Browsing by Author "Paltakari, Jouni, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland"

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    Application of biodegradable substrates and inkjet printing in dye-sensitized solar cells
    (Aalto University, 2017) Özkan, Merve; Hashmi, Syed Ghufran, Dr., Aalto University, Department of Applied Physics, Finland; Lobato, Killan, Prof. Auxiliar, Universidade de Lisboa, Portugal; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Paper Converting and Packaging; University of Lisbon; Kemian tekniikan korkeakoulu; School of Chemical Technology; Paltakari, Jouni, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland; Santos Silva, Carlos Augusto, Asst. Prof., Universidade de Lisboa, Portugal
    Dye-sensitized solar cells (DSSCs) are electrochemical devices, which convert photon energy to electrical energy and they are promising alternative power unit candidates for small-scale electronics. Despite of efforts devoted to the research of DSSCs, the integration of efficient devices onto cellulose-based substrates is yet to be achieved, due to the challenging liquid electrolyte within the device. Additionally, the precursor wastage produced during the manufacture of solution processable layers, uncontrolled levels of deposition and layer positioning as well as the dependence on the pre-drilled glass substrates are not practical for many applications. The aims of this work were to determine the consequences of replacing the conventional counter electrode (CE) and glass substrate with a cellulose based alternative. Moreover, an assessment of the introduction of the inkjet printing method into the device fabrication was also performed. In first part of this thesis, alternative CEs were produced on a laminated cellulose sheet by first coating it with a carbon nanotube ink and subsequently p-toluenesulfonate doped poly(3,4-ethylenedioxythiophene) ink. The new CEs exhibited flexibility and low charge transfer resistance. Additionally, the cells produced with these CEs demonstrated only a 20% less efficiency compared to the reference cells with glass/fluorine-doped tin oxide (FTO)/platinum (Pt). The remainder of the thesis was devoted to the inkjet printing of the dye and Pt layers as well as the electrolyte of DSSCs. Initially, the three most popular electrolytes in DSSC research were characterized in terms of their physiochemical properties. Subsequently, the least dilatant electrolyte was inkjet-printed on sensitized mesoporous oxide to produce DSSCs. Thanks to this method, the device fabrication sequence was simplified and the device containing inkjet-printed electrolyte exhibited enhanced stability and less resistive losses. The conventional way of sensitizing mesoporous oxide surface entails exposure to a dilute solution of dye for long hours. In addition to the environmental burden of wasting ruthenium based dyes, the accuracy in the position and amount of the dye layer is uncontrolled. In order to overcome all these aforementioned challenges, inkjet printing was proposed as a new method for the sensitization step and the cells with inkjet-printed dyes provided the opportunity for tailor-made devices of various colors with tuned intensity. Pt, traditional catalyst for the DSSCs, is deposited by casting a drop on the FTO coated glass substrates for the lab-scale production of DSSCs, however it is both an expensive and is currently defined by the EU as a critical metal resource. In order to minimize Pt wastage and create precisely patterned catalyst layers with custom-made transparency, inkjet printing of Pt precursor was investigated. The cells with inkjet-printed catalyst exhibited a similar performance and stability to the reference cells.
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    Foam as a carrier phase – a multipurpose technology for industrial applications
    (Aalto University, 2017) Kinnunen-Raudaskoski, Karita; Hjelt, Tuomo, Dr., VTT Technical Research Centre of Finland, Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Kemian tekniikan korkeakoulu; School of Chemical Technology; Paltakari, Jouni, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
    The applicability of foam in paper/board manufacturing processes was studied. The pulp and paper production in Finland has been forecast to decrease by up to a third from 2007 to 2020. The declining trend is mainly due to the weakening of main export markets. (Hetemäki et al., 2009). For the renewal of paper industry new solutions for savings in energy and raw materials are needed. Newly developed materials like nano materials may also challenge the conventional pro-cesses. New technologies are needed and the interest towards foam technology is growing. The main focus in this thesis was on foam forming and coating and on nano/microfibrils. The suitability of foam in biosludge treatment was also studied. The work showed that the strength loss due to the bulky structure of the foam formed paper, can be regained by using cellulose microfibrils (CMF) as strength additives, instead of wet pressing or beating. The strength enhancement was received with a lower bulk lost. The studied CMF grades had different responses to the strength properties of the pulps used; bleached soft wood pulp and chemi-thermo mechanical spruce pulp. This indicates that CMF used has to be chosen depending of paper properties needed. Dewatering was more effective due to the porous structure of the foam formed sheets and the formation of the papers better than in water forming, even with 12 mm synthetic fibers. Foam coating applications were done both to dry and wet fiber webs. Two different coating methods were used in the dry web ap-plications. The work showed that using foam it is possible to create thin functional surfaces on paper/board. Titanium dioxide and zinc oxide functionalized cellulose nanofibrils (CNF) created antimicrobial and photocatalytic properties on the paper and grease and water vapour barriers were achieved with polyvinyl or ethylene vinyl alcohol foam. In wet web application done at the former section polymers known to enhance the strength properties of paper were used. Due to foam destruction using vacuums, the whole web structure was treated with the chemical. The enhance-ment both on wet and dry web strength properties was detected with an increase in the dry matter content of the paper and without bulk lost. In addition to 'a carrier phase' function, the ability of foam to displace liquid water from a porous medium, was investigated. The foam enhanced dewa-tering in foam forming as well as in foam coating of the wet web. Based on these observations the foam assisted dewatering was studied on biosludge treatment. According to the results, the filtration time was shortened, the filtrate was cleaner and the sludge cake 10% drier. The change in dry solids content was quite small due to the insufficient vacuum level in filtration, 2 kPa. However, the result indicates that with a more efficient filtration vacuum it is possible to use foam to assist filtration. This thesis shows that foam technology offers several benefits for the paper/board industry, and combining it with nanomaterials enables the development of novel paper products.
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    Foam-laid forming technology for fiber webs
    (Aalto University, 2022) Lehmonen, Jani; Retulainen, Elias, Dr., VTT Technical Research Centre of Finland, Finland; Kinnunen-Raudaskoski, Karita Dr., Paptic Ltd, Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Kemian tekniikan korkeakoulu; School of Chemical Technology; Paltakari, Jouni, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
    The forest industry is in the midst of a structural change. The goal is to renew the paper and board industry to produce higher value-added products for future markets. The launch of new wood fiber-based products also requires novel production technologies to achieve the goals of renewal. Current fiber web production technologies are based on water as a flowing medium and a carrier phase of raw materials. In these water-laid processes, a huge amount of water is used and recirculated, and reducing the total amount of water is challenging. Processes are also typically energy intensive. A foam-based process makes it possible to reduce the amount of water as it replaces about two-thirds of the flowing medium with air. In addition, it allows the broad utilization of raw materials in terms of length and density since foam as a flowing medium is more viscous than water, thus leading to a homogeneous distribution of materials, even though the nature and properties of the used raw materials vary considerably. From this perspective, the focus of this dissertation was to investigate the role of flowing medium in the production of wood-fiber containing sheets using an academic approach and applying novel research environments. The studies were performed on the laboratory, semi-pilot and pilot scale. The fundamental research was done on the laboratory scale, where water- and foam-formed sheets were produced using a dynamic vacuum-assisted sheet former simulating the dynamic initial dewatering phase of the forming section. The water-laid semi-pilot-scale process, formerly used for the water process, was modified to foam. The potential of foam-laid technology was investigated by examining the effects of essential process and product parameters. Despite the fact that foams are much more viscous than water, the results showed that the dewatering times were approximately the same in water and foam processes at higher vacuum levels, while at the lowest vacuum level the dewatering time for foam was about 50% higher. From the perspective of dewatering, process efficiency and the functionality of water vs. foam processes and sheets, an increase in the solids content of the foam-formed sheets after the forming section was observed on the laboratory, semi, and pilot scales when a foam density level of ∼ 400 kg/m3 was applied. In addition, the effect of a wet pressing load on the sheet density decreased as a function of the foam density, especially at the highest wet pressing loads. The sheets formed by water and foam were identical in density at the highest wet pressing load and a foam density level of 400 kg/m3. It must be highlighted that a production machine converted to use foam technology can still be run in water mode. This aspect opens up new possibilities for conventional smaller-scale production capacity machines, which in principle are more suitable for converting into foam operating machines.
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    Methods for Analysing Paper Machine Efficiency
    (Aalto University, 2017) Airola, Niiles; Paulapuro, Hannu, Prof. Emeritus, Aalto University, Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Kemian tekniikan korkeakoulu; School of Chemical Technology; Paltakari, Jouni, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
    Calculation of paper machine efficiency is used to analyze and benchmark operational performance of paper machines. It is one of the factors affecting the profitability of the papermaking line. Efficiency can be described as the first-pass retention figure for saleable paper on a paper machine. This figure has a great impact on financial performance, where sales price, fixed and variable costs with sufficiently high efficiency, are optimized. There are several ways to perform efficiency comparability. Due to the variety of existing methods, the main objective of this study was divided to three sub goals: (1.) identify, analyze and understand the discrepancies in line efficiency calculation rules currently in use, (2.) to make recommendations on how to improve and harmonize them and (3.) create more precise calculation methods. The theoretical part of this study focused on understanding of the currently available methods for efficiency calculations. The industrial practices part presents methods and knowledge that have been dominated the industry for decades. Moreover, this part outlines the presentations and internal articles from the companies that have been adopted as daily practice in the industry. The existing methods are mainly tactical, relative and history-based methods. As the tools, have been in tactical use, the industry has learned to reach close to 100% line efficiencies. In the new, novel approach the full efficiency capacity of a paper machine splits the efficiency into three operational horizons: tactical, strategic, and normative and three dimensions of its information: detailed, relative and absolute. This matrix allows the users to identify the method according to the decision need. All the methods were simulated on different types of paper machines, from newsprint to double-coated fine paper due to the modularity of the calculation methods. This study provided the basis for the creation of a new, more focused global guideline. It was created in co-operation with papermakers and machine suppliers from the Zellcheming paper technological committee during 2003-2005. A new Zellcheming Merkblatt III -guideline was published based on this study at the beginning of 2005. This work clearly points out the need for more precise methods to analyze efficiency. The new guideline and this study creates a platform which facilitates more detailed efficiency analyses and calculation of efficiency more precisely from mill to mill. It gives us a more accurate base for benchmarking, for improved target setting, for measuring actions and for making easier decision-making.
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    Modeling and Optimization of Energy services in Net Zero Energy House
    (Aalto University, 2017) Dao Thi Thu, Hang; Jalas, Mikko, Dr., Aalto University, Department of Design, Finland; Biotuotteiden ja biotekniikan laitos; Department of Bioproducts and Biosystems; Kemian tekniikan korkeakoulu; School of Chemical Technology; Santos Silva, Carlos Augusto, Prof., Instituto Superio Tecnico, University of Lisbon, Portugal; Paltakari, Jouni, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland
    The building sector consumes about 40% of primary energy in Europe, of which, residential building accounts for 26% - as the largest single energy consumption. As a result, the building sector plays a decisive role to reduce Europe's energy consumption. This led to the release of European Energy Performance Building Directive in 2010 known as EPBD recast 2010 which introduced the objective that all new buildings - and existing large buildings, by retrofitting – be Net Zero Energy Building (NZEB) from 2020 onwards. As a result, this PhD thesis intends to contribute to the design of better policies that foster the implementation of NZEB concept or Net Zero Energy House (NZEH), as a subset, with a particular emphasis on residential building in Europe. In this context, Portugal and Finland are chosen as the cases of the two climatically distinct European countries (Mediterranean vs. Boreal/Sub-Arctic) that also possess a large socio-economic gap. The thesis proposes that in order to develop policies that lead to the successful NZEH implementation in Europe, a clearly defined energy-service framework with numerical reference values for the residential energy services demand is required. As a result, the thesis proposes an energy service modeling framework for residential energy services: space heating and cooling, water heating, lighting, cooking, kitchen appliances and other media appliances. Additionally, a multi-objective optimization method that uses genetic algorithms is carried out, which can help to determine the optimal choice of energy systems to supply the demand energy services. The optimization objectives combine: minimize the energy system cost and minimize the energy demand. Furthermore, implications for future technology development and policy recommendations are defined with the emphasis on the end-use and demand side of residential energy services. With respect to Portugal, the results are water heat pump is best suited for water heating, whereas biomass boiler is preferable for both water and space heating. Moreover, PV is found to be the best option for the electricity demand of media, cooking, and lighting. Of all the investigated options, geothermal remains the least cost-effective, whilst energy storage deployment needs more effective incentive mechanism to ensure cost feasibility. For Finland, it is found that a water heat pump is the most suitable means for water heating in detached houses, whereas district heat systems based on renewable energy resources offer the best option for water and space heating in an apartment building scenario. In contrast to Portugal, geothermal heat pumps offer a cost-effective alternative for space heating in the Finland's climate.