Study of the properties of composite aerogels
Aerogels were discovered by Steven Kistler in 1931, who defined them as “gels in which the liquid has been replaced by air, with very moderate shrinkage of the solid network”. They are therefore porous materials with a very low density (approx. 0.1 g/cm3 ). Due to their low weight, low thermal condu...
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| Tipo de recurso: | tesis de maestría |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/377405 |
| Acceso en línea: | https://hdl.handle.net/2117/377405 |
| Access Level: | acceso abierto |
| Palabra clave: | Aerogels Àrees temàtiques de la UPC::Enginyeria dels materials |
| Sumario: | Aerogels were discovered by Steven Kistler in 1931, who defined them as “gels in which the liquid has been replaced by air, with very moderate shrinkage of the solid network”. They are therefore porous materials with a very low density (approx. 0.1 g/cm3 ). Due to their low weight, low thermal conductivity and high specific surface, they have great potential in many technological fields such as selective absorption of pollutants, catalysis, energy storage or thermal insulation to mention a few. Inorganic aerogels tend to be brittle which has led to the generation of polymer-based aerogels which are materials that can exhibit properties similar to polymeric foams. Incorporation of polymers into aerogels increases, however, the flammability of those materials, potentially restricting their use in applications requiring fire safety, such as thermal insulation materials in building construction. A significant effort has targeted to the enhancement of the flame retardancy of aerogels, including the use of intrinsically flame-retardant polymers, polymer crosslinking, addition of flame retardants, and post-treatment of the resulting aerogels. Another possibility consists in adding fillers that can simultaneously increase the mechanical and thermal resistance of these materials. Furthermore, in this historical period there is a focus on the environmental impact of industrial products, which is why there is also a strong development in the world of aerogels on the creation of bio-based products. Several studies have been conducted on the use of polysaccharides such as cellulose, starch, chitosan, alginate, carrageenan or pectin as precursors for aerogels in order to find viable alternatives to petroleum-based foams on the market, such as polystyrene or polyurethane foams. Thus, the objective of this project is the creation and characterisation of eco-friendly composite aerogels made of bio-based materials: Ammonium alginate, a polysaccharide from seaweed, serves as a biopolymer, tannic acid, extracted from certain trees, was used as an additive due to its flame retardant and crosslinker characteristics. Finally, montmorillonite clay was used to significantly increase fire resistance and modify the mechanical properties. This inorganic material, found in abundance in the earth, allows the residue to increase considerably if the material is thermally degraded. The solvent used was deionised water and a sol-gel process followed by freeze-drying was performed, which allowed aerogels to be obtained with a moderate environmental impact. The different compositions were characterised using: Compression test, thermal conductivity analyser, thermogravimetric analysis, cone calorimeter, moisture analyser, Fourier transform infrared spectroscopy. In this way, it was possible to evaluate the influence of the additives on the material properties, noting that the samples with the best thermo-mechanical performance are those containing all chemical species, in particular as they increase, the properties improve. Only bulk density and thermal conductivity improve as the number of components in the aerogels decreases, as they are both also a function of the amount of solid phase present in a micro- and mesoporous material. |
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