Artificial weathering of tropical woods. Part 2: Color change

This paper describes the change in diffuse reflectance Fourier transform infrared (DRIFT) and ultravioletvisible (UVVis) diffuse reflectance spectra of the following eight tropical woods during artificial weathering up to 600 h in relation to their color changes, especially to yellowing: Amnurana acreana, Acacia auriculiformis, Dipterocarpus spp., Eucalyptus marginata, Eucalyptus robusta, Shorea spp. and Tabebuia spp. with relatively high and low specific gravity. For A. acreana, A. auriculiformis, Dipterocarpus spp. and both Tabebuia spp., Deltab* (yellowing) increased with exposure up to 50 h, and decreased above 50 h. For E. marginata, E. robusta and Shorea spp., on the other hand, both Deltaa* (shift to red) and Deltab* decreased with increased exposure time. For woods in which Deltab* increased, the Deltab* showed a positive dependence on the difference in relative intensity ratio of a band at 1740 cm(-1) to that at 2900 cm(-1) (DeltaD(1740)/D-2900) in DRIFT spectra of specimens before and after exposure. This result indicated that the increased band at 1740 cm(-1) played a significant role in the increased Deltab*. Then again, also for woods in which Deltab* decreased, the DeltaD(1740)/D-2900 increased, but was not related to the Deltab*. The DeltaD(1740)/D-2900 for woods in which Deltab* decreased had a positive relationship to the difference in remission function at 410 nm (DeltaF(Rinfinity)(410)) in UVVis diffuse reflectance spectra for specimens before and after exposure, while woods in which Deltab* increased were independent of the DeltaF(Rinfinity)(410). Therefore, it is suggested that woods in which Deltab* increased and decreased differ from one another in the contribution to the increase in the band at 1740 cm(-1), resulting in either an increase or decrease of Deltab*.