Modeling weather degradation of wooden facades using NIR hyperspectral imaging on thin wood samples

Untreated wooden surfaces degrade differently when exposed to varying doses of natural weathering. This study aims to assess the degradation of wooden surfaces caused by weathering and to determin a weather dose for the degradation. Several sets of very thin wood samples have been exposed to natural weathering and one set of samples was exposed to UV-radiation in a AtlasUV. The samples have been studied with multisensory techniques including near-infrared hyperspectral imaging. Spectra of earlywood and latewood could be extracted from the hyperspectral image cubes and changes in the spectra were modeled as a function of UV solar radiation to see if the weathering deterioration was reflected in the NIR spectra. The lignin and holocellulose content were estimated on selected samples separately for early- and latewood using a thermogravimetric analysis (TGA). The thermogravimetric results showed a clear correlation with the progress of weathering of the samples, for both earlywood and latewood and both for the outdoor samples and the samples is in the UV chamber exposed. The result from this work is a first step towards fining a weather dose model determined by temperature and moisture content on the wooden surface in addition to the solar UV radiation.