| 1. |
- Garemark, Jonas
(författare)
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Integrated Cellulosic Wood Aerogel Structures
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Highly porous aerogels based on renewable materials that possess structural functionality are appealing for sustainable energy regulation and harvesting. Achieving structural anisotropy provides advantageous directional diffusion and mechanical strength, however, introduces great engineering challenges, such as complex, costly, and time-consuming processing. Direct use of wood, where nanocellulose is favorably orientated, offers the opportunity of forming low-cost, scalable, and eco-friendly aerogels.This thesis explores a new type of nanostructured wood material design by filling the empty wood space with cellulosic aerogel structures based on its intrinsic biopolymers. The structure control is achieved through selective reassembly of the cell wall nanocomponents by cell wall partial dissolution and regeneration. The resultant structures, named integrated wood aerogels, show a unique combination of high specific surface area and strength due to partial retention of the wood hierarchical structure and formation of mesoporous nanofibrillated networks occupying the lumen. Different chemical systems are investigated, including DMAc/LiCl, ionic liquid (IL), and aqueous NaOH, and the processing-structure-property relationships are investigated. DMAc/LiCl is successfully used as proof of concept for integrated wood aerogel formation, but moisture sensitivity and toxicity of the system hinder further development. The IL [MTBD][MMP] is developed to solve the issues and to improve the structure control in cell wall dissolution and regeneration. An aqueous NaOH system advances the integrated cellulosic wood aerogel preparation further, considering low cost and greener chemistry. Wood composition, lignin in particular, is critical to the processing and final properties of the integrated wood aerogel. The influence of lignin content is investigated based on IL and NaOH systems. The influence of processing (such as chemical system, time and temperature) on the structure and properties (e.g. porosity, specific surface area, mechanical performance, thermal conductivity and charge density) of the aerogels are studied. Ascribing to the structure-property profile, the application of the integrated aerogel for efficient thermal insulation is demonstrated. Inspired by the water uptake in plants, high-performing pH-responsive wood power generators are formed based on water evaporation-induced electricity. The integrated aerogel structure greatly increases the solid/liquid interphase while allowing excellent mass diffusion.The methodologies presented in this thesis for selective nanoscale reassembly of the wood cell wall pave the way for advanced wood nanostructure control. The integrated wood aerogel structure reported here provides a universal material platform for advanced material design, such as a self-sustaining wood power generator. The facile and scalable processing contribute toward sustainable high-performing bioaerogels which can compete with fossil-based materials.
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| 2. |
- Garemark, Jonas, et al.
(författare)
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Nanostructurally Controllable Strong Wood Aerogel toward Efficient Thermal Insulation
- 2022
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 14:21, s. 24697-24707
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Tidskriftsartikel (refereegranskat)abstract
- Eco-friendly materials with superior thermal insulation and mechanical properties are desirable for improved energy- and space-efficiency in buildings. Cellulose aerogels with structural anisotropy could fulfill these requirements, but complex processing and high energy demand are challenges for scaling up. Here we propose a scalable, nonadditive, top-down fabrication of strong anisotropic aerogels directly from wood with excellent, near isotropic thermal insulation functions. The aerogel was obtained through cell wall dissolution and controlled precipitation in lumen, using an ionic liquid (IL) mixture comprising DMSO and a guanidinium phosphorus-based IL [MTBD][MMP]. The wood aerogel shows a unique structure with lumen filled with nanofibrils network. In situ formation of a cellulosic nanofibril network in the lumen results in specific surface areas up to 280 m2/g and high yield strengths >1.2 MPa. The highly mesoporous structure (average pore diameter 20 nm) of freeze-dried wood aerogels leads to low thermal conductivities in both the radial (0.037 W/mK) and axial (0.057 W/mK) directions, showing great potential as scalable thermal insulators. This synthesis route is energy efficient with high nanostructural controllability. The unique nanostructure and rare combination of strength and thermal properties set the material apart from comparable bottom-up aerogels. This nonadditive synthesis approach is believed to contribute significantly toward large-scale design and structure control of biobased aerogels.
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| 3. |
- Ram, Farsa, et al.
(författare)
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Functionalized Wood Veneers as Vibration Sensors : Exploring Wood Piezoelectricity and Hierarchical Structure Effects
- 2022
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:10, s. 15805-15813
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Tidskriftsartikel (refereegranskat)abstract
- Functional wood materials often rely on active additives due to the weak piezoelectric response of wood itself. Here, we chemically modify wood to form functionalized, eco-friendly wood veneer for self-powered vibration sensors. Only the piezoelectricity of the cellulose microfibrils is used, where the drastic improvement comes only from molecular and nanoscale wood structure tuning. Sequential wood modifications (delignification, oxidation, and model fluorination) are performed, and effects on vibration sensing abilities are investigated. Wood veneer piezoelectricity is characterized by the piezoresponse force microscopy mode in atomic force microscopy. Delignification, oxidation, and model fluorination of wood-based sensors provide output voltages of 11.4, 23.2, and 60 mV by facilitating cellulose microfibril deformation. The vibration sensing ability correlates with improved piezoelectricity and increased cellulose deformation, most likely by large, local cell wall bending. This shows that nanostructural wood materials design can tailor the functional properties of wood devices with potential in sustainable nanotechnology.
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| 4. |
- Ram, Farsa, et al.
(författare)
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Scalable, efficient piezoelectric wood nanogenerators enabled by wood/ ZnO nanocomposites
- 2022
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Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 160
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Tidskriftsartikel (refereegranskat)abstract
- The need for sustainable development creates opportunities for biomass-based materials design toward piezo-electric mechanical energy harvesting. Wood is promising due to its hierarchical, porous structure. Here, piezoelectric nanogenerators (PENGs) were prepared through nanostructure-controlled zinc oxide (ZnO) growth inside the outer wood layers of veneers. Mechanisms for formation of various ZnO nanostructures in wood are analyzed. Controlled morphologies of nanoparticles, nanorods, nanowires, and nanoflakes were realized and characterized by field emission-scanning electron microscopy (FE-SEM) and small angle x-ray scattering (SAXS), allowing tunable piezoelectric output. Nanostructures with higher aspect ratios i.e. nanorods and nanowires resulted in higher voltage during cyclic loading. An optimum voltage of 1.3-1.4 V was obtained with wood/ZnO nanowire or nanorod composites at a force of approximate to 8 N. The current output is in the range of 0.85-11 nA, which could be scaled up to ~130 nA with a larger area device. When mounted in shoe soles, these wood/ZnO PENGs generated 1-4 V from walking/jogging motions. The hydrothermal growth method is scalable, which facilitates practical applications.
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