| 1. |
- Apostolopoulou-Kalkavoura, Varvara, 1988-
(författare)
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Thermal Conductivity of Hygroscopic Foams Based on Cellulose Nanomaterials
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biobased super-insulating materials could mitigate climate change by minimizing the use of petroleum-based materials, creating artificial carbon sinks and minimizing the energy needed to maintain pleasant interior conditions. Cellulose nanomaterials (CNM) produced from abundantly available cellulose sources constitute versatile, highly anisotropic raw materials with tunable surface chemistry and high strength. This thesis includes the evaluation of the thermal conductivity of isotropic and anisotropic CNM-based foams and aerogels and analysis of the dominant heat transfer mechanisms. We have developed a customized measurement cell for hygroscopic materials in which the humidity and temperature are carefully controlled while the thermal conductivity is measured. Anisotropic cellulose nanofibrils (CNF) foams with varying diameters showed a super-insulating behavior perpendicular (radial) to the nanofibril direction, that depended non-linearly on the relative humidity (RH) and foam density. Molecular simulations revealed that the very low thermal conductivity is related to phonon scattering due to the increase of the inter-fibrillar gap with increasing RH that resulted in a 6-fold decrease of the thermal boundary conductance. The moisture-induced swelling exceeds the thermal conductivity increase due to water uptake at low and intermediate RH and resulted in a minimum thermal conductivity of 14 mW m-1 K-1 at 35% RH and 295 K for the foams based on the thinnest CNF.The density-dependency of the thermal conductivity of cellulose nanocrystal (CNC) foams with densities of 25 to 129 kg m-3 was investigated and a volume-weighted modelling of the solid and gas thermal conductivity contributions suggested that phonon scattering was essential to explain the low radial thermal conductivity, whereas the replacement of air with water and the Knudsen effect related to the nanoporosity in the foam walls had a small effect. Intermediate-density CNC foams (34 kg m-3) exhibited a radial thermal conductivity of 24 mW m-1 K-1 at 295 K and 20% RH, which is below the value for air.The moisture uptake of foams based on CNMs with different degree of crystallinity and surface modifications decreased significantly with increasing crystallinity and temperature. Molecular simulations showed that the narrow pore size distribution of the amorphous cellulose film, and the relatively low water adsorption in the hydration cell around the oxygen of the carboxyl group play an important role for the moisture uptake of amorphous and crystalline CNM-based materials.Isotropic CNF- and polyoxamer based foams as well as CNF-AL-MIL-53 (an aluminum‑based metal-organic framework) foams were both moderately insulating (>40 mW m-1 K-1) and comparable with commercial expanded polystyrene. The thermal conductivity of CNF and polyoxamer foams displayed a very strong RH dependency that was modelled with a modified Künzel’s model. The presence of hydrophobic AL-MIL-53 decreased the moisture uptake of CNF-AL-MIL-53 aerogels by 42% compared to CNF-polyoxamer foams.Solid and gas conduction are the main heat transfer mechanisms in hygroscopic nanofibrillar foams and aerogels that depend on the interfacial phonon scattering, Knudsen effect and water uptake. It is essential that the thermal conductivity measurements of hygroscopic CNM-based foams and aerogels are determined at controlled RH and that parameters such as the temperature, density, nanoporosity, fibril dimensions and alignment are characterized and controlled for systematic development and upscaling of biobased foams for applications in building insulation and packaging.
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| 2. |
- Budtova, Tatiana, et al.
(författare)
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Biorefinery Approach for Aerogels
- 2020
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Ingår i: Polymers. - : MDPI. - 2073-4360. ; 12:12
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Forskningsöversikt (refereegranskat)abstract
- According to the International Energy Agency, biorefinery is “the sustainable processing of biomass into a spectrum of marketable bio-based products (chemicals, materials) and bioenergy (fuels, power, heat)”. In this review, we survey how the biorefinery approach can be applied to highly porous and nanostructured materials, namely aerogels. Historically, aerogels were first developed using inorganic matter. Subsequently, synthetic polymers were also employed. At the beginning of the 21st century, new aerogels were created based on biomass. Which sources of biomass can be used to make aerogels and how? This review answers these questions, paying special attention to bio-aerogels’ environmental and biomedical applications. The article is a result of fruitful exchanges in the frame of the European project COST Action “CA 18125 AERoGELS: Advanced Engineering and Research of aeroGels for Environment and Life Sciences”.
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| 3. |
- Gericke, Martin, et al.
(författare)
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The European Polysaccharide Network of Excellence (EPNOE) research roadmap 2040: Advanced strategies for exploiting the vast potential of polysaccharides as renewable bioresources
- 2024
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 326
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Tidskriftsartikel (refereegranskat)abstract
- Polysaccharides are among the most abundant bioresources on earth and consequently need to play a pivotal role when addressing existential scientific challenges like climate change and the shift from fossil-based to sustainable biobased materials. The Research Roadmap 2040 of the European Polysaccharide Network of Excellence (EPNOE) provides an expert's view on how future research and development strategies need to evolve to fully exploit the vast potential of polysaccharides as renewable bioresources. It is addressed to academic researchers, companies, as well as policymakers and covers five strategic areas that are of great importance in the context of polysaccharide related research: (I) Materials & Engineering, (II) Food & Nutrition, (III) Biomedical Applications, (IV) Chemistry, Biology & Physics, and (V) Skills & Education. Each section summarizes the state of research, identifies challenges that are currently faced, project achievements and developments that are expected in the upcoming 20 years, and finally provides outlines on how future research activities need to evolve.
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