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- Valencia, Luis, 1990-
(författare)
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Cellulose Nanofibril-based Hybrid Materials : Eco-friendly design towards separation and packaging applications
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanocellulose has been lately considered as the “Holy-Grail” in the design of sustainable materials due to its bio-origin and an unprecedented combination of prominent features, including good mechanical properties, anisotropy and versatile surface chemistry. In addition, nanocellulose in the form of cellulose nanofibrils, can adopt variable structures and morphologies depending on the processing technique, such as aerogels, films and monoliths.However, there are limitations that hinder the implementation of cellulose nanofibrils in “real-life applications”, such as inherent interaction with bacteria and proteins, thus leading to surface-fouling; and loss of integrity due to water-induced swelling. A way to overcome these challenges, and provide further functionality, is through hybridization strategies, at which the multiple components act synergistically towards specific properties and applications. In this thesis, the aim is to present multiple strategies for the synthesis of novel cellulose nanofibril-based hybrid materials, in the form of 2D-films and 3D-foams, towards their employment for separation applications or active food packaging.A novel strategy to surface-functionalize cellulose nanofibril-membranes is proposed via grafting zwitterionic polymer brushes of poly (cysteine methacrylate). The modification can suppress the absorption of proteins in an 85%, as well as decreasing the adhesion of bacteria in an 87%, while introducing antimicrobial properties, as demonstrated against S. aureus.The spontaneous formation of functional metal oxide nanoparticles occurring in situ on cellulose nanofibrils-films during the adsorption of metal ions from water is investigated, which occurs without the additional use of chemicals or temperature. Notably, this process not only enables the upcycling of materials through multi-stage applications, but also provides a cost-effective method to prepare multifunctional hybrid materials with enhanced dye-removal/antimicrobial activity.The processing of functional composite films from cellulose nanofibril-stabilized Pickering emulsions and their suitability to be used as active edible barriers was demonstrated. The presence of oil in the films fine-tuned the properties of the films, as well as acted as the medium to encapsulate bio-active hydrophobic compounds, providing further functionality such as antioxidant and antimicrobial properties.Anisotropic porous hybrid foams with ultra-high loading capacity of sorbents (e.g., zeolites and metal-organic frameworks) were produced via unidirectional freeze-casting method using cellulose nanofibrils/gelatin as template material. The foams indeed exhibited ultra-high loading capacity of sorbent nanomaterials, a linear relationship between sorbent content and CO2 adsorption capacity, and high CO2/N2 selectivity.
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| 2. |
- Eyholzer, Christian
(författare)
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Dried nanofibrillated cellulose and its bionanocomposites
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the past decade there has been a growing interest in the reinforcement of synthetic polymers with cellulose nanowhiskers and nanofibrillated cellulose (NFC) obtained from plants or bacteria. Their beneficial mechanical properties like high stiffness and strength, in combination with their low mass allowed successful reinforcement of water based polymer dispersions (latexes) for the production of solution cast composite films. However, the production of fully degradable or biocompatible nanocomposites containing NFC with high aspect ratio and diameters below 100 nm is still a challenging task. One of the main issues to overcome is irreversible agglomeration (hornification) of NFC. Hornification can occur during drying of aqueous NFC suspensions or during compounding of NFC with hydrophobic polymers and it can be explained with the formation of a large number of hydrogen bonds between the hydroxyl groups of adjacent nanofibrils. This process is accompanied by a considerable decrease of the NFC aspect ratio and consequently results in the complete loss of its beneficial properties. Therefore, the objective of this PhD work was to chemically functionalize NFC in order to prevent hornification during drying and to develop novel bionanocomposites with well dispersed NFC, displaying improved properties compared to the neat polymers. Successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In this study, a method for the preparation of water-redispersible NFC in powder form was developed, comprising carboxymethylation and mechanical disintegration of refined, bleached beech pulp (RBP). The powders formed stable gels when dispersed in water and SEM images confirmed that carboxymethylation had successfully prevented hornification of NFC during drying. Dynamic mechanical analysis (DMA) of poly(vinyl acetate) latex composites showed that carboxymethylation did not negatively influence the reinforcing potential of NFC. Consistently, the reinforcing potential of c-NFC was not altered by the drying procedure, as was shown by DMA experiments and tensile tests of hydroxypropyl cellulose composites containing dried and never-dried c-NFC. In a subsequent study, bionanocomposites were developed by UV-photopolymerization of N-vinyl-2-pyrrolidone in presence of a trimethacrylate crosslinker and water-redispersed c-NFC powder to yield a biocompatible hydrogel for the replacement of degenerated human Nucleus Pulposus (NP) in intervertebral discs. The native structure and function of the NP was mimicked by the randomly oriented c-NFC fibrils in the hydrogel matrix. The biocomposite hydrogels showed similar values for swelling ratio and modulus of elasticity in compression, compared to native NP. A final study focused on the feasibility of an industrial up-scaling of poly(lactic acid) composites containing compatibilized c-NFC using extrusion.
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| 3. |
- Guccini, Valentina, 1988-
(författare)
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Nanocellulose: Energy Applications and Self-Assembly
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Technologies based on renewable materials are required to decrease the environmental cost and promote the development of a sustainable society. In this regard, nanocellulose extracted from wood finds many applications thanks to its intrinsic mechanical and chemical properties as well as the versatility in its manufacturing processes. In this thesis, I present the results of the investigations on carboxylated cellulose nanofibres (CNF) as ionic conductive membranes and electrode component in fuel cells and lithium ion batteries. Moreover, I also show the results of the assembly of CNF suspension and cellulose nanocrystals (CNC) - lepidocrocite nanorods (LpN) hybrids.The fuel cell performance of CNF-based proton conductive membranes was evaluated as a function of intrinsic material parameters such as membrane thickness and surface charge density as well as extrinsic parameters such as the relative humidity (RH). It was found that the proton conductivity is about 2 mS cm-1 at 30 °C between 65 and 95 % RH. At the same time, the water uptake of the membrane was measured and correlated with the structural evolution of the membrane using small angle X-ray scattering.The performance of the CNF-based separator in lithium ion batteries was investigated as a function of membrane porosity and protonation of the functional groups. The Li-ion battery assembled with the protonated separators showed stable and good rate performance.The CNF was also tested as binder in lithium ion battery, showing that the morphology and mechanical properties of the cathode depend on the nanofibre surface charge and degree of defibrillation. In particular, high surface charge and medium degree of defibrillation give the best electrochemical performance.Pyrolysed CNF (cCNF) improved the electrochemical performance of silicon nanoparticles-based anode thanks to the carbon network derived from the nanofibres. Si-cCNF has a capacity retention of 72.2 % after 500 cycles at 1 C and better performance rate than the pristine silicon nanoparticles.Regarding the assembly of nanocellulose, the nematic order of CNF suspension at different nanofibre concentrations (0.5 – 4.9 wt%) was studied by small angle X-ray scattering, polarized optical microscopy and rheological measurements. The order parameter reaches a maximum value of 0.8 depending on the CNF concentration. Small angle neutron scattering with contrast matching experiments reveals that the natural alignment of CNC and LpN can be switched using a combination of magnetic fields of up to 6.8 T and varying the amount of LpN incorporated in the CNC.
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