Otimização de estruturas geopoliméricas leves para incorporação em bombas de calor

Abstract

As alterações climáticas são um tema de crescente importância no panorama global. Neste contexto, existe uma preocupação crescente com a sustentabilidade dos processos produtivos e dos materiais utilizados. O desenvolvimento de materiais com menor pegada de carbono, mas que assegurem os requisitos de desempenho exigidos para as aplicações, é uma das estratégias que pode permitir a descarbonização do setor industrial. Este trabalho consistiu no desenvolvimento de estruturas geopoliméricas leves com potencial para substituir as espumas poliméricas (polipropileno expandido) atualmente utilizadas pela Bosch como material de atenuação acústica em bombas de calor. Definiram-se como principais objetivos a otimização da densidade geométrica de materiais estudados anteriormente, a adaptação da dimensão das estruturas a uma dimensão próxima da operação e a caracterização do fator de perda dos geopolímeros leves. Foram produzidos geopolímeros densos, porosos, compósitos geopoliméricos contendo agregados leves e estruturas multicamada, associados a aumentos de escala em formulações selecionadas. Os agentes formadores de poros utilizados na produção de geopolímeros porosos foram o pó de alumínio (0,100, 0,125 e 0,150%, adição em massa) e o peróxido de hidrogénio (0,8, 1,2 e 1,6%, adição em massa). Verificou-se a diminuição da densidade geométrica e da resistência mecânica com o aumento do teor de agente formador de poros. Observaram-se também valores de resistência mecânica mais elevados aquando da utilização de peróxido de hidrogénio por comparação com as formulações preparadas com pó de alumínio (para valores de densidade geométrica comparáveis). Para os geopolímeros porosos, a densidade geométrica mais baixa obtida neste trabalho foi de 0,35 g/cmᵌ (1,6% H₂O₂). O poliuretano (PU) foi um resíduo industrial utilizado como agregado leve nos compósitos geopoliméricos (50 a 95 vol.%), tendo-se obtido estruturas com densidade geométrica igual a 0,18 g/cmᵌ para teores de 95 vol.% PU incorporado. Verificou-se que a densidade geométrica diminui com o aumento do teor de agregado leve. À medida que o teor de geopolímero (fase ligante) diminui, surge o fenómeno de desagregação, motivo pelo qual a formulação de 95 vol.% PU não é compatível com a aplicação em estudo. Contudo, a utilização de teores de PU até 93 vol.% (0,27 g/cmᵌ), e as estruturas multicamada apresentam estabilidade e resistência mecânica compatível com a aplicação. A partir de formulações avaliadas em projetos anteriores (80 vol.% cortiça – fina, grosseira e expandida negra, 90 vol.% borracha e 0,100 a 0,150% Al) e outras desenvolvidas neste trabalho (91 vol.% PU, 1 e 2% H₂O₂), foram produzidas amostras de dimensões superiores (16 x 14 x 2 cmᵌ e 15 x 15 x 15 cmᵌ). O aumento de escala foi conseguido sem constrangimentos para todas as formulações exceto para as de cortiça, onde a retração não uniforme do agregado leve resultou em empeno. Verificou-se também uma diminuição da densidade geométrica das amostras com o aumento da escala de produção. Através da análise dinâmica, quantificou-se um fator de perda de aproximadamente 10% para amostras geopoliméricas porosas e compósitas (0,100% Al, 80 vol.% cortiça e 91 vol.% PU). Os resultados mostram ainda uma relação entre a capacidade de amortecimento das amostras e a sua densidade geométrica (para amostras da mesma natureza). Estruturas geopoliméricas mono (PU) e multicamada foram testadas em termos de desempenho acústico, tendo-se verificado valores de coeficiente de absorção acústica superiores aos do (polipropileno expandido) na gama de frequências considerada. Relativamente à perda de som por transmissão, as estruturas geopoliméricas estudadas apresentam valores inferiores por comparação com as espumas de polipropileno expandido. Os resultados mostram que a natureza das camadas exteriores das estruturas multicamada influencia o comportamento acústico da estrutura, o que sugere que a utilização de uma camada externa com menor porosidade pode permitir superar a limitação identificada.

Climate change is an issue of growing importance in the global scenery. In this context, the concern with the sustainability of production processes and the materials used has been asserting itself. Therefore, it is mandatory to develop materials with a smaller footprint yet meeting the performance requirements demanded for the target application. This work aims the development of lightweight geopolymer structures with potential to replace the polymeric foams currently used by Bosch, in order to reduce the environmental impact. The main goals of the project include the optimization of the density of previously studied materials, the adjustment of the size of structures to a size close to that of the operation and the characterization of the loss factor of lightweight geopolymers. Dense, porous and composites (containing lightweight aggregates) geopolymers were produced, following a scale up strategy onto a selection of formulations. The aluminium powder (0,100, 0,125 and 0,150%) and the hydrogen peroxide (0,8, 1,2, 1,6%) were the foaming agents used in the production of porous geopolymers. A decrease in the density and in the mechanical strength was found when increasing the foaming agent content. An improvement in the mechanical strength was also observed when the hydrogen peroxide was used instead of the aluminium powder (for comparable density values). For porous geopolymers, the minimum density obtained was 0,35 g/cmᵌ (1,6% H₂O₂). Polyurethane (PU) was an industrial waste used as light aggregate in the geopolymer composites (50 to 95 vol.%). Structures with density equal to 0,18 g/cmᵌ were obtained for contents of 95 vol.% of aggregates incorporated to the composite. It was found that density decreases with the increase of the light aggregate content. As the geopolymer content (binder) decreases, the phenomenon of crumbling appears. For that reason, the 95 vol.% PU formulation is considered to be incompatible with the target application of this study. However, the use of PU contents up to 93 vol.% (0,27 g/cm3) and the use of multilayer structures can be considered for the intended effect, with valuable levels of mechanical strength. From formulations evaluated in previous studies (80 vol.% cork – fine, coarse, and black expanded, 90 vol.% rubber and 0,100 to 0,150% Al) and others developed within this work (91 vol.% PU, 1 and 2% H₂OClimate change is an issue of growing importance in the global scenery. In this context, the concern with the sustainability of production processes and the materials used has been asserting itself. Therefore, it is mandatory to develop materials with a smaller footprint yet meeting the performance requirements demanded for the target application. This work aims the development of lightweight geopolymer structures with potential to replace the polymeric foams currently used by Bosch, in order to reduce the environmental impact. The main goals of the project include the optimization of the density of previously studied materials, the adjustment of the size of structures to a size close to that of the operation and the characterization of the loss factor of lightweight geopolymers. Dense, porous and composites (containing lightweight aggregates) geopolymers were produced, following a scale up strategy onto a selection of formulations. The aluminium powder (0,100, 0,125 and 0,150%) and the hydrogen peroxide (0,8, 1,2, 1,6%) were the foaming agents used in the production of porous geopolymers. A decrease in the density and in the mechanical strength was found when increasing the foaming agent content. An improvement in the mechanical strength was also observed when the hydrogen peroxide was used instead of the aluminium powder (for comparable density values). For porous geopolymers, the minimum density obtained was 0,35 g/cm3 (1,6% H₂O₂). Polyurethane (PU) was an industrial waste used as light aggregate in the geopolymer composites (50 to 95 vol.%). Structures with density equal to 0,18 g/cmᵌ were obtained for contents of 95 vol.% of aggregates incorporated to the composite. It was found that density decreases with the increase of the light aggregate content. As the geopolymer content (binder) decreases, the phenomenon of crumbling appears. For that reason, the 95 vol.% PU formulation is considered to be incompatible with the target application of this study. However, the use of PU contents up to 93 vol.% (0,27 g/cmᵌ) and the use of multilayer structures can be considered for the intended effect, with valuable levels of mechanical strength. From formulations evaluated in previous studies (80 vol.% cork – fine, coarse, and black expanded, 90 vol.% rubber and 0,100 to 0,150% Al) and others developed within this work (91 vol.% PU, 1 and 2% H₂OClimate change is an issue of growing importance in the global scenery. In this context, the concern with the sustainability of production processes and the materials used has been asserting itself. Therefore, it is mandatory to develop materials with a smaller footprint yet meeting the performance requirements demanded for the target application. This work aims the development of lightweight geopolymer structures with potential to replace the polymeric foams currently used by Bosch, in order to reduce the environmental impact. The main goals of the project include the optimization of the density of previously studied materials, the adjustment of the size of structures to a size close to that of the operation and the characterization of the loss factor of lightweight geopolymers. Dense, porous and composites (containing lightweight aggregates) geopolymers were produced, following a scale up strategy onto a selection of formulations. The aluminium powder (0,100, 0,125 and 0,150%) and the hydrogen peroxide (0,8, 1,2, 1,6%) were the foaming agents used in the production of porous geopolymers. A decrease in the density and in the mechanical strength was found when increasing the foaming agent content. An improvement in the mechanical strength was also observed when the hydrogen peroxide was used instead of the aluminium powder (for comparable density values). For porous geopolymers, the minimum density obtained was 0,35 g/cm3 (1,6% H₂O₂). Polyurethane (PU) was an industrial waste used as light aggregate in the geopolymer composites (50 to 95 vol.%). Structures with density equal to 0,18 g/cm3 were obtained for contents of 95 vol.% of aggregates incorporated to the composite. It was found that density decreases with the increase of the light aggregate content. As the geopolymer content (binder) decreases, the phenomenon of crumbling appears. For that reason, the 95 vol.% PU formulation is considered to be incompatible with the target application of this study. However, the use of PU contents up to 93 vol.% (0,27 g/cm3) and the use of multilayer structures can be considered for the intended effect, with valuable levels of mechanical strength. From formulations evaluated in previous studies (80 vol.% cork – fine, coarse, and black expanded, 90 vol.% rubber and 0,100 to 0,150% Al) and others developed within this work (91 vol.% PU, 1 and 2% H₂O₂), samples of larger dimensions were produced (16 x 14 x 2 cm3 e 15 x 15 x 15 cm3). Scaling up was achieved without constraints for all formulations except for those with cork aggregates, where non-uniform shrinkage of the lightweight aggregate resulted in warping. A decrease in geometric density was verified with the increase of the sample dimension. Through dynamic mechanical analysis, a loss factor of approximately 10% was quantified for porous and composite geopolymeric samples (0,100% Al, 80 vol.% cork e 91 vol.% PU). It has also been possible to identify an inverse relation between the damping of the material and its density for samples of the same nature. Single (PU) and multi-layer geopolymeric structures were tested in terms of acoustic performance. Those samples verified higher acoustic absorption values higher than those typically observed for the Expanded Polypropylene (EPP) foams in the considered frequency range. Regarding sound transmission loss, geopolymers underperformed in comparison to the reference material (EPP). Additionally, higher values were observed for higher densities, and it was possible to conclude that the outer layers of multilayer structures have a great influence on the acoustic behaviour of the structure.), samples of larger dimensions were produced (16 x 14 x 2 cm3 e 15 x 15 x 15 cm3). Scaling up was achieved without constraints for all formulations except for those with cork aggregates, where non-uniform shrinkage of the lightweight aggregate resulted in warping. A decrease in geometric density was verified with the increase of the sample dimension. Through dynamic mechanical analysis, a loss factor of approximately 10% was quantified for porous and composite geopolymeric samples (0,100% Al, 80 vol.% cork e 91 vol.% PU). It has also been possible to identify an inverse relation between the damping of the material and its density for samples of the same nature. Single (PU) and multi-layer geopolymeric structures were tested in terms of acoustic performance. Those samples verified higher acoustic absorption values higher than those typically observed for the Expanded Polypropylene (EPP) foams in the considered frequency range. Regarding sound transmission loss, geopolymers underperformed in comparison to the reference material (EPP). Additionally, higher values were observed for higher densities, and it was possible to conclude that the outer layers of multilayer structures have a great influence on the acoustic behaviour of the structure.), samples of larger dimensions were produced (16 x 14 x 2 cm3 e 15 x 15 x 15 cm3). Scaling up was achieved without constraints for all formulations except for those with cork aggregates, where non-uniform shrinkage of the lightweight aggregate resulted in warping. A decrease in geometric density was verified with the increase of the sample dimension. Through dynamic mechanical analysis, a loss factor of approximately 10% was quantified for porous and composite geopolymeric samples (0,100% Al, 80 vol.% cork e 91 vol.% PU). It has also been possible to identify an inverse relation between the damping of the material and its density for samples of the same nature. Single (PU) and multi-layer geopolymeric structures were tested in terms of acoustic performance. Those samples verified higher acoustic absorption values higher than those typically observed for the Expanded Polypropylene (EPP) foams in the considered frequency range. Regarding sound transmission loss, geopolymers underperformed in comparison to the reference material (EPP). Additionally, higher values were observed for higher densities, and it was possible to conclude that the outer layers of multilayer structures have a great influence on the acoustic behaviour of the structure.