| 1. |
- Butchosa Robles, Núria, 1984-
(författare)
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Tailoring Cellulose Nanofibrils for Advanced Materials
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose nanofibrils (CNFs) are nanoscale fibers of high aspect ratio that can be isolated from a wide variety of cellulosic sources, including wood and bacterial cellulose. With high strength despite of their low density, CNFs are a promising renewable building block for the preparation of nanostructured materials and composites. To fabricate CNF-based materials with improved inherent rheological and mechanical properties and additional new functionalities, it is essential to tailor the surface properties of individual CNFs. The surface structures control the interactions between CNFs and ultimately dictate the structure and macroscale properties of the bulk material. In this thesis we have demonstrated different approaches, ranging from non-covalent adsorption and covalent chemical modification to modification of cellulose biosynthesis, to tailor the structure and surface functionalities of CNFs for the fabrication of advanced materials. These materials possess enhanced properties such as water-redispersibility, water absorbency, dye adsorption capacity, antibacterial activity, and mechanical properties.In Paper I, CNFs were modified via the irreversible adsorption of carboxymethyl cellulose (CMC). The adsorption of small amounts of CMC onto the surface of CNFs prevented agglomeration and co-crystallization of the nanofibrils upon drying, and allowed the recovery of rheological and mechanical properties after redispersion of dried CNF samples.In Paper II, CNFs bearing permanent cationic charges were prepared through quaternization of wood pulp fibers followed by mechanical disintegration. The activation of the hydroxyl groups on pulp fibers by alkaline treatment was optimized prior to quaternization. This optimization resulted in individual CNFs with uniform width and tunable cationic charge densities. These cationic CNFs demonstrated ultrahigh water absorbency and high adsorption capacity for anionic dyes.In Paper III, via a similar approach as in Paper II, CNFs bearing polyethylene glycol (PEG) were prepared by covalently grafting PEG to carboxylated pulp fibers prior to mechanical disintegration. CNFs with a high surface chain density of PEG and a uniform width were oriented to produce macroscopic ribbons simply by mechanical stretching of the CNF hydrogel network before drying. The uniform grafted thin monolayer of PEG on the surface of individual CNFs prevented the agglomeration of CNFs and facilitated their alignment upon mechanical stretching, thus resulted in ribbons with ultrahigh tensile strength and modulus. These optically transparent ribbons also demonstrated interesting biaxial light scattering behavior.In Paper IV, bacterial cellulose (BC) was modified by the addition of chitin nanocrystals (ChNCs) into the growing culture medium of the bacteria Acetobacter aceti which secretes cellulose in the form of entangled nanofibers. This led to the in situ incorporation of ChNCs into the BC nanofibers network and resulted in BC/ChNC nanocomposites exhibiting bactericidal activity. Further, blending of BC nanofibers with ChNCs produced nanocomposite films with relatively lower tensile strength and modulus compared to the in situ cultivated ones. The bactericidal activity increased significantly with increasing amount of ChNCs for nanocomposites prepared by direct mixing of BC nanofibers and ChNCs.In Paper V, CNFs were isolated from suspension-cultured wild-type (WT) and cellulose-binding module (CBM) transformed tobacco BY-2 (Nicotiana tabacum L. cv bright yellow) cells. Results from strong sulfuric acid hydrolysis indicated that CNFs from transgenic cells overexpressing CBM consisted of longer cellulose nanocrystals compared to CNFs from WT cells. Nanopapers prepared from CNFs of transgenic cells demonstrated significantly enhanced toughness compared to CNFs of WT cells.
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| 2. |
- Jiang, Kun
(författare)
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Modulating the structure-function relationship of mucin materials
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mucus covers the epithelium surfaces playing a key role in the barrier, hydration, lubrication and bioactivity functions for the human body, and mucins are the fundamental components of mucus which provide such functions. However, many details in how these functions are related to the many structural features of mucins are still unknown. In this thesis, strategies were developed to modify mucin structures in defined ways to gain insights and controls over several key functions of this molecule. We altered functional motifs on the mucin molecules, and changed the conformation of mucin networks to modulate the accessibility of such functional motifs. Then functional outcomes, including macrophage responses, diffusion of molecules through mucin networks, and mucin lubricity were studied. This thesis is organized into three parts according to the three functions. We found that the responses of macrophage to mucins were modulated by changing the location of crosslinks between mucins and by the immobilization of mucins onto surfaces. Mucins’ bottle-brush structure allowed their crosslinking either via the protein backbone or via the glycan side chains with similar crosslinking density. With the same crosslinking structure, the placement of mucin thin film on hard substrate and soft substrate led to different macrophage responses, and only mucin coating on soft gel induced similar immune responses as that of mucin gels. A better understanding of how mucin bioactivity, and specifically immune-modulating properties, can be modulated, provide new strategies to develop biomaterials with defined bioactivities. This work could also inspire innovative treatments to modulate mucin bioactivities in vivo to treat mucin-related diseases such as for mucinous cancers. The diffusion of molecules through mucin gels was modulated by changing the gel network and their affinity filtration capacity. By locating the crosslinking sites on the protein backbone or the glycan chains, the gel network remained the same with similar diffusion profiles of dextrans. However, with simple change of mucin concentration, molecules of different size diffused faster in gels with lower mucin concentration. The affinity filtration of mucin gel was modulated by removing sialic acids, which acts as binding sites for molecules or cells via electrostatic interactions or specific binding, and the binding can slow down diffusion of cells or molecules. By altering sialic acid contents, the diffusion of charged dextran was modulated and the penetration of sperms was increased. With the understanding, mucin gels with controlled permeability can be designed for loading drugs or encapsulating tissue. And strategies can be developed in the future for treating mucus barrier related disease in vivo, such as inflammatory bowel disease.The hydration & lubrication of mucin coating was modulated with changed mucin structure and removal of associated impurities. The hydration of mucin coatings remained the same, but their lubricity was lost by removing negatively charged sugars. However, the components associated with mucin, such as DNA, compensated for the missing of negative sugars. Commercial PGM was found with damaged glycosylation and missing peptide domains, and its lubricity was lost completely compared to lab-purified mucins. With this knowledge, mucin structure can be modulated for desired hydration and lubrication performance, and this can inspire to develop strategies for restoring their hydration and lubricity in vivo during diseases, such as dry eye.
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| 3. |
- Koskela, Salla, 1990-
(författare)
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Lytic polysaccharide monooxygenases for green production of cellulose nanomaterials
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose is the main structural polymer in wood, and its potential in the form of nanomaterial building blocks, nanocelluloses, has now been recognized. Nanocelluloses, including cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs), have become increasingly important in development of modern sustainable materials. Nanocelluloses are typically produced from wood pulp fibers by chemical pre-treatments that deposit charged functional groups onto cellulose microfibril surfaces, thereby promoting disintegration of the fiber cell wall during mechanical fibrillation. Due to environmental risks related to the use of harsh chemical treatments, it is crucial to develop greener, nature-inspired alternatives. As renowned decomposers of wood, fungi secrete cellulose-active enzymes that work in aqueous reaction conditions. Of these, lytic polysaccharide monooxygenases (LPMOs) have piqued a special interest in green production of nanocellulose owing to their ability to introduce charged carboxyl groups onto cellulose surfaces. However, little is known about the properties of LPMO-oxidized nanocelluloses, their mechanical performance in bulk materials, and the mechanism how LPMOs facilitate fibrillation of the wood fiber cells.This PhD thesis aimed to dissect the potential of C1-oxidizing LPMOs in the production of nanocelluloses and to clarify the mechanism of LPMO oxidation that facilitates the disintegration of wood cell wall. LPMOs with and without attached carbohydrate-binding modules (CBMs) were recombinantly produced in Pichia pastoris and studied for the production of CNFs and CNCs, which were further processed into bulk materials. The morphology and properties of the nanocelluloses, and the optical and mechanical properties of the bulk materials were characterized. In addition, delignified wood with a preserved cellular structure was used as a model substrate for LPMO oxidation, and the LPMO-induced changes in the wood cell wall structure were investigated using advanced scattering techniques.The results on CNF production showed that LPMO-oxidized wood pulp fibers can be transformed into discrete and colloidal CNFs by mild mechanical disintegration, analogous to chemical pre-treatments such as 2,2,6,6-tetramethylpyperidine-1-oxy radical (TEMPO)-mediated oxidation. Importantly, these CNFs were well individualized with an average width of 4 nm, resembling that of cellulose microfibrils in wood. Such CNFs were obtained from softwood holocellulose- and kraft pulp fibers with a hemicellulose content of 16–19%, but not from dissolving pulp with a lower hemicellulose content of 4%. Nanopapers prepared from the LPMO-oxidized CNFs were transparent and they demonstrated tensile strengths of ca. 260 MPa and Young’s moduli of ca. 17 GPa. The water suspensions of LPMO-oxidized CNFs also exhibited acid-triggered gelation behavior due to the enzymatically introduced carboxyl groups.LPMO oxidation was also found applicable in the preparation of CNCs from microcrystalline cellulose. The LPMO-oxidized CNCs had a needle-like morphology and they formed stable colloidal suspensions in water that demonstrated flow-induced birefringence. Solution cast films showed that the CNCs bearing C1 carboxyl groups possessed the pivotal ability to undergo self-assembly into an anisotropic phase. As some LPMOs are appended to a non-catalytic CBM, the effect of this module on nanocellulose production was also determined. CBM was found to increase the release of carboxyl groups from cellulose microfibril surfaces in the form of soluble cello-oligosaccharides. By contrast, a non-modular LPMO introduced more carboxyl groups to the cellulose surfaces, up to 0.53 mmol g-1 on CNFs, and 0.70 mmol g-1 on CNCs. Indeed, a non-modular LPMO was found advantageous in production of both CNFs and CNCs.Despite the important role of LPMOs for natural and biotechnological degradation of wood biomass, the LPMO-induced changes in the wood cell wall structure have remained unknown. In this work, these changes were characterized for the first time. It was shown that a C1-oxiding LPMO can modulate cellulose microfibrils and disrupt the wood cell wall ultrastructure by modifying cellulose surface chemistry. After the LPMO oxidation, the average distance between cellulose microfibril centers increased from 4.1 nm to 10.7 nm, signifying the separation of microfibrils in a microfibril bundle. This result revealed a previously unidentified role for C1-oxidizing LPMOs in degradation of cellulose at the nanoscale. Remarkably, LPMO-treated wood veneers could be further compressed into anisotropic, transparent films with an ultrahigh tensile strength of 824 MPa.In summary, this PhD thesis clarified the potential of C1-oxidizing LPMOs in green production of nanocelluloses and showed that LPMO oxidation is a suitable method to obtain high-performing isotropic and anisotropic bulk materials from wood. On the basis of the obtained findings, a new model was also proposed which elucidates the mechanism of cellulose degradation at the nanoscale. This study broadened the understanding of LPMOs including their biological- and biotechnological significance and provided new insights into the use of LPMOs for the preparation of cellulose-based nanomaterials.
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| 4. |
- Mastantuoni, Gabriella G.
(författare)
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Engineering of lignin in wood towards functional materials
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Through 270 million years of evolution, the finely tuned hierarchical structure of wood has been optimized for efficient nutrient transport and exceptional mechanical stability. Its distinctive orthotropic constitution can provide inspiration and design opportunities for the development of novel functional materials. In recent years, top-down modification approaches have adapted the wood structure for innovative applications, utilizing the hierarchical arrangement at different length scales. In doing so, preserving the structural integrity is of the essence.This thesis explores new top-down modification techniques for the functionalization and structural control of wood-based materials. With the intent of better preserving and utilizing the natural wood organization and native components, two different modification routes were explored on softwood Scots pine: complete lignin removal and in-situ lignin modification. Complete delignification was achieved through preventive crosslinking of the polysaccharide matrix, enhancing intercellular adhesion between tracheids and preventing the disintegration of the cellular arrangement after lignin removal. The second approach focused on chemical modification of lignin by sulfonation as an alternative to complete lignin removal, resulting in wood templates of high negative charge up to 375 µmol g-1 and with well-preserved residual lignin. Hot compression of the delignified wood veneers produced thin wood films with high optical transmittance of 71 % alongside exceptional tensile strength of 449 MPa and Young’s modulus of 50 GPa. Densification of lignin-retaining wood veneers yielded strong and transparent thin films with UV blocking ability. Additionally, these densified films could be easily recycled into discrete wood fibers. The integration of conductive polymers including poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and polypyrrole in in-situ sulfonated wood resulted in bio-composites with high conductivity up to 203 S m-1 and high pseudo-capacitance up to 38 mF cm-2, indicating that tailoring the wood chemistry and activating the redox activity of lignin by sulfonation are important strategies for the fabrication of composites with potential for sustainable energy applications. By tailoring both wood chemistry and morphology, a wood foam with unique microstructure, enhanced permeability, along with high ultimate strength of 9 MPa and Young’s modulus of 364 MPa was obtained. When combined with the conductive polymer PEDOT:PSS, the composite demonstrated uniform conductivity of 215 S m-1 and mechanoresponsive electrical resistance, showing promise in sensing and mechanoresponsive devices.Therefore, in-situ engineering of lignin proved to be a versatile toolkit to obtain wood templates of improved permeability and porosity, greater compliance to densification, and enhanced compatibility with conductive polymers.
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| 5. |
- Mushi, Ngesa Ezekiel, 1979-
(författare)
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Chitin nanofibers, networks and composites : Preparation, structure and mechanical properties
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chitin is an important reinforcing component in load-bearing structures in many organisms such as insects and crustaceans (i.e. shrimps, lobsters, crabs etc.). It is of increasing interest for use in packaging materials as well as in biomedical applications. Furthermore, biological materials may inspire the development of new man-made material concepts. Chitinmolecules are crystallized in extended chain conformations to form nanoscale fibrils of about 3 nm in diameter. In the present study, novel materialshave been developed based on a new type of chitin nanofibers prepared from the lobster exoskeleton. Improved understanding about effects of chitin from crustaceans and chitin material preparation on structure is provided through Atomic Force Microscopy(AFM) (paper I&II), Scanning Transmission Electron Microscopy(STEM) (paper I&II), X-Ray Diffraction (XRD), Intrinsic Viscosity, solid state 13C Nuclear Magnetic Resonance (NMR) (paper II), Field Emission Scanning Electron Microscopy(FE-SEM) (paper I, II, III, IV & V), Ultraviolet-Visible Spectrophotometryand Dynamic Light Scattering (DLS) (paper III). The presence of protein was confirmed through colorimetric method(paper I & II). An interesting result from the thesis is the new features of chitin nanofiber including small diameter, high molar mass or nanofiber length,and high purity. The structure and composition of the nanofibers confirms this (paper I & II). Furthermore, the structure and properties of the corresponding materials confirm the uniqueness of the present nanofibers: chitin membrane (I & II), polymer matrix composites (III),and hydrogels (paper IV).Improved mechanical properties compared with typical data from the literature were confirmed for chitin nanofiber membranes in paper II, chitin-chitosan polymer matrix composites in paper III, and chitin hydrogel in paper IV. Mechanical tests included dynamic mechanical analysis and uniaxial tensile tests. Mechanical properties of chitin hydrogels were evaluated based onrheological and compression properties (paper IV). The values were the highest reported for this kind of chitin material. Furthermore, the relationships between materials structure and properties were analyzed. For membranes and polymer matrix nanocomposites, the degree of dispersion is an important parameter. For the hydrogels, the preparation procedure is very simple and has interesting practical potential.Chitin-binding characteristics of cuticular proteins areinteresting fornovel bio-inspired material development. In the present work(paper V), chitin nanofibers with newfeaturesincluding high surface area and low protein content were combined with resilin-like protein possessing the chitin-binding characteristics. Hydrated chitin-resilin nanocomposites with similar composition as in rubber-like insect cuticles were prepared. The main objective was to improve understanding on the role of chitin-binding domain on mechanical properties. Resilin is a rubber-like protein present in insects. The exon I (comprising 18 N-terminal elastic repeat units) together with or without the exon II (a typical cuticular chitin-binding domain) from the resilin gene CG15920 found in Drosophila melanogasterwere cloned and the encoded proteins were expressed as soluble products in Escherichia coli.Resilin-like protein with chitin-binding domain (designated as ResChBD) adsorbedin significant amount to chitin nanofiber surface andprotein-bound cuticle-like soft nanocomposites were formed. Although chitin bindingwas taking place only in proteinswith chitin-binding domain, the global mechanical behavior of the hydrated chitin-resilin nanocomposites was not so sensitive to this chitin-resilin interaction.In summary, chitin is an interesting material component with high potential as mechanical reinforcement in a variety of nanomaterials. The present study reports the genesisof novel chitin nanofibers and outlines the basic relationships between structure and properties for materials based on chitin. Future work should be directed towards both bio-inspired studies of the nanocomposite chitin structures in organisms, as well as the industrial applications of chitin waste from the food industry. Chitin nanofibers can strengthen the properties of materials, andprovide optical transparency as well as biological activities such as antimicrobial properties.
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| 6. |
- Wang, Shennan, MS, 1992-
(författare)
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Chemical Modification of Nanostructured Wood for Functional Biocomposites
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recently emerged top-down processing concept has provided new insights into the chemical modification of wood at the nanoscale. Nanostructured wood with naturally aligned cellulose microfibrils, cell wall nanoporosity, and precisely tuned chemical composition has opened up numerous possibilities for advanced design of functional materials. In this thesis, novel chemical modification strategies have been developed to obtain nanostructural control and surface functionalization of nanostructured wood. Functional biocomposite materials with superior mechanical and optical performance, high CO2 adsorption capacity, and immobilized protein have been fabricated using the novel chemically modified nanostructured wood. The direct preparation of nanostructured wood from hardwood balsa was achieved by structure retaining delignification using acidic sodium chlorite. Crosslinking of the matrix polysaccharides using a homobifunctional epoxide compound was necessary as a pretreatment step for softwood spruce to maintain its structure integrity after complete delignification. Further chemical modification of delignified balsa wood through 2,2,6,6-tetrametylpiperidin-1-oxyl (TEMPO)-mediated oxidation selectively oxidized surface hydroxyls to carboxyl groups and induced fibrillation of cellulose microfibrils within the cell wall. Therefore, TEMPO-oxidized wood (TO-wood) with high carboxylate content (0.78 mmol g-1), high specific surface area (249 m2 g-1), and large mesopore volume (0.78 cm3 g-1) was successfully produced. Tunable microstructure of TO-wood was subsequently obtained by incorporating different counterions (H+, Cu2+, Al3+, Zn2+) or by employing different drying methods (super critical drying and freeze drying). In addition, surface amination method was also developed on highly mesoporous delignified spruce cellulose scaffold to introduce a reactive handle for immobilization of biomolecules. These chemically modified nanostructured wood have inspired the fabrication of wood-based biocomposites with new functionalities that are not possible with traditional wood materials.Delignified balsa wood showed stronger hydrophilicity and larger porosity, which allowed the formation of composite hydrogels through infiltration of gelatin and crosslinking with genipin. The composite hydrogels showed high mechanical strength under compression and low swelling in physiological condition. The preserved cellular structure and fibrillated cellulose microfibrils in TO-wood enabled facile fabrication of compressible aerogel and exceptionally strong film (tensile strength of 449 MPa and Young’s modulus of 51 GPa) upon different drying conditions. Fibrillation of cellulose microfibrils was also found critical to the inter-penetration between cell wall and poly(N-isopropylacrylamide) (PNIPAM) hydrogel network, producing tough and highly transparent composite hydrogel with a total transmittance of 85.8% at thickness of 2 mm. The TO-wood/PNIPAM hydrogel was able to reversibly switch between transparent and brightly white in response to environmental temperature change between 25 and 40 °C. Surface carboxyl groups of TO-wood also facilitated the surface coordination of cell wall to multivalent metal ions, which subsequently enhanced the in situ synthesis of metal organic frameworks (MOFs). The resulting TO-wood/Cu3(BTC)2 (copper benzene-1,3,5-tricarboxylate) composite aerogel showed high specific surface area of 471 m2 g-1 and high CO2 adsorption capacity of 1.46 mmol g-1 at 25 °C under atmosphere pressure. The highly mesoporous and mechanical robust spruce derived cellulose scaffold laden with reactive amine groups allowed covalent immobilization of functional biomolecules, such as a lectin protein concanavalin A, which demonstrated potential glycoprotein-binding and separation applications.
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| 7. |
- Yuan, Yusheng, 1992-
(författare)
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Development of Functionalized Protein Materials
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many proteins are available as side-streams from food production, and in some cases even from industrial waste-streams. This means that proteins are available in large scale and at a relatively low price. As protein are highly complex molecules it is interesting to try to use protein as starting materials in for applications in materials science. Most proteins have the ability to self-assemble into nanofibrils. These fibrils have a regular repeating substructure that consists of β-strands running perpendicular to the fibril axis, resulting in cross-β sheets that run parallel along the fibril axis. The extended β-sheets structure results in the formation of hydrophobic grooves that can act as potential binding sites organic molecules. This means that the functionality of the material may be modified by addition of e.g. light emitting molecules or drug molecules. By such functionalization the protein material may accordingly be suitable for applications such as light-conversion materials (e.g. for use as coatings of light emitting diodes (LEDs)) or for drug-delivery. For such applications, the protein fibrils must be processes into macroscopic structures such as films or gels. Against this background, we employ the food proteins hen egg white lysozyme and β-lactoglobulin as model proteins for fibrillation and functionalization. Through a mechanochemical process the hydrophobic dyes can conveniently be combined with proteins, that can be converted into functionalized protein nanofibrils by liquid-phase self-assembly. By employing protein fibrils functionalized with three dyes, we have been able to form films that enables conversion of UV light to white light (and can thus be employed as a coating on UV-LEDs) with protein fibrils functionalized with multiple dyes. By mixing biodegradable polymers with functionalized protein fibrils, luminescent bioplastic films can be prepared that are processable when wet; a cut film will also self-heal if water is applied. We have also turned functionalized protein fibrils into gel states, including hydrogels or aerogels. In the case of protein fibrils functionalized with Hydantoins (a type of drug molecule) hydrogels were prepared, and the release of the drug was investigated. In addition, aerogels can be prepared from hydrogels by freeze drying, and in this manner lightweight functionalized aerogels are achieved. By functionalization with an electrically conductive polymer, an elastic conductive aerogel is formed that employed as a piezoelectric pressure sensor. In summary a wide range of materials have been prepared suitable for various applications demonstrating the flexibility of the developed functionalization methodology and that the structural richness of protein self-assembly can be employed to prepare a wide variety of types of materials of varying functionality.
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| 8. |
- Zha, Li
(författare)
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Surface Engineering of Cellulose Nanofibers for Advanced Biocomposites
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanocellulose, originated from cellulose, the primary structural component of the cell walls of plants, has garnered significant attention for its excellent mechanical, optical, and barrier properties, as well as its renewable and sustainable nature. Various forms of nanocellulose, including cellulose nanocrystals and cellulose nanofibers (CNFs), are produced by breaking down lignocellulosic fibers into nanoscale dimensions, typically through mechanical or chemical processes. The large surface area and rich hydroxyl groups of CNFs are ideal for surface modifications, offering great versatility in the development of functional biocomposite materials. This thesis aims to design CNF-based composites with integrated multifunctionalities, including redispersibility, biocompatibility, mechanical robustness, wet integrity, as well as optical transparency, through surface engineering of cellulose nanofibers. The methodology involves strategically selecting CNFs, integrating CNFs with biopolymers, applying surface modifications, and implementing facile processing techniques. In Paper I, inspiration from plant cell wall was drawn to customize the interaction between water and CNFs. By Incorporating mixed-linkage beta-glucan from barley, superior rehydration, redispersion, and recycling of dried CNFs have been achieved. This advancement holds the potential to enhance the transportation and processability of CNF-based materials.In Paper II, by leveraging the interaction between CNF and water, a facile material processing technique was introduced to fabricate CNF/regenerated silk fibroin (RSF) composites. This involved rehydration and swelling of TEMPO-oxidized CNF nanopaper structures with both random-oriented CNF and nematic-ordered CNF in the RSF solutions. Remarkably, the CNF/RSF composite films thus prepared exhibited exceptional mechanical properties in both dry conditions and in PBS, and demonstrated excellent biocompatibility when cultured with L929 fibroblast cell.In Paper III, CNF/alginate double-network composites were prepared to investigate the impact of interfibrillar interactions and the G/M ratio (guluronic acid/mannuronic acid) of alginates on mechanical performance. The composite incorporating TEMPO-oxidized CNF and alginate with higher mannuronic acid content and molecular weight, exhibited high Young’s modulus of 20.3 GPa and high tensile strength of 331 MPa. The interfacial calcium ion crosslinking between CNF and alginate played a pivotal role in improving these properties. Furthermore, this composite was successfully demonstrated as a barrier spray coating for banana, significantly reducing weight loss when stored under ambient conditions, suggesting its potential for applications in food packaging.In paper IV, carboxymethyl cellulose (CMC) was functionalized with quaternary ammonium salts, and subsequently used to modify the interface between holocellulose fibers network and acrylic resin. Strong and transparent composites were successfully fabricated, without the need for organic solvents or harsh chemicals that are often used during the covalent surface modification of cellulose. The hydrophobic functionalized CMCs facilitated homogeneous resin impregnation in cellulose fiber network, producing composites with enhanced interfacial adhesion strength, increased optical transparency and mechanical strength.
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