Browsing by Author "Rojas, Orlando, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland"

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  • Electrodialysis for upgrading water streams in Kraft pulp mills
    (2024) Gonzalez-Vogel, Alvaro
     School of Chemical Engineering | Doctoral dissertation (article-based)
    The sustainability of water resources has emerged as a relevant driving force in our economy, particularly for large industries. This concern is especially pertinent to water and energy-intensive mills, such as cellulose pulp industrial plants. Water scarcity is becoming increasingly prevalent, and prioritizing its consumption, along with adhering to stringent environmental regulations, makes this issue challenging to address. It remains essential to properly treat substantial volumes of effluents in these plants before discharging them, to minimize the environmental impact of such operations. To achieve this, mechanical and biological treatments are typically employed. Other water treatment technologies are often cost-prohibitive. However, in certain cases, it remains necessary to incorporate additional treatments for achieving water recirculation and chemical recovery. Otherwise, detrimental non-process elements could accumulate in the pulping process if water is recirculated. Alternatively, salts may be disposed of in water bodies or landfills unless they are converted into useful chemicals. Among various water treatment options, electrodialysis (ED) is a versatile technology capable of demineralizing effluent and internal streams, storing and recovering energy, and transforming salts into useful chemicals for reuse. However, ED encounters compatibility issues when treating effluents from cellulose pulp industrial plants, as organics in these streams cause fouling problems. In this thesis, additive manufacturing was used to improve hydraulics of ED systems, while power electronics was employed to address the fouling issue, enhancing the compatibility of ED for upgrading the water resources of Kraft pulp mills. New techniques allow the application of polarity reversal pulses on the order of kHz. By applying high-frequency pulses, turbulence mediated by electric fields are promoted, overcoming the system's limits imposed by the depletion of ions on the surface of the membranes, reducing not only fouling occurrence, but also membrane area requirement. ED and its variants were tested at both laboratory and pilot scale in industrial facilities, in conjunction with a device called the Asymmetric Bipolar Switch (ABS), which enabled the application of high-frequency pulses. Two variations of electrodialysis were tested at pilot scale, when coupled with the ABS, demonstrating improved operation by decreasing fouling over time and increasing productivity. The operations proved to be more robust when using the high-frequency pulses during tests spanning several weeks, enhancing ED compatibility. This advancement represents a significant step in surpassing the technical and cost barriers associated with electrodialysis in the effluent treatment of cellulose pulp industrial plants.
  • Functional fibres by Wet-spinning of Bio-based Colloids
    (2020) Wang, Ling
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Chitin nanofibrils (ChNF), TEMPO-oxidized cellulose nanofibrils (TOCNF), lignocellulose nanofibrils (LCNF), and lignin were isolated from marine and plant biomass. Microfibres were synthesized by wet spinning of aqueous suspensions of the respective bio-based colloid. The influence of coagulant type in wet spinning as well as the properties of the microfibers obtained from TOCNF and ChNF were studied. In general, fibres coagulated via ion exchange demonstrated better mechanical properties and water/moisture stability. Meanwhile, a clear difference was found in thermal properties: TOCNF microfibres coagulated in aqueous electrolyte presented better thermal stability compared to those coagulated in organic solvents. All the TOCNF and ChNF microfibres were biocompatible as shown by in vitro tests, which indicate prospective applications in the biomedical fields. Lignin-based fibres were manufactured from either LCNF or aqueous lignin suspensions in the presence of TOCNF. An increased lignin loading resulted in microfibres of lower mechanical strength and better thermostability. Carbon microfibres were obtained by one-step carbonization. The higher lignin content in the precursor led to carbon microfibres at higher mass yields and displaying smoother surfaces and higher electroconductivity. The measured electroconductivity (up to 103 S/cm) make them suitable for microelectrodes and wearable electronics. Moreover, the carbon microfibres developed from LCNF suspensions were demonstrated in uses as fibre-shaped supercapacitors, which showed a promising performance. A prototype system for continuous wet-spinning was developed to increase the spinning rate and to optimize the process. This work highlights the use of renewable bioresources in the production of microfibers with no need for molecular dissolution. Thus, the wet-spinning technique is shown as a feasible and versatile approach to produce microfibres, furthering their potential in functional materials. Biobased colloids are suitable alternatives for adoption in fibre production, replacing petroleum-based precursors and opening new opportunities for green processing.
  • Functional Materials from Nanocellulosic Networks and Uses in Water Purification
    (2020) Lehtonen, Janika
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Due to their nano-scaled dimensions and mechano-chemical versatility, nanocelluloses have generated interest in the production of various types of bioproducts. However, the full potential of these materials and their applications, which are strongly coupled to their structural features, is yet to be realized. In this thesis, two types of nanocelluloses, cellulose nanofibrils (CNF) and bacterial nanocellulose (BNC), are introduced to achieve different types of porous networks and functional materials. The performance of CNF and CNF-based materials is investigated in applications related to water purification. Composites incorporating cationic CNF and silver nanoparticles are studied for use in drinking water disinfection. Phosphorylated CNF is implemented for the removal of uranium from water via batch adsorption. With BNC, the opportunities provided by biological fabrication of nanofibrous materials are considered in the synthesis of 2D membranes as well as intricate 3D structures. The impact of physico-chemical modifications of the fibrous networks in the BNC membranes are investigated to give insights on their potential use in pressure-driven filtration. To produce 3D structures from BNC, a simple method is developed utilizing hydrophobic particles for stabilization of air-water interfaces. Utilizing this method, capsules were produced and applied as sensors and enzymatic reactors in aqueous media. This thesis provides insights and novel pathways for the production and application of porous nanocellulose-based structures. They are expected to contribute to the development of future functional materials, for instance in the field of water purificaton.
  • Interfacial Adsorption and Stabilization of Nanopolysaccharides in Multifunctional Emulsion Systems
    (2024) Zhu, Ya
     School of Chemical Engineering | Doctoral dissertation (article-based)
    This thesis explores the roles of biobased polysaccharide nanoparticles, including cellulose nanofibrils (CNF), cellulose II nanospheres (NPcats) and chitin nanofibrils (NCh), as stabilizers of emulsion systems. We demonstrate the potential application of these emulsions in the development of advanced materials. The thesis discusses phenomena relevant to colloidal behaviors and adsorption of nanopolysaccharides at oil/water and water/water interfaces, in the form of Pickering emulsions. Variables relevant to the emulsion behaviors, including the particle's interfacial wetting properties, hydrophilicity, functional groups, electrostatic charge, axial aspect ratio and entanglement were evaluated by complementary characterization platforms. The complexation of two oppositely charged nanopolysaccharides, CNF and NCh, were demonstrated to effectively stabilize oil-in-water Pickering emulsions with adjustable droplet size and stability against creaming and oiling-off, imparting long-term stability and remarkable environmental tolerance. Likewise, driven by electrostatic interactions, tuning the mass and charge ratio of NPcat and bovine serum albumin (BSA), the formation of a soft and dense NPcat/BSA layer, is shown to enable the formation of dense NPcat/BSA interfacial layers, stabilizing water-in-water emulsions. Furthermore, NCh was used to formulate high internal phase Pickering emulsions (HIPPEs) through pre-emulsification followed by continuous oil feeding that facilitated a "scaffold" with high elasticity, which arrested droplet mobility and coarsening, achieving edible oil-in-water emulsions with a high internal phase volume fraction (as high as 88%). These green Pickering emulsions offer potential in applications relevant to foodstuff, pharmaceutical, and cosmetic formulations. Direct ink writing (DIW) was applied as a platform to engineer biobased Pickering emulsions to extend their applications. The HIPPEs were easily textured by leveraging their elastic behavior and resilience to compositional changes, making them suitable for 3D printing edible functional foods via DIW. Additionally, we structured emulsion stabilized by NCh (50% oil fraction) through onestep processing into hierarchically and spatially-controlled porous structures defined by emulsion droplet size, ice templating, and DIW infill density. The obtained scaffolds are demonstrated for their excellent modulation of cell adhesion, proliferation, and differentiation, as tested with mouse dermal fibroblast expressing green fluorescent proteins. Taken together, the findings in this thesis are of interest in developing and understanding fundamental emulsion stabilization mechanisms and advancing practical applications. The obtained green Pickering emulsion systems are expected to have an important role in food emulsions, encapsulation, pharmaceuticals, (bio)catalysis, and advanced synthetic cell mimetics.
  • Interfacial Stabilization of Multiphase Systems with (Ligno)cellulosic (Nano)materials and Surfactants
    (2019) Xiang, Wenchao
     School of Chemical Engineering | Doctoral dissertation (article-based)
    This thesis explores the interactions between (ligno)cellulosic (nano)materials and surfactants and evaluates their impact on interfacial activities relevant to multiphase systems, namely, foams and emulsions. The main plant-based components consider supramolecular constructs of cellulose, wood fibers, nanofibrils, cellulose carrying residual cell-wall molecules as well as non-cellulosics that are leached from fibers. The presented discussion focuses on phenomena relevant to the gas/liquid and liquid/liquid interfaces, the synergism between an anionic surfactant (sodium dodecyl sulfate, SDS) and like-charged (nano)cellulosic materials (wood fibers and cellulose nanofibrils, CNF). SDS is found to induce the leaching of non-cellulosics from wood fibers or CNF, which form surface-active aggregates with SDS. They effectively lower the gas/liquid interfacial tension and enhance foamability and foam stability, mainly by reducing drainage, coalescence, and coarsening. As an extension of the work with foams, they were used to produce wood fiber networks (foam-laying) from a wide selection of fibers and surfactant types. The cause-effect relations, the structuring mechanisms and the physico-mechanical properties of the fiber networks are revealed. The major drawback of typical foam-laid materials, namely, the loss of in-plane and out-of-plane strength, is addressed by replacing synthetic surfactants with an alternative surface active substance, carboxymethylated lignin. As an extension to foams and based on the uncovered interactions between cellulose and surfactants, the study turned to cellulose nanocrystals (CNC), which were considered in the formulation of food-grade emulsions. The synergism between an oppositely-charged surfactant (food-grade ethyl lauroyl arginate, LAE) and CNC is found to provide Pickering emulsions with outstanding stability. Taken together, the incorporation of plant-based components in the formulation of foams and emulsions is presented as an option in the framework of the future bioeconomy. The findings presented contribute to the effective and efficient utilization of natural resources for growing areas pertaining to multiphase systems.
  • Long-range order in nanocellulose films and coatings for next generation materials
    (2023) Klockars, Konrad
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Aqueous dispersions of cellulose nanocrystals (CNCs) undergo a concentration-driven self-assembly which leads to chiral nematic (N*) structuring in dried coatings. The structural color provided by the N* order offer promise as a sustainable alternative to decorative iridescent, metallic, and shimmering effects. This dissertation studied the effects of the self-assembly on both structural and optical properties of dried films and coatings. The progress of the self-assembly in the dispersion state, altered through equilibration at different concentrations, was found to significantly impact the resulting dried coating, in terms of the sizes and distribution of the regions of N* order. The internal mechanical stresses that build up during the drying of CNC dispersions were quantified during coating formation and after ageing. A desirable stress reduction was achieved by mixing non-interacting plasticizing additives into the dispersion prior to coating formation. Of interest particularly in decorative applications, are the gradients in structural color at the edges of coated areas, known as coffee rings, which were examined in non-circular coatings. Lastly, an infiltration setup was investigated by introducing highly interacting compounds into CNC films, including proteins, which interfere with the self-assembly when mixed into the dispersion prior to drying. The findings of this dissertation are of interest to both technological and decorative implementations of structured cellulose nanocrystal coatings, and in the development of biocolloidal coatings.
  • Nanocellulose Interactions with Protein and Water in Advanced Sensing Systems
    (2022) Solin, Katariina
     School of Chemical Engineering | Doctoral dissertation (article-based)
    In this work, cellulosic nanomaterials were investigated for application as fluidic and sensing platforms. These platforms were used for humidity measurement, biosensors, and immunoassays, which are relevant to the areas of diagnostics, printed electronics, and smart packaging. A systematic investigation was carried out to study the interactions between water and protein molecules with cellulosic materials, which was facilitated by advanced techniques such as quartz microgravimetry, surface plasmon resonance, and confocal microscopy. Humidity responsive and electroactive composite films were developed using hybrid materials composed of nanocellulose and carbon nanotubes. The changes in relative humidity of air were monitored by measuring the shift in electroacoustic admittance and electrical resistivity of composite films upon water uptake. Other systems that incorporated mineral particles and nano-and microcellulose were used for lateral flow assays (LFA) based on fluidic wicking. For this purpose, inkjet printing was used to produce hydrophobic channel sidewalls on nanopaper. Alternatively, stencil printing of the fluid-wicking element was applied on hydrophobic supports. These wicking systems showed the potential as new types of LFA devices with excellent sensitivity. Glucose, non-specific protein, and antigen detection were demonstrated by colorimetric sensing at clinically relevant concentrations. A new type of cellulose nanomaterial, cellulose II nanoparticles, was introduced as a substrate for controlled protein adsorption. The interactions and protein accessibility to surfaces treated with such cellulose II nanoparticles, which formed a hydrogel film, were investigated in detail. Cationic cellulose II nanoparticles (NPcat) showed one of the highest levels of accessibility recorded, following both specific and non-specific protein interactions, and suggested NPcat suitability as a new immobilizing agent for biomolecular sensing. Oppositely charged anionic cellulose II nanoparticles (NPan) were used for surface passivation and indicated a great potential as a blocking agent that can be deposited on substrates to minimize non-specific molecular interactions. Both cellulose nanospheres, NPcat and NPan were deployed in protein-accessible and protein-repellent materials, respectively, and facilitated the design of a rapid antigen sensing system for SARS-CoV-2 nucleocapsid.
  • Pilot-scale filler-reinforced biodegradable coatings for paperboard packaging
    (2023) Helanto, Karoliina
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Environmental impact and regulation of packaging materials are topics that critically influence the adoption of alternatives to fossil-based systems that are in current use. In this context, paperboards represent suitable renewable and biodegradable options that also have the advantage of recyclability. However, the nature and structure of paperboard-based products limit their use and undermine other competitive advantages. A main reason is the limited barrier properties displayed by paperboard products. Gaining control of the transport of moisture, grease, liquids and gases is the most relevant requirement for packaging materials together with heat sealability. A possible route to achieve barrier control includes consideration of biodegradable thermoplastic polymer coatings, such as poly(lactic acid) (PLA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(butylene adipate terephthalate) (PBAT). However, the application of these materials needs adjustments in the processability aspects. They also affect the interactions with the packaged goods and the overall functionality, demanding the adoption of auxiliary components, including plasticizers, nucleating agents and fillers. These subjects are complex and should be examined carefully, not only from the fundamental viewpoint but for actual deployment. This thesis discusses these topics from the perspective of scalable and deployable technologies. The effect of mineral fillers on biodegradable polymer coatings for paperboard packaging is examined at a pilot scale. The utilized thermoplastic polymers included PLA and PLA-based blends, PHBV and PBAT. The fillers introduced to the polymer matrices included talc, kaolin and calcium carbonate. Production processes typical of the packaging industry were contemplated, such as injection and compression moulding and pilot-scale extrusion coating. The potential of the packaging materials and their combinations was evaluated from the perspective of processability to the end-of-life. The addition of fillers benefited processability in the extrusion coating process by reducing neck-in and improving adhesion formation. As a drawback, they contributed to the formation of pinholes at lower coating weights. The barrier properties of intact films and coatings were improved, whereas the introduction of the fillers did not significantly impact on the biodegradability characteristics. This thesis provides insights on the filler-reinforcement of biodegradable polymers and their utilization as coating layers. This work is expected to serve as a guide for future developments of sustainable extrusion coatings for paperboard packaging.
  • Superstructured wood-based carbon materials for broadband light absorption and CO2 capture
    (2025) Zhao, Bin
     School of Chemical Engineering | G5 Artikkeliväitöskirja
    Light is an abundant resource; however, stray light can significantly impact the performance and longevity of optical systems. Adverse effects such as reduced image contrast and signal degradation highlight the need for advanced solutions to effectively mitigate these challenges. Superblack materials, with near-zero light reflectance, are in high demand to enhance several light-based technologies. In this study, we developed wood-based spectral shielding materials with exceptionally low reflectance across the UV-VIS-NIR (250–2500 nm) and MIR (2.5–15 μm) ranges. Using a straightforward top-down approach, we produced robust superblack materials by removing lignin from wood and carbonizing the delignified wood at 1500 °C. This process induced shrinkage stresses in subwavelength severed wood cells, forming vertically aligned carbon microfiber arrays (~100 μm thick) with light reflectance as low as 0.36 %. We further synthesized multiscale carbon supraparticles (SPs) through a soft-templating process involving lignin nano- and microspheres bound with cellulose nanofibrils (CNFs). Following oxidative thermostabilization, these lignin SPs exhibited high mechanical strength due to their interconnected nanoscale networks. In further work, by inserting lignin particles (LPs) into delignified wood and carbonizing the structure, we created a carbonized reconstituted wood (cRW) system with enhanced dimensional fidelity and finely tuned light-absorbing fibrillar microstructures. They resulted in broadband light traps that achieved superabsorbance, exceeding 99.8% across a wide range of wavelengths, from infrared to ultraviolet. Tiled cRW structures, optically welded for customizable size and shape, demonstrated superior laser beam reflectivity compared to commercial light stoppers, eliminating thermal ghost reflections. This makes them promising candidates as reference infrared radiators for thermal imaging device calibration. Beyond optical applications, the carbon SPs also offer hierarchical adsorption sites, achieving a CO₂ adsorption capacity of 77 mg CO2·g-1. This innovation in the area of carbon capture was shown to solve the diffusion and kinetic limitations of conventional nanoparticle-based systems. Overall, this thesis summarizes wood-derived solutions that go from multispectral shielding to carbon capture technologies.
  • Surface and inter-fibre interactions in aqueous cellulose-based systems for open fibrous structures
    (2023) Ketola, Annika
     School of Chemical Engineering | Doctoral dissertation (article-based)
    In the thesis, the morphology of cellulose-based fibre surfaces immersed in water and their interactions with air bubbles in the presence of surfactants were investigated. The cellulose-based fibres included those from wood pulps obtained by chemical and chemi-thermomechanical processing as well as regenerated cellulose. The revealed surface characteristics and interaction mechanisms were connected to the fibre behaviour in water and in foam forming and to the resulting dry material properties. Fibre surface morphology and cellulose microfibrils (CMF) were explored using helium ion microscopy. Freeze drying and critical point drying were used to preserve the open cellulose fibril structure. Well preserved fibre surface fibrils had a significant resemblance with CMF. As wet CMF was known to be gel-like, it was suggested that fibrillated fibre surfaces bore similar gel-like behaviour. The gel-likeness of fibre surfaces was connected to the increased force transmittance capacity of fibre webs, seen as higher shrinkage and elongation of water-formed fibre webs. Bubble-cellulose interactions were investigated with a stepwise approach: 1) Hydrophobised and hydrophilic cellulose model surface studies were conducted with a captive bubble method in anionic sodium dodecyl sulphate (SDS) and non-ionic Tween 20 solutions with varying surface tensions. 2) CMF model surface was used to study the effect of surface roughness. 3) The bubble-fibre interaction was elaborated with actual cellulose fibres by using a fibre bed method. 4) Low-density foam-formed materials were prepared to test the findings from the model surface studies in the context of fibre-foam behaviour and dry structure properties. In conclusion, the bubble interaction with hydrophilic cellulose fibres was generally very weak. The hydrophobic content of cellulose (amphiphilicity and lignin) together with the entrapped air on a fibre surface can drive the bubble adhesion to the fibre. This weak interaction can be cancelled out by higher surfactant concentration. Lightweight materials prepared with hydrophilic and hydrophobized cellulose fibres (with SDS and Tween 20) showed differences in structure and mechanical behaviour, as well as formation of microscale fibre networks inside the structure. These findings increase the general understanding of fibre surface properties and interaction mechanisms between bubbles and cellulose fibres and can be applied in material design in both water-and foam-forming processes.
  • Wet-spinning of cellulose nanofibril hydrogels
    (2018) Lundahl, Meri
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Filaments were produced from cellulose nanofibrils (CNF) through wet-spinning for developments toward renewable fibre-based materials, such as absorbents or fibre-reinforced composites. The possibility to spin long filaments (i.e., spinnability) and resulting filament quality were related with the rheological behaviour of the CNF hydrogels used as precursors. A prototype wet-spinning line was developed for high-throughput filament production by co-extrusion with a supporting biopolymer shell around the CNF core. This system was also employed to spin absorbent filaments from CNF in combination with a shell that had limited compatibility with cellulose and coagulated effectively in aqueous media. The moisture sorption capacity was also increased by increasing the CNF surface charge, which also enhanced fibril alignment during filament formation. Filament mechanical integrity in wet conditions was improved through hydrophobic coating and interfibrillar crosslinking. The results highlight the use of wet-spinning as a simple and versatile approach to generate tuneable filaments from cellulose, an abundant bioresource. This will eventually enable the adoption of renewable options in applications that currently rely on fibres made from fossil carbon.