Caractérisation des mécanismes naturels de vieillissement de lambris de bâtiments en bois

Authors: Cogulet, Antoine
Advisor: Blanchet, PierreLandry, Véronic
Abstract: Four lines of research have been studied in this manuscript in order to answer at the goal of this PhD: having a better understanding of the degradation mechanisms of wood siding building. The first line was designed to provide recommendations regarding good practice for effective use of the different weathering methods. Sample degradation was characterised with FTIR and colorimetric analysis. An original interpretation of color modifications observed on samples allowed recommendations to be provided. In addition, suitable exposures were chosen for each line of research. The second line of this PhD was about a fundamental study of wood photodegradation by using a Raman spectrophotometer. Interpretation of Raman contribution did not provide new relevant information on chemical modification underwent by the wood due to the photodegradation. Thus, this technique was not used to further study the degradation of wood. However, the sensitivity of this device to fluorescence has led to the identification of a new mechanism of lignin degradation. The sensitivity of α and β carbons to photodegradation has been demonstrated as well as the strength of the 5-5 carbon-carbon bond. The third line of this project was concerned with the development of a method taking into account the interactions that may exist between photodegradation and biological degradation. A visual scale was created in order to monitor the colonisation of samples coated with a clear protection. It was found that the photodegradation promotes the colonisation by two black stain fungi: Aureobasidium pullulans and Epicoccum nigrum. Infrared analyses did not reveal the mechanisms by which fungi take advantage of photodegradation to colonize the samples. The presence of bubbles in the paint finish was demonstrated by microscopic observations. After photodegradation, these bubbles form weak points for colonization by fungi through the protective layer. The use of structures such as a transpressorium has been highlighted. Photodegradation and biological degradation leads to a decrease of coating adhesion. The last line of this doctoral project was to identify the influence of the coalescing agent, the application method and a sanding step onto the paint properties and the quality and morphology of the film. The ability of the paint to degas, the curing time and the minimal film formation temperature (MFFT) were linked with the properties of the coalescing agent. Gloss as well as topography of the coating surface were characterized in order to qualify the coating quality. The use of a hydrophobic agent showed the best results concerning the parameters studied. Overall, the results obtained throughout the PhD allowed the identification of fragilities and weaknesses of an acrylic finish based on (i) its formulation, (ii) the quality of the dry finish, (iii) and its exposure to weathering. Specific goals determined in this PhD have been addressed. The whole of the information obtained helps to better understand of the mechanisms and causes involved in the loss of performance of a wood protection of a wood siding building.
Document Type: Thèse de doctorat
Issue Date: 2018
Open Access Date: 22 December 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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