Surface Investigation of Photo-Degraded Wood by Colour Monitoring, Infrared Spectroscopy, and Hyperspectral Imaging

Abstract

The aim of this investigation is to study the changes occurring on the surface of poplar wood exposed to artificial irradiation in a Solar Box. Colour changes were monitored with a reflectance spectrophotometer. Surface chemical modifications were evaluated by measuring the infrared spectra. Hyperspectral imaging was also applied to study the surface wood changes in the visible-near infrared and the short wave infrared wavelength ranges. The data obtained from the different techniques were compared to find the possible correlations in order to evaluate the applicability of the Hyperspectral imaging to investigate wood modifications in a non-invasive modality. The study of colour changes showed an important variation due to photo-irradiation which is the greatest change occurring within the first 24 hours. Infrared spectroscopy revealed that lignin degrades mainly in the first 48 hours. Concerning Hyperspectral imaging, the spectral features in the visible-near infrared range are mainly linked to the spectral shape, whereas in the short wave infrared cellulose and lignin affect shape and reflectance levels. The proposed approach showed that a correlation can be established between colour variation and wood degradation in the visible-near infrared range; furthermore in the short wave infrared region surface chemical changes can be assessed.

Effects of Air Relative Humidity and Temperature on Photodegradation Processes in Beech and Spruce Wood

“…The IR measurements give more detailed information on the structural changes appearing during the treatments of the wood samples; these results may be correlated with the color changes (Müller et al 2003;Agresti et al 2013;Teacǎ et al 2013;Bonifazi et al 2015). Generally, infrared spectra of wood samples are complex, consisting of two separate regions, namely, the 3800 to 2700 cm -1 region assigned to the different stretching vibrations of the hydroxyl, methyl, and methylene groups from the wood structure, and the so called "fingerprint" region (1900 to 900 cm -1 ), which consists of different stretching and deformation vibrations from different groups of the wood components.…”

“…The color change of wood is the most sensitive indicator of the degradation caused by UV light (Butler et al 2001;Agresti et al 2013;Esteves et al 2008;Schnabel et al 2009;Matsuo et al 2010;Oltean et al 2010). Tolvaj and Faix (1995) examined three coniferous and two deciduous species irradiated by a mercury lamp.…”

Colour and chemical changes on photodegraded beech wood with or without red heartwood

“…This result indicates that during the photodegradation process, new and different carbonyl compounds were produced on the wood surface. The intensities of the peak associated with carbohydrates at 1,375 cm -1 is not significantly affected by irradiation, so this band has been used as internal reference to evaluate the lignin decay (Pandey 2005a;Agresti et al 2013;Calienno et al 2014;Pelosi et al 2013;Popescu et al 2011).…”

Colour stability of oil-heat treated black locust and poplar wood during short-term UV radiation

“…The colour change caused by the sunshine and the rain for natural wood is a well investigated phenomenon [12][13][14][15][16][17][18][19]. But the colour change caused by the photodegradation for thermally treated wood is not well researched, and the published results are sometimes contradictory.…”