Colour modifications and hyperspectral imaging: non-invasive analysis of photo-degraded wood surfaces

The aim of this investigation is to study the changes occurring on the surface of poplar wood exposed to solar irradiation, in a controlled environment. Poplar is poor of coloured extractive, so that the surface changes are attributed to the main wood constituents’ modifications and the contribution of extraneous substances to holocellulose and lignin can be considered negligible. The poplar wood samples were irradiated in a Solar Box chamber, equipped with a 280 nm UV filter, until reaching 504 hours. The colour changes were monitored with the reflectance spectrophotometer of X-Rite CA22 according to the CIELAB system. The surface chemical modifications were evaluated by measuring the infrared spectra with a Fourier Transform Infrared spectrometer (FT-IR) operating in DRIFT modality. Hyperspectral imaging (HSI) was also applied to study the surface wood changes by using a SisuCHEMA XL Workstation operating in the SWIR range (1000-2500 nm). The data obtained from the different techniques applied were put in comparison in order to find possible correlations between them also with the aim to evaluate the applicability of the HSI technique to the investigation of wood modifications, in a totally non-invasive modality. The possibility to find a correlation between colour changes and chemical modifications, investigated both with traditional and innovative methodologies, in wood surfaces can have practical application in cultural heritage and contemporary objects

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

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

Indicators of sustainable forest management: application and assessment

Report of the international project Life ManForCBD