de 198 kg m-3 et 987 kg m-3. Les résultats indiquent que la masse volumique est, en effet, une variable significative par rapport aux propriétés physiques de l’ébauche étudiées. Une chute importante de la perméabilité au gaz a été observée autour de 598 kg m-3 de masse volumique. Ceci a un impact important lors du pressage à chaud lorsque la densité locale de l’ébauche des fibres est autour de cette valeur. En outre, la taille des fibres est un facteur dominant sur la conduction de la chaleur et la structure poreuse de l’ébauche. Étant donné les résultats actuels, l’impact de la taille des fibres sur la conductivité thermique et la porosité a été significatif. Cependant, la taille des fibres n’a pas eu un effet statistiquement significatif sur la perméabilité au gaz. En conséquence, il n’y a pas eu d’éléments suffisants dans cette étude pour affirmer que la taille des fibres a un impact significatif sur la pression de la vapeur de gaz produite lors du pressage.In panel manufacturing, the hot-pressing process is a fundamental step because it has a great influence on final product quality. Hot-pressing modeling allows predicting the main variables that it has a direct effect on the development of density profile through the thickness during hot pressing, namely temperature, moisture content and vapour pressure. The study of the heat and mass transfer and mat internal conditions is complex owing to their interaction and changing conditions. Establish and characterize properly the relations between fiber mat physics properties during hot-pressing process it allows to increase the accuracy of predictions made by mathematic model. This research project was conducted in order to study the mass and heat transfer phenomena in fiber mat. Thereby the gas permeability, thermal conductivity and porosity were determined to five density levels and three different fiber sizes in order to evaluate the relationship of these properties and densification level representing the local density though the fiber mat thickness during the hot-pressing process. Furthermore, fiber size effect on these properties already mentioned has been evaluated. Gas permeability was determined to four-inlet pressure: 50 kPa, 100 kPa, 150 kPa et 200 kPa on specimens conditioned to 65% of relative humidity and 21C of temperature. During gas permeability measurements, the air flux though the disk thickness showed slip flow. Thermal conductivity was measured using a gradient of 1,6°C mm-1 on specimens with a moisture content of 7.6% (s=0,3). Mat porosity measurements were performed using the white-black color contrast method. This procedure use images taken from layers impregnated with acrylic resin, which were extracted previously from panels with homogeneous density, profile through the thickness. Gas permeability, thermal conductivity and porosity obtained in this research work were between 5.96 x10-12 and 2.16 x10-13 m2; 0.05 - 0.15 W m-1 K-1 and 0.44 - 0.93 respectively in a range of 198 kg m-3 and 987 kg m-3 of density. The results indicated that the mat density was, in fact, a significate variable in relation to the physical properties of fiber mat considered in this study. Additionally, the fiber size was a dominant factor on heat conduction and porous structure of the fiber mat. Given these results, the fiber size had anoticeable effect on both mat properties thermal conductivity and porosity. Conversely, the fiber sizes studied had no significant effect on gas permeability. Hence, there was not enough evidence to affirm that the fiber size has a significant impact on vapour pressure produced during the hot-pressing process

Gas permeability of fiberboard mats as a function of density and fiber size

Gas permeability and structure of fiberboard mats are essential properties because of their impact on mat internal gas pressure, moisture content and temperature evolution during the hot-pressing process. The objectives of this work were to determine the effect of fiber size and mat density on the intrinsic gas permeability of the mat. For the study of these mat properties, panels with a homogeneous density profile through the thickness were manufactured at five density levels (200, 400, 600, 800 and 1000 kg m−3) for three different fiber sizes. Fiber refining was performed in a disk refiner at three plate spacings. Gas permeability was measured with an in-house built apparatus. The results showed that the fiber sizes studied had no significant effect on the intrinsic permeability. This was likely due to a more significant impact of the internal porous structure of the mat compared to fiber size. Besides, the intrinsic permeability decreased significantly when the panel density increased from 198 to 810 kg m−3. This suggests that the decrease of the intrinsic gas permeability during the last seconds of press closure plays an essential role in the bulk moisture mass transfer through the fiberboard mat

Variation of internal checks related to anatomical structure and density in Eucalyptus nitens wood

The occurrence of internal checks and their relationship with anatomical structure and basic density in three clones of Eucalyptus nitens plantation trees grown in the eighth region of Chile were studied. Two trees per clone were sampled. The number, radial location, and length of internal checks were determined in samples oven-dried at temperatures increasing from 50 to 100 C. Wood anatomical features including vessel frequency and diameter and annual growth ring width were measured by image analysis. Results show that internal checks were greater for clones with lower basic density. Internal check frequency decreased with height in the tree and increased from pith to bark. A low wood basic density was related to greater ring width and vessel frequency, which contributed to the development of internal checks