Étude paramétrique d'un procédé d'imprégnation des bois feuillus

Authors: Frias de Albuquerque, Mariana
Advisor: Blanchet, Pierre; Bégin-Drolet, André
Abstract: Wood is a renewable resource that has been used as a material in appearance products for years. Despite its superior mechanical resistance, different modification processes have been developed to enhance the hardness of wood and make it an even more durable material. Impregnation using monomers is a promising modification method, given its cost and availability. This process is currently being implemented to produce wood polymer composites (WPC), which can have modified and improved physical qualities compared to an untreated wood product. Industrial development is mostly focused on the production of these composites for many applications such as civil construction, furniture, flooring and sports equipment. Currently, monomer impregnation is carried out by the vacuum-pressure method. The amount of chemical that can be obtained by this method is considered to be high; in some cases, up to 200%. The WPCs produced have improved mechanical properties and greater resistance to water impregnation. However, the impregnation process takes about 1 hour, and the wood must be immersed in the liquid (Bethell’s full-cell process). This can be seen as a waste of both material and time in the process. Previous studies have concluded that performing a monomer impregnation on a hardwood surface using a short vacuum period was successful and could reduce these problems. Therefore, it became necessary to find ways to reduce the time and cost of industrial impregnation. The objective of this work was to evaluate the parameters influencing monomers penetrationin tangential surface samples of yellow birch (Betula alleghaniensis Brit.) and red oak (Quercus rubra L.). The factors analyzed were the viscosity of the monomer formulation, surface temperature, vacuum level applied to the process, sample anatomy, and absorption time. After impregnation, the weight gain of the samples was calculated. The penetration depth of the monomer was calculated using density profiles (for yellow birch samples) and the penetration was visualized using X-ray tomography imaging. The results showed that surface temperature did not influence weight gain for any of the species studied. However, the increase in temperature accelerated the polymerization process of monomeric formulations, which may have limited the increase in chemical retention at higher temperatures. Microtomographic images after the temperature study showed that the impregnation was concentrated near the surface of the samples, i.e., there was no deep penetration of monomers. Subjecting the samples to a short vacuum level increased the weight gain of the samples compared to impregnation under atmospheric pressure. The driving force behind the monomer penetration was the pressure difference imposed by the vacuum level, which overcame capillary action. For Yellow birch samples, the variation of vacuum levels did not significantly affect the weight gain results, possibly due to the size of its pores. For red oak, the vacuum level was significant, and the chemical retention increased with pressure differential. Microtomographic scans showed a more controlled and uniform distribution of the monomers. Finally, the absorption time after vacuum relaxation was significant in monomer retention. The contact of both species with the formulations for more than 5 minutes significantly increased monomers intake. X-ray scans showed that for both species, more pores were filled. The depth of penetration did not increase so much for yellow birch but increased for red oak. Thus, it can be said that a longer absorption time allows capillarity to continue filling the empty vessels of the wood until the internal pressure is equal to the external pressure. This research may encourage future work to study the feasibility of reducing vacuum pressure cycles in industrial processes. This method can enable hardening the surface of interest of a wood product in a controlled manner, with reduced costs and avoid wasting of impregnation materials.
Document Type: Mémoire de maîtrise
Issue Date: 2021
Open Access Date: 29 March 2021
Permalink: http://hdl.handle.net/20.500.11794/68633
Grantor: Université Laval
Collection:Thèses et mémoires

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