[diss] Kemian tekniikan korkeakoulu / CHEM

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  • Particle-stabilized foams as advanced materials for energy management
    (2026) Abidnejad, Roozbeh
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-03-06
    This thesis develops a scalable, water-based route to renewable, multifunctional foams that integrate steady-state thermal insulation, fire safety, phase-change heat storage, and acoustic damping. The materials are built from cellulose nanofibers and fumed silica nanoparticles; these serve as cooperative stabilizers of wet Pickering foams, which form hierarchical, open-cell solids upon drying. The interfacial energy is tuned (H₂O/EtOH) to promote particle adsorption at the bubbles, while cellulose nanofibers form an entangled network that suppresses drainage and preserves the gas-templated architecture after drying. The resulting foams exhibit a porosity > 98%, a density of ~22–30 kg m⁻³, specific surface areas of ~200 m² g⁻¹, and a multimodal pore system spanning the micro/meso/macro scales. Structure–property relationships reveal a compressive modulus of ~170–320 kPa, attributable to silica-reinforced nanofiber lamellae. The thermal conductivity ranges from 33 to 36 mW m⁻¹ K⁻¹, comparable to conventional polymer foams, despite a sustainable composition. Thermogravimetric and gas evolution analyses indicate the onset of major mass loss near 330–345 °C, significant char yields, and a predominance of CO₂/H₂O evolution. Fire retardancy testing demonstrates selfextinguishing behavior and superior results versus the polyurethane benchmark. To ensure dynamic thermal regulation, polyethylene glycol was incorporated into the Pickering foams as a phase-change material. Capillary confinement and hydrogen bonding prevent leakage up to a polyethylene glycol loading of ~80 wt%, while differential scanning calorimetry demonstrates sharp, repeatable melting/crystallization with latent heat values of ~55–130 J g⁻¹. Infrared thermography under irradiative heating reveals a lower maximum temperature and delayed cooling compared with the Styrofoam benchmark, evidencing coupled insulation and latent heat buffering. The thesis provides a critical mechanistic understanding of stabilizing foams using sustainable nanofibers and nanoparticles and validates the use of these materials for multifunctional energy management applications. The insights provided in this thesis are significant in terms of accelerating the industrial deployment of next-generation, high-performance, and sustainable porous materials.
  • Evaluation of battery recycling processes using exentropy: A novel multi-dimensional circularity indicator of materials concentration and energy preservation
    (2026) Vierunketo, Minerva
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-03-13
    The linear economy model dominates the consumption in our current society, which causes damage to e.g., critical resources and the environment. Thus, the transition from a linear economy into circular one is crucial and proper end-of-life (EoL) strategies are needed. To measure CE, several circularity indicators have been developed. However, the issue at hand is that the current productivity indicators focus mainly on one dimension at a time and therefore, indicators lack a consensus in the analysis and comparison of different technological solutions. Therefore, in this thesis, a newly developed multidimensional circularity indicator called “exentropy” (χ) is presented to account simultaneously for material concentration action and useful energy utilization of transformative stages using statistical entropy analysis (SEA) and exergy analysis (ExA), respectively. To provide a proof-of-concept of χ, a leaching reagent in a hydrometallurgical lithium-ion battery (LIB) recycling process was studied and optimized under the concentrations of 0.1 M, 1 M, and 2 M. χ was also used to compare a pyrometallurgical, a hydrometallurgical, and a direct LIB recycling process, and evaluate different LIB electrochemical discharge units using NaCl, Na2SO4, and Na2CO3. All the studied systems were simulated with HSC Chemistry® process simulation software to obtain mass and energy flows for the calculation of SEA, ExA, and χ. With the electrochemical discharge system, a weighting factor was applied for SEA to consider the irreversible loss of materials due to corrosion of batteries. The results showed that in the process optimization and comparison, SEA identified 0.1 M LiOH and pyrometallurgical process the optimal ones. On the contrary, ExA identified these two scenarios the least optimal. Exergy preservation was the best in the 2 M LiOH and hydrometallurgical systems. According to χ, the optimal systems were the 1 M LiOH and the direct recycling process. In discharge systems, exergy is not significantly destroyed, but it was discovered that corrosion preserves exergy by producing highly concentrated H2 from the water splitting reaction by inhibiting the production of O2. However, corrosion is not useful according to SEA. χ identified Na2CO3 as the most promising electrolyte over NaCl and Na2SO4, indicating that corrosion in electrochemical discharge systems is inefficient from the perspective of circularity despite the production of highly concentrated H2 gas. The overall results imply that there is indeed a need for more robust analysis using multidimensional indicators. In general, χ could identify the processes that offered the most useful compromises for material and useful energy preservation, which is a step closer to the circular economy goals.
  • Dissolution and regeneration of cellulose: Towards plastic-free films via systematic engineering: A versatile toolbox for processing regenerated cellulose films
    (2026) Ahokas, Pauliina
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-03-13
    Fossil-based plastics, especially in the packaging sector, create significant environmental and health burdens. They lead to persistent waste, marine pollution, and the accumulation of micro- and nanoplastics in organisms. These impacts highlight the urgent need for renewable alternatives that combine functionality and sustainability. While cellulose-based materials offer a biodegradable option to replace fossil-based films, current films lack flexibility and barrier properties required for demanding applications such as food packaging. This thesis addresses these challenges by engineering regenerated cellulose films through systematic design strategies using non-derivatizing solvent systems, ensuring preservation of the unique cellulose backbone and its inherent biodegradability. Three complementary approaches were explored: 1) increasing material utilization via hemicellulose-rich kraft pulps; 2) enhancing mechanical performance through controlled pulp blending; and 3) improving film functionality predictably by systematic plasticizer mixing. These strategies enabled precise control over dissolution, rheology, and film formation, supported by predictive regression models explaining up to 98% of the property variation. Hemicellulose retention improved process efficiency and film strength, while mixture design enhanced elasticity and toughness through multi-level molecular effects. Plasticizer choice and optimization achieved up to 50% higher strength and barrier improvements of 89% (water vapor) and 93% (oxygen) compared to traditional glycerol-plasticized films, surpassing commercial cellophane benchmarks. Predictive regression models enabled a data-driven approach to material design. These findings demonstrate that regenerated cellulose films can be tailored to meet packaging requirements while remaining biodegradable and structurally faithful to native cellulose. This work provides a scalable pathway toward plastic-free films, aligning with global circular economy goals and advancing cellulose-based materials as viable replacements for certain conventional plastics.
  • Formulation development of a biodegradable silica depot for long-acting injectable delivery of small molecules to biologics
    (2026) Noppari, Panu
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-03-06
    This thesis investigates the development and characterization of long-acting injectable (LAI) silica-based drug delivery systems, integrating sol-gel processing, formulation optimization, in vitro, and in vivo performance evaluation.The delivery platform comprises sol-gel derived silica microparticles embedded in a silica hydrogel matrix, herein referred to as the silica depot injection. The work begins by characterizing the fundamental sol-gel process for colloidal silica sols, where the sol-gel transition was characterized by time-resolved rheometry (TRR). The impact of varying silica content and pH on gelation behavior and transition times was assessed, confirming a linear increase in sol-gel transition time with solid content, and an exponential decrease with rising sol pH.The optimized TRR measurement enabled accurate monitoring of transition times and unexpectedly showed that the resulting gels exhibited viscoelastic properties typical of colloidal glasses rather than colloidal gels. The following study examined how incorporating alginate as an excipient could modulate the rheological properties of the silica depot injection. Silica microparticles containing levothyroxine were prepared by spray-drying and combined into conventional silica hydrogels and silica/alginate hydrogels. In vitro characterization demonstrated that alginate inclusion allowed lower microparticle concentrations in the depot injections while improving injectability. The in vitro and in vivo performance of a silica–triptorelin acetate depot injection is also evaluated. Triptorelin acetate, used to treat hormone-sensitive conditions such as prostate cancer, was similarly encapsulated in silica microparticles and formulated into an injectable depot. Following subcutaneous administration in Sprague-Dawley rats, pharmacokinetics and pharmacodynamics were compared to a commercial reference product (Pamorelin®). The silica depot exhibited five-fold lower maximum plasma concentrations (Cmax) and sustained triptorelin plasma concentrations over 91 days, effectively maintaining testosterone suppression, demonstrating potential as a long-acting peptide delivery system. Collectively, this thesis highlights the versatility and translational potential of silica-based LAI formulations, offering tunable rheology, prolonged drug release, and preserved biological activity for both small molecules and biologics.
  • Harnessing biomolecular click reactions for modular protein engineering and functionalization
    (2026) Fan, Ruxia
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-03-06
    Proteins are essential building blocks for advanced biological and bioinspired materials. Their extraordinary structural diversity, modularity, and functional versatility enable the programmable design of intricate materials and architectures. However, fully harnessing the potential of proteins remains challenging. Achieving precise control over protein assembly, constructing multicomponent architectures, and introducing site-specific functionalities are often hindered by the limited availability of covalent protein conjugation tools, which tend to lack versatility and orthogonality. Biomolecular click reactions present promising solutions by expanding the ligation toolkit with genetically encodable and efficient reactions, thus facilitating reliable and modular protein assembly and functionalization. In this thesis, I systematically explored the applications of Catcher/Tag-mediated biomolecular click reactions as a modular platform for protein assembly and functionalization, employing spider-silk-like proteins as primary model building blocks. I engineered a novel minimal Catcher/Tag pair, termed SilkCatcher/SilkTag (SilkC/SilkT), derived from the CnaB1 domain of the cell surface protein lp2578 from Lactobacillus plantarum (L. plantarum). The SilkC/SilkT system demonstrated efficient formation of covalent isopeptide bonds over a broad range of mild conditions and exhibited a distinct pH-activated reaction. Its reaction profile was comparable to the well-established SpyCatcher/SpyTag (SpyC/SpyT) system, while its ligation specificity remained strictly orthogonal to the SpyC/SpyT pair, thereby expanding the toolkit available for orthogonal protein ligations. Fusion of Catcher domains to aggregation-prone proteins, including spider-silk-like proteins and β-glucosidase, significantly enhanced their soluble expression in Escherichia coli (E. coli). The improved solubility of spider-silk-like proteins enabled the production of artificial spider silk fibers, exhibiting outstanding extensibility and toughness, via a fully aqueous wet-spinning system. The intrinsic structural affinity and covalent reactivity between Catcher domains and Tag peptides were further leveraged for multiple functional applications, such as site-specific fiber functionalization, enzyme immobilization, protein purification, as well as controlled polyphosphorylation of spider-silk-like proteins. Additionally, the compatible reaction conditions and orthogonality of the SilkC/SilkT and SpyC/SpyT pairs facilitated multiple-fragment protein conjugation, allowing the construction of native-sized and ultrahigh-molecular-weight spider-silk-like proteins. In summary, this thesis demonstrates that the Catcher/Tag-mediated biomolecular click reactions provide a versatile and modular platform for protein engineering. Their efficient covalent ligation and strict orthogonality enable controlled protein assembly, targeted immobilization, and precise functional modification. These studies highlight the broad potential of biomolecular click reactions for advanced protein engineering and their use for the development of functional biomaterials.
  • Conception of platform materials based on self‐assembly between biosurfactants and cellulose nanocrystals
    (2026) Phi, Thuy-Linh
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-03-06
    The increasing global production of plastics underscores the urgent need for sustainable alternatives to fossil-based plastics. Due to their renewability, biodegradability, strong mechanical properties, and specific water interactions cellulose nanocrystals (CNCs) have attracted considerable attention as bio-based nanomaterials. However, challenges related to their dispersion, stability, and gelation limit their direct use in advanced material applications. This dissertation explores the potential of combining CNCs with sugar-based biosurfactants prepared by microbial fermentation to design fully bio-based and sustainable material systems. The overarching aim was to investigate how biosurfactants can enhance the dispersion and functionality of CNCs while maintaining simplicity and renewability in the resulting materials. Three objectives guided the work: (i) elucidating the dispersion of uncharged CNCs using biosurfactants, (ii) developing multicomponent hydrogels combining CNCs and biosurfactants, and (iii) evaluating the role of biosurfactants in CNC gelation. These objectives have been met through three publications. The results demonstrate that biosurfactants can effectively stabilize CNC dispersions, significantly enhance the mechanical and responsive properties of CNC-based hydrogels and reduce the gelation threshold of negatively charged CNCs. Taken together, this dissertation provides the first systematic evidence that biosurfactants can act as versatile, fully bio-based agents to overcome key limitations of CNCs. Building on this groundwork, future research should focus on examining biosurfactant–cellulose interactions at the molecular level, optimizing preparation conditions, and translating these insights into application-driven designs. These findings establish a foundation for the rational design of sustainable CNC–biosurfactant systems, paving the way toward impactful real-world applications.
  • Multifunctional coatings and encapsulations for improved light management and durability in perovskite solar cells
    (2026) Mousavi, Seyede Maryam
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-02-20
    Rising global electricity demand is driving the need for increased generation and the development of sustainable energy solutions. Ensuring affordable and reliable energy access worldwide remains a pressing challenge, motivating the shift from fossil fuels towards renewable energy sources. Solar energy is an abundant and virtually limitless resource. Photovoltaic devices, which directly convert sunlight into electricity, are therefore a central technology for improving energy efficiency and promoting sustainable energy generation. Among photovoltaic technologies, perovskite solar cells (PSCs) have emerged as a highly promising class of devices due to their exceptional light-harvesting efficiency and potential for low-cost, scalable fabrication. This doctoral thesis addresses two critical challenges in the development of PSCs: optical losses and long-term stability. To mitigate optical losses, a nature-inspired multifunctional light management layer (LML) was fabricated by replicating the micro- and nanoscale surface morphology of leek leaves onto cellulose acetate. The resulting coatings enhanced light harvesting, improved PSC performance, and imparted self-cleaning functionality. To further expand the functionality of LMLs, an optically transparent bio-based composite was developed. This composite not only enhanced device efficiency by extending the optical path but also provided thermal regulation and ultraviolet UV shielding, thereby contributing to improved stability. In addition, to address the extrinsic instability of PSCs under environmental exposure, an in-situ encapsulation and patterning strategy was developed. In this approach, the encapsulation layer was formed directly on the device, while simultaneously replicating the micro–nano surface features of leek leaves. The bio-inspired surface pattern enhanced light management, while the encapsulation effectively shielded the PSCs from air and moisture. This in-situ process simplified device fabrication and resulted in significant improvements in both the efficiency and long-term stability of the PSCs. In conclusion, this research presents a holistic strategy combining bio-inspired design, multifunctional coatings, and encapsulations to address optical and stability challenges in PSCs. This approach can contribute to overcoming the key challenges associated with perovskite solarcells. Looking ahead, further optimization of material composition, interface engineering, and scalable fabrication methods could advance the practical implementation of such multifunctional designs, bringing PSCs closer to reliable, long-term operation and sustainable commercialization.
  • Modifying the structure of microcrystalline cellulose by different drying methods and mechanical treatments
    (2026) Lähdeniemi, Annina
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-02-13
    Recently, wood-derived cellulosic micro- and nanomaterials have shown significant potential for pulp and paper technology. However, their adoption and commercialization have not progressed as expected. Therefore, there is currently an increasing research interest in using cellulosic micro- and nanomaterials in various industries outside pulp- and papermaking, such as pharmaceuticals, cosmetics and the food industry. Microcrystalline cellulose (MCC) is a purified, partially depolymerized nonfibrous form of cellulose, a crystalline powder composed of porous particles. MCC (holding E-code E460i) as such is safe for oral consumption for both human and animal purposes. Reflecting MCC's multiple current applications and future potential, it is important to further investigate the possibility of producing MCC with different cross-sectional shapes to increase the surface area due to its great importance for specific applications. Microfibrillated cellulose (MFC), that can be produced from MCC, consists of microfibril bundles forming a weblike fiber network and providing its multiple uses as thickeners, emulsifiers or additives in food, paints, and coatings, as well as cosmetics and medical products. In addition, MFC is ideal as a reinforcement in composites and, concurrently, to reduce the utilization of petroleum-based components. The modification of the never-dried form of MCC with novel techniques and thus producing new types of micro-sized cellulose products, are the focus of this doctoral research. Firstly, the study investigated the drying of the never-dried MCC with two different solids contents using three different drying methods: high-velocity cyclone drying, spray drying, and fluidized bed drying (Paper 1). The effects of these drying techniques on the geometrical dimensions and morphology of the dried MCC particles and aggregates were studied. The results revealed that the morphology of the dried MCC was highly dependent on the initial raw material properties and the liquid removal mechanism during drying. Fluidized bed drying best preserved the original MCC morphology, yielding discrete particles with high surface area and less aggregation. Spray drying produced small, circular particles with homogeneous size distributions, while high-velocity cyclone drying resulted in the largest, most heterogeneous, and irregularly shaped particles and aggregates. Secondly, the study focused on the production of MFC-hydrogels from never-dried MCC using high-pressure mechanical treatment (Paper 2) and later with a Masuko laboratory grinder with different refining degrees (Paper 3). The effects of the treatments on the crystalline structure, morphology, geometrical dimensions, specific surface area, and rheological properties of the resulting MFC gel were analyzed. Results indicated that both mechanical processes produced partially detached crystalline areas, increasing surface area and porosity, leading to the formation of more stable MFC hydrogels due to enhanced hydrogen bonding between cellulose particles. Additionally, using never-dried MCC as a raw material in refining resulted in a stronger MFC gel with superior storage and loss moduli compared to the ones produced with pre-dried MCC. Specific energy consumption data from Masuko grinder also indicated that mechanical energy is more effectively transferred to the never-dried MCC structure, suggesting that energy can be saved when producing MFC from never-dried MCC via refining.
  • Controlling self-assembly of cellulose nanocrystals for multiphase colloids and chiral photonics
    (2026) Tao, Han
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-02-06
    The growing concern over the environmental costs of synthetic materials has motivated a shift toward renewable, biodegradable, and biocompatible alternatives. Cellulose nanocrystals (CNCs) serve as such building blocks, being notable for their ability to self-organize in water into a lyotropic cholesteric liquid crystal whose helicoidal order can be preserved in the solid state. This doctoral thesis establishes a novel framework for controlling the cholesteric self-assembly behaviour of CNCs via aqueous two-phase systems (ATPSs) and harnesses the cholesteric CNC structure as substrates for engineering plasmonic chiral metamaterials. The thesis first demonstrates the controllable cholesteric self-assembly of CNCs within ATPSs formed by the liquid-liquid phase separation (LLPS) of uncharged poly(ethylene glycol) (PEG) and dextran polymer solutions. The polymer acting as depletants modulate the interaction between CNCs, while the LLPS-induced two distinct polymer compartments provide the spatial confinement for CNCs assembly. By controlling the thermodynamics of the CNC-PEG-dextran aqueous mixtures, we obtain a series of multiphase LC colloids that display hierarchical organization from the micro- to the macroscale. Specifically, under equilibrium conditions, the multicomponent aqueous mixtures separate into two, three or four coexisting phases, displaying alternating stacks of cholesteric and isotropic phases. The structural heterogeneity in the fluid state can be retained upon drying, producing stratified cholesteric CNC films with a compartmentalized polymer distribution and an anisotropic microporous morphology. In contrast, when phase separation in the multicomponent aqueous system is arrested before reaching equilibrium, gradients in osmotic and chemical potential drive the uneven partitioning of CNCs of the two polymer compartments. At a critical nanoparticle concentration, CNCs confined within one polymer phase self-assemble into a cholesteric structure, while those in the other remain isotropic, resulting in a bicontinuous structured LC emulsion. Our findings provide a promising platform for designing novel heterogeneous complex colloidal systems whose functionalities can mimic the intricate structures observed in biology. Cholesteric CNC structures retained in the dried films exhibit birefringence and polarizationselective optical responses, providing a bio-based platform to manipulate light. In the final part of the thesis, cholesteric CNC films are used as substrates to support plasmonic metasurfaces composed of linearly assembled gold nanoparticles (AuNPs), enabling the engineering of chiral lightmatter interactions. The centimetre-scale hybrid plasmonic CNC composites are produced by casting CNC dispersions onto pre-assembled achiral AuNP arrays. During the drying process, the CNCs co-assemble with the AuNPs at the liquid-solid interface, maintaining the array’s linear arrangement and keeping it isolated from the overlying cholesteric CNC layers. This unique configuration displays both the linear dichroism (LD) of the plasmonic arrays and the linear birefringence (LB) of CNC substrate. Despite the achiral geometry of the AuNP arrays, the obtained composites exhibit strong and spectrally tuneable plasmonic circular dichroism, with a maximum value of 1217 mdeg and a dissymmetry factor of −0.19 at the surface lattice resonance wavelength. The enhanced chiroptical activity originates from synergistic LB-LD coupling, offering a new biobased design principle for scalable and controllable chiral photonic materials. Overall, this thesis advances the understanding and control of cholesteric self-assembly of CNCs, enabling the design of multiphase LC colloids and hierarchical photonic architectures that combine compositional heterogeneity, interfacial organization and structural gradients across multiple length scales.
  • Computational modelling of block copolymer surface coatings at multiple length scales
    (2026) Hasheminejad, Kourosh
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-02-06
    Block copolymer films are a promising class of materials for surface coatings and thin-filmtechnologies. Their ability to self-assemble into ordered nanostructures makes them highly versatilefor a wide range of applications, from protective and barrier layers to membranes andnanolithography. One particularly important application is producing moisture preventing films,where the characteristics of the polymeric films directly affect their effectiveness and durability. This doctoral thesis explores how such coatings form and resist water penetration at the molecularlevel. The work focuses on understanding how the chemical structure of the copolymer chains andthe composition of the coating mixture influence the resulting film structure and its performanceagainst water penetration. To achieve this, two complementary computational approaches wereused. Coarse-grained dissipative particle dynamics simulations capture how block copolymer chainsself-assemble into film structures, and atomistic detail molecular dynamics modelling examineswater interactions at the molecular scale. Together, these methods provided a multiscale view of thecoating formation process and the resulting barrier properties. The results show that the balance between the hydrophilic and hydrophobic parts of the amphiphilicblock copolymer, used to produce the protective coatings, plays an important role in determining thecoating formation on a surface. Copolymer chains with nearly symmetric hydrophobic-hydrophilicblock architecture form continuous layers that can act as effective barriers, while asymmetriccopolymer chains produce patchy, defective coating structures. The relative amount of eachcomponent in the coating mixture was also found to be important: too little or too much of onecomponent leads to structural imperfections. In addition to the barrier performance of the coating, the chemical nature of the hydrophobic part ofthe copolymer was found to determine how well the coating retains its structure when exposed tostrain. Several copolymers were examined by simulations to extract guidelines for maintaining highbarrier performance and limiting water penetration even under strain. The findings offer crucialknowledge for the real-world usage of such coatings. Overall, this thesis clarified the relationships between the molecular structure of the blockcopolymers, coating morphology, and their water penetration performance. The insights gainedestablish principles that can guide a rational design of moisture-barrier coatings for applications,e.g., in packaging and other surface protection technologies.
  • Reactions of neutral sodium sulphite solutions with chemical components of wood and wood pulps
    (2026) Warsta, Elina
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-01-30
    Global targets for climate change mitigation require drastic reduction of fossil fuels and materials produced from petrochemicals. At the same time forests are expected to serve as carbon sinks, which should help reaching the national climate neutrality targets such as the one in Finland for 2035, as well as regional targets such as EU 2030, 2040 and 2050 climate targets. In addition to climate targets, global and regional biodiversity commitments impose increasing pressure on forest protection and restoration. Altogether the global outlook, combined with climate and nature targets for forests, indicate that we should make better use of the wood we already produce in our forests and plantations. Too large part of the valuable wood material is still burned to energy, either directly or as pulping process liquors. In Publication 1, the binding of sulphite to the reactive carbonyl groups of lignin was investigated with the help of lignin model compounds as well as lignin-rich chemithermomechamical pulp (CTMP). The model compound studies with vanillin, verataldehyde and acetovanillone established that the rate and equilibrium of the addition reaction of bisulphite to carbonyl groups depends on the carbonyl structure type: the bisulphite addition appears to be fast and extensive with aldehyde structures, while only minor part of ketones react in same conditions. In Publication 2, a spectroscopic method was developed for assessing the phenol content of lignin with the help of multiple lignin model compounds as well as pulp samples. UV resonance Raman (UVRR) spectroscopy was used for structural studies of the samples. The traditional method for phenolic hydroxyl group determination and the UVRR band shift from neutral to alkaline produced similar trends but could not be straight connected with each other. The spectroscopic method developed in Publication 2 was used to evaluate the effect of neutral sulphite treatment on the demethylation of lignin in Publication 3. In addition to lignin demethylation and dissolution, sulphite treatment at high temperature was also found to cleave cellulose chains. Sulphonated cellulose can be applied e.g. in concrete industry as viscosity increasing agent or as so-called superplasticizer, which interacts with the surface of cement particles by provoking dispersion and decreasing coagulation tendency. Cellulose sulphonic acid can be also used as solid acid catalyst by the chemical industry for example in biodiesel production. Conventional homogenous catalysts have serious limitative features due to the toxic, corrosive reagents, tedious preparation, neutralization of effluents, long reaction time, and high temperature. Publication 4 examined the applicability of neutral sulphite cooking to produce high-yield pulp from softwood. Sodium sulphite pulping experiments of pine chips under neutral and slightly alkaline pH resulted in pulps with high yields between 52 and 73% and kappa numbers ranging from 35 to 106. The number of acidic groups of the pulps correlated linearly with the residual lignin content showing highly charged fibres. The treatments resulted in pulps with a high content of hemicelluloses combined with relatively high lignin content. The high content of hemicelluloses can be beneficial in hindering hornification (i.e. stiffening of fibres) during drying, as well as in promoting fibrillation during refining. These results demonstrate the possibility to reach much higher yields than in kraft pulping, and potential for applications in bio-based materials, which require modifiable hydrophilicity and water interaction.
  • Sustainability and technical feasibility of smart tags as data carriers for intelligent packaging and digital product passports
    (2026) Hakola, Liisa
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-01-23
    Smart tags that merge identification and condition monitoring into a single data carrier offer a practical way to provide dynamic life cycle data in applications, such as intelligent packaging and digital product passports (DPPs). They integrate visual identifiers (e.g. 2D barcodes) or electronic identifiers (e.g. RFID (Radio Frequency Identification)) with monitoring elements, such as functional inks, indicators and sensors. This thesis examined their technical and sustainability potential in two application cases: reusable packaging and DPPs for electronics. For both, a value chain analysis based on interviews and questionnaires was conducted to determine the specific requirements for smart tags and information sharing. There insights were then used to evaluate the potential of the developed smart tag concepts in the selected application cases. Technical feasibility was investigated by testing several design and manufacturing variables for visual tags, including material selection, printing methods, process parameters and feature sizes. Among these the choice of the printing method had the greatest impact; specifically, screen printing performed the best. Inkjet printing was advanced by developing functional inks for temperature, light and humidity, thus enabling the production of individualised smart tags. A humidity indicator concept was created using two inks and integrated with a 2D barcode. This approach showed potential for semi-quantitative assessment of both the duration and level of humidity exposure, as the colour difference increased over time and varied with the humidity levels to which the smart tags were exposed to. Durability under repeated contact with water and heating was investigated by testing three approaches: protective coatings, laser engraved 2D barcodes and overmoulding of tags within the surface. Each had its pros and cons, but protective coatings were recommended for smart tag applications. They effectively protected both the visual and electronic smart tags from heat and water while preserving monitoring functionality. They also offer potential for more sustainable development. Laser engraving proved robust for durability, but it does not support integrated monitoring capabilities. Overmoulding trials were unsuccessful, and the embedded tags could complicate end-of-life management of the host product. A set of parameters affecting the sustainability and circularity of electronic tags was compiled and used to create a holistic and streamlined tool for benchmarking electronic smart tags at the design stage. The largest differences between the benchmarked concepts stemmed from material and manufacturing choices. The methodology is proposed for adaptation to other domains to enable early-stage comparison of emerging technologies with careful selection of domain-relevant criteria. Furthermore, the approach could be developed into sustainability impact indicators. The thesis identified key selection criteria for smart tag concepts across manufacturing, durability, and sustainability dimensions. It concludes that smart tag technologies should be chosen case by case, balancing technical performance with sustainability.
  • Advancements in copper flow battery systems: performance, modelling, and control strategies
    (2026) Badenhorst, Wouter
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-01-23
    Transition to an economy based on renewable energy demands scalable, efficient, and long-duration energy storage solutions to become a reality, with flow batteries having emerged as a leading technology to fulfil this need. This work focuses on the development and optimization of the all-copper redox flow battery and addresses critical performance and characterization challenges that are currently limiting commercial viability. Through systematic engineering and development, the systems current and voltage efficiencies have been greatly improved through stable copper deposition and improved material selection. Further advancements were made through the use of ion exchange membranes and the modification of porous substrates with ion selective polymers to achieve low rates of self-discharge together with high current efficiency over hundreds of hours of continuous operation. In addition to this characterization, this work developed novel methodologies to deepen our understanding of the all-copper flow battery, including the implementation of streaming potential measurements, and the development of a scanning electrochemical microscopy technique to gain temporal and spatial insights into membrane permeability and species crossover. These developments were complemented by the creation of a first principles control-oriented electrochemical model which was calibrated using a genetic algorithm technique, enabling accurate estimations of the systems state, degradation, and state of health over extended operation. Through targeted material development and dynamic modelling the efficiency, durability, and practicality of the all-copper flow battery was improved. Furthermore, the work provides guidance for the future scaling-up of the all-copper flow battery and informs strategies for continued development, thereby supporting the broader goal of the adoption of sustainable energy storage.
  • Engineering of lignin and lignin-carbohydrate complexes for high-value applications
    (2026) Diment, Daryna
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-01-23
    Industrial development has led to a dramatic increase in fossil fuel consumption. These nonrenewable energy sources, while currently accessible and cost-effective, contribute heavily to greenhouse gas emissions, therefore accelerating anthropogenic climate change. Addressing this global environmental challenge requires a transition toward sustainable, low-carbon energy alternatives. Within this paradigm, lignocellulosic biomass has emerged as a promising solution, offering a renewable, carbon-neutral feedstock that can be converted into biofuels and bioproducts. Its valorization not only supports the reduction of fossil fuel dependence but also contributes to the mitigation of climate change by harnessing a circular bio-based economy. However, despite its high availability and low cost, lignocellulosic biomass exhibits significant resistance to degradation, presenting substantial challenges for its effective valorization. While considerable progress has been made in the efficient conversion and application of cellulose, lignin remains a challenging component of lignocellulosic biomass, often assigned to combustion or disposal, thus extremely underestimating its unique chemical potential. To address the challenges in lignin utilization, a novel strategy was developed based on structure–property–performance correlation, representing a first step toward efficient lignin engineering. The approach involves selective modification of targeted functional groups while keeping others unchanged, followed by comprehensive property and performance evaluation. It was particularly useful for investigating how specific functional groups affect the physicochemical behavior of lignin and its performance in methylene blue adsorption. For instance, benzylic −OH groups were found to contribute approximately 3 and 2.3 times more than phenolic and aliphatic −OH groups, respectively. Overall, this work established a robust framework for tailoring lignin properties to meet the demands of high-value applications. Following that, a recently developed green biorefinery concept (AqSO Omni) was advanced using the power of artificial intelligence (AI) to provide simultaneous maximization of both lignincarbohydrate complexes (LCCs) yield and content in acetone-extracted lignin as LCCs hold great potential for high-value applications, yet achieving high yields remains challenging. Using Bayesian Optimization, optimal processing conditions were identified, achieving LCC yields of 8–15 wt% and carbohydrate contents up to 60/100 Ar. Importantly, LCCs with higher carbohydrate content showed lower glass transition (Tg) and surface tension, highlighting a significant step toward scalable production of tailor-made LCCs with tuned properties. Based on the previous outcomes, lignin demonstrated strong radical scavenging potential, that marked the urgent need for the development of a reliable and fast screening method for quantitative evaluation of the antioxidant properties of lignin. It was achieved by assessing the impact of the solvent, time, and the type of substrate on the antioxidant activity using a well-established 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. This work unveiled the importance of appropriate solvent choice as it predetermines the DPPH scavenging mechanism, steady state establishment, and the DPPH stability with 90 vol% acetone (aq.) exhibiting the greatest suitability for the antioxidant evaluation. While a small-scale and rapid performance evaluation method for lignin engineering is concerned, the concluding stage of the study involved the development of the UV-shielding lignocellulosic film, where a small addition of lignin into the formulation allowed to block over 90% of the UV rays.
  • Catalytic conversion of enzymatic hydrolysis lignin: Solvolysis and upgrading
    (2026) Li, Gen
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2026-01-16
    Enzymatic hydrolysis lignin (EHL), a major byproduct of the cellulosic ethanol industry, represents a promising feedstock for biomass valorisation due to its high aromatic carbon content. However, its extensive cross-linking and poor solubility significantly limit its efficient utilization. To overcome these challenges, this thesis proposes a systematic three-step approach—solvolysis, catalytic depolymerization, and hydrodeoxygenation (HDO)—to convert EHL into valuable aromatic monomers and cycloalkane fuels. The solvolysis behaviour of EHL was systematically investigated using alcohol–water mixtures, ethylene glycol, and other organic solvents. Among these, an isopropanol–water mixture (3:2 v/v) demonstrated excellent solubility, resulting in complete liquefaction at 250 °C. Separately, ethylene glycol was capable of fully dissolving EHL even at room temperature, highlighting its strong solvating power under mild conditions. Molecular dynamics simulations further revealed that van der Waals interactions disrupted π–π stacking between lignin units, while hydrogen bonding with oxygenated groups facilitated both liquefaction and β-O-4 bond cleavage. Catalytic depolymerization was conducted using Raney Ni in the isopropanol–water system, achieving a monomer yield of 45.6% at 320 °C with full cleavage of β-O-4 linkages. In contrast, the ethylene glycol system at 200 °C, in the presence of Ni and NaOH, yielded 18.8% monomers. Mechanistic analysis indicated that NaOH played a key role in bond cleavage, while Ni catalyzed hydrogen generation from H₂. Ethylene glycol also acted as a hydrogen carrier, facilitating hydrogen transfer to lignin fragments. In the final HDO step, guaiacol was employed as a lignin-derived model compound to study its transformation over nickel phosphide (Ni2P). The catalyst efficiently promoted C–O bond cleavage and aromatic ring hydrogenation under mild conditions, leading to the formation of high-energy cycloalkane fuels. Density functional theory (DFT) calculations revealed that phenolic intermediates strongly adsorbed onto Ni2P surfaces, underwent π-electron rearrangement and loss of aromaticity, thereby facilitating hydrogenation. Hydrogen atoms dissociated on the Ni2P surface and migrated via spillover to active sites, promoting efficient HDO. In conclusion, this thesis establishes a robust and mechanistically supported strategy for the conversion of EHL into high-value fuels and chemicals. The integration of solvent design, catalytic depolymerization, and selective hydrogenation provides important insights and a theoretical foundation for advancing lignin valorisation technologies.
  • Superhydrophobic bio-repellent surfaces
    (2025) Awashra, Mohammad
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2025-12-19
    Superhydrophobic surfaces trap a thin air film (plastron) at the solid–liquid interface, drastically reducing the effective contact area with the liquid. This enables them to repel biofluids, resist protein adsorption, and inhibit cell adhesion. However, a key challenge lies in maintaining plastron stability upon exposure to complex biological environments with biomolecules that destabilise the air layer. Plastron collapse compromises the surface’s bio-repellent properties. This doctoral thesis approaches bio-repellency through the lens of plastron stability, examining how superhydrophobic surface design influences interactions with proteins, culture media, and cell suspensions. In particular, we used optical imaging and wettability analysis to investigate how entrapped air layers resist collapse in the presence of complex biofluids and how this relates to antifouling performance. Through systematic design of micro- and nanoscale topography and surface chemistry, we achieved plastron lifetimes exceeding 120 hours in protein-rich media. Proteins (albumin, fibronectin) and sugars (glucose) were identified as key agents responsible for plastron destabilisation. Larger air-volume plastrons, greater Wenzel roughness and solid fraction, and smaller microfeature sizes were found to enhance plastron stability. The thesis also investigated the cell-repellent properties of superhydrophobic structures using A549 epithelial cells. Using fluorescence microscopy and scanning electron microscopy, we determined that the most effective cell-repellent superhydrophobic surfaces strike a balance: the solid fraction must be low enough to create air gaps wider than cell dimensions, yet high enough to maintain a stable plastron. Increasing Wenzel roughness or reducing feature size enhances plastron stability but narrows the gap, enabling cell bridging. Thus, optimal designs preserve the Cassie state while keeping gaps unbridgeable. Optimised micropillar arrays with low solid–liquid contact (7.4%) reduced cell attachment by 95% relative to smooth hydrophilic surfaces. In the final part of the thesis, the use of superhydrophobic interfaces is demonstrated through two novel biomedical applications. First, superhydrophilic-superhydrophobic droplet microarrays enabled high-throughput digital nucleic acid detection using low surface tension strand invasionbased amplification (SIBA) reagents. This array enabled robust single-RNA molecule analysis using minimal reagent volumes. Second, transparent superhydrophobic alumina nanograss-coated glass capillaries, fabricated via atomic layer deposition and hydrothermal treatment, exhibited reduced protein adsorption and up to 50% drag reduction in fetal bovine serum, highlighting their potential for surgical tubing applications.
  • Fabrication of multifunctional superhydrophobic surfaces
    (2025) Mirmohammadi, Mehran
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2025-12-12
    This thesis explores the development of multifunctional superhydrophobic surfaces using microfabrication techniques. It investigates a range of fabrication strategies, including replication, lithography, film deposition, and etching, to produce these robust multifunctional surfaces. The surfaces are intended for use in wear-resistant, anti-icing, and antibacterial applications. These surfaces can be achieved by applying a low surface energy coating to a structured surface and by introducing roughness, such as fabricating hierarchical micro- and nanostructures on inherently hydrophobic materials. Polymer replication, known as soft lithography or direct templating, is a highly effective technique for creating topographical surfaces from hydrophobic materials. This approach involves using original structures derived from nature or rough metal surfaces. This direct templating from leaves or other biological templates provides a straightforward means of replicating surface topography, enabling the precise copy of micro- and nanotextures of superhydrophobic surfaces found in nature. The key advantage of fabricated superhydrophobic surfaces in this thesis is their mechanical durability, which addresses a common vulnerability of fragile micro- and nanostructures. To overcome these challenges and improve mechanical robustness, this thesis explores various strategies, including creating overhanging structures, shielding nanostructures with microstructures, and applying hard coatings. We demonstrate the successful fabrication of durable superhydrophobic surfaces without the use of fluorine-based compounds. Our approach emphasizes that avoiding thin coatings is crucial for maintaining the robustness of these surfaces. Superhydrophobic materials and surfaces offer multifunctional benefits, including enhanced antibacterial effects and reduced ice adhesion. Their nanostructured design minimizes the solid contact area, hindering bacterial adhesion and growth by maintaining a trapped air layer between the surface and bacteria. We show that combining superhydrophobicity with copper significantly improves antibacterial properties compared to superhydrophobic-only surfaces and copper-only surfaces, as indicated by a notable decrease in the number of viable cells. Additionally, superhydrophobic surfaces exhibit remarkably low ice adhesion, especially in low-humidity conditions during freezing. The air pockets under water droplets slow heat transfer, delay ice formation, and further contribute to their multifunctionality. However, the micro- and nanostructures may sustain damage through repeated freezing and de-icing cycles. Our surfaces exhibit low ice adhesion after a number of icing–shearing cycles; however, after repeated freeze-thaw cycles, some degradation in their properties remained. Overall, the work demonstrates that superhydrophobic properties can be integrated into multifunctional surfaces, enabling them to function in practical applications.
  • Insights into the dissociation kinetics of phosphorylated nanocellulose through conductometry
    (2025) Kröger, Marcel
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2025-12-10
    Cellulose nanocrystals are highly crystalline, rod-shaped particles that can be obtained from native cellulose fibres though acid hydrolysis. Colloidal stability can be achieved for these particles by imparting chargeable functional groups, which induce electrostatic repulsion between the particle surfaces. Consequently, besides the particle morphology, the amount of imparted charge is one of the most important characteristics of cellulose nanocrystals. In this context, nanocelluloses carrying phosphate halfesters are of particular interest, given their potentially high charge and additional affinities for ion capture, biomineralization, or, in dry conditions, increased thermal stability. In this work, a methodology relying on separate phosphorylation of cellulose fibres and subsequent hydrolysis and dispersion is presented, which conveniently and reliably produces highly substituted phosphorylated cellulose nanocrystals at high yields. Nevertheless, in line with previous works on phosphorylated nanocellulose, the determination of the degree of phosphorylation by elemental analysis disagrees with the conclusions drawn from conductometric titrations. This is due to flaws in the contemporary methodology, which ignores the influence of so-called counterion condensation. To demonstrate the relevance of this influence and to reconcile the two analytical techniques, a theoretical model for the dissociation of phosphate halfesters on the surface of cellulose nanocrystals was developed. The model is capable of predicting the measured conductivities with reasonable agreement and attributes the discrepancy between elemental analysis and titrimetry to reduced acidities of the surface groups. As such, upon dissociation, the phosphate halfesters contribute to a rising charge on the particle surface, which, in turn, impedes further dissociation. This effect is not taken into account in the conventional interpretation of conductometric titration curves, which leads to an overestimation of the achieved functionalization and thus the observed discrepancy to elemental analyses. The developed model further allows insight into the significant reduction of the achievable surface charge to 0.16 to 0.42 per phosphate unit, demonstrating and quantifying the outstanding capacity for ion capture and ion exchange applications. This work further shows how divalent Ca2+ ions, through strong interactions with the phosphate halfesters, actuating ion exchange processes which, in turn, are visible in conductometry, as the interactions alter the shape of the observed titration curves. Again, these effects are reciprocated with reasonable agreement in the modelled datasets. These findings may help to further the current understanding of the surface charge of dispersed nanoparticles and remedy the current methodology of analysing conductometric titration curves, which may reconcile discrepancies in the reported studies on phosphorylated nanocelluloses.
  • Leaching of gold and battery metals from industrial tailings
    (2025) Karppinen, Anssi
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2025-12-05
    The modern world requires multiple metals due to the phase-out of fossil fuels and increasing electrification. At the same time, the ore grades of critical metals are declining and there is a lot of room for improvement regarding recycling efficiency. In addition to primary ores and recycled metals, metallurgical processes produce diverse side streams such as tailings, slags, dusts, residues, and scrap which contain low grades of valuable metals but are not often recovered. Tailings are leftover material from primary production where the less valuable fraction of the raw material is separated from the more valuable fraction. Typically, tailings are produced in the froth flotation process where metal grades of the ore are enriched in the concentrate and tailings are generated in the underflow. In addition, other types of wastes have been classified as tailings, such as leach residue from the cyanide leaching of gold. Tailings are stored in ponds or dried and stacked near the mine site. Cumulative storage of tailings requires a great deal of space and is an environmental concern due to acid mine drainage. This thesis investigates leaching as treatment for tailings originating from sulfide ores. The aim was to extract valuable metals—Au, Co, Ni, Cu—by acidic leaching in chloride and sulfate media. Additionally, tailings were utilized as a reductant for battery cathode material leaching to facilitate the simultaneous extraction of battery metals from the investigated materials. Gold leaching from cyanide tailings was performed in chloride solution in the presence of Fe3+ or Cu2+ as an oxidant. Up to 40% of gold was extracted and recovered from cyanide tailings by leaching and in-situ adsorption on activated carbon. Cu2+ ions were shown to be a more efficient oxidant for gold extraction than Fe3+ ions. This was attributed to more efficient regeneration of Cu+ ions to Cu2+ions by dissolved oxygen when compared to the regeneration of Fe2+ ions to Fe3+ ions. Due to the preg-robbing of gold, the presence of activated carbon increased the extraction of gold by providing an immediate adsorption site for the extracted gold. About 33% of Ni and 18% of Co were extracted in water leaching from low-grade and weathered tailings, which showed that the material had been partially oxidized during the long weathering period. With a mild oxidant (0.1 M) and acid (0.1 M), Ni extraction was increased to 47–48% and Co extraction to 23–24%. Ni extraction was further increased to 63% with leaching in more oxidative leaching conditions ([Cu2+] = 0.5 M, [Cl-] = 4 M, [HCl] = 0.1 M). From higher-grade sulfide tailings, up to 20% of Ni and 9% Co were extracted in sulfate leaching with Fe3+ as the oxidant. Co extraction was increased to about 15% when using H2O2 or battery cathode material as an oxidant. Increasing the supplementary Fe3+ concentration resulted in a decrease in acid consumption and decrease in the leaching rate of pyrrhotite. This was attributed to the increasing oxidative dissolution and conversion of sulfide sulfur to elemental sulfur on the pyrrhotite surface, which limits diffusion. Both pyrrhotite and pyrite were shown to be efficient reductants for battery cathode material leaching. Full valorization of metals from cathode material was achieved simultaneously with partial extraction of battery metals from tailings (up to 17% of Ni, 15% of Co, and 27% of Cu). Pyrite was shown to have no active role as a reductant if pyrrhotite was present in the leaching system. In the absence of pyrrhotite, pyrite acted as the primary reductant, and the reductive effect of both Fe2+and S2 2- was evident. All of the dissolved Fe was present as Fe3+ until the cathode material had fully dissolved. This illustrates that the reduction of cathode material via Fe2+ occurs faster than the oxidation of tailings via Fe3+.
  • Functionalizing regenerated cellulose and bio-based polyamide textile fibers towards active environmental responsiveness
    (2025) Madani, Zahra
    School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2025-12-05
    In response to increasing environmental and consumer demands, the textile industry must adopt sustainable solutions to mitigate the challenges of resource depletion and waste generation by emphasizing eco-friendly materials and efficient manufacturing processes. Beyond basic protection, functional textiles enhance comfort and durability, minimizing the need for frequent replacements and contributing to waste reduction. This thesis focuses on the development of sustainable, functional fibers by synthesizing bio-based polyamides with tailored functionalities and enhancing man-made cellulosic fibers through the incorporation of functional additives, thereby improving performance and adding value to conventional textiles. In approach one, two different bio-based shape-changing polyamides were developed: in one, starch was incorporated to increase biosourced content, with heat used to activate the shape-changing performance; in the other, a polypyrrole/graphene oxide composite was incorporated to enable light-responsive shape-changing actuation. In the second approach, Ioncell® fibers, derived through an environmentally friendly cellulose fiber production process, served as the base material for functionalization. Thermal regulation and hydrophobicity were introduced through phase change materials and an eco-friendly hydrophobizing coating, namely octadecenyl succinic anhydride. Additionally, pectin was incorporated to impart photothermal properties, enabling the fibers to harness solar energy for heat generation. As showcased by the above mentioned examples, combining sustainability with functionality paves the way for a more responsible textile production. In the presented scenarios, the environmental impact of textile production is decreased, while simultaneously catering to evolving consumer demands. One key achievement of this dissertation is the development of stimuli-responsive, shapechanging fibers for smart textile applications. These types of textiles can enable new use cases, such as indoor curtains that modify the lighting and acoustics of the space. Beyond this, the developed multifunctional cellulosic textiles are expected to enhance thermal comfort of the future users, particularly in cold outdoor environments. Overall, by combining two conventional but rather different textile raw materials, this thesis demonstrates how both polyamide and cellulosic fibers can be effectively enhanced to meet demanding functionality and sustainability goals, showcasing their potential in next-generation smart textiles.