Jan Baar

The analysis of tropical wood discoloration caused by simulated sunlight

This study investigated the wood surface discoloration due to simulated sunlight of tropical woods native to South America. Wood of jatoba (Hymenaea courbaril L.), massaranduba (Manilkara bidentata A. Chev.), tigerwood (Astronium graveolens Jacq.), angelim amargoso (Vatairea spp.), angelim pedra (Hymenolobium spp.) and angelim vermellho (Dinizia excelsa Ducke) was exposed to a treatment by xenon-arc lamp light simulating outdoor sunlight, for 144 hours. Colour measurement of exposed and non-exposed areas of samples was performed by means of a spectrophotometer measuring in CIEL∗a∗b∗ colour system. The resulting wood discoloration was evaluated according to the value of the overall colour change ΔE∗. Changes of particular parameters (L∗,a∗ and b∗) were also observed during exposure. The wood surface darkened rapidly during the first hours of exposure to simulated sunlight. Later, samples showed only a slight increase in lightness. Within one wood species the colour changes were more significant (higher ΔE∗) for lighter samples.ZusammenfassungIn dieser Studie wurde die Verfärbung von Holzoberflächen aufgrund von simulierter Sonneneinstrahlung an den in Südamerika beheimateten tropischen Holzarten Jatoba (Hymenaea courbaril L.), Massaranduba (Manilkara bidentata A. Chev.), Tigerwood (Astronium graveolens Jacq.), Angelim amargoso (Vatairea spp.), Angelim pedra (Hymenolobium spp.) und Angelim vermellho (Dinizia excelsa Ducke) untersucht. Dabei wurden diese über eine Dauer von 144 Stunden mit einer Xenonlampe bestrahlt. Mit einem Spektralphotometer wurden Farbmessungen an bestrahlten und nicht bestrahlten Probenflächen unter Verwendung des CIEL∗a∗b∗ Farbsystems durchgeführt. Die Gesamtverfärbung wurde entsprechend des Wertes ΔE∗ beurteilt. Bei der Bestrahlung wurde die Änderung der Parameter L∗,a∗ und b∗ ebenfalls bestimmt. In den ersten Stunden der Bestrahlung dunkelte die Holzoberfläche schnell, später nahm die Helligkeit leicht zu. Innerhalb einer Holzart waren die Farbveränderungen bei den helleren Proben stärker ausgeprägt (größeres ΔE∗).

The influence of wood density on longitudinal wave velocity determined by the ultrasound method in comparison to the resonance longitudinal method

The paper deals with the relationship between density and the velocity of sound wave propagation in wood. The wave velocity was measured using the heartwood of doussie (Afzelia bipindensis), merbau (Intsia bijuga), panga panga (Miletia stuhlmannii Taub.), tigerwood (Astronium graveolens Jacq.) and zebrano (Microberlinia brazzavillensis) by the two methods: ultrasound and resonance longitudinal. The velocity measured by the ultrasound method was always higher than the values gained by the resonance longitudinal method. However, there is a high correlation between the results of both methods. A change in sound wave velocity due to a change in density was not confirmed for any of the species. A similar conclusion was reached in the comparison among species.

The Relation of Fibre Length and Ray Dimensions to Sound Propagation velocity in wood of selected Tropical Hardwoods

This study investigates the relation of fibre length and ray dimensions to the sound propagation velocity in four commercial tropical hardwoods. The species used in the study were Doussie (Afzelia bipindensis Harms), Merbau (Intsia bijuga (Colebr.) Kuntze), Muiracatiara (Astronium graveolens Jacq.) and Wenge (Millettia laurentii De Wild.). The sound propagation velocity was established by the frequency-resonance method. A positive correlation was obtained between fibre length and sound velocity within species. The correlation was stronger in species with a higher proportion of libriform fibres. A trend analogous to fibre length within species was observed for ray ratio but, in contrast to fibre length, the correlation was strong also between species. The samples with higher and at the same time narrower rays (higher ray ratio) showed a higher velocity of sound propagation along the grain.

Wood anatomy and acoustic properties of selected tropical hardwoods

Selected anatomical features and ground tissue composition were studied in four tropical hardwoods (Afzelia sp. [Doussie], Intsia sp. [Merbau], Astronium sp. [Muiracatiara] and Millettia sp. [Wenge]). These woods can be applied in musical instrument production, especially for xylophone bars. The measured density, 1st bending natural frequency and the logarithmic decrement of damping were used to calculate other acoustic properties such as dynamic young modulus of elasticity (Erf ), specific modulus of elasticity (E´/ρ), internal friction (tan δ), and acoustic conversion efficiency (ACE).The correlations between anatomy and acoustic properties were determined. Despite difficulties in specifying general characteristics of hardwoods due to their complicated and variable structure, correlations valid between species were found for specific modulus of elasticity. Specific modulus of elasticity was negatively correlated with ray tissue volume and positively with ray height to width ratio and fiber length. The diversity in ground tissue composition was the main criterion for the species choice and probably should condition diverse correlations of anatomical features found for individual species. It seems that better acoustic properties (higher stiffness, ACE or specific modulus of elasticity) are performed by wood with longer fibers and slender rays, causing minimal deflection of adjoining fibers.