Impact of annual growth pattern on swelling of selected wood species

Abstract

Impact of annual growth pattern on swelling of selected wood species. Unit swelling was investigated in radial and tangential directions as well as in the intermediate directions for wood of density ranging from 300÷500 kg/m3 and 500÷700 kg/m3 and above 700 kg/m3. Species selected included pine – PNSY (Pinus sylvestris L.), oak – QCXE (Quercus. robur L.) and bangkirai – SHBL (Shorea spp.), teak – TEGR (Tectona grandis), merbau – INXX (Intsia bijuga), jatoba – HYCB (Hymenaea courbaril L). For all the studied wood species, the lowest swelling in the radial direction (0°) was found after both 2 h and 24 h of wetting in water, which increased with the angle of inclination of the annual growth and, after reaching 90°, corresponded to the maximum swelling in the tangential direction. For pine (PNSY) sapwood and heartwood and for oak (QCXE), a high swelling unit was obtained after a wetting time of 2 h, with little change after 24 h of wetting. Swelling increments for the other wood species were lower, ranging from 1% to over 2% after a wetting time of 2 h, showing slight differences between radial and tangential directions. For these wood species, after 24 h of wetting the swelling was higher and varied from more than 2% to nearly 5% in the radial direction and from more than 4% to 10% in the tangential direction. The study showed that, for high-density wood species, it becomes necessary to extend the wetting time in order to determine the actual maximum swelling per unit. The swelling anisotropy coefficients ε of the studied wood species corresponded to the values found in the literature. Higher coefficients were found for oak (QCXE) and teak (TEGR), bangkirai (SHBL) and jatoba (INXX), and were related to the characteristic features of the density structure and anatomical structure. The unit swelling values calculated with the Krzysik (1974) and Vorreiter (1949) equations may be used to assess changes in the dimensions of elements in intermediate directions. The discrepancies between the experimental and theoretical values are smaller for the unit swelling values calculated with the Vorreiter (1949) equation compared to the Krzysik (1974) equation.