Artificial weathering of tropical woods. Part 2: Color change

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., Db* (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 Da* (shift to red) and Db* decreased with increased exposure time. For woods in which Db* increased, the Db* showed a positive dependence on the difference in relative intensity ratio of a band at 1740 cm y1 to that at 2900 cm y1 (DD 1740 /D 2900 ) in DRIFT spectra of specimens before and after exposure. This result indicated that the increased band at 1740 cm y1 played a significant role in the increased Db*. Then again, also for woods in which Db* decreased, the DD 1740 /D 2900 increased, but was not related to the Db*. The DD 1740 / D 2900 for woods in which Db* decreased had a positive relationship to the difference in remission function at 410 nm (DF(R`) 410 ) in UV-Vis diffuse reflectance spectra for specimens before and after exposure, while woods in which Db* increased were independent of the DF(R`) 410 . Therefore, it is suggested that woods in which Db* increased and decreased differ from one another in the contribution to the increase in the band at 1740 cm y1 , resulting in either an increase or decrease of Db*.

Preparation and Characterization of Outdoor Bamboo-Fiber-Reinforced Composites with Different Densities

“…Sample Bw underwent yellowing to the greatest extent during the weathering process. Previous studies have shown that a quick change in color occurs in the rapid phase of the photochemical reaction (Arnold et al 1991;Müller et al 2003;Kishino and Nakano 2004;Baysal et al 2014). This kind of reaction tends to reach a point of equilibrium because of the slow diffusion of oxygen and the free radicals (which are necessary for the reaction) from the material surface to its interior (Arnold et al 1991).…”

Influence of Post-extraction on Photostability of Thermally Modified Scots Pine Wood during Artificial Weathering

“…Pietta (2000) found that phenolics in plant extractives absorb free radicals and have effective antioxidant activity. Kishino and Nakano (2004) attributed the improved antioxidant ability of thermally modified wood to the increased phenol content and the higher concentrations of stable phenoxyl-free radicals. Hence, it is likely that the presence of phenolics extractives had a protective effect against the degradation of thermally modified Scots pine.…”

Study on the degradation mechanism of heat-treated wood by UV light /

“…It is possible to perceive differences of about 3.8 units of AE* [17,192]. Thus, the difference of AE between heat-treated and untreated wood surfaces during artificial sunlight irradiation is due to the difference in their initial colors.…”

“…Pandey [44] reported that the color changes on wood surfaces were mainly due to the formation of C=O groups as a result of the photodegradation of lignin. Masanori and Tokato [192] suggested that the formation of non-conjugated carbonyl functional group played an important role in the color change in woods for which Ab* increased but not for woods for which Àb* decreased. However, it can be observed from the color results shown in As stated in Section 4.5, the degradation of lignin by weathering can increase the content of other components on wood surface and consequently make the surface more hydrophilic.…”