[dipl] Kemian tekniikan korkeakoulu / CHEM

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  • Elemental analysis of anodically bonded borosilicate glass in MEMS
    (2025-11-23) Haiminen, Maria
    School of Chemical Engineering | Master's thesis
    The trend towards smaller dimensions and increasing complexity in MEMS components presents significant challenges for their characterisation. These challenges are particularly pronounced when studying the effects of wafer bonding techniques, such as anodic bonding, on patterned MEMS structures, where analysis areas are inherently limited. In anodic bonding, ions migrate under an applied electric field, typically within an alkali-containing glass matrix. The sensitivity of glass to ion beam damage and the mobility of ions under energetic particle bombardment further complicate the characterisation of silicon-glass bonds. This thesis evaluated the suitability of available characterisation techniques for studying bonding-induced ion migration in Si-glass bonds. Techniques examined include energy-dispersive spectroscopy (EDS) in scanning electron microscope (SEM), dynamic secondary ion mass spectrometry (SIMS), and time-of-flight SIMS (ToF-SIMS). Alternative methods were also discussed, and their challenges and suitability for this study assessed. Two test samples were analysed at two locations to evaluate the performance of the techniques. The results highlighted challenges in characterising ion migration and assessed the reliability of findings through comparison with previous studies of anodic bonding in Si-glass systems. Among the techniques considered, ToF-SIMS demonstrated the highest sensitivity, the lowest measurement error, and the ability to detect alkali ions at low concentrations. This thesis emphasised the need for developing more suitable techniques to analyse low ion concentrations in small glass areas (less than 100 μm), as encountered in patterned MEMS components with Si-glass anodic bonds.
  • Heterologous expression of ACS-CODH variants and characterisation of the cdh operon in Methanococcus maripaludis
    (2025-11-24) Pärkinen, Jenni
    School of Chemical Engineering | Master's thesis
    Methanogenic archaea are anaerobic microorganisms capable of converting CO2 and H2 into methane, making them promising candidates for CO2 valorisation and bio-based fuel production. The ACS/CODH enzyme complex, which catalyses carbon–carbon bond formation, is central to this metabolism and therefore a key target for metabolic engineering. This thesis investigates the physiological role of the cdh operon in Methanococcus maripaludis and explores strategies for heterologous expression of ACS/CODH variants in M. maripaludis and Methanosarcina acetivorans. Optical density assays, gas chromatography and NMR spectroscopy were used to assess the impact of cdh deletion on growth and metabolism. Heterologous expression efforts involved CRISPR/Cas12-based genomic integration in M. maripaludis and plasmid-based expression in M. acetivorans. (Delta)cdh M. maripaludis strains exhibited growth in acetate-deficient medium, suggesting a partial deletion strain due to polyploidy. Heterologous expression efforts produced intermediate CRISPR donor plasmids and successfully amplified ACS/CODH variant fragments from a variety of Methanobacteriota, providing a foundation for future studies. These findings highlight the physiological complexity and biotechnological potential of ACS/CODH in methanogens, informing strategies for the engineering of synthetic pathways for CO2 valorisation and bio-based fuel production.
  • Accelerating hydration of blast furnace slag in low-carbon concrete: Use of concrete wash water in 24-hour strength development in cement/slag-systems
    (2025-11-22) Louhi, Luka
    School of Chemical Engineering | Master's thesis
    The main objective of this study is to examine which chemical mechanisms are present and dominant in hardening of cement/slag-systems. This thesis aims to give understanding about how said mechanisms can be harnessed to accelerate strength development. Mechanisms of interest are effect of nucleation points to hydration product formation and effect of alkalinity to slag dissolution. Main objective regarding results is to obtain improvement in slag hydration using alkaline concrete truck wastewater. Aim is to improve early age compressive strength of concrete. Other main objective is to achieve this with lowered carbon footprint. The thesis reviews chemical nature of supplementary cementitious materials and especially concentrates on blast furnace slag, a byproduct of steel production. Experimental part of the thesis studied accelerating 24-hour compressive strength development of cement/slag-systems. This was done by simulating concrete truck wash water which was added to cement/slag-system to boost early age strength development. Wash water was prepared by dissolving cement to water, which creates highly alkaline solution as formed calcium hydroxide dissolves. It was determined that alkaline cement hydration products do accelerate slag hydration on slag rich systems, but do not work as well when percentage of cement is high. Alkalinity of system was found to be more important than availability of nucleation points. As effect of nucleation points was found to be negligible, future research could be directed towards chemical kinetics of slag dissolution. This study contributes to understanding of how slag can be utilised to lower carbon emissions of concrete industry.
  • Lignin-based fire retardants for wood-based panels
    (2025-10-27) Hyvärinen, Patrick
    School of Chemical Engineering | Master's thesis
    Fire-retardants are a class of materials designed self-extinguish or inhibit spread of flames during combustion. The increased use of fire-retardants has led to a decrease in fire related deaths and overall contributed towards improved fire safety. However, many traditional fire-retardants are based on harmful chemicals, and many safer alternatives are researched. One such potential alternative is lignin, a biopolymer produced by plants that is recovered in high amounts as a technical side-product in pulp mills. The purpose of this study was to modify softwood Kraft lignin by phosphorylation and nitrogenation, and then test the modified lignin in a commercial coating to verify if it could improve the fire retardance of wood-based panels. Lignin was phosphorylated with sodium trimetaphosphate or aminated with 2-chloroethylamine. Additionally, aminated lignin was phosphorylated to add both phosphorous and nitrogen groups. XRF and elemental analysis were used to quantify the phosphorous and nitrogen content of the modified lignins. Up to 4.1 wt.% phosphorous content was reached with lignin phosphorylation, while up to 8.5 wt.% nitrogen with lignin amination. FTIR was used to confirm successful chemical reaction. TGA showed that the phosphorylated lignin had greater thermal resistance than unmodified or aminated lignin. The modified lignins were mixed with the reference coating at 5 and 10 wt.%. The coated panels were tested with cone calorimetry and reaction to fire tests. Unexpectedly, the panel coated with the unmodified coating showed the best results at the cone calorimeter. This notwithstanding, the lignin that was both phosphorylated and nitrogenated reported the longest time to ignition and lowest peak heat release rate, and the vertical burning test showed the modified lignins could prevent after-flame. Despite the TGA tests, no char formation was noticed.
  • Characterization of foam properties for optimized surfactant performance in the flotation separation of polyester and cotton fibers
    (2025-11-24) Savikurki, Mirka
    School of Chemical Engineering | Master's thesis
    Globally, the most manufactured fiber blend is so-called ‘polycotton’, a mixture of synthetic polyester fiber and natural cotton fiber. Unfortunately, recycling of fiber blends is particularly problematic, as the fibers must be separated from each other before recycling, which is challenging due to their inherently different properties. The methods used for separating these fibers are often expensive, consume a lot of harmful chemicals, and degrade the quality of the separated fibers. Flotation is a non-destructive, scalable separation method that has been established especially in the mining industry, recycled paper deinking, and wastewater treatment. The method is based on the surface chemical differences of the particles to be separated: hydrophobic particles can be separated from hydrophilic ones by enriching them into foam using air bubbles and surfactants. Since polyester fibers, which are mainly produced from polyethylene terephthalate (PET), are hydrophobic whereas cellulosic cotton fibers are hydrophilic, flotation could be considered an ideal approach for their separation. The aim of this research was to identify the main foaming and foam structure properties that enable efficient and precise separation of PET and cotton fibers using flotation. Three different surfactants were selected for the study, and their foamability, foam stability, and foam structure were investigated at varying concentrations and compositions in a two-phase system (gas-liquid). Based on the results, four systems with the most varied foaming properties possible were selected to perform flotation experiments for separating PET fibers from cotton fibers. The best PET recovery (~72%) and grade (~88%) were achieved with three out of the four selected surfactant systems. This indicates that the foam properties of the selected two-phase systems do not have a significant effect on the selectivity or efficiency of PET and cotton fiber flotation separation. However, the results suggest that when selecting surfactants, their surface activity should be considered in relation to the critical surface tension of the fibers to be separated. Overall, the results demonstrate that although further research is needed to optimize the process, flotation as a separation method is a promising and viable option for recycling polyester and cotton fiber blends.
  • Investigating the influence of forced-air pneumatic flotation cell on the recovery of fine pentlandite
    (2025-11-18) Pekkanen, Lassi
    School of Chemical Engineering | Master's thesis
    Due to depleting ore reserves around the world, extraction of more complex orebodies has become more common. This has led to the need for finer grinding in order to liberate the valuable minerals from the gangue minerals. Traditional flotation cells are not able to recover particles under 25 microns efficiently and thus need for new flotation technologies for fine particle floatation has emerged. Metso’s Concorde Cell™ is a forced-air pneumatic flotation cell which operates at high shear rates, high circulating load and with fine disseminated bubbles to enhance recovery of fine particles. In January 2025 Concorde Cell™ was commissioned at Boliden Kevitsa mill with the goal to improve recovery of nickel. This thesis focused on studying the effects of Concorde Cell™on the recovery of total and fine nickel particles. Paired sampling campaigns, with and without Concorde, were conducted for four days to observe Concorde Cell™ performance with two different feed streams namely rougher concentrates and cleaner three tails. Due to the small size of the Concorde cell™, effects on the circuit were not significant. Varying feed grades impacted the final recoveries of the circuit. Plant performance improved slightly with one of the feeds to the Concorde Cell™. Concorde Cell™ itself was able to produce high-grade concentrates.
  • Characterization of thermal connections using electrochemical and surface sensitive methods
    (2025-11-21) Stahl, Yannic
    School of Chemical Engineering | Master's thesis
    This Thesis investigated the corrosion behavior of thermally connected aluminum joints in an industrial component, focusing on how alloy choice, joining parameters, surface machining, pretreatment, and cathodic dip coating systems influence performance. The experimental program combined surface roughness characterization, Modified Environmental Cycle Tests according to norm 1, and electrochemical methods to establish correlations between surface state, coating integrity, and corrosion kinetics. Three norm 1 variants (1, 2, and 3) were applied for durations of six and twelve weeks to simulate real-world cyclic exposure under varying severity. Electrochemical investigations employed two complementary setups: a large-area three-electrode configuration for coated samples and a microelectrode system for localized measurements on pretreated, uncoated surfaces. In these tests, open circuit potential (OCP), linear polarization resistance Rp, cyclic potentiodynamic polarization, Electrochemical Impedance Spectroscopy (EIS), and galvanostatic load measurements were performed to quantify coating barrier properties, interfacial kinetics, and localized corrosion susceptibility. The results clearly show that the heat-affected zone (HAZ) is the most vulnerable region across all coatings, test severities, and durations. Corrosion consistently initiated and propagated in the HAZ, while the joining zone and flat sheet generally remained better protected. This trend intensified with longer exposure and under the aggressive test variant 3. Alloy composition also played a decisive role: M2 exhibited superior corrosion resistance compared to M1, particularly in the HAZ. This difference is attributed mainly to the higher magnesium content in M2, which promotes passivity and microstructural stability. However, the morphology of the two alloy types likely also influences their corrosion susceptibility. Surface preparation emerged as another critical factor. Method I alone produced low roughness and minimal profile length increase, resulting in excellent corrosion resistance even after twelve weeks of exposure. Optimized I delivered the smoothest finish and the lowest corrosion classes recorded. In contrast, methods II and III significantly increased roughness and relative profile length LR, amplifying corrosion susceptibility under cyclic exposure. The combined sequence of surface machining methods I, II, and III produced the highest profile length increase and the largest attacked surface fractions at long duration. Strong correlations between surface metrics and corrosion behavior were revealed. Corrosion classes increased proportionally with Rz, while the profile length ratio LR was more closely related to the relative attacked area. Once LR exceeded the profile length ratio threshold LR,c corrosion severity rose sharply, whereas LR values below a lower threshold consistently corresponded to low corrosion classes. These findings confirm that geometric enlargement of the surface and deformation-induced heterogeneity both amplify corrosion risk. Joining parameters and associated surface modifications also influenced coating performance. The joining parameter B lead to surface changes and introduced adhesion defects in the HAZ, leading to disbondment of the cathodic dip coating (CDC), particularly under Z coatings. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed needle-like Al6(Fe, Mn) intermetallics and Mg-rich eutectic phases in these regions, which likely impaired oxide layer formation and coating adhesion. Removing modified surface regions by machining method I mitigated this failure mode. Coating systems exhibited distinct performance hierarchies. The B CDC provided the most robust and long-term protection across all surface states, maintaining low corrosion classes even on surfaces machined with methods II and III while also showing minimal progression at scribes. The Z CDC performed well on smooth surfaces or regions machined with method I but was sensitive to the modified HAZ and heavy machining, with pronounced degradation under aggressive conditions. The T CDC offered excellent protection on planar surfaces but showed reduced stability at joining zones and heavily machined regions, particularly under severe cyclic exposure. Electrochemical investigations added additional insight into these observations, revealing how pretreatment and surface morphology influence interfacial stability and barrier integrity. Polarization resistance measurements confirmed that pretreated surfaces generally exhibit one to two orders of magnitude higher Rp compared to untreated references, demonstrating the effectiveness of conversion layer formation. The microcell measurements further resolved local differences between joining zone, HAZ, and surface, showing that Rp is consistently lowest at the joining zone and highest at the outer surface. However, hysteresis and breakdown potential analyses identified the HAZ as electrochemically most unstable, with wider hysteresis loops and more negative breakdown potentials, confirming its tendency for localized breakdown and slow repassivation. Furthermore, surfaces machined with methods II and III exhibit wider hysteresis compared to surfaces machined with method I or unmachined regions, mirroring their high corrosion classes observed in norm 1. The T pretreatment produced narrower hysteresis loops and higher charge transfer resistances on surfaces machined with method I, while Z pretreatments exhibited more positive breakdown potentials but delayed repassivation. EIS measurements on pretreated and coated samples revealed that most intact coatings could be modeled with a single Randles circuit, while degraded or roughened surfaces required additional time constants, indicating the formation of porous layers or defects filled with electrolyte. Under galvanostatic load, samples with higher roughness reached permanent voltage drops significantly faster and passed larger total charges, confirming faster barrier failure and electron transfer once electrolyte penetration occurred. These measurements confirmed that heterogeneity induced by machining accelerates pit initiation and compromises passive film stability, aligning with the trends observed in environmental cycling. From these findings, several practical recommendations emerge. Alloy selection should favor M2 over M1 for thermally joined components. Surface modifications created by joining parameter B should be avoided or their effects removed with method I before pretreatment and coating. Surface machining should prioritize method I only, preferably under optimized parameters, while methods II and III should be minimized. Quantitative surface limits should be defined, aiming for low Rz and LR values avoiding LR,c. For thermally joined assemblies, the B CDC offers the most reliable long-term protection, while T coatings may be suitable for planar geometries if edge coverage is improved. Pretreatment location had no measurable effect on roughness. The best-performing configuration identified in this study combines M2 alloy, optimized method I without II or III, and the B CDC, with careful removal of the edge caused by joining and adversely modified surfaces. This setup achieved the lowest corrosion classes across all test durations and severities. Overall, the integration of environmental and electrochemical data enables a comprehensive understanding of degradation mechanisms in thermally joined aluminum assemblies. The electrochemical techniques provided time resolved insight into interface kinetics and passive film evolution, bridging the gap between laboratory exposure and real-world performance. However, to fully validate the observed trends, the tests and measurements should be repeated to exclude potential influences from fluctuations in material paint shop quality, CDC bath chemistry, or variability in machining. This would increase statistical reliability and ensure that the observed differences are intrinsic to the material and process parameters rather than external variability. The work contributes to understanding degradation in joined 6xxx assemblies under cyclic exposure and clarifies the interplay between composition, microstructure, and coating performance. It introduces a dual-metric approach, Rz and LR, to define the ideal surface state prior to pretreatment and coating. These insights translate laboratory electrochemistry and environmental testing into possible manufacturing guidelines. Limitations include incomplete long-term data for T coatings, and variability in microcell measurements and roughness statistics. Future research should decouple geometric and metallurgical effects, refine pretreatment chemistry for challenges specific to the HAZ, and investigate the origin of adhesion failures associated with surface modifications caused by thermal joining in greater detail. In conclusion, corrosion durability in thermally joined aluminum components is determined primarily by HAZ integrity and surface preparation. Selecting M2, applying optimized method I, avoiding II and III, while using a robust CDC such as B can significantly enhance long-term corrosion resistance. These optimizations provide clear, implementable measures for improving the reliability of structural components.
  • Fabrication of superhydrophobic surfaces for self-cleaning application
    (2025-11-03) Oladosu, Ikeoluwapo
    School of Chemical Engineering | Master's thesis
    Contamination of surfaces such as solar panels and skyscrapers, through air pollution such as dirt or dust, is a major problem resulting in significant waste of money, labor, and energy for restoration. There is a need for a self-cleaning. Superhydrophobic surfaces were fabricated through a top-down fabrication approach, which includes optical lithography and replication molding. The fabrication process started with the design of micro/nano-scale structures using KLayout, followed by pattern transfer through a maskless aligner (MLA) to enable high-resolution structuring without the need for a physical mask. The pattern substrate undergoes plasma deposition for anti-adhesion coating, and finally, the substrate was replicated with PDMS molding for a self-cleaning experiment. To understand the effectiveness of the structured surfaces, their ability to repel water and self-cleaning performance were compared with plain, unstructured PDMS. The experiments were carried out by spreading contaminant (DMT Test Dust A2 fine quartz-free) on a surface, followed by 100µL of water droplets being dropped on the contaminated surface six consecutive times on the same spot, making a total volume of 600µL of water droplets. The rolling motion of water droplets facilitated the removal of the contaminant. This was captured and further analyzed with ImageJ software. The results show that the patterned PDMS structure (honeycomb) exhibits 99% self-cleaning efficiency at a 30º tilting angle, whereas the unstructured PDMS achieves only 29% self-cleaning efficiency under the same conditions. The results confirmed strong self-cleaning capability of the fabricated surfaces.
  • Enhancing sustainability in bagasse pulping: Hexenuronic acid removal and membrane-based chemical recovery
    (2025-11-24) Ouyang, Kun
    School of Chemical Engineering | Master's thesis
    This study focused on two significant challenges in sustainable bagasse pulping: high chlorine dioxide (ClO2) consumption during bleaching and inefficient chemical recovery from silica-rich spent liquor. To address this, a combined approach of acid pretreatment (A-stage) to remove hexenuronic acid (HexA) from bagasse, and ultrafiltration (UF) for soda liquor fractionation was systematically explored. In the bleaching trials, the conventional ECF sequence D0–Ep–D1 was compared with a modified A/D0–Ep–D1 sequence. The A-stage effectively hydrolyzed 49% of the initial HexA (reducing it from 14.4 to 7.4 μmol/g), resulting in a 25% reduction in ClO2 demand when active chlorine charge applied on pulp. Although with saving of ClO2 demand, the A-stage sequence led to about 5% lower final ISO brightness (75% vs 80%) and a 21% decrease in viscosity (685 vs 874 ml/g) when comparing to the ECF sequence D0–Ep–D1, indicating a trade-off between chemical savings and pulp quality. Concurrently, ultrafiltration (UF) of spent liquor with a 0.5 kDa-sized membrane effectively fractioned the stream: the retentate was enriched in high-molecular-weight lignin (Mw = 980 g/mol), while the permeate contained recoverable low-molecular-weight hydroxy acids (HAs, e.g., lactic acid, GISA, XISA) with over 60% recovery rate. Furthermore, NMR spectroscopy revealed that hemicelluloses existed possibly in the form of lignin-carbohydrate complexes (LCCs) in the retentate. Overall, UF enables promise of converting soda spent liquor into sources of lignin, HAs, and residual alkali, providing a potential alternative to traditional recovery boilers for small-scale mills utilizing non-wood feedstocks.
  • Development of a new martensitic low carbon ODS stainless steel
    (2025-10-10) Buisson, Jean-Baptiste
    School of Chemical Engineering | Master's thesis
    The elaboration and characterization of a new ferritic/martensitic oxide dispersion strengthened (ODS) steel, 13Cr4Ni ODS, with very low carbon content and nickel as the main austenite stabilizer, were investigated. The objective of this work was to assess the suitability of this alloy for fuel cladding applications in sodium-cooled fast reactors (SFR). The material was processed by mechanical alloying followed by hot isostatic pressing (HIP). Two grades were prepared for comparison: an unreinforced 13-4 grade (NR) and an oxide-dispersion-strengthened grade (ODS). Chemical analyses (ICP and EDS) confirmed the effectiveness of this processing route in limiting carbon contamination, while scanning electron microscopy revealed a fine and homogeneous microstructure. Thermal analyses (DSC and dilatometry) showed an austenitic phase transformation around 650 °C, within the targeted operating temperature range, representing a major drawback for the intended application. Heat treatments were applied in order to reduce hardness, but their effect remained limited (−28 HV). The high hardness (415 HV) was identified as the main factor limiting the workability of the material. Furthermore, EBSD analysis revealed the formation of residual austenite grains representing about 8% of the microstructure, and EDS measurements showed that these austenitic domains were correlated with nickel-enriched regions. Room-temperature tensile tests showed a high yield strength (1315 MPa) but limited elongation at fracture (8.4%), confirming the poor formability of the alloy. At 600 °C and 800 °C, tensile tests demonstrated combinations of yield strength and elongation suggesting good creep resistance. Overall, the alloy exhibited low viability for the intended application. Thermodynamic simulations nevertheless indicated that reducing the nickel content could represent a promising optimization route by lowering the fraction of residual austenite and improving the suitability of the alloy for cladding applications.
  • Developing cellulose-based opacifiers through enzymatic treatment of microcrystalline cellulose
    (2025-10-27) Hussain, Shamila
    School of Chemical Engineering | Master's thesis
    The growing demand for sustainable materials has driven efforts to reduce dependence on titanium dioxide, the dominant opacifier in paints, coatings and cosmetics. Although TiO2 is highly efficient, its production has a significant carbon footprint and raises health and environmental concerns, motivating the search for bio-based alternatives. Light scattering in biopolymers like cellulose is influenced by porosity, offering a model for designing sustainable opacifiers from low-refractive-index materials. This thesis investigates enzymatic modification of microcrystalline cellulose to develop cellulose-based opacifiers. Porosity was introduced using cellulase, with the aim of producing pores in the 200-350 nm range, roughly half the wavelength of visible light, to maximize multiple scattering and thereby improve opacity. Some samples also received ultrasonication pretreatment to assess its effect on enzymatic efficiency. Reaction parameters including enzyme dose, hydrolysis time, reaction temperature, and suspension consistency were varied to optimize porosity formation. Untreated MCC and TiO2 were used as a reference and porosity, pore size distribution, and optical properties were measured to evaluate the effect of treatments on light scattering and whiteness. Enzymatically treated MCC, including samples pretreated with ultrasonication, developed porosity in the 200-350 nm range, enhancing light scattering and opacity. Low enzyme dose at 3% consistency yielded better optical performance than higher doses at 5% consistency and surface roughness also contributed to improved light scattering. Ultrasonication likely enhanced enzyme efficiency. A clear correlation between increased porosity and higher opacity was observed. Although opacity remained below that of TiO2, treated MCC showed promise as a sustainable, bio-based opacifier and provides foundation for further optimization and exploration of alternative pretreatments and cellulose sources.
  • Turning different pulps into fibers by the use of a monofilament dry-jet wet spinning unit
    (2025-11-08) Kokko, Monika
    School of Chemical Engineering | Master's thesis
    The textile industry has major environmental impacts due to its high carbon emissions, water use, and waste. Man-made cellulosic fibers (MMCFs) are a more sustainable alternative to conventional fibers such as cotton and fossil-based synthetics. Although viscose is currently the most common MMCF, its production involves toxic solvents. Lyocell offers a greener solution through its closed-loop process that recycles chemicals and water. However, Lyocell production is limited by the high cost of production. The use of paper-grade pulps with a higher hemicellulose content has been proposed to reduce costs while maintaining acceptable fiber quality. The objective of this thesis is to produce Lyocell textile fibers using various types of pulps. The study focuses on understanding the impact of the hemicellulose content and the type of wood (hardwood, softwood) on fiber properties and spinning performance. Pulp sources include kraft, pre-hydrolyzed kraft, acid sulfite, and recycled cotton, each differing in the cellulose and hemicellulose content. This research aims to provide information on the relationship between pulp composition and the mechanical and spinning properties of Lyocell fibers. The results show that softwood pulps generally performed better in spinning and mechanical properties than hardwood pulps. Kraft pulps generally showed inconsistencies while spinning however, fibers produced from softwood kraft pulps performed better in mechanical properties, such as tensile properties than dissolving-grade pulps. Understanding the effect of pulp composition on the properties of Lyocell fibers enables more efficient use of raw materials and supports the transition to more sustainable textile manufacturing.
  • Fluidized bed drying and modelling
    (2025-11-02) Alam, Imtiaz
    School of Chemical Engineering | Master's thesis
    The study in this master's thesis focuses on the fluidization behaviour and drying kinetics of spherical catalyst support particles, 5 mm in diameter, in a fluidized bed dryer system. The primary objective was to establish a comprehensive hydrodynamic baseline that supports future studies on the shape effect. This thesis conducted a thorough study on the influence of various operating parameters affecting drying processes, including air temperature settings, superficial air velocity, and bed load weights, on drying performance. It was found that the drying processes in wet particles rely on a certain hydrodynamic limit. The lack of airflow stimulated agglomeration through the liquid bridge, which is characterized as the primary mechanical obstacle to the drying process. The effective moisture diffusivity (D_eff) values were computed and possess an Arrhenius-type temperature dependence with a low activation energy, indicating loosely bound moisture and effective drying at moderate temperatures once fluidization is achieved. The process demonstrates exceptional energy efficiency when proper fluidization conditions are met. Finally, this study establishes a precise timeframe for effective drying operations at moderate settings without triggering hydrodynamic collapse. The results provide a validated spherical-diffusion baseline and model fits for subsequent studies on non-spherical particles.
  • Phase equilibria and thermodynamic modeling of the Cu-Fe-Sn-O-SiO2 system
    (2025-11-24) Anto, Bayu
    School of Chemical Engineering | Master's thesis
    The rapid growth of electronic waste (e-waste) generation has become a global concern, prompting continuous efforts to improve its treatment and material recovery. One of the key metals of interest for recovery from e-waste is tin. Because primary tin ore deposits are geographically concentrated, tin is classified as a critical raw material in some countries. Furthermore, the high market value of tin makes tin recovery from e-waste economically attractive. Among the available recycling routes, black copper smelting is considered one of the most promising methods, where tin recovery occurs during the slag cleaning stage. In this study, the equilibration-quenching-electron probe microanalysis method was employed to investigate the phase equilibria of the Cu-Fe-Sn-O-SiO₂ system. Thermodynamic simulations were also performed using available databases in FactSage and MTDATA. Two types of slags were used in the experiment, iron-saturated slag and iron-silica-saturated slag. Experiments were conducted at 1200 °C, 1250 °C, and 1300 °C, with tin concentrations in the copper-tin alloy varied from 2.5 wt% to 20 wt%. Comparison of the experimentally determined compositions with the Cu-Fe-Sn ternary diagram generated using the FSstel database in FactSage revealed discrepancies in the liquid alloy phase equilibrium line, indicating the need for further optimization of the liquid phase. Additionally, simulations using the MTOX database in MTDATA provided the estimation of the prevailing oxygen partial pressure, a key factor in many pyrometallurgical processes, that was not possible to be directly measured or controlled in the closed system used in this study. The tin concentration in the studied system did not significantly influence the prevailing oxygen partial pressure. However, the effect of tin on oxygen partial pressure can be calculated with minor approximations from the experimental data. Whereas temperature had a clear effect on the oxygen partial pressure. Evaluation on the metal-slag distribution coefficient revealed that tin recovery improves at lower Sn concentrations in the alloy and at reduced temperatures. This contrasts with the reports suggesting higher temperatures enhance the recovery. The discrepancy might arise because oxygen partial pressure was not independently controlled in this study, but varied with temperature in a closed system, affecting Sn behavior and its distribution between metal and slag.
  • Potential of red seaweed-based dispersion barrier for paperboard
    (2025-11-13) Vahanto, Tiia-Maria
    School of Chemical Engineering | Master's thesis
    Growing environmental concerns along with the EU’s Single-Use Plastics directive (SUP), have driven innovations towards biobased alternatives to fossil-based barrier coatings. According to the directive, bio-based solutions should be chemically unmodified natural polymers to avoid classification as plastic. Currently, food products are packed in paperboard packaging, which are traditionally coated with plastic-based barrier layers. Paperboard provides mechanical strength, while the barrier coating ensures protection against grease, water, water vapor, oxygen, and microorganisms. This thesis focuses on the barrier properties of carrageenan-based barrier coatings applied to paperboard considering the requirements set by SUP-directive. The carrageenan-based barrier coating was applied to paperboard as a water-based dispersion. The barrier properties of carrageenan were evaluated in its pure form, mixed with bio wax and crosslinker and as a multilayer structure. The coatings performance was evaluated by surface characteristics and barrier properties. Results showed that carrageenan alone provide moderate grease resistance but poor water resistance due to its hydrophilic nature. The addition of crosslinkers improved grease resistance, while wax additives enhanced water resistance. A multilayer structure combining crosslinked carrageenan base layer and a hot melt coated bio wax as top layer, offered balanced barrier properties. However, challenges were observed in coating uniformity, layer thickness and gluability. The study demonstrates that carrageenan, especially when combined with suitable additives, show promising properties for bio-based solution for paperboard food packaging. Further research is needed for example to find solutions to moisture resistance properties and to evaluate long-term performance under varying environmental conditions.
  • Smart lignin capsules: Next-generation microbial factories
    (2025-11-14) Khanum, Safoorah
    School of Chemical Engineering | Master's thesis
    Encapsulation technologies have long been employed to improve the stability and delivery of micro-organisms and biomolecules in industrial and biotechnological applications. Probiotic bacteria and enzymes, among the most commonly encapsulated compounds, benefit greatly from this approach. However, conventional hydrogel-based encapsulation matrices often face limitations in sustainability, mechanical strength, and cost-efficiency. To address these limitations, we developed a lignin-alginate composite hydrogel and demonstrated its applicability for the encapsulation of a biotechnologically relevant microbe, Lactiplantibacillus plantarum, and enzyme, β-galactosidase. Lignin, a biodegradable and abundant biopolymer, was incorporated into an alginate matrix to enhance its structural integrity and protective capacity. The resulting composite beads achieved encapsulation efficiencies of up to 90% and maintained both cell viability and enzyme functionality, following exposure to stress conditions. Additionally, the lignin-alginate matrix improved bacterial viability post-freeze-drying, outperforming alginate-only systems. These findings highlight the potential of lignin-based hydrogels as an eco-friendly, sustainable, and novel approach for biological encapsulations with broad applications in functional foods, controlled drug delivery, and biotechnology.
  • Mechanical properties of slow cooled copper slag
    (2025-10-22) Toivonen, Robi
    School of Chemical Engineering | Master's thesis
    Production of copper creates slag, which still contains some amounts of copper. Considering the large amounts of slag, the recovery of copper from slag is important to ensure efficient copper production. Slag cleaning by flotation relies on slow cooling the slag which increases the size of copper containing particles and liberation of copper containing particles by comminution. Between these processes the slag needs to be disintegrated so it can be conveyed and stored properly. The slow cooled slag at Boliden Harjavalta’s smelter is normally quite brittle this disintegration happens when emptying the slag from ladles. However there has been occasionally observed though slag which does not disintegrate and can cause blockages and damage the equipment. While vastly studied material there are not many studies on mechanical properties of this type of slag. The purpose of this thesis was to find out a suitable method for testing slag strength and find out what chemical and mineralogical properties could affect the slag strength and hardness. X-ray fluorescence was used for chemical composition and x-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy for mineralogical analysis. Vickers hardness and compressive strength were determined as mechanical properties. Seven sample batches was collected in five week sample campaign. Slag consisted mainly of fayalite (Fe2SiO4), magnetite (Fe3O4) and intergranular glass. Largest exception was high magnetite content in one batch which also had the highest compressive strength of 243MPa. Other batches were in the range of 80MPa and 160MPa. Thus, some correlation with strength and magnetite content observed but plotting magnetite content against compressive strength gives a correlation coefficient of 0.78. All batches had large deviation and therefore the results may not be completely reliable. The Vickers hardness values for all batches were in a range of 625 to 711.
  • TEMPO-oxidized cellulose nanofibrils as a functional component in ultra-low solid double network hydrogels for biomedicine
    (2025-09-26) Bozzhigitova, Dinara
    School of Chemical Engineering | Master's thesis
    This thesis explores the potential of TEMPO-oxidized cellulose nanofibrils (TCNF) as a component in the ultra-low solid double network (DN) hydrogels for biomedical use. The main goal was to determine the gelling point (GP) of TCNF and how sonication and surface charge influence the rheological behaviour and structure of TCNF, using rheological analysis, Atomic Force Microscopy (AFM), and light microscopy. TCNF with low (705 mmol/kg), medium (1011 mmol/kg), and high (1205 mmol/kg) charge densities were studied. The results showed that both the charge, and sonication affect the GPs of TCNF. Low charge TCNF had lower GP due to fibrillar aggregation, while the high and medium charge TCNF showed higher GP due to electrostatic repulsion between more extensively carboxylated fibrils. Sonication affected the GPs of more carboxylated TCNF of high and medium charge, while the GP of the low charge TCNF was affected the least due to lower concentration of carboxylic groups. AFM scans of spin-coated TCNF showed dense fibrillar network with individual fibrils and flocks on all samples, regardless of sonication or charge difference. The light microscopy images revealed the same pattern, with flocks and individual fibers on all spin-coated TCNF. The TCNF hydrogels did not display expected sol-gel transition in rheological tests, instead, they stayed in the critical gel (CG) state. Additionally, the TCNF samples exhibited a self-similar structure with repeating fibril flocks and individual fibers across multiple scales (AFM, light microscopy, and the naked eye). Thesis also explored the enzymatic digestibility of hemicellulosic components using endoglucanase enzymes from VTT. One of the tested endoglucanases showed high specific activity towards both substrates. The thesis confirms the formation of hydrogels at ultra-low solid concentrations of TCNF, which facilitates the further assisted degradation and tunable structure for controlled drug delivery systems. The prolonged CG state behaviour and self-similar structure of TCNF was not reported in previous studies, hence, opens a new research direction on application of nanocellulose in biomedicine.
  • Simulation-based model optimization for a center launder retrofit
    (2025-10-30) Saikkonen, Aino
    School of Chemical Engineering | Master's thesis
    Effective froth management is crucial to ensure high recovery of metals and operational profitability. In recent decades the size of the operational flotation cells has increased significantly, with cell volumes exceeding 600 m^3. This significant increase in flotation cell volumes has increased the flotation surface parameters, which have been seen to negatively affect sufficient froth management by destabilizing the froth layer and decreasing the probability of particles to be collected. These challenges led to the need for different launder and crowder arrangements to improve froth collection and movement towards the launder lip. One of the leading flotation launder configurations, the center launder, has enabled significant improvements in the recovery of valuable metals by enhancing froth management in many operations worldwide. This thesis aims to model how consistently the simulation can reproduce results, and how accurately the observed recovery improvements after the center launder upgrade can be simulated using HSC software. Additionally, a center launder upgrade has been observed to positively impact electricity and water consumption as well as CO_2 emissions. To further quantify these impacts and assess the overall environmental benefits, HSC was applied to carry out a Life Cycle Assessment (LCA), alongside metallurgical performance modelling. The methodology for the research work was created to replicate real-world process conditions as closely as possible, using previous case studies as a reference. The simulation results indicate a clear correlation between the changes in simulated and measured recoveries as the feed characteristics vary. Moreover, the estimated overall recovery improvements after the center launder installation follow a similar trend to the calculated improvements, although with certain limitations. Overall, drawing final conclusions about the reliability of the results is difficult, as it would require further testing of the methodology in practice. However, this thesis provides a very good foundation for the future development of the model, helping to understand its limitations and approach to modelling.
  • Dimensionering av batterilagringssystem för en vindkraftspark i en hybrid konfiguration för ett basvolym-kontrakt och reducering av obalanskostnader
    (2025-10-19) Mäenpää, Aron
    School of Chemical Engineering | Master's thesis
    As the rapid expansion of wind power in Finland has led to declining energy prices, increased market volatility and rising imbalance costs, mitigative measures are at the forefront for renewable energy producers. To address these challenges, hybridization of a windfarm and BESS has been modelled to reduce balancing costs and enhance long-term profitability. This thesis examines the methods and feasibility for scaling a battery energy storage system (BESS) to a windfarm behind the meter. The thesis examines two specific cases for this configuration. The first case reviews the economic feasibility of delivering a baseload PPA contract through a hybrid plant, to assess the suitable size of the BESS. The first case is modelled by assigning a set optimal lode for every hour of the year for the hybrid plant. The hybrid plant produces this load through the windfarm output, BESS output, and balancing market draw to cover for any missing energy output. The BESS operates through a partial discharging and charging pattern, depending on windfarm output relative to set target baseload. The second cases examine the feasibility of a BESS mitigating imbalance costs related to day-ahead electricity sales for the windfarm. This case uses the same partial discharge and charge pattern as the first case, however, with the objective of covering the errors between the actual hourly production and forecasted hourly production. The economic results indicate through IRR, NPV and payback period, that the Baseload PPA case is not viable with the current configuration of producing a fixed baseload volume for every hour of a year. The imbalance mitigation case present more feasible results through a viable IRR and NPV and a realistic payback period. The imbalance mitigation case indicates that the lower to mid-range BESS capacities can substantially mitigate the imbalance costs of a large 203 MW windfarm. The results of the thesis, suggest that there are emerging opportunities for hybrid plants in the Finnish energy market. Additional value could be realized through multi-market participation, improving system flexibility and project profitability.