Percorrer por autor "Andrade, Djems"
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- Tensile shear strength of wood adhesives with fire-retardants under elevated temperaturesPublication . Silva, Luana; Alves, Matheus Henrique; Andrade, Djems; Ferreira, Débora; Piloto, Paulo A.G.; Mesquita, Luís M.R.The utilization of wood and wood derivatives is growing in building construction due to sustainability and circularity, despite the inherent flammability of wood. Woodworking often requires bonding elements with adhesives, which are prone to degradation under fire. A potential solution to improve the fire resistance of wood joints and their derivatives involves incorporating fire retardants into the adhesive compositions. This study explores the adhesion properties of bonded joints of medium-density fibreboard and pinewood panels using resins based on urea and polyurethanes derived from diphenylmethane diisocyanate (MDI). Various proportions of ammonium polyphosphate, borax, and expandable graphite were incorporated as fire retardants. Shear testing was conducted on lap joints under room and elevated temperatures to evaluate their adhesive performance. MDI-based resin demonstrated higher shear resistance at elevated temperatures than the urea-based resin. The addition of fire retardants to MDI revealed a complex mechanism: they decreased strength at room temperature but improved it at 100 and 200 degrees C through protective actions and a later reverse behaviour at 230 degrees C, suggesting the onset of catalytic degradation. The transition from panel tear to cohesive failure at higher temperatures confirmed that adhesive degradation became the limiting factor. The MDI formulations proved competitive with, and in some cases superior to, established formaldehyde-based structural adhesives at elevated temperatures. The study concludes that the optimal formulation is application-dependent: for fire-resistance applications, the MDI resin without fire retardant proved to be the most robust at 230 degrees C, whereas for high-temperature service, MDI with APP maximizes strength at 100-200 degrees C.
- Thermomechanical behaviour of bonded joints of wood and wood-based panels at room and elevated temperaturesPublication . Andrade, Djems; Alves, Matheus Henrique; Mesquita, L.M.R.; Barreira, Luísa; Manhique, Jocyla; Santamaria-Echart, Arantzazu; Barreiro, Filomena; Mofreita, FilipeWood is a natural material traditionally used in the construction industry. In recent decades, developments in scientific research have turned wood into a high-tech construction material. Increased interest in bonded joints in wood construction is due to the advantages of adhesive technology compared to traditional mechanical joining techniques. It is very important to understand the influence of elevated temperatures on adhesives due to their use in multilayer systems such as compartmentation walls and fire-resistant doors, which require adequate mechanical and thermal resistance in fire situations. The purpose of this study is to investigate the mechanical behaviour of different structural adhesives on bonded connections of wood and wood-based panels at room and elevated temperatures through experimental testing. The performance of the adhesives was evaluated at room temperature and at 50 °C, 100 °C, 150 °C, and 200 °C.
- Thermomechanical behaviour of bonding joints of wood and wood-based panels at room temperature and elevated temperaturesPublication . Alves, Matheus Henrique; Andrade, Djems; Mesquita, L.M.R.; Barreira, Luísa; Manhique, Jocyla; Santamaria-Echart, Arantzazu; Barreiro, M.F.; Mofreita, FilipeWood is a natural material traditionally used in the construction industry. In recent decades, developments in scientific research have turned wood into a high-tech construction resource. Increased interest in bonded joints in wood construction is due to the advantages of adhesive technology compared to traditional mechanical joining techniques. It is very important to understand the influence of elevated temperatures on adhesives due to their use in multilayer systems such as compartmentation walls and fire-resistant doors, which require adequate mechanical and thermal resistance in fire situations. The purpose of this study is to investigate the mechanical behaviour of different structural adhesives on bonded connections of wood and wood-based panels at room and elevated temperatures through experimental testing. The performance of the adhesives was evaluated at room temperature and at 50 °C, 100 °C, 150 °C, and 200 °C. The resins tested were a polyurethane prepolymer resulting from the reaction between polyols and diphenylmethane diisocyanate (MDI), Flexpur151, and urea resin glue for hot pressing. The tensile shear tests with lap joints were performed using combinations of pinewood-pinewood and MDF-MDF. The experimental tests were done according to EN 205:2016, which allows for determining the tensile shear strength of bonded joints. The failure mode of the tested specimens was classified according to ASTM D5573. The results show that the bonding strength and the displacement of the specimens decrease with the increase of the temperature. The failure mode presents a different result for different temperatures. For example, for the urea resin, the shear resistance of MDF-MDF panels decreases about 50 % when exposed to 100 ºC with the failure mode usually occurring on the panel, and 98 % when exposed to 200 ºC with the failure mode in the adhesion plane. For the MDI based resin, the shear resistance of MDF-MDF panels decreases about 35 % when exposed to 100 ºC with the failure usually occurring on the panel, and 65 % when exposed to 200 ºC with the failure mode occurring in the adhesion plane.