Browsing by Author "Nieminen, Kaarlo"

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  • Carbon sequestration potential of wooden residential buildings
    (2024-06-11) Kumlin, Mikaela
     Kemian tekniikan korkeakoulu | Master's thesis
    This thesis investigates the carbon sequestration capacity of wooden residential buildings in the Uusimaa region of Finland. It emphasizes the need to optimize the lifetime of wooden buildings to maximize their ecological benefits. The study employs a generalized data analytical method, analysing the trends in construction and demolition of residential buildings in relation to population growth and GDP. The study concludes that using wood as a building material significantly reduces carbon footprints in the construction sector due to its carbon-sequestering properties. During the growth of trees used for wood, carbon dioxide is captured, aiding in the net reduction of atmospheric CO2 levels. The study also includes life comparisons between wooden buildings and those made from steel and concrete. The comparisons reveal that wooden buildings have lower carbon emissions throughout their lifecycle, and the greenhouse gases generated during the production and use of wood are significantly lower. The thesis discusses durability and fire safety in the context of modern innovations that enhance the resilience and longevity of wooden buildings. For example, modern fire-retardant treatments improve wooden structures' performance against high temperatures, addressing fire safety concerns. Policy recommendations include supporting the use of wood in residential buildings through incentives and stricter regulations on carbon emissions in the construction sector. The promotion of research and development in wood technology is also advocated. These policies aim to create an environment where wooden buildings become more prevalent, reducing the overall carbon footprint of urban areas. This highlights the potential of wooden buildings not only to lower carbon emissions but also to contribute to sustainable and resilient urban environments.
  • Cellulose dissolution in aqueous NaOH–ZnO : cellulose reactivity and the role of ZnO
    (2021-02) Väisänen, Saija; Ajdary, Rubina; Altgen, Michael; Nieminen, Kaarlo; Kesari, Kavindra K.; Ruokolainen, Janne; Rojas, Orlando J.; Vuorinen, Tapani
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Abstract: Cellulose utilization at its full potential often requires its dissolution which is challenging. Aqueous NaOH is the solvent of choice due to the rapid, non-toxic, low cost and environmentally friendly dissolution process. However, there are several limitations, such as the required low temperature and cellulose´s moderately low degree of polymerization and concentration. Moreover, there is a tendency for gelation of semidilute solutions with time and temperature. The addition of ZnO aids cellulose dissolution and hinders self-aggregation in the NaOH solution; however, the exact role of ZnO has remained as an open question. In this work, we studied cellulose dissolution in the aqueous NaOH–ZnO system as well as the reactivity of the dissolved cellulose by oxidation with 4-AcNH-TEMPO+ (TEMPO+). Based on Raman spectroscopic studies and the TEMPO+-reactivities, we propose a new structure for cellulose dissolved in aqueous NaOH–ZnO. Graphic abstract: [Figure not available: see fulltext.]
  • Characterising exfoliated few-layer graphene interactions in co-processed nanofibrillated cellulose suspension via water retention and dispersion rheology
    (2019-03-01) Dimi-Misic, Katarina; Phiri, Josphat; Nieminen, Kaarlo; Maloney, Thad; Gane, Patrick
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Few-layer graphene has been produced by mechanical delamination of exfoliated and naturally obtained graphite in aqueous suspension using the dispersion and suspension properties of nanofibrillated cellulose (NFC). Various degrees of graphene platelet integrity were obtained depending upon the processing conditions and the optional adoption of surfactant to aid dispersion of the hydrophobic agglomerates of nanometre-thin carbon material. The presence of NFC in the suspension acts similarly to the presence of surfactant, increasing the hydrodynamic coupling between the particles and water as a function of processing time, regardless of the graphene-comprising source. By fitting the stress growth region in the stress-shear rate relation to a concatenated series of single exponential functions of shear rate, the power law exponent and suspension consistency parameters (n and k), within a shear rate-localised Herschel-Bulkley (HB) expression, provide a straightforward characteristic for monitoring the desired suspension coupling response, and hence a measure of product constancy.
  • Comparative evaluation of different kinetic models for batch cooking: A review
    (2012-10) Nieminen, Kaarlo; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Degradation of cellulose polymorphs into glucose by HCl gas with simultaneous suppression of oxidative discoloration
    (2023-02-15) Wang, Yingfeng; Pääkkönen, Timo; Miikki, Kim; Maina, Ndegwa Henry; Nieminen, Kaarlo; Zitting, Aleksi; Penttilä, Paavo; Tao, Han; Kontturi, Eero
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    As cellulose is the main polysaccharide in biomass, its degradation into glucose is a major undertaking in research concerning biofuels and bio-based platform chemicals. Here, we show that pressurized HCl gas is able to efficiently hydrolyze fibers of different crystalline forms (polymorphs) of cellulose when the water content of the fibers is increased to 30–50 wt%. Simultaneously, the harmful formation of strongly chromophoric humins can be suppressed by a simple addition of chlorite into the reaction system. 50–70 % glucose yields were obtained from cellulose I and II polymorphs while >90 % monosaccharide conversion was acquired from cellulose IIIII after a mild post-hydrolysis step. Purification of the products is relatively unproblematic from a gas-solid mixture, and a gaseous catalyst is easier to recycle than the aqueous counterpart. The results lay down a basis for future practical solutions in cellulose hydrolysis where side reactions are controlled, conversion rates are efficient, and the recovery of products and reagents is effortless.
  • Delignifieringens inverkan på fiberstyrkan
    (2016-04-17) Grahn, Julius
     Kemiantekniikan korkeakoulu | Bachelor's thesis
  • Development of cellulose films by means of the Ioncell® technology, as an alternative to commercial films
    (2023-12) González Carmona, Eva; Schlapp-Hackl, Inge; Jääskeläinen, Seppo; Järvinen, Masi; Nieminen, Kaarlo; Sawada, Daisuke; Hummel, Michael; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In recent years, the search for alternatives to petroleum derived products, such as plastic films, has become a priority due to the growing depletion of fossil reserves and the pollution of water resources by microplastics, microscopically small plastic particles which are harmful to ocean and aquatic life. Cellulose-based films, e.g., cellophane and cuprophane, have been on the market for almost a century. Despite being a more ecological option compared to plastic films, the manufacture of these cellulose films involves high production costs and the use of harmful chemicals. As an alternative, a sustainable and eco-friendly process based on the Lyocell-type Ioncell® technology is presented to produce cellulose films. Regenerated cellulose films are created by continuous extrusion via dry-jet wet spinning of an ionic liquid–cellulose solutions. The influence of the polymer concentration (8–13 wt%) and processing temperature (50–100 °C) on the properties of the films were studied by the determination of the thickness, mechanical properties, physical appearance, morphology, chemical composition, and hydrophobicity. The obtained films are thin (12–21 μm), transparent (transmittance = 91%) and of homogeneous structure. Moreover, they exhibit excellent mechanical properties: stress values up to 210 MPa and elongations up to 19% in machine (longitudinal) direction. These values clearly outperform commercial cellophane, which presents stress values of 125 MPa and elongations of 22%. The films presented herein hold great potential to become an eco-friendly and sustainable option to commercial films.
  • Fast furfural formation from xylose using solid acid catalysts assisted by a microwave reactor
    (2018-12-15) Gómez Millán, Gerardo; El Assal, Zouhair; Nieminen, Kaarlo; Hellsten, Sanna; Llorca, Jordi; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The production of furfural (FUR) from xylose was carried out using sulfated zirconia (SZ) on cordierite, alumina on cordierite and commercially-available polymeric solid catalysts (Amberlyst DT and Nafion NR40) to provide insights into the reaction pathways and kinetics for the dehydration of xylose in aqueous phase. Experiments conducted at three temperatures were investigated (170, 190 and 210 °C) in a stirred microwave-assisted batch reactor, which established the optimal conditions to obtain the highest FUR yield as well as extensive and fast xylose conversion. The maximum FUR yields obtained from xylose were 41 mol% when using SZ on cordierite in 2 min (at 210 °C), 43 mol% when using alumina on cordierite in 30 min (at 210 °C) and 48 mol% for an auto-catalyzed system in 60 min (at 210 °C). Based on the experimental results, a reaction mechanism was proposed considering the formation of an intermediate from xylose when solid acid catalysts were added. After five reusability cycles using SZ on cordierite, this catalyst can be regenerated with a similar performance and similar FUR yield on the 6th cycle.
  • The fiber-matrix interface in Ioncell cellulose fiber composites and its implications for the mechanical performance
    (2021-05-05) Bulota, Mindaugas; Sriubaite, Simona; Michud, Anne; Nieminen, Kaarlo; Hughes, Mark; Sixta, Herbert; Hummel, Michael
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Fiber-reinforced composites based on natural fibers are promising alternatives for materials made of metal or synthetic polymers. However, the inherent inhomogeneity of natural fibers limits the quality of the respective composites. Man-made cellulose fibers (MMCFs) prepared from cellulose solutions via wet or dry-jet wet spinning processes can overcome these limitations. Herein, MMCFs are used to prepare single fiber epoxy composites and UD composites with 20, 30, 40, and 60 wt% fiber loads. The mechanical properties increase gradually with fiber loading. Young's modulus is improved three times while tensile strength doubles at a loading of 60 wt%. Raman spectroscopy is employed to follow conformational changes of the cellulose chains within the fibers upon mechanical deformation of the composites. The shift of the characteristic Raman band under strain indicates the deformation mechanisms in the fiber. Provided stress transfer occurs through the interface, it is a direct measure of the fiber-matrix interaction, which is investigated herein. The shift rate of the 1095 cm−1 band decreases in single fiber composites compared to the neat fibers and continues to decrease as the fiber loading increased.
  • From vapour to gas: Optimising cellulose degradation with gaseous HCl
    (2018-06-01) Pääkkönen, Timo; Spiliopoulos, Panagiotis; Knuts, Aaro; Nieminen, Kaarlo; Johansson, Leena Sisko; Enqvist, Eric; Kontturi, Eero
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A cellulose degradation technique utilizing a pressurized HCl gas (up to 100 kPa) device is introduced. High pressure HCl quickly degraded cellulose in purified cotton linters, reaching the so-called levelling-off degree of polymerisation (LODP) in less than 1.5 h. LODP marks the point where the disordered portions of cellulose microfibrils have been degraded and only the crystalline portions remain, generally signalling the end of cellulose degradation unless remarkably high concentrations are used. In the present high pressure system, however, continued hydrolysis following the LODP was detected by incremental release of sugars from the hydrolysate after its exposure to water, supposedly caused by erosion from the cellulose crystallite ends. With minimal water consumption and the ease of recycling the gaseous acid, the technique could be a potential candidate for pre-treatment considering the future production of cellulose nanomaterials, particularly cellulose nanocrystals.
  • Improved stabilisation of graphite nanoflake dispersions using hydrothermally-produced nanocellulose
    (2021-02-05) Dimic-Misic, Katarina; Buffiere, Jean; Imani, Monireh; Nieminen, Kaarlo; Sixta, Herbert; Gane, Patrick
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Dispersing graphite nanpoflakes in aqueous suspension is essential both during their processing and to realise the high level of functionality they offer. In this study two types of chemical-free nanocelluloses were assessed as possible dispersing agent for graphite nanoflakes. Hydrothermally-produced nanocellulose (HTC) obtained by supercritical water treatment of microcrystalline cellulose, showed superior dispersing than the more conventional, mechanically-produced microfibrillated nanocellulose (MFC) alternative, effectively preventing nanoflake agglomeration. Thanks to the specific processing method, the HTC material displayed higher total surface energy and a favourable particle morphology. These properties resulted in a 2-fold reduction in the volume median colloidal particle size of nanographite in suspension upon addition of only 2 w/w% nanocellulose. The improved single particle dispersion within the suspension matrix could be observed microscopically and was reflected rheologically. The latter was achieved by parameterising the stress-shear rate response and fitting the linear segments displaying the suspension coupling response. Using chemical-free nanocellulose as dispersant in aqueous medium is a positive step toward the exfoliation of nanographite into graphene in a more affordable and environmentally-friendly way.
  • Influence of DP and MMD of the pulps used in the Ioncell® process on processability and fiber properties
    (2023-09-01) Ma, Yibo; You, Xiang; Nieminen, Kaarlo; Sawada, Daisuke; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this study, we have demonstrated for the first time the ability of the Ioncell fiber spinning process to produce high-quality regenerated cellulose fibers from dissolving pulps with a wide range of intrinsic viscosity from 140 to 1300 mL g−1 and different molecular mass distributions prepared by the applied acid, enzyme and sequential acid-enzyme pretreatments. To minimize the influence of the hemicellulose content, only dissolving pulps with a hemicellulose content of less than 4% were used. The rheological properties exhibited certain threshold values beyond which the spinnability of the prepared dope can be severely affected. A spinning dope with a dynamic modulus higher than 6000 Pa s or less than 1600 Pa s is not spinnable or results in an acceptable draw ratio. The best spinnability can be obtained at a crossover point for the dynamic moduli between 2800 and 3500 Pa and for the angular frequency between 0.4 and 1.2 rad s−1. In these ranges, the highest draw ratios of the spun filaments can be obtained for pulps with a viscosity of 420 to 500 mL g−1 and the lowest linear density (fiber titer) for pulps with viscosity from 500 to 730 mL g−1. The strength of the spun fibers is strongly DP dependent. The fiber tenacity gradually decreases with reducing pulp viscosity until non-spinnable dopes are prepared at a pulp viscosity below 300 mL g−1. Compared to acid-treated pulp, fibres made from enzyme-treated pulp generally have lower strength, which is due to a high polydispersity expressed in a high proportion of short-chain cellulose. At a suitable pulp viscosity between 360 and 820 mL g−1 and a cellulose concentration in the spinning dope of 11 to 15 wt%, Ioncell fibres with excellent tensile strength and toughness properties can be produced.
  • Möjliga användningsområden för lignin
    (2013-12-02) Törnblom, Malin
     Kemiantekniikan korkeakoulu | Bachelor's thesis
  • New insights into the air gap conditioning effects during the dry-jet wet spinning of an ionic liquid-cellulose solution
    (2020-06-01) Guizani, Chamseddine; Nieminen, Kaarlo; Rissanen, Marja; Larkiala, Sauli; Hummel, Michael; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this paper, we report new results related to the development of a novel regenerated cellulose fiber process of the Lyocell type, denoted Ioncell™, and characterized by the use of a powerful direct cellulose solvent, 1,5-diaza- bicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) a superbase-based ionic liquid (IL). The focus of this work is on the effects of air gap conditioning (AGC) during the dry-jet wet spinning operation. The installation of an AGC system on the spinning line led to significant improvements of the fiber properties. The fiber titer variation decreased significantly, and the fiber toughness increased by approximately 50% when controlling the temperature and the relative humidity in the airgap using a convective air flow. The presence of water vapor in the air stream was a determinant factor for the improvement of the fiber elongation. The interaction of water vapor with the spinning dope was investigated using dynamic vapor sorption. The diffusion coefficient of water vapor inside the dope could be identified from those experiments and used in a numerical simulation model of the heat and water vapor transfer in the air gap between the spinning dope and the surrounding air. The experimental and simulation results suggest that dope convective cooling and surface hydration lead to a higher fiber toughness.
  • Novel insight in carbohydrate degradation during alkaline treatment
    (2015) Nieminen, Kaarlo; Testova, Lidia; Paananen, Markus; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Optimization of Dry-Jet Wet Spinning of Regenerated Cellulose Fibers Using [mTBDH][OAc] as a Solvent
    (2023-09-19) Fang, Wenwen; Lim, E Yee; Nieminen, Kaarlo; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Superbase-based ionic liquids (ILs) have demonstrated excellent dissolution capability for cellulose, and employing the dry-jet wet spinning process, high-tenacity regenerated textile fibers have been made. Among a range of superbase-based ILs, [mTBDH][OAc] exhibited not only good spinnability but also exceptional recyclability, making it highly suitable for a closed-loop production of regenerated cellulose fibers. To further optimize the spinning process, we investigated the influence of the cellulosic raw materials and the IL with residual water on spinnability and fiber properties. In addition, single-filament spinning and multifilament spinning using spinnerets with different hole densities were investigated to reveal the upscaling challenges of the dry-jet wet spinning process. The air gap conditions, for example, temperature and moisture concentration were simulated using COMSOL multiphysics. The results indicate that the presence of a small amount of water (3 wt%) in the IL has a positive effect on spinnability, while the mechanical properties of the fibers remain unchanged.
  • Pretreatment to Retrieve Xylose and Xylooligosaccharides by HCl Gas Directly from Biomass
    (2024-02-12) Kilpinen, A. Topias; Nieminen, Kaarlo; Kontturi, Eero
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this study, anhydrous hydrogen chloride gas was employed to selectively hydrolyze hemicellulose from aspen wood flour utilizing a gas-solid system. Selectivity toward hemicellulose was achieved by adjusting the acid concentration inside wood flour to 36% during gas hydrolysis, so only hemicellulose and disordered cellulose would be degraded during hydrolysis. Process parameters included the moisture content of the aspen wood flour (20%, 40%, and 60%) and reaction times from 30 min to 24 h. The optimal reaction conditions for the production of xylose and xylooligosaccharides was achieved with 40% moisture content and 6 h reaction time. Under these parameters, it was possible to retrieve 84% of the available xylan from aspen wood flour with only 1% glucan degradation.
  • Production of Water-Soluble Carbohydrates from Aspen Wood Flour with Hydrogen Chloride Gas
    (2023-10-18) Kilpinen, A. Topias; Pääkkönen, Timo; Nieminen, Kaarlo; Kontturi, Eero
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The aim of this study was to optimize the reaction conditions for concentrated acid hydrolysis of aspen wood flour by employing anhydrous hydrogen chloride gas to produce fermentable sugars. Gas hydrolysis with HCl was conducted both with and without temperature control during hydrolysis under a relatively low pressure of 0.1 MPa. Process parameters for HCl gas hydrolysis included the moisture content of aspen wood flour (0.7-50%) and reaction time under pressure (30 min to 24 h). In addition, liquid-phase hydrolysis with concentrated hydrochloric acid was conducted in concentrations of 32-42% and 15 min to 24 h reaction times for comparison with the gas-phase process. The highest yields (>90%) for water-soluble carbohydrates from aspen wood flour were achieved with temperature-controlled gas hydrolysis using 50% moisture content and 2 h total reaction time, which is in line with the previous research and comparable to hydrolysis with concentrated (42%) hydrochloric acid.
  • Spinneret geometry modulates the mechanical properties of man-made cellulose fibers
    (2021-11) Moriam, Kaniz; Sawada, Daisuke; Nieminen, Kaarlo; Ma, Yibo; Rissanen, Marja; Nygren, Nicole; Guizani, Chamseddine; Hummel, Michael; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The production of cellulose-based textile fibers with high toughness is vital for extending the longevity and thus developing a sustainable textile industry by reducing the global burden of microplastics. This study presented strategies to improve fiber toughness by tuning spinneret geometries. Experimental studies were conducted by spinning with different spinneret geometries and measuring the mechanical and structural properties of the spun fibers. In addition, numerical simulation tools were used to better understand the effects of spinneret geometry. The altering parameters of the spinneret geometries were the capillary diameters D, the angle of the entry cone into the spinning capillary, and the ratio of capillary length to diameter L/D. The highest fiber toughness could be achieved at a capillary aspect ratio of 1 to 2. The obtained maximum fiber toughness was 93 MPa with a tensile strength of 60 cN/tex and a concomitant elongation of 16.5%. For these fiber properties, a 13 wt% solution of a high-purity pulp with higher viscosity in [DBNH][OAc] was spun into a 1.3 dtex fiber using a D100 spinneret with a capillary of 1:1 length/diameter and an entrance angle of 8°. It was noticeable that the microvoid orientations decreased almost linearly with increasing toughness of the fibers. The morphologies of the fibers were similar regardless of the spinneret geometries and the raw materials used in the spinning process. In summary, by modulating the spinneret geometries, Ioncell fibers obtained high toughness that have the potential to replace synthetic fibers.
  • Stability of gamma-valerolactone under pulping conditions as a basis for process optimization and chemical recovery
    (2021-12) Granatier, Marianna; Schlapp-Hackl, Inge; Lê, Huy Quang; Nieminen, Kaarlo; Pitkänen, Leena; Sixta, Herbert
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    This study focuses on the investigation of the extent of the γ-valerolactone (GVL) hydrolysis forming an equilibrium with 4-hydroxyvaleric acid (4-HVA) in aqueous solutions over a wide pH range. The hydrolysis of a 50 wt% GVL solution to 4-HVA (3.5 mol%) was observed only at elevated temperatures. The addition of sulfuric acid (0.2 × 10–5 wt% to 6 wt%) at elevated temperatures (150–180 °C) and reaction times between 30 and 180 min caused the formation of 4 mol% 4-HVA. However, with decreasing acidity, the 4-HVA remained constant at about 3 mol%. The hydrolysis reactions in alkaline conditions were conducted at a constant time (30 min) and temperature (180 °C) with the variation of the NaOH concentration (0.2 × 10–6 wt% to 7 wt%). The addition of less than 0.2 wt% of NaOH resulted in the formation of less than 4 mol% of sodium 4-hydroxyvalerate. A maximum amount of 21 mol% of 4-HVA was observed in a 7 wt% NaOH solution. The degree of decomposition after treatment was determined by NMR analysis. To verify the GVL stability under practical conditions, Betula pendula sawdust was fractionated in 50 wt% GVL with and without the addition of H2SO4 or NaOH at 180 °C and a treatment time of 120 min. The spent liquor was analyzed and a 4-HVA content of 5.6 mol% in a high acidic (20 kg H2SO4/t wood) and 6.0 mol% in an alkaline (192 kg NaOH/t wood) environment have been determined.