Abstract Introduction: Gmelina arborea Roxb. is planted in reforestation programs with clones to improve productivity. Objectives: We aimed to evaluate wood properties and determine the heritability of 14 clones of G. melina to establish a genetic ranking for selection. Materials and methods: The trial was established with a randomized complete block design (six blocks of six individuals of each clone of 36 months of age). Basal area and volume, tree morphological properties (diameter, bark, sapwood and heartwood) and wood physical properties (specific gravity, green density and moisture content) were estimated for each individual. Results and discussion: Growth parameters were not significantly different (P > 0.05) among the 14 clones. Clone had no significant effect on specific weight and moisture content in the genetic analysis, while tree stem height had a significant impact on all variables. The clone*height interaction was not significant for the variables studied. As for genetic control, high individual heritability values were determined only for heartwood percentage. The ranking analysis evidenced that the best clones were 1, 7, 12 and 13, positioning themselves in category 1. Conclusions: Four clones were higher regarding growth and some wood properties, showing potential for further genetic improvement of G. arborea in reforestation programs.

Resumen Introducción: Gmelina arborea Roxb. es plantada en los programas de reforestación con clones para mejorar la productividad. Objetivos: Evaluar las propiedades de la madera y determinar la heredabilidad de 14 clones de G. melina para establecer un ranking genético de selección. Materiales y métodos: El ensayo se estableció con un diseño de bloques completos al azar (seis bloques de seis individuos de cada clon de 36 meses de edad). El volumen y área basal, las propiedades morfológicas del árbol (diámetro, corteza, albura y duramen) y físicas de la madera (peso específico, densidad verde y humedad) se determinaron en cada individuo. Resultados y discusión: Los parámetros de crecimiento no variaron significativamente (P > 0.05) entre los 14 clones. En el análisis genético, el clon no tuvo efecto significativo sobre el peso específico ni el contenido de humedad, mientras que la altura del fuste del árbol sí influyó significativamente sobre todas las variables. La interacción clon*altura no fue significativa en las variables estudiadas. En cuanto al control genético, se determinaron valores altos de heredabilidad individual solo para el porcentaje de duramen. El análisis de ranking evidenció que los mejores clones fueron el 1, 7, 12 y 13, posicionándose en la categoría 1. Conclusiones: Cuatro clones fueron superiores considerando el crecimiento y algunas propiedades de la madera, los cuales presentan potencial para seguir mejorando genéticamente a G. arborea en los programas de reforestación.

Resumen Se determinaron propiedades físico-mecánicas de tableros contralaminados (CLT) de tres capas, elaborados con madera de Tectona grandis y Gmelina arborea, procedente de plantación forestal. Se usaron dos tipos de adhesivo, emulsión de polímero de isocianato (EPI) y acetato vinílico pre-catalizado modificado con 3% de nanoarcilla (PVA-na). Se aplicaron dos tratamientos para activar la superficie de adhesión: lijado e impregnación con acetona. Los resultados mostraron que, aplicando ambos adhesivos (EPI y PVA-na) y ambos tratamientos de activación superficial (lijado y acetona) el tablero CLT con T. grandis obtuvo mejor comportamiento mecánico (modulo elástico dinámico, esfuerzo cortante y compresión paralela) y de densidad que el tablero CLT con madera de G. arborea. En cuanto a la absorción de humedad y el contenido de humedad entre los tableros CLT no se obtuvo diferencia estadística significativa. Los tableros CLT construidos con ambas especies, cumplen con las propiedades mecánicas (esfuerzo cortante y compresión paralela) y de densidad que establece la norma internacional ANSI/APA PRG 320 CLT.

Abstract Physical-mechanical properties of three-layer counter-laminated boards (CLT) were determined, made with Tectona grandis and Gmelina arborea wood, from forest plantations. Two types of adhesive were used, isocyanate polymer emulsion (EPI) and pre-catalyzed vinyl acetate modified with 3% nanoclay (PVA-na). They applied two treatments to activate the adhesion surface: sanding and impregnation with acetone. The results showed that, by applying both adhesives (EPI and PVA-na) and both surface activation treatments (sanding and acetone), the CLT board with T. grandis obtained better mechanical performance (dynamic elastic modulus, shear stress, and parallel compression) and density than the CLT board with G. arborea wood. Regarding moisture absorption and moisture content between the CLT boards, no statistically significant difference was obtained. CLT boards built with both species comply with the mechanical properties (shear stress and parallel compression) and density established by the international standard ANSI / APA PRG 320 CLT.

RESUMO A madeira de Dipteryx panamensis é usada no reflorestamento na Costa Rica, tendo um programa de melhoramento genético iniciado recentemente no país. O objetivo do presente estudo foi estudar o efeito da altura do tronco das árvores na variação de casca, alburno, cerne, densidade verde (GD), densidade básica (SG) e teor de umidade na condição verde (MC-G) em uma coleção de procedências/progênies aos 8 anos de idade, plantados na vila de Florencia no município de San Carlos na região nordeste da Costa Rica. De cada uma das 17 famílias, a madeira foi investigada em três progênies e as propriedades foram avaliadas em 0, 25, 50, 75 e 100 % da altura comercial. Os resultados mostraram que o diâmetro das árvores e a espessura da casca não apresentaram valores com diferenças estatísticas nas diferentes alturas da árvore. Houve diferenças significativas em diâmetro e porcentagem de cerne e alburno entre procedências e famílias. A espessura e porcentagem de alburno, espessura e porcentagem de casca, diâmetro, porcentagem e porcentagem de excentricidade da medula não registraram diferenças significativas entre as famílias. Nas propriedades físicas da madeira, determinou-se que o SG e o MC-G apresentaram uma variação significativa entre procedências em todas as alturas das árvores. Enquanto o GD registrou diferenças ao 25 %. A variação nas propriedades físicas, especialmente a SG, entre famílias dentro de cada proveniência, mostra o potencial de seleção para melhoramento genético, com ênfase na seleção com base na parte mais basal do tronco das árvores.

ABSTRACT Dipteryx panamensis is used in reforestation in Costa Rica and a genetic improvement program has been recently started in the country. The objective of the present study was to study the effect of tree trunk height on the variation of bark, sapwood, heartwood, green density (GD), specific gravity (SG) and green moisture content in green condition (MC-G), in a collection of 8-year-old provenances/progenies planted in the town of Florencia in San Carlos in the northern region of Costa Rica The wood of each of 17 families were studied based on 3 of their progenies, evaluating the properties relative to 0, 25%, 50%, 75% and 100% of the commercial height. According to the results, tree diameter and bark thickness showed no statistical differences in their values across trunk. Significant differences were found in diameter and percentage of heartwood and sapwood between provenances and families. The thickness and percentage of sapwood, thickness and percentage of bark, diameter, pith percentage and percentage of pith eccentricity, showed no significant differences between families. SG and the MC-G presented significant variation between provenances, while GD registered differences at above 25 % commercial height. The variation of physical properties, especially SG, between families within each provenance, shows selection potential for genetic improvement, focusing particularly on the bottom section of the tree.

Abstract: Densification is one method used to modify low-density woods to make them achieve the hardness required for flooring application. The purpose of this study was to investigate the effect of thermo-mechanical densification with pre-heating in wood of Alnus acuminata, Vochysia ferruginea and Vochysia guatemalensis from, seeking to stabilize and reduce spring-back of the densified wood and evaluate its performance in flooring applications. The results showed that the wood of the three species turned dark. This is because brightness diminished and yellowness and redness increased. Weight loss due to pre-heating was statistically higher in V. ferruginea and V. guatemalensis. The final density and spring-back were statistically similar in the three species. The percentage of densification of A. acuminata and V. guatemalensis were statistically higher than for V. ferruginea and the degree of compression was statistically higher in V. guatemalensis. As for flooring evaluation, the percentage of densification, temperature and time of pre-heating affected the behavior of densified wood flooring. The low percentage of densification and high weight loss in the pre-heating stage caused greater values of wear, wear index, residual deformation, residual indentation for the falling ball indentation test, and more damages in the surface indentation test in wood of V. ferruginea.

RESUMO A pesquisa e a implementação de plantios energéticos usando espécies lenhosas de rotação curta (SRWC) estão aumentando na América Latina, especialmente para a produção de biomassa e uso na bioenergia. Para esse fim, um dos principais fatores a considerar é a avaliação de espécies. O objetivo do presente estudo foi avaliar as características de crescimento da árvore, a produção e distribuição de biomassa e as propriedades químicas, físicas e energéticas da biomassa de um plantio energético de Dipteryx panamensis de três anos de idade em SRWC em três diferentes espaçamentos (1,0x2,0 m, 1,0x0,5 m e 1,0x1,0 m) e, assim estabelecer a melhor condição de espaçamento para esta espécie tropical. Os resultados mostraram que a produção de biomassa varia entre 1,1 e 42,36 t.ha-1 e que 33-44% dessa produção está concentrada nas folhas. Aos três anos, o SRWC apresentou 50% de mortalidade com um diâmetro de 4,8 cm a 30 cm de altura do solo e com alturas totais de árvores de 5,17 a 6,98 metros. A avaliação da biomassa mostrou um valor calorífico foi de 18,9 a 19,4 MJ/kg, 1,81% de cinzas e 86% de conteúdo volátil. A densidade verde da madeira e o teor de umidade aumentaram com o aumento do espaçamento. Os espaçamentos 1,0x1,0 m e 1,0x0,5 m apresentaram o melhor comportamento em relação à produção anual de biomassa.

ABSTRACT Research and implementation of energy crops using short-rotation woody species (SRWC) are increasing in Latin America, especially for biomass production and use in bioenergy. For this purpose, one of the main factors to consider is species assessment. Therefore, the objective of the present study was to evaluate the growth characteristics, the production and distribution of biomass, and the chemical, physical, and energetic properties of the biomass of three-year-old Dipteryx panamensis plantations in SRWC in three different spacings (1.0x2.0 m, 1.0x0.5 m and 1.0x1.0 m) and establish the best spacing condition for this tropical species. The results showed that the production of biomass varies between 1.1 and 42.36 t.ha-1, and that 33-44% of the production are concentrated in the leaves. At three years, the SRWC presented 50% mortality, with a diameter of 4.8 cm at 30 cm-height from the ground, with total tree heights ranging from 5.17 to 6.98 meters. The evaluation of the biomass showed a calorific value between 18.9 and 19.4 MJ/kg, less than 1.81% of ash content and 86% of volatile content. As for the effect of the spacing, the green density of the wood and the moisture content increased with increasing spacing, while spacings of 1.0x1.0 m and 1.0x0.5 m showed the best behaviour regarding annual biomass production.

Resumen La gasificación es un proceso termoquímico en el que materias primas orgánicas se convierten en gases que contienen H2 y CO (gas de síntesis), los cuales pueden utilizarse para obtener productos como electricidad, combustibles y otras sustancias químicas. El proceso se encuentra influenciado por características propias del sistema donde se desarrolla la conversión térmica, las condiciones de operación y las materias primas empleadas. Se simuló un proceso de gasificación de biomasas enriquecidas con hidrocarburos en el que los gases generados son aprovechados para generación eléctrica, con tal de evaluar el uso de dichas materias primas. Se empleó un modelo de gasificación no estequiométrico, la ecuación de estado de Peng-Robinson, así como reacciones de gasificación conocidas. Se consideró un gasificador de corriente descendente trabajando con 22 kg/h de alimentación de mezcla 3:1 biomasa:hidrocarburos, 20 kg/h de aire (agente gasificante), 1 atm de presión absoluta y temperatura de gasificación de 900-1000°C. Los gases generados se componen de 27,44 % H2; 39,79 % CO; 5,73 % CH4; 0,1 % CO2 y 27,01 % N2. La potencia neta del gasificador es 27,82 kW y el consumo de la mezcla 3:1 biomasa:hidrocarburos 0,79 kg/kWh. La adición de hidrocarburos a biomasa mejora las características del gas de síntesis obtenido y disminuye los requerimientos de materia prima para el funcionamiento del gasificador. La mezcla 3:1 biomasa:hidrocarburos es adecuada para el desempeño del proceso, permitiendo aprovechar residuos que de otra manera tendrían que ser dispuestos y tratados, generando beneficios energéticos, ambientales y económicos.

Abstract Gasification is a thermochemical process in which organic raw materials are converted into gases containing H2 and CO (syngas), which can be used to obtain products such as electricity, fuels and other chemicals. It is influenced by characteristics of the system where the thermal conversion takes place, the operating conditions and the raw materials used. It was simulated a process of gasification of hydrocarbons-enriched biomass in which the gases generated are used for electricity generation, to evaluate the use of such raw materials. A non-stoichiometric gasification model, the Peng-Robinson equation of state as well as known gasification reactions were used. A downdraft gasifier was considered working with 22 kg/h of mix feed 3:1 biomass: hydrocarbons, 20 kg/h of air (gasifying agent), 1 atm of absolute pressure and gasification temperature of 900-1000 °C. The gases generated are composed of 27.44 % H2, 39.79 % CO, 5.73 % CH4, 0.1 % CO2 and 27.01 % N2. The net power of the gasifier is 27.82 kW and the consumption of the mixture 3:1 biomass:hydrocarbons 0.79 kg/kWh. The addition of hydrocarbons to biomass improves the characteristics of the syngas obtained and reduces the raw material requirements for the operation of the gasifier. The mixture 3:1 biomass:hydrocarbons is adequate for the performance of the process, allowing to take advantage of wastes that otherwise would have to be disposed of and treated, generating energy, environmental and economic benefits.

Resumen El conocimiento de las propiedades de la biomasa proveniente de clones de Gmelina arborea Roxb en cultivos energéticos en sistemas de corta rotación (SRC en inglés) en Costa Rica es limitado. Los primeros intentos están basados en el uso de clones para la producción de madera, pero plantados en SRC. Así, el presente estudio tuvo como objetivo evaluar las propiedades físicas (peso específico, densidad y contenido de humedad), energéticas (poder calorífico, contenido de cenizas y materiales volátiles) y contenido de carbón de dos clones de G. arborea utilizados para la producción de madera, pero plantados en SRC bajo tres espaciamientos (1,0x1,0 m, 0,75x0,75 m y 1,0x0,5 m), entre 6 y 24 meses de edad. Los resultados muestran que el peso específico básico fue de entre 0,30 a 0,38, la densidad verde de 0,9 a 1,0 g/cm3, el contenido de humedad entre 40 y 70%, el poder calorífico de 18.000 a 20.000 kJ/kg, la cantidad de cenizas fue menor a 4,8% y el contenido de volátiles de entre un 70 a 86%, mientras que el contenido de carbono disminuyo con la edad. Se observaron diferencias entre los dos clones en edades tempranas, pero estás tienden a desaparecer con el aumento de la edad, en especial a la edad de 24 meses, que es cuando se pretende que la plantación sea cosechada, siendo esto una ventaja ya que se tiene una biomasa uniforme si los dos clones son utilizados.

Abstract The knowledge of biomass properties from Gmelina arborea clones Roxb in energy crops in short rotation crops systems (SRC) in Costa Rica is limited. The first attempts are based on the use of clones for the production of wood, but planted in SRC. Thus, the present study aimed to evaluate the physical properties (specific gravity, density and moisture content), energy (net calorific value, ash content and volatile materials) and carbon content of two clones of G. arborea used for wood production, but planted in SRC under three spacings (1.0x1.0 m, 0.75x0.75 m and 1.0x0.5 m), between 6 and 24 months of age. Results show that the basic specific gravity was between 0.30 to 0.38, the green density of 0.9 to 1.0 g/cm3, the moisture content between 40 and 70 %, the net caloric value of 18,000 a 20,000 kJ/kg, ash content was less than 4.8 % and the volatile content between 70 and 86%, while the carbon content decreased with age. Differences were observed between the two clones at early ages, but they tend to disappear with increasing age, especially at the age of 24 months, which is when the plantation is intended to be harvested, this being an advantage since we have a uniform biomass if the two clones are used.

Resumen En construcción de viviendas, las estructuras más eficientes para soportar las cargas provenientes de techumbres corresponden a las cerchas. Cuando se trata de fabricarlas con madera, un punto importante de estas son las uniones. Actualmente se ha introducido la utilización de placas metálicas dentadas para estas uniones, sin embargo, el mercado aún conoce poco de ellas y su posibilidad de utilización en casas. Por lo que, este estudio reporta un primer sondeo cualitativo por medio de una encuesta estratificada por público objetivo, del uso de cerchas de madera con placas metálicas dentadas fabricadas con madera de plantación en Costa Rica. Fue encontrado que el 100 % de los encuestados considera a la madera como un material viable para la construcción, por almacenar dióxido de carbono y ser un recurso renovable. Además, el 90 % de los encuestados, considera que la madera de las plantaciones nacionales es de buena calidad. Sin embargo, sólo un 28 % prefiere la utilización de las cerchas como elemento estructural en techumbres y el 40 % coincide en que el uso de la placa es una buena opción tecnológica. Según este primer sondeo de mercado de la cercha de madera con placa metálica, el 80 % de encuestados estaría dispuesto a adquirirla; dándole un rango de precio entre ¢45 000 a ¢50 000 por cercha.

Abstract In housing construction, the most efficient structures to support the loads coming from roofs correspond to the trusses. When it comes to manufacturing them with wood, an important point of these are the joints. Currently the use of metal plates has been introduced for these unions, however, the market still knows little about them and its possibility of use in wooden houses. Therefore, this study reports a first qualitative survey by means of a survey stratified of the use of wooden trusses with metal plates fabricated with plantation wood in Costa Rica. It was found that 100 % of respondents consider wood as a viable material for construction, for storing carbon dioxide and for being a renewable resource. In addition, most consider that the wood from trees growing in plantations in Costa Rica is of good quality. However, only 28 % prefer the use of trusses as a structural element in roofs and 40 % agree that the use of the metal plate is a good technological option. According to this first market survey of the wooden truss with metal plate, 80 % of respondents would be willing to acquire it; giving it a price rango between ¢ 45 000 to ¢ 50 000 per truss.

ABSTRACT In countries like Costa Rica, there is an interest in developing wooden trusses in a versatile and light way. However, there is a key aspect in the behavior of truss connections in this product. Therefore, the present study determines the structural behavior of the truss connections and the displacement, the resistance, the stiffness values and the failure mode of truss connections made with Gmelina arborea and Tectona grandis timber for angles of 0° and 90°; and three types of truss connectors (metal plates, screws and nails), subject to tension and compression loads. The results showed that metal plates show the highest load values with respect to the nails and screws in both species. Likewise, in the design and critical displacement stress, metal plates surpass the nails and screws in both species; and in the two angles. From these stress values, we proposed a model for the prediction of the stiffness for the truss connections of the intermediate angles (30°, 45° and 60°) and the test showed that the prediction was low, the bias was 3%.

Abstract A composite between particles obtained residual pallets of Pinus sp and cement was manufactured. Also, three methods were performance for wood particles: hot water washed, unwashed and unwashed with calcium carbonate (CaCO3). Different concrete-wood particle ratios were tested. Curing time was evaluated with ultrasonic pulse velocity (USV) and density of composites. Water absorption, module of rupture (MOR) in flexion, abrasion strength and resistance to decay by fungi attack were too determined. Results showed that using USV and density, curing occurs within 8 days. Moisture absorption ranges15 and 22% and decreases with decreasing of the amount of particles. MOR ranged from 0.40 a 1.23 MPa and the blocks with unwashed wooden particles and with CaCO3 addition had the greatest significant differences. In abrasion strength, blocks with unwashed wooden particles reported the best results. Finally, it was concluded that mixture with proportion of 60:40 (concrete:wood) and CaCO3 had the best performance and were not attacked by fungi decay.

Resumen Fue fabricado un compuesto de partículas de Pinus sp proveniente de tarimas y 3 métodos fueron practicados en las partículas: lavado con agua caliente, sin lavar y sin lavar con adición de carbonato de calcio. Diferentes proporciones de cemento-maderas fueron probadas. El endurecimiento fue evaluado por la velocidad de pulso ultrasónico (VPU) y la densidad. Así mismo fue evaluado la absorción de agua, módulo de ruptura (MOR) en flexión, resistencia a la abrasión y resistencia al ataque de hongos de pudrición. Los resultados mostraron que utilizando VPU y densidad, el endurecimiento ocurre a los 8 días. La absorción de humedad fluctúa entre 15 y 22% y disminuye con la disminución de la cantidad de partículas de madera. El MR varió de 0,40 a 1,23 MPa y los adoquines con partículas de madera sin lavar y agregado cal presentaron las mayores diferencias significativas. En la resistencia a la abrasión, los adoquines con partículas de madera sin lavar reportan los mejores resultados. Finalmente se concluyó que la mezcla con proporciones de 60:40 (concreto: madera) y agregando cal presenta el mejor comportamiento y no son atacados por los hongos de pudrición.

Resumen En un proceso de gasificación la geometría de la biomasa es un factor necesario que considerar. El tamaño, forma y densidad de las partículas del biocombustible influyen en el transporte de las especies del sistema de reacción, velocidades de secado y descomposición térmica; los cuales son factores relacionados al desempeño general del proceso. Este trabajo evaluó las diferencias significativas que existen en el rendimiento y eficiencia del sistema de generación de energía eléctrica y térmica por la incidencia de dos geometrías en la biomasa de alimentación (pellets y astillas de madera), en el desempeño de un gasificador tipo “downdraft”. El perfil de temperatura de la zona de pirólisis fue en promedio (147 ± 15) °C mayor al utilizar astillas como alimentación en comparación con el uso de pellets. La caída de presión dentro del reactor fue menor en promedio, así como su variabilidad en el sistema, al utilizar astillas como alimentación; esto a pesar de que el poder calorífico del gas de síntesis obtenido fue levemente mayor para pellets (8,00 MJ/Nm3) que con respecto al obtenido con astillas (6,18 MJ/Nm3). Se obtuvo una Eficiencia de Gas Frío, así como la Eficiencia Térmica Global mayor al utilizar astillas de madera. La capacidad de aprovechamiento de la energía del syngas para producir potencia eléctrica, medido como la Eficiencia del Motor/Generador, estuvo dentro de los valores típicos para este sistema de conversión, y fue de (21,41 ± 3,23) % para astillas y (18,94 ± 3,68) % para pellets. Se obtuvo 564,50 kWh/t de rendimiento de proceso en términos eléctricos al emplear astillas, el cual fue mayor que al utilizar pellets (487,35 kWh/t), esto a una potencia de 6,2 kW. Con respecto al rendimiento de producción de gas de síntesis, con pellets fue menor con respecto a las astillas de madera (i.e. en promedio se produjo 1,75 kg de gas de síntesis por kilogramo de astillas, lo que significa un 25 % más que con pellets de madera). En conclusión, a pesar de que el manejo de astillas de maderas requiere ciertos cuidados para evitar el atascamiento dentro del sistema de conversión “downdraft” para producir gas combustible, en general las ventajas en proceso y eficiencias son mayores al utilizar madera en forma de astillas en comparación con pellets.

Abstract The size, geometry, density and mechanical properties of the biofuel particles are important factors in the performance of any biomass gasification process. They influence the mass transfer rates of the reacting species just as the drying and the thermal decomposition rates in the rest of the system. This work evaluates the significant differences between two different feedstocks, wood pellets and woodchips, on the performance and efficiency of a pilot scale “downdraft” gasifier unit with a combined heat and power system. When using woodchips as feedstock, on average, the temperature profile of the pyrolysis zone was 147 ± 15 °C higher, while the pressure drop inside the reactor and its variability were lower. The Cold Gas Efficiency and Global Thermal Efficiency of the system were higher as well with the woodchips as feedstock, despite the fact that the calorific value of the synthesis gas produced from the wood pellets was 8.00 MJ/Nm3 and the one obtained from the woodchips was slightly lower at 6.18 MJ/Nm3. At a power generation of 6.2 kW, the syngas and electrical energy yields, were also higher on average for the woodchips at 1.75 kg/kg and 564.50 kWh/t, compared to the wood pellets as feedstock at 1.40 kg/kg and 487.35 kWh/t respectively. The relationship between the electrical energy yield and the calorific value of the syngas flow was stablished by means of the Motor/Generator Efficiency, and it was within typical range for this type conversion systems, at 21.41 ± 3.23 % for the woodchips and 18.94 ± 3.68 % for wood pellets. In conclusion, even though the transport of the woodchips within system is more prone to clogging, the higher efficiency and better overall process performance obtained when using woodchips, makes it the preferred feedstock for the system compared to the wood pellets.

Resumen Se analizó el sistema de clasificación visual de la madera por defectos admisibles estructurales en Costa Rica. Se propuso incluir en la norma INTECO 06-07-03:2011 de Costa Rica un cuadro de evaluación visual de la madera aserrada por tres grados estructurales, según defectos admisibles. Se muestra su aplicabilidad en madera aserrada de Cupressuss lusitanica y Alnus acuminata y se compara la clasificación con los valores reales de módulo de elasticidad en flexión para los diferentes grados estructurales 1, 2 y 3. Se encontró que con la adición de los nuevos parámetros en la norma se puede tener una clasificación estructural próxima a los valores reales de módulo de elasticidad de la pieza de madera.

Abstract The system of visual classification of wood was analyzed by admissible structural defects in Costa Rica. It was proposed to include in the INTECO standard 06-07-03: 2011 of Costa Rica a visual evaluation table of the sawn wood by three structural grades, according to admissible defects. Its applicability in Cupressuss lusitanica and Alnus acuminata sawn wood, is shown and the classification is compared with the real values of lumber modulus of elasticity for the different structural grades 1, 2 and 3. It was found that with the addition of the new parameters in the standard a structural classification is obtained close to the real values of lumber modulus of elasticity.

Abstract: Physical and mechanical properties were evaluated on cross-laminated panels (plywood) fabricated with three plantation species (Cordia alliodora, Gmelina arborea and Vochysia ferruginea) from tropical climates in Costa Rica. The panels were glued with urea-formaldehyde resin modified with nanoclay at four concentrations (0,75; 1,00; 1,50 and 2,00 %) and unmodified resin. It was determined that addition of nanoclay to urea-formaldehyde adhesive positively decreased moisture absorption and swelling of the plywood panel with statistical significance. However, nano-modification did not have a significant effect on the density and specific weight of plywood. Nano-modification of urea-formaldehyde resin with nanoclay at 0,75 % improved the Module of rupture and Modulus of elasticity in flexure parallel to surface in the three species, also increasing mechanical resistance to strains in parallel tension, shear and compression. By means of electronic microscopy, it was evidenced that the nano-modified adhesive became diffused at the inside of the cellular structure of wood in a better way, allowing for the generation of a transition zone that increased the mechanical properties at the macro level. According to the properties evaluated, it was determined that 0,75 % is the optimal percentage to use of nanoclay on urea-formaldehyde resin.

Abstract This study evaluated the properties of juvenile wood from 7-year-old Cedrela odorata trees in two populations with the same provenance and planted in an agroforestry system with Theobroma cacao (cacao). The morphological characteristics (diameter at breast height; heartwood, sapwood, bark, and pith percentages; and eccentricity of pith), physical properties (shrinkage, green moisture content, green density, and specific gravity) and mechanical properties (modulus of rupture (MOR) and modulus of elasticity (MOE) in bending, compression stress, Janka hardness, tension stress and shear stress) were determined between two populations. The variation of the physical properties and morphological characteristics at different tree heights was also evaluated. The results showed that there were differences in both populations in terms of bark, pith, volumetric shrinkage, green moisture content, green density, MOR and MOE in bending, longitudinal compression and perpendicular tension. The results showed that population 2 presents better characteristics of growth and quality of wood for structural and furniture uses; hence, this population planted in agroforestry systems has good plantation conditions and wood quality.

Resumen En este estudio se evaluaron las propiedades de la madera juvenil proveniente de árboles de 7 años de Cedrela odorata de dos poblaciones con la misma procedencia, plantadas en un sistema agroforestal con Theobroma cacao (cacao). Se evaluaron las características morfológicas del árbol (diámetro a la altura del pecho, porcentaje de médula, duramen, albura y corteza en relación al área total y excentricidad de la médula), las propiedades físicas (contracciones y contenido de humedad, la densidad verde y el peso específico básico) y las propiedades mecánicas (módulos de ruptura (MOR) y de elasticidad (MOE). De estas últimas, se obtuvieron esfuerzos en compresión longitudinal, tensión paralela y perpendicular, cortante y la dureza. Los resultados mostraron diferencias en las dos poblaciones en porcentajes de corteza, médula, contracción volumétrica, contenido de humedad, densidad verde, MOR y MOE en flexión, así como en la resistencia en compresión longitudinal y tensión perpendicular. Los resultados muestran que la población 2 presenta mejores características de crecimiento y de calidad de la madera, por lo que la población plantada en sistemas agroforestales presenta buenas condiciones de desarrollo y de calidad de madera para su uso estructural o en mueblería.

Abstract Torrefaction and pelletizing were studied in the generation of energy from lignocellulosic residues to increase the energy properties of the biomass. The aim of this study was torrefied sawdust from Gmelina arborea and Dipteryx panamensis at 200 °C in three time period: 0, 15 and 20 minutes. Then with the biomass, pellets of 6 mm diameter were manufactured and their physical properties, calorific value, density and compression force were evaluated. Both species had similar physical characteristics according to the average diameter (0.50 mm), length (21.50 mm), and water absorption rate (6.00 %). The calorific value increased from 9,749 kJ•kg-1 in un-terrified biomass to 18,126 kJ•kg-1 with torrefied biomass. The pellets from D. panamesis had greater density and compression force compared to G. arborea biomass. Based on the results, pellet compression force decreases as the torrefaction time increases. There is positive correlation between bulk density of pellets and compression force. The D. panamensis species has better torrefaction behavior and pelletizing than the wood of G. arborea.

Resumen La torrefacción y peletización se han estudiado en la generación de calor a partir de residuos lignocelulósicos, para incrementar las propiedades energéticas del material. El objetivo del presente trabajo fue torrefaccionar aserrín de Gmelina arborea y Dipteryx panamensis a 200 °C en tres tiempos: 0, 15 y 20 minutos. Con las biomasas obtenidas se fabricaron pellets de 6 mm de diámetro y se evaluaron sus propiedades físicas, el poder calórico, la densidad y la propiedad mecánica de resistencia a la compresión. Ambas especies presentaron características físicas similares con respecto al diámetro (0.50 mm), longitud (21.50 mm) y porcentaje de absorción de agua (6.00 %). El poder calórico aumentó de 9,749 kJ•kg-1 en la biomasa sin torrefaccionar a 18,126 kJ•kg-1 en la biomasa torrefaccionada. Los pellets de D. panamesis presentaron mayor densidad y resistencia a la compresión que los de G. arborea. Con base en los resultados, la resistencia a la compresión del pellet disminuye cuando el tiempo de torrefacción aumenta. Existe correlación positiva entre la densidad de los pellets y la resistencia a la compresión. La especie D. panamensis presenta mejor comportamiento a la torrefacción y peletización que la madera de G. arborea.