Modification de couleur du bois de chênes européens exposés à la lumière solaire

Abstract

(fig 22) to take into account the discoloration of wood under solar-type light exposure at the molecular level. In this paper, this model was extended to European species of oak (Quercus robur and petraea) with high levels of colored extractable substances and for which the color characteristics are a quality criterion. In addition to the observed and analyzed yellowing in Abies grandis wood, a color lightening corresponding to a lowered absorption over the spectral range (500-600 nm) (figs 2, 6) has been observed. Lignin photodegradation is certainly in part responsible for this decoloration. It has also been shown that oak sapwood and heartwood undergo different kinds of photodecoloration (fig 3). For color photostabilization of oak wood under solar light, the results indicate that it is necessary to use UV absorbers to lower the yellowing due to UV light and antioxidants to inhibit color lightening due to reactions with oxygen.

UV light impact on ellagitannins and wood surface colour of European oak (Quercus petraea and Quercus robur)

“…In the course of homolytic scission of intramolecular connections phenoxy free radicals arise. Most of them belong to the guaiacyl type [5]. The reactivity of these radicals is dependent of the quantity of oxygen in the surrounding [6,7].…”

Antioxidant properties of wood extracts and colour stability of woods

“…Monitoring surface properties of grand fir samples impregnated by oak (Quercus pedunculata) extracts evidenced grand fir wood protection by these extracts. Comparison of photodegradation of grand fir and oak woods evidenced the involvement of extractives in the degradation process [16,17]. An ESR study showed that these phenolic coloured compounds not only act as filters, but also play a role in the radical processes involved in the photodegradation of wood: by radical transfer reactions, they deactivate radical oxygen species carrying oxidation process by producing stable phenoxyl (ΦO·) free radicals [10].…”

Evaluation of Color Variability of Oak Veneers for Sorting

“…A negative correlation between wood lightness and sapwood width was found by Hoffmann (1987). Mazet et al (1993) showed significant differences between the sapwood and heartwood of sessile oak and European oak regarding their photochemical behavior. The abundant amount of extractives in heartwood, such as ellagitannins, explains such behavior (Scalbert et al 1987;Stich and Ebermann 1987).…”