Non-Destructive Surface Characterization of Wood Façade Materials and Wood Fungi by Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy
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Wood material is the dead xylem part of a tree that is being used for building construction, furniture, decorative items etc. Building façade is the outer envelope of a building. Wood façade materials are exposed against natural degradation agents like insects, fungi, wind-blown particles, rain, snow, solar radiation. In Northern Europe, softwoods are the primary sources of façades materials. Coated or impregnated woods are also used to increase the durability of façade. The objective of this work was to estimate degradation of wood façade material in situ, under accelerated ageing and natural outdoor ageing conditions, primarily by attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. In total, nine different types of wood material were aged in natural outdoor conditions and in accelerated laboratory conditions. Initially, with four types of wood materials, it was possible to use spectral information to discriminate the nature of surface texture, namely, rough surface and machine planed surface (Article 1). In order to understand the degradation rate of various components of wood (Article 2), the acceleration factor was calculated that showed that the wood components with lower activation energy have smaller acceleration factors. With the aim of discriminating fungal species by FTIR spectroscopy, four mould fungi species were cultured in lab and sprayed on fresh wood specimen (Article 3). It was observed that there were four regions in the FTIR spectra that show qualitative variation in cell contents for different fungi species. The rate of fungal growth on coated and fresh wood surface was evaluated by FTIR (Article 4). It was observed that the fungi that were grown on fresh wood surfaces have cellulose content on their cell structures, which were either absent or unidentifiable in cell structure of fungi grown on coatings. The intricacies of fungal cellular structure were evaluated by FTIR spectroscopy (Article 5). It was proposed that the hydrogen bond in the cell structure of fungi could be a possible identifier of fungi species. The comparison of wood decay and wood mould fungi showed that the amide I index of wood rot fungi have higher presence over the lipids in the cellular structure compared to mould fungi (Article 6). The long term natural outdoor exposure and accelerated laboratory exposure showed a correlation between the cellulose absorbance peaks obtained from FTIR spectra of aged and non-aged wood (Article 7). Lignin index was proposed as an indicator to verify surface chemistry change during degradation. It was observed that there were accumulations of impurities on the substrate surface beneath the coated film of coated wood surfaces (Article 8). It was observed that the ageing and coating failure had a faster rate of occurrence on the inclined surfaces compared to the vertical surfaces in natural outdoor exposure conditions. It was concluded that the ATR-FTIR spectroscopy is a promising tool to compare decay induced in different wood materials at diverse environmental conditions. Moreover, it was possible to separate fungi phyla. Furthermore, it was observed that the data obtained by FTIR spectroscopic analysis could possibly be used as ‘wood quality’ to estimate service life.