Caracterización del xilema de 352 coníferas

Following the traditional methods of preparation and description of wood at microscopy level, 352 descriptions of the woods of conifers were made. For the characterisation of each wood a multiple entry key was prepared, with a total of 81 features divided into four groups: tracheids with 29 features, axial parenchyma with 8, wood rays with 37 and resin canals with 7.Siguiendo los métodos tradicionales de preparación y descripción de la madera a nivel microscópico, se han realizado 352 descripciones de maderas de coníferas. Para la caracterización de cada madera se ha elaborado una clave de múltiple entrada con un total de 81 caracteres dividida en cuatro grupos: traqueidas con 29 caracteres, parénquima axial 8, radios leñosos 37 y canales resiníferos 7

Caracterización físico-mecánica de la madera de Abies alba Miller procedente del pirineo español mediante probetas libres de defectos

This study provides up-to-date, representative values of the physical and mechanical properties of silver fir wood from the Spanish Pyrenees for comparison with other provenances and timber species. Tests were conducted with clear specimens obtained throughout the tree stem and properties were determined following the UNE standards of the corresponding tests. The wood was found to be light (ρ = 0.48 g/cm3), soft (H = 1.71 mm-1) and moderately stable (v = 39.43%). Its bending strength (MOR = 78.70 N/ mm2) is low and its compressive strength (MCS = 44.88 N/mm2) is average. Impact behaviour is average (K = 41.46 N/mm) and cleavage behaviour (C = 19.92 N/ mm) is low, as are tangential and radial tension perpendicular to the grain (1.71 and 1.68 N/mm2). The differences obtained in comparison with other provenances of this species may be the result of the location of the silver firs at the edge of their geographical distribution and thus the specific conditions of the site have a greater effect on the wood properties.El objetivo de esta investigación es proporcionar valores actualizados y representativos de las propiedades físicas y mecánicas de la madera de abeto del Pirineo español para permitir su comparación con otras procedencias y especies maderables. Los ensayos se realizaron a partir de probetas libres de defectos obtenidas a lo largo del fuste y se determinaron las propiedades de acuerdo a las normas UNE de los ensayos correspondientes. Se concluye que la madera es ligera (ρ = 0,48 g/cm3), blanda (H = 1,71 mm-1) y moderadamente nerviosa (v = 39,43%). La resistencia a flexión (MOR = 78,70 N/mm2) es baja y a compresión (MCS = 44,88 N/ mm2) media. Presenta un comportamiento al impacto medio (K = 41,46 N/mm) y bajo a hienda (C = 19,92 N/mm), tracción perpendicular tangencial y radial (1,71 y 1,68 N/mm2). Las diferencias obtenidas con respecto a otras procedencias de esta especie pueden deberse a que el abeto se encuentra en su límite de distribución geográfica y en consecuencia las condiciones específicas de sitio tienen mayor influencia en las propiedades de la madera

Histéresis de la madera de Pinus sylvestris L. para isotermas de 35 ºC mediante el método de sales saturadas

The saturated salts method was used in this study to quantify hysteresis in Pinus sylvestris L. wood, in an exercise that involved plotting the 35 ºC desorption and sorption isotherms. Nine salts were used, all of which establish stable and known relative humidity values when saturated in water The wood was kept at the relative humidity generated by each of these salts until the equilibrium moisture content (EMC) was reached, both in the water loss or desorption, and the water uptake or sorption processes. The Guggenheim method was used to fit the values obtained to the respective curves. Hysteresis was evaluated in terms of the hysteresis coefficient, for which a mean value of 0.87 was found.Con este trabajo se ha cuantificado la histéresis de la madera de Pinus sylvestris L. Para ello, se han construido las isotermas de 35 ºC de adsorción y sorción, mediante el método de las sales saturadas. Se han utilizado nueve sales que cuando se saturan en agua dan lugar a unas humedades relativas estables y conocidas. La madera fue colocada bajo las distintas humedades relativas que confieren cada una de las sales hasta que alcanzaron las distintas humedades de equilibrio higroscópico, tanto en el proceso de pérdida de agua o desorción, como en el de adquisición de agua o de sorción. Los valores obtenidos fueron ajustados a las respectivas sigmoides, haciendo uso del método de Guggenheim. La valoración de la histéresis se determinó mediante el coeficiente de histéresis, obteniendo un valor medio de 0,87

Comparison of the hygroscopic behaviour of 205-year-old and recently cut juvenile wood from Pinus sylvestris L

The hygroscopic response of the juvenile wood of Pinus sylvestris L. from recently cut trees from the Valsaín Forest in Segovia, Spain (new wood) was compared to that of the juvenile wood of the same species used in roof rafters installed at the end of the eighteenth century (old wood), which came from the same forest. The 35 ºC isotherms were plotted using the saturated salts method, and the mathematical fit used was the GAB model. The infrared spectrums and the X-ray diffractograms were used in order to study the possible chemical variations and crystallinity indices of the cell wall. The adsorption-desorption loop of the old wood is above the loop of the new wood, although the hysteresis coefficient is higher in the old wood. The peaks corresponding to the -OH groups are similar, although the degree of crystallinity is significantly lower in the old wood. While cellulose crystallinity differs between the old and new wood, and has a major influence on wood hygroscopicity, other modifications in the amorphous components of the cell wall may have contributed to the changes in hygroscopicity between the old and new wood.Comparaison du comportement hygroscopique d’un bois juvénile de Pinus sylvestris L. âgé de 205 ans avec celui d’un bois juvénile récemment coupé. La réponse hygroscopique du bois juvénile de Pinus sylvestris L. provenant d’arbres récemment coupés de la forêt de Valsaín en Segovia, Espagne (bois récent) a été comparée à celle de bois juvénile de la même espèce utilisé comme bois de charpente à la fin du xiiie siècle (vieux bois), originaire de la même forêt. Les isothermes de sorption à 35 ºC ont été obtenus par la méthode des sels saturés, et l’ajustement mathématique utilisé était le modèle GAB. La spectrographie infrarouge et la diffractométrie par rayons X- ont été utilisées pour étudier d’éventuelles différences de composition chimique et d’indices de cristallinité de la paroi cellulaire. La boucle d’adsorption-désorption du vieux bois est au-dessus de celle du bois récent, tandis que le coefficient d’hystérésis est plus élevé dans le vieux bois. Les pics correspondant aux groupes -OH sont similaires, bien que le degré de cristallinité soit significativement plus bas dans le vieux bois. Bien que ces différences de cristallinité puissent expliquer pour une bonne part le contraste hygroscopique entre bois vieux et actuel, des modifications au niveau des composés amorphes de la paroi peuvent également être invoquées

Sorption and thermodynamic properties of juvenile Pinus sylvestris L. wood after 103 years of submersion

The hygroscopicity and thermodynamic properties of juvenile Pinus sylvestris L. wood taken from the submerged piles of a bridge built in 1903 over the Jiloca River, in Spain, were compared with the corresponding values of juvenile wood of the same species from recently cut trees. The 35°C and 50°C isotherms were plotted and subsequently fitted using the Guggenheim-Anderson-Boer-Dent method, and the isosteric heat of sorption was obtained through the integration method of the Clausius-Clapeyron equation. The isotherms were compared by means of the hysteresis coefficients. Infrared spectra were recorded to study the chemical modifications, and the crystal structure of the cellulose was studied by X-ray diffractograms. The submersion in water resulted in hemicellulose degradation and a decrease in the crystallinity index and the crystallite length, accompanied by a corresponding increase in the proportion of amorphous zones. Owing to this, the equilibrium moisture contents of the water logged wood are higher than in the recent wood, both in adsorption and in desorption. In terms of the thermodynamic properties, the bond energy is higher in the recent wood than in the water logged wood. © 2008 by Walter de Gruyter