Artificial weathering of tropical woods. Part 2: Color change

Abstract

Abstract This paper describes the change in diffuse reflectance Fourier transform infrared (DRIFT) and ultraviolet-visible (UV-Vis) 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., Δb* (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 Δa* (shift to red) and Δb* decreased with increased exposure time. For woods in which Δb* increased, the Δb* showed a positive dependence on the difference in relative intensity ratio of a band at 1740 cm –1 to that at 2900 cm –1 (ΔD 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 Δb*. Then again, also for woods in which Δb* decreased, the ΔD 1740 /D 2900 increased, but was not related to the Db*. The ΔD 1740 /D 2900 for woods in which Δb* decreased had a positive relationship to the difference in remission function at 410 nm (Δ F (R ∞ ) 410 ) in UV-Vis diffuse reflectance spectra for specimens before and after exposure, while woods in which Δb* increased were independent of the Δ F (R ∞ ) 410 . Therefore, it is suggested that woods in which Δb* 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 Δb*.