Change search
Refine search result
1 - 41 of 41
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Online fibre property measurements: foundations for a method based on ultrasound attenuation2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents the foundations of a method for estimating fibre properties of pulp suitable for online application in the pulp and paper industry. In the pulp and paper industry, increased efficiency and greater paper quality control are two of the industry's main objectives. It is proposed that online fibre property measurements are a means of achieving progress in both of these objectives. Optical based systems that provide valuable geometric data on the fibres and other pulp characteristics are commercially available. However, measurements of the elastic properties of the fibres are not currently implemented using these systems. To fill this gap an ultrasound based system for measuring the elastic properties of the wood fibres in pulp is proposed. Ultrasound propagation depends on the elastic properties of a solid. Hence attenuation measurements from suspensions of fibres depend on their elastic properties. The method is based on solving the inverse problem where the output is known and the objective is to establish the inputs. In this case, attenuation is measured and a model of attenuation based on ultrasound scattering is developed. A search algorithm is used for finding elastic properties that minimize the error between the model and measured attenuation. The results of the search are estimates of the elastic properties of the fibres in suspension. The results show resonance peaks in the attenuation, in the frequency region tested, for fibres with radii of the order of 10 microns. These peaks are found in both the measured and modelled attenuation spectra. Further investigation of these resonances suggests that they are due to modes of vibration in the fibre where the fibre modelled as an infinitely long cylinder. These resonances are shown to aid in the identification of the elastic properties. The attenuation is found to depend heavily on the geometry of the fibres. Hence fibre geometry, which can be obtained from online optical fibre measurement system, provides the key to extracting the elastic properties from the attenuation signal. Studies are also carried out on the effect of viscosity on attenuation as well as the differences in attenuation between hollow and solid synthetic fibres in suspensions. The measurement method is also applied to hardwood and softwood Kraft pulps. The results of these studies show that using the model derived in the thesis and attenuation measurements, estimates of the elastic properties can be obtained. The elastic property estimates for synthetic fibres agree well with values from other methods. The elastic property estimates for pulps require further validation due to the difficulty in comparing between different testing methods and different types of pulp. The conclusions, based on the work so far and under three realisable conditions, are that the shear modulus and the transverse Young's modulus of pulp fibres can be measured. Once these conditions are met a system based on this method can be implemented. By doing this the industry would benefit from the increase in paper quality control and energy saving such system could provide.

  • 2.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Towards a measurement of paper pulp quality: ultrasonic spectroscopy of fibre suspensions2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    For the paper and pulp industry in Sweden and Finland to remain competitive against countries with lower overheads, they have to constantly strive to improve the quality and the efficiency of the manufacturing processes. One of the ways of doing this is to introduce sensors that will provide valuable online feedback on the characteristics of the pulp so that adjustments can be made to optimise the manufacturing process. The measurement method proposed in this thesis is based on ultrasound, since it is rapid, inexpensive, non-destructive and non-intrusive. Thus could be done online. Since ultrasound propagation and attenuation depends on the material properties through which is propagates, it has the potential to provide measurements of material properties such as pulp fibre density and elasticity. The aim of this thesis is to investigate the possibility of using ultrasound to measure pulp fibre material properties. The idea is to solve the inverse problem of estimating these properties from attenuation measurements and to establish the degree of accuracy to which this can be done. Firstly a model is developed and is tested with synthetic fibres to establish is validity. It is then used to solve the inverse problem of estimating material properties from attenuation measurements, again with synthetic fibres, to test the accuracy to which these properties can be estimated. Resonance peaks in the frequency response of the attenuation were found. On closer investigation it was established that the location of these peaks in the frequency domain is sensitive to the diameter of the fibres and their material properties. If the diameter is known, these peaks improve the accuracy of the estimation process. The results of the estimation process for synthetic fibre suspensions show values for the shear modulus are within known ranges but the estimation of Poisson's ratio and Young's modulus is poor. Improving the model or the estimation procedure may lead to better results. For the method as it is to have application in the paper and pulp industry there are certain conditions that need to be fulfilled. These are that we find peaks in the frequency response of the attenuation in pulp, know the diameter distribution of the fibres and the hollow nature of the fibres does not significantly alter the results. We can then, potentially, be able to establish the shear modulus of the pulp fibres. If the shear modulus is a factor in paper quality, we may be close to an online measurement of paper pulp quality using ultrasonic spectroscopy. Improving the model may allow us to estimate further properties and take into account the fibres being hollow. The thesis consists of two parts. The first part includes an overview of the pulp and paper industry and current testing methods, background theory on which the model is based and an overview of the model that is used in predicting ultrasound attenuation. There then follows a summary of the work done, some addition points are raised in the discussion before drawing conclusions. Finally we discuss what needs to be done to take this further. The second part contains a collection of four papers describing the research.

  • 3.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Allard, Christina
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    Lin, Janet
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Sandström, Anders
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    LTU Teaching guide to e-learning: how to clear the mist of teaching through the cloud2015Conference paper (Other academic)
  • 4.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Linder, Tomas
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Light scattering in cellulose nanofibre suspensions: Model and experiments2016In: Computers in Chemistry Proceeding from ACS National Meeting San Diego: Proceeding from ACS National Meeting San Diego, American Chemical Society (ACS), 2016, p. 122-, article id CELL 235Conference paper (Other academic)
    Abstract [en]

    Here light scattering theory is used to assess the size distribution in a suspension of cellulose as it is fibrillated from micro-scaled to nano-scaled fibres. A model based on Monte carlo simulations of the scattering of photons by different sizes of cellulose fibres was used to predict the UV-IF spectrum of the suspensions. Bleached cellulose hardwood pulp was tested and compared to the visually transparent tempo-oxidised hardwood cellulose nanofibres (CNF) suspension. The theoretical results show that different diameter size classes exhibit very different scattering patterns. These classes could be identified in the experimental results and used to establish the size class dominating the suspension. A comparison to AFM/microscope size distribution was made and the results indicated that using the UV-IF light scattering spectrum maybe more reliable that size distribution measurement using AFM and microscopy on dried CNF samples. The UV-IF spectrum measurement combined with the theoretical prediction can be used even at this initial stage of development of this model to assess the degree of fibrillation when processing CNF.

  • 5.
    Aitomäki, Yvonne
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Hagström, Bengt
    SWEREA IVF AB.
    Långström, Runar
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Fernberg, Patrik
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Novel reactive bicomponent fibres: Material in composite manufacturing2012In: Journal of Nanostructured Polymers and Nanocomposites, ISSN 1790-4439, Vol. 8, no 1, p. 5-11Article in journal (Refereed)
    Abstract [en]

    The hypotheses that reactive uncured, thermoset bicomponent fibres can be prepared and mixed with reinforcing fi- bres and ultimately used in preparation o f a composite was tested and is described. I t is thought that such fibres have the two potential advantages: ( 1) to enable manufacturing with pai1icle doped resins e.g. nanocomposites which add functionality to composites and (2) increased efficiency ofstructural composite manufacturing by increasing the level of automation. The structure of the thermoset fibres comprises of a sheath of thermoplastic and a core of uncured the1moset resin. Once manufactured, the fibres were wound with a reinforced fibre onto a plate, consolidated and cured. The resulting composite was examined and compared to other composites made with the same manufacturing method from commercially available materials. The results show that a laminate can be produced using these reactive bicomponent fibres. The resin system successfully impregnates the reinforcing carbon fibres and that the thermoplas- tic separates from the epoxy resin system during consolidation. In comparison to reference material, the bicomponentlaminate shows promising characteristics. However, the processes developed are currently on a lab-scale and consid- erable improvement of various bicomponent fibre properties, such as the strength, are required before the technology can be used on a larger scale

  • 6.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB, Box 271, SE-941 26 Piteå.
    Hagström, Bengt
    werea IVF AB.
    Långström, Runar
    Swerea SICOMP AB, Box 271, SE-941 26 Piteå.
    Fernberg, Patrik
    Swerea SICOMP AB, Box 271, SE-941 26 Piteå.
    Novel reactive bicomponent fibres: Material in composite manufacturing2012In: Journal of Nanostructured Polymers and Nanocomposites, ISSN 1790-4439, Vol. 8, no 1, p. 5-11Article in journal (Refereed)
    Abstract [en]

    The hypotheses that reactive uncured, thermoset bicomponent fibres can be prepared and mixed with reinforcing fibres and ultimately used in preparation of a composite was tested and is described. It is thought that such fibres have the two potential advantages: (1) to enable manufacturing with particle doped resins e.g. nanocomposites which add functionality to composites and (2) increased efficiency of structural composite manufacturing by increasing the level of automation. The structure of the thermoset fibres comprises of a sheath of thermoplastic and a core of uncured thermoset resin. Once manufactured, the fibres were wound with a reinforced fibre onto a plate, consolidated and cured. The resulting composite was examined and compared to other composites made with the same manufacturing method from commercially available materials. The results show that a laminate can be produced using these reactive bicomponent fibres. The resin system successfully impregnates the reinforcing carbon fibres and that the thermoplastic separates from the epoxy resin system during consolidation. In comparison to reference material, the bicomponent laminate shows promising characteristics. However, the processes developed are currently on a lab-scale and considerable improvement of various bicomponent fibre properties, such as the strength, are required before the technology can be used on a larger scale.

  • 7.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jonoobi, Mehdi
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Impregnation of cellulose nanofibre networks with a thermoplastic polymer2013Conference paper (Other academic)
    Abstract [en]

    The emphasis of this study have been to study if impregnation of cellulose nanofibre networks can be made using a thermoplastic polymer as a matrix and to estimate the reinforcing efficiency of the cellulose nanofibres in this composite. A nanofibre network with higher porosity that water-dried nanofibre network was prepared from a cellulose waste byproduct (sludge). This was impregnated using a diluted solution of cellulose acetate butyrate polymer to produce a 60 wt. % CNF/CAB composite. This composite was characterized using microscopy and mechanical testing. High porosity is seen in the SEM images of the acetone-dried fibre network and SEM and film transparency was used to qualitatively assess the impregnation of the network. A significant improvement in the visible light transmittance was observed for the nanocomposite film compared to the nanofibre network as a result of the impregnation. The reinforcing efficiency was calculated based on a model of the nanocomposite and compared to other nanocomposites in the literature. The efficiency factor takes into account the volume fraction and the stiffness of the matrix. This showed that this CNF/CAB combination is similar in efficiency to CNF/PLA nanocomposites and more efficient that nanocomposites using when using stiffer matrices. It was also more efficient CNF nanocomposites based on Chitosan, which has the same stiffness. It is still however not as efficient as traditional glass polymer composites due to the random orientation of the fibres nor nanocomposites with very soft matrices due to the dominating network effect of the CNF in such composites. In conclusion, CAB impregnated cellulose nanofibre networks are promising biocomposite materials that could be used in applications where transparency and good mechanical properties are of interest. The key elements in the impregnation process of the nanocomposites were the use of a porous networks and a low viscosity thermoplastic resin solution.

  • 8. Aitomäki, Yvonne
    et al.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Estimating suspended fibre material properties by modelling ultrasound attenuation2006In: Mathematical Modeling of Wave Phenomena: conference on mathematical modeling of wave phenomea, Växjö, Sweden, 14 - 19 August 2005 / [ed] Börje Nilsson; Louis Fishman, Melville, NY: American Institute of Physics (AIP), 2006, p. 250-259Conference paper (Refereed)
    Abstract [en]

    An analytical model for use in the inverse problem of estimating material properties of suspended fibres from ultrasonic attenuation has been developed. The ultrasound attenuation is derived theoretically from the energy losses arising when a plane wave is scattered and absorbed off an infinitely long, isotropic, viscoelastic cylinder. By neglecting thermal considerations and assuming low viscosity in the suspending fluid, we can make additional assumptions that provide us with a tractable set of equations that can be solved analytically. The model can then be to used in inverse methods of estimating material properties. We verify the model with experimentally obtained values of attenuation for saturated Nylon fibres. The experimental results from Nylon fibres show local peaks in the attenuation which are thought to be due to the resonant absorption at the eigenfrequencies of the fibres. The results of the experiments show that the model is sufficiently sensitive to detect differences in different types of Nylon. Applications for suspended fibre characterization can be found in the paper manufacturing industry.

  • 9. Aitomäki, Yvonne
    et al.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Material property estimates from ultrasound attenuation in fibre suspensions2009In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 49, no 4-5, p. 432-437Article in journal (Refereed)
    Abstract [en]

    An investigation of a new method for measuring fibre material properties from ultrasonic attenuation in a dilute suspension of synthetic fibres of uniform geometry is presented. The method is based on inversely solving an ultrasound scattering and absorption model of suspended fibres in water for the material properties of the fibres. Experimental results were obtained from three suspensions of nylon 66 fibres each with different fibre diameters. A forward solution to the model with reference material values is compared to experimental data to verify the model's behaviour. Estimates of the shear and Young's modulus, the compressional wave velocity, Poisson's ratio and loss tangent from nylon 66 fibres are compared to data available from other sources. Experimental data confirms that the model successfully predicts that the resonance features in the frequency response of the attenuation are a function of diameter. Consistent estimated values for the compressional wave velocity and the Poisson's ratio were found to be difficult to obtain but in combination gave values of shear modulus within previously reported values and with low sensitivity to noise. Young's modulus was underestimated by 54% but was consistent and had low sensitivity to noise. The underestimation is believed to be caused by the assumption of isotropic material used in the model. Additional tests on isotropic fibre would confirm this. Further analysis of the model sensitivity and the reasons for the resonance features are required.

  • 10.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Sounding Out Paper Pulp: Ultrasound Spectroscopy of Dilute Viscoelastic Fibre Suspensions Acoustics and Ultrasonics2006Conference paper (Other academic)
    Abstract [en]

    A model of attenuation of ultrasound in fibre suspensions is compared to a model of backscattering pressure from submersed cylinders subjected to a sound wave. This analysis is carried out in the region where the wavelength is of the same order as that of the diameter of the fibre. In addition we assume the cylinder scatterer to have no intrinsic attenuation and the longitudinal axis of the scatterer is assumed to be perpendicular to the direction of propagation of the incident wave. Peaks in the frequency response of both the backscattering pressure, expressed in the form of a form function, and the attenuation are shown to correspond. Similarities between the models are discussed. Since the peaks in the form function are due to resonance of the cylinder, we infer that the peaks in the attenuation are also due to resonance. The exact nature of the waves causing the resonance are still unclear however the first resonance peaks are related to the shear wave and hence the shear modulus of the material. The aim is to use the attenuation model for solving the inverse problem of calculating paper pulp material properties from attenuation measurements. The implications of these findings for paper pulp property estimation is that the supporting fluid could, if possible, be matched to density of that of pulp fibres and that the estimation of material properties should be improved by selecting a frequency range that in the region of the first resonance peaks.

  • 11.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Delsing, Jerker
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Estimating material properties of solid and hollow fibers in suspension using ultrasonic attenuation2013In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 60, no 7, p. 1424-1434Article in journal (Refereed)
    Abstract [en]

    Estimates of the material properties of hollow fibers suspended in a fluid using ultrasound measurements and a simple, computationally efficient analytical model are made. The industrial application is to evaluate the properties of wood fibers in paper pulp. The necessity of using a layered cylindrical model (LCM) as opposed to a solid cylindrical model (SCM) for modeling ultrasound attenuation in a suspension of hollow fibers is evaluated. The two models are described and used to solve the inverse problem of estimating material properties from attenuation in suspensions of solid and hollow polyester fibers. The results show that the measured attenuation of hollow fibers differs from that of solid fibers. Elastic properties estimates using LCM with hollow-fiber suspension measurements are similar to those using SCM with solid-fiber suspension measurements and compare well to block polyester values for elastic moduli. However, using the SCM with the hollow-fiber suspension did not produce realistic estimations. In conclusion, the LCM gives reasonable estimations of hollow fiber properties and the SCM is not sufficiently complex to model hollow fibers. The results also indicate that the use of a distributed radius in the model is important in estimating material properties from fiber suspensions.

  • 12.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Moreno, Sergio
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vacuum infusion of cellulose nanofibre network composites: Influence of porosity on permeability and impregnation2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 95, p. 204-211Article in journal (Refereed)
    Abstract [en]

    Addressing issues around the processing of cellulose nanofibres (CNF) composites is important in establishing their use as sustainable, renewable polymer reinforcements. Here, CNF networks of different porosity were made with the aim of increasing their permeability and suitability for processing by vacuum infusion (VI). The CNF networks were infused with epoxy using two different strategies. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated. Calculated fill-times for CNF networks with 50% porosity were the shortest, but are only less than the gel-time of the epoxy if capillary effects are included. In experiments the CNF networks were clearly wetted. However low transparency indicated that impregnation was incomplete. The modulus and strength of the dry CNF networks increased rapidly with decreasing porosity, but their nanocomposites did not follow this trend, showing instead similar mechanical properties to each other. The results demonstrated that increasing the porosity of the CNF networks to ≈ 50% gives better impregnation resulting in a lower ultimate strength, a higher yield strength and no loss in modulus. Better use of the flow channels in the inherently layered CNF networks could potentially reduce void content in these nanocomposites and thus increase their mechanical properties.

  • 13.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Moreno, Sergio
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vacuum Infusion of Nanocellulose Networks of Different Porosity2015In: 20th International Conference on Composite Materials: Copenhagen, 19-24th July 2015, ICCM , 2015, article id 4109-1Conference paper (Refereed)
    Abstract [en]

    Cellulose nanofibres (CNF) have shown good potential as sustainable, biobased reinforcing materials in polymer composites. Addressing issues around the processing of these composites is an important part of establishing their use in different applications. Here, CNF networks of different porosity are made from nanofibrillated hardwood kraft pulp with the aim of increasing the impregnation of the CNF networks and to allow vacuum infusion to be used. Two different vacuum infusion strategies: in-plane and out of plane were used to infuse the CNF networks with a low viscosity epoxy. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated and compared to a micro-fibre based network. Using the out-of-plane permeability measurements and Darcy’s law, the fill-time was calculated and showed that the CNF network with 40% porosity had the lowest fill-time when an out-of-plane impregnation strategy is used. However this exceeded the gel-time of the epoxy system. In experiments, the resin reached the other side of the network but low transparency indicated that wetting was poor. The dry CNF preforms showed a very strong dependence on the porosity with both modulus and strength increasing rapidly at low porosity. Interestingly, the composite based on the 60% porosity network showed good wetting particularly with the in-plane infusion strategy, exhibiting a much more brittle fracture and a high yield strength. This shows that in CNF composites produced by VI, lowering the fibre volume content of the CNF composites gives better impregnation resulting in a lower ultimate strength but higher yield strength and no loss in modulus.

  • 14.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Cellulose nanofibril nanocomposites processing2013In: Production and Applications of Cellulose Nanomaterials, Peachtree Corners, GA: TAPPI Press, 2013, p. 271-274Chapter in book (Refereed)
    Abstract [en]

    Impregnation of a preformed network of nanofibrils leads to high fibre volume fraction nanocomposites and with this good mechanical properties have been achieved. However, comparing nanofibrils composite made with different volume fractions and different matrices is difficult. In order to do this, and in doing so gain insight into the most promising approaches, methods of measuring reinforcing efficiencies are being developed. The results show that for matrices with low stiffness the stiffness reinforcing efficiency is high. However with high fibre volume fraction and high stiffness, this network effect may lead to a lack of exploitation of the properties of the nanofibrils. Alignment of the nanofibrils is also a key in effective reinforcement. In addition, upscaling of the impregnation process requires a good understanding of permeability and adaptation of existing permeability models for cellulose nanofibrils networks as well as experiments on their permeability are ongoing.

  • 15.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Quantifying reinforcing efficiency of nanocellulose fibres2013In: Processing of fibre composites-challenges for maximum materials performance: Proceedings of 34th Risø International Symposium on Materials Science / [ed] Bo Madsen; Hans Lilholt; Y Kusano; S Fäster; B Ralph, Risö: Dept. of Wind Energy, Technical University of Denmark , 2013, p. 149-160Conference paper (Refereed)
    Abstract [en]

    Cellulose nanofibres are found in all plants and have the potential to provide a sustainable biobased material source. These nanofibres can be used for reinforcing polymers and thus as structural materials. Very promising results have been reported for different nanocomposites but to compete with existing materials, it is important to understand what progress has been made towards structural materials using nanocellulose. To do this the reinforcing efficiency of the stiffness and strength of nanocellulose in different nanocomposites has been calculated for a number of reported nanocellulose fibre based composites. For the stiffness this is done by back-calculating a reinforcing efficiency factor from a Halpin-Tsai model and laminate theory. For the strength efficiency, two models are used: a classic short fibre composite model and a network model. The results show that orientation is key to the stiffness efficiency, as shown by the high efficiency of aligned natural fibres. The stiffness efficiency is, as expected, high in soft matrices but in stiff matrices, the network effect of the nanofibres is possibility limiting their reinforcing potential. The strength efficiency results show that in all the nanocomposites evaluated the network model is closer to predicting strength than the short fibre composite model. The correlation between the network strength and the composite strength suggest that much of the stress transfer is from fibre to fibre and strong nanocomposites depend heavily on having a strong network. Also noted is that in composite processing a good impregnation of the nanofibers is also seen as an important factor in the efficiency of both strength and stiffness.

  • 16.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Reinforcing efficiency and the manufacture nanocellulose fibre based composites by vacuum infusion2015Conference paper (Other academic)
    Abstract [en]

    Nanocomposites based on cellulose have received a rapidly rising attention over the last 10 years however the method of manufacturing these composites on a scale larger than that in the lab remains challenging. Another challenge is that low fraction nanocomposites, whilst they can show excellent improvement in polymer properties, have difficultly to compete with traditional fibre reinforced composites [1,2]. A commonly used liquid composite moulding method for producing composites is vacuum infusion and the possibility of trading glass fibre for nanocellulose networks sheets in this type of manufacturing could results in a upscale method for producing high volume fraction cellulose nanocomposites. CNF networks are stiff and strong but have high fibre packing and thus difficult to impregnate. This paper evaluates the effectiveness of increasing the porosity to improve their processability by VI.

  • 17.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Reinforcing efficiency of nanocellulose in polymers2014In: Reactive & functional polymers, ISSN 1381-5148, E-ISSN 1873-166X, Vol. 85, p. 151-156, article id 6Article in journal (Refereed)
    Abstract [en]

    Nanocellulose extracted from renewable sources, is a promising reinforcement for many polymers and is a material where strong interfibre hydrogen bonds add effects not seen in microfiber composites. Presented is a tool for comparing different nanocellulose composites based on estimating the efficiency of nanocellulose reinforcement. A reinforcing efficiency factor is calculated from reported values of elastic modulus and strength from various nanocellulose composites using established micromechanical models. In addition, for the strength, a network model is derived based on fibre-fibre bond strength within nanocellulose networks. The strength results highlight the importance of the plastic deformation in the nanocellulose composites. Both modulus and strength efficiency show that the network strength and modulus has a greater effect than that of the individual constituents. In the best cases, nanocellulose reinforcement exceeds all model predictions.

  • 18.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Reinforcing Efficiency of Nanocelluloses in Polymer Nanocomposites2014In: Handbook of Green Materials: Processing Technologies, Properties and Applications, Singapore: World Scientific and Engineering Academy and Society, 2014Chapter in book (Refereed)
  • 19.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Westin, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. University of Jyvaskyla, Department of Physics.
    Korpimäki, Jani
    CSI Composites.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nanofibre distribution in composites manufactured with epoxy reinforced with nanofibrillated cellulose: model prediction and verification2016In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 139, article id 012011Article in journal (Refereed)
    Abstract [en]

    In this study a model based on simple scattering is developed and used to predict the distribution of nanofibrillated cellulose in composites manufactured by resin transfer moulding (RTM) where the resin contains nanofibres. The model is a Monte Carlo based simulation where nanofibres are randomly chosen from probability density functions for length, diameter and orientation. Their movements are then tracked as they advance through a random arrangement of fibres in defined fibre bundles. The results of the model show that the fabric filters the nanofibres within the first 20 µm unless clear inter-bundle channels are available. The volume fraction of the fabric fibres, flow velocity and size of nanofibre influence this to some extent. To verify the model, an epoxy with 0.5 wt.% Kraft Birch nanofibres was made through a solvent exchange route and stained with a colouring agent. This was infused into a glass fibre fabric using an RTM process. The experimental results confirmed the filtering of the nanofibres by the fibre bundles and their penetration in the fabric via the inter-bundle channels. Hence, the model is a useful tool for visualising the distribution of the nanofibres in composites in this manufacturing process.

  • 20.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Westin, Mikael
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hydrogel state impregnation of cellulose fibre-phenol composites: effects of fibre size distribution2016In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper (Refereed)
    Abstract [en]

    Whilst it has been well established that cellulose nanofibres (CNF) networks produce films that have high stiffness and strength, they are difficult to impregnate. Investigated in this study is whether by controlling the degree of nanofibrillation of cellulose, composites based on micro- and nano-size cellulose fibres can be made that are more easily manufactured and have better impregnation than solely cellulose nano-fibre based composites. To evaluate this, cellulose at different stages of ultrafine grinding, extracted at time intervals of 30, 60 and 290 mins, were used to make composites. To achieve good impregnation a novel strategy was used based on impregnation with phenol resin whilst the fibrillated cellulose is in a hydrogel state. The composites were subsequently dried and consolidated by hot press. The current results show that this method of impregnation is successful and the phenol matrix greatly improves the properties of the cellulose with a low degree of fibrillation. In general, as the degree of fibrillation and the proportion of nanofibres increases, the mechanical properties of the networks and their composites increase. The addition of the matrix appears to restrict the deformation of CNF network, increasing the modulus and yield strength but decreasing the ultimate strength. The method also appears to restrict the consolidation and voids remain in the composite, which reduces the modulus when compared to theoretical maximum values for this material. More work on the consolidation process is necessary to achieve the full potential of these composites.

  • 21.
    Berglund, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Anugwom, Ikenna
    Technical Chemistry, Department of Chemistry, Chemical-Biological Centre, Umeå University .
    Hedenström, Mattias
    Technical Chemistry, Department of Chemistry, Chemical-Biological Centre, Umeå University .
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mikkola, Jyri-Pekka
    Technical Chemistry, Department of Chemistry, Chemical-Biological Centre, Umeå University.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu.
    Switchable ionic liquids enable efficient nanofibrillation of wood pulp2017In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, no 8, p. 3265-3279Article in journal (Refereed)
    Abstract [en]

    Use of switchable ionic liquid (SIL) pulp offers an efficient and greener technology to produce nanofibers via ultrafine grinding. In this study, we demonstrate that SIL pulp opens up a mechanically efficient route to the nanofibrillation of wood pulp, thus providing both a low cost and chemically benign route to the production of cellulose nanofibers. The degree of fibrillation during the process was evaluated by viscosity and optical microscopy of SIL treated, bleached SIL treated and a reference pulp. Furthermore, films were prepared from the fibrillated material for characterization and tensile testing. It was observed that substantially improved mechanical properties were attained as a result of the grinding process, thus signifying nanofibrillation. Both SIL treated and bleached SIL treated pulps were fibrillated into nanofibers with fiber diameters below 15 nm thus forming networks of hydrophilic nature with an intact crystalline structure. Notably, it was found that the SIL pulp could be fibrillated more efficiently than traditional pulp since nanofibers could be produced with more than 30% less energy when compared to the reference pulp. Additionally, bleaching reduced the energy demand by further 16%. The study demonstrated that this switchable ionic liquid treatment has considerable potential in the commercial production of nanofibers due to the increased efficiency in fibrillation.

  • 22.
    Berglund, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Öman, Tommy
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Production potential of cellulose nanofibers from industrial residues: Efficiency and nanofiber characteristics2016In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 92, p. 84-92Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to evaluate the production potential of cellulose nanofibers from two different industrial bio-residues: wastes from the juice industry (carrot) and the beer brewing process (BSG). The mechanical separation of the cellulose nanofibers was by ultrafine grinding. X-ray diffraction (XRD) and Raman spectroscopy revealed that the materials were mechanically isolated without significantly affecting their crystallinity. The carrot residue was more easily bleached and consumed less energy during grinding, using only 0.9 kWh/kg compared to 21 kWh/kg for the BSG. The carrot residue also had a 10% higher yield than the BSG. Moreover, the dried nanofiber networks showed high mechanical properties, with an average modulus and strength of 12.9 GPa and 210 MPa, respectively, thus indicating a homogeneous nanosize distribution. The study showed that carrot residue has great potential for the industrial production of cellulose nanofibers due to its high quality, processing efficiency, and low raw material cost

  • 23.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wei, Jiayuan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu, Oulu, Finland .
    Well-dispersed cellulose nanocrystals in hydrophobic polymers by in situ polymerization for synthesizing highly reinforced bio-nanocomposites2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 25, p. 11797-11807Article in journal (Refereed)
    Abstract [en]

    In nanocomposites, dispersing hydrophilic nanomaterials in a hydrophobic matrix using simple and environmentally friendly methods remains challenging. Herein, we report a method based on in situ polymerization to synthesize nanocomposites of well-dispersed cellulose nanocrystals (CNCs) and poly(vinyl acetate) (PVAc). We have also shown that by blending this PVAc/CNC nanocomposite with poly(lactic acid) (PLA), a good dispersion of the CNCs can be reached in PLA. The outstanding dispersion of CNCs in both PVAc and PLA/PVAc matrices was shown by different microscopy techniques and was further supported by the mechanical and rheological properties of the composites. The in situ PVAc/CNC nanocomposites exhibit enhanced mechanical properties compared to the materials produced by mechanical mixing, and a theoretical model based on the interphase effect and dispersion that reflects this behavior was developed. Comparison of the rheological and thermal behaviors of the mixed and in situ PVAc/CNC also confirmed the great improvement in the dispersion of nanocellulose in the latter. Furthermore, a synergistic effect was observed with only 0.1 wt% CNCs when the in situ PVAc/CNC was blended with PLA, as demonstrated by significant increases in elastic modulus, yield strength, elongation to break and glass transition temperature compared to the PLA/PVAc only material.

  • 24.
    Hassan, Mohammad L.
    et al.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Abou-zeid, Ragab Esmail
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Hassan, Enas A.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Membranes based on cellulose nanofibers and activated carbon for removal of Escherichia coli bacteria from water2017In: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 9, no 8, article id 335Article in journal (Refereed)
    Abstract [en]

    Cellulosic nanomaterials are potential candidates in different areas, especially in water treatment. In the current work, palm fruit stalks cellulose nanofibers (CNF), TEMPO-oxidized CNF (OCNF), and activated carbon (AC) were used to make thin film membranes for removal of E. coli bacteria from water. Two types of layered membranes were produced: a single layer setup of crosslinked CNF and a two-layer setup of AC/OCNF (bottom) and crosslinked CNF (up) on hardened filter paper. The prepared membranes were evaluated regarding their microstructure and layers thickness using scanning electron microscopy (SEM). Water flux and rejection of E. coli bacteria was tested using dead end stirred cells at 1 MPa pressure. Thickness of the cosslinked CNF layer in both types of membranes was about 0.75 micron. The results showed that exchanging water by isopropyl alcohol before drying increased porosity of membranes, and thus resulted in increasing pure water flux and flux of bacteria suspension. The two-layer AC/OCNF/CNF membrane had much higher water flux than the single layer CNF due to higher porosity seen on the surface of the former. Both types of membranes showed high capability of removing E. coli bacteria (rejection ~96–99%) with slightly higher efficiency for the AC/OCNF/CNF membrane than CNF membrane. AC/OCNF/CNF membrane also showed resistance against growth of E. coli and S. aureus bacteria on the upper CNF surface while the single layer CNF membrane did not show resistance against growth of the aforementioned bacteria

  • 25.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Enhanced alignment and mechanical properties through the use of hydroxyethyl cellulose in solvent-free native cellulose spun filaments2017In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 150, p. 79-86Article in journal (Refereed)
    Abstract [en]

    In this study, the addition of hydroxyethyl cellulose (HEC) in cellulose nanofiber filaments is shown to improve the solvent-free processing and mechanical properties of these biobased fibers as well as their compatibility with epoxy. An aqueous dope of cellulose nanofiber (CNF) with HEC was spun and the resulting filaments cold-drawn. The HEC increased the wet strength of the dope allowing stable spinning of low concentrations of CNF. These lower concentrations promote nanofiber alignment which is further improved by cold-drawing. Alignment improves the modulus and strength and an increase of over 70% compared to the as-spun CNF only filaments was achieved. HEC also decreases hydrophilicity thus increasing slightly the interfacial shear strength of the filaments with epoxy resin. The result is continuous biobased fibers with improved epoxy compatibility that can be prepared in an upscalable and environmentally friendly way. Further optimization is expected to increase draw ratio and consequently mechanical properties.

  • 26.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dry-spinning of continuous cellulose fibers using only nanofibers from a bio-residue2014Conference paper (Refereed)
    Abstract [en]

    IntroductionFibers are widely used in polymer composites and the highest mechanical properties are achieved when fibers are continuous and aligned in the direction of the applied load. For this reason continuous glass fiber composites are commonly used in structural applications. These glass fibers have high stiffness (70 GPa) and strength (3400 MPa) but have a high environmental impact. An alternative is to use natural fibers since they have a low environmental impact and good mechanical properties, e.g. flax fibers have a stiffness of 70 GPa and strength of 900 MPa. However, natural fibers are short and discontinuous and conventional spinning results in highly twisted yarns, which negatively impact the mechanical properties of the composites1. One solution to overcome these limitations is to prepare continuous biobased man-made fibers from cellulose. Thermoplastic cellulose-based biopolymers such as cellulose acetate butyrate (CAB) can be melt-spun but the low mechanical properties of these fibers make them unsuitable for use in structural composites. Nanoreinforcing as well as aligning the polymer chains and nanoreinforcements were investigated but the improvements in the final properties of CAB nanocomposites fibers were still far below the desired values2,3. Regenerated cellulosic fibers are another type of continuous cellulosic man-made fibers but again their mechanical properties are lower than that of native cellulose, e.g. Lyocell has a stiffness of 16 GPa and strength of 660 MPa. Therefore, of interest is the manufacture of aligned continuous native cellulose fibers. Cellulosic fibers have been prepared by simply wet spinning tempo-mediated oxidized cellulose nanofibers (CNF) through a syringe into an organic liquid 4, 5. Though, high mechanical properties of the fibers have been reported, tempo-mediated oxidation and using solvents for precipitation does not make the process economical. In the current study, low-cost continuous cellulose fibers from a bio-residue CNF without additional chemicals and solvents were prepared. The effect of spinning rates as well as the effect of CNF concentration on the mechanical properties of the fibers was investigated.ExperimentalCellulose nanofibers were extracted from bleached banana rachis waste using ultra-fine grinder (Masuko Sangyo Co., Saitama, Japan). The bleached fibers were supplied by ECLIPSE project. A suspension of 2wt% was concentrated to different concentrations (8, 10 and 12 wt%) using centrifugation. Dry spinning of the fibers were carried out at three spinning rates (72, 144 and 216 mm/s) using a Rheo-tester 1000 (Göttfert, Buchen, Germany) equipped with a 1 mm single hole die with length of 20 mm. The spun fibers were then collected and mounted on glass sheets before being dried at room temperature followed by oven drying to remove any remaining moisture (Fig. 1). For comparison a nanopaper from the CNF was also made by vacuum filtration and drying.References1. Goutianos et al.: Appl Compos Mater, 2006, 13 199-215.2. Hooshmand et al.: Plast Rubber Compos, 2014, 43 (1) 15-24.3. Hooshmand et al.: Cellulose, 2014 accepted.4. Walter et al.: Adv Mater, 2011, 23 2924-2928.5. Iwamoto et al.: Biomacromolecules, 2011, 12 831-836.AcknowledgementsThe authors thank Bio4Energy for financial support of this project as well as ECLIPSE project (grant agreement nº: 280786) for the banana nanofibers.

  • 27.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Exploiting the self-assembly of cellulose nanofibers in wet and dry spun fibers2014Conference paper (Refereed)
    Abstract [en]

    In the current study, self-assembled cellulose fibers were prepared by wet spinning and dry spinning of the cellulose nanofibers (CNF). The CNF were prepared using a low-cost and energy efficient procedure from a bio-residue source without using any additional chemical treatments. Different concentrations of CNF in water were simply wet spun into an acetone coagulation bath as well as dry spun into the air. These different spinning conditions as well as the effect of concentration and shear force on the orientation of the CNF in the spun fibres and mechanical properties of these fibers were investigated. Using viscosity measurements, the theoretical shear forces are calculated and related to orientation and the mechanical properties. It is this shearing during the loosely bound suspension state of the CNF that is thought to allow an increase in orientation of the CNF in the spun fibre. This orientation is then maintained by the presence of the hydroxyl group on the surface of the CNF resulting in hydrogen bonds between the CNF. This self-assembly of the more orientated CNF as the fibres dry provided high stiffness and low ductility to the resulting fiber. These characteristics and the fact that they are continuous fibres make them very suitable to use in the structural composites. The fibers were further characterized regarding viscoelasticity behavior and thermal properties as well as crystallinity and microstructure.

  • 28.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of Matrix and Cold-drawing on Dry Spun Filaments of Cellulose Nanofibers2015Conference paper (Refereed)
    Abstract [en]

    In this study, two different types of single filament fibers were prepared by dry-spinning an aqueous suspension of cellulose nanofibers (CNF) as well as CNF and water-soluble hydroxyethyl cellulose (HEC) suspension. The filaments were prepared using a capillary rheometer with a single-hole die. Based on our previous study1, the lowest spinnable concentration was used to increase the CNF orientation induced by the shear force in the die. To further increase the orientation of the CNF in the fibers and subsequently increase their mechanical properties, the semi-dried fibers were cold-drawn to ≈4%. The effect of drawing on both CNF-only and CNF-HEC nanocomposite fibers was investigated. The addition of HEC improved the processability of the fibers and allowed a lower spinnable concentration (≈4.5wt%) to be used compared to the CNF-only fiber (≈7wt%). The HEC improved the modulus, strength and the strain of the non-drawn CNF-HEC fiber compared to the CNF-only fiber. The higher modulus and strength of the CNF-HEC fiber is thought to be due to an increase in orientation of CNF in the fiber because of the lower concentration of the suspension. The drawn CNF-HEC fiber showed further improved in the mechanical properties, with a modulus of 15 GPa and strength of 260 MPa, an increase of 76% and 72 % respectively, compared to undrawn CNF-only fiber. The continuous nature of these nanocomposites fibers and their characteristics mean they have potential for use in fiber-reinforced composites.

  • 29.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Norberg, Nicholas
    PANalytical.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dry-Spun Single-Filament Fibers Comprising Solely Cellulose Nanofibers from Bioresidue2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 23, p. 13022-13028Article in journal (Refereed)
    Abstract [en]

    We demonstrated that low-cost and environmentally friendly filaments of native cellulose can be prepared by dry spinning an aqueous suspension of cellulose nanofibers (CNF). The CNF were extracted from banana rachis, a bioresidue from banana cultivation. The relationship between spinning rate, CNF concentration, and the mechanical properties of the filaments were investigated and the results showed that the modulus of the filaments was increased from 7.8 to 12.6 GPa and the strength increased from 131 to 222 MPa when the lowest concentration and highest speed was used. This improvement is believed to be due to an increased orientation of the CNF in the filament. A minimum concentration of 6.5 wt % was required for continuous filament spinning using the current setup. However, this relatively high concentration is thought to limit the orientation of the CNF in the filament. The process used in this study has a good potential for upscaling providing a continuous filament production with well-controlled speed, but further work is required to increase the orientation and subsequently the mechanical properties.

  • 30.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Skrifvars, Mikael
    School of Engineering, University of Borås.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    All-cellulose nanocomposite fibers produced by melt spinning cellulose acetate butyrate and cellulose nanocrystals2014In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, no 4, p. 2665-2678Article in journal (Refereed)
    Abstract [en]

    Bio-based continuous fibers were prepared by melt spinning cellulose acetate butyrate (CAB), cellulose nanocrystals (CNC) and triethyl citrate. A CNC organo-gel dispersion technique was used and the prepared materials (2 and 10 wt% CNC) were melt spun using a twin-screw micro-compounder and drawn to a ratio of 1.5. The microscopy studies showed that the addition of CNC in CAB resulted in defect-free and smooth fiber surfaces. An addition of 10 wt% CNC enhanced the storage modulus and increased the tensile strength and Young's modulus. Fiber drawing improved the mechanical properties further. In addition, a micromechanical model of the composite material was used to estimate the stiffness and showed that theoretical values were exceeded for the lower concentration of CNC but not reached for the higher concentration. In conclusion, this dispersion technique combined with melt spinning can be used to produce all-cellulose nanocomposites fibers and that both the increase in CNC volume fraction and the fiber drawing increased the mechanical performance

  • 31.
    Jonoobi, Mehdi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Thermoplastic polymer impregnation of cellulose nanofibre networks: Morphology, mechanical and optical properties2014In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 58, p. 30-35Article in journal (Refereed)
    Abstract [en]

    Biobased nanocomposite sheets of cellulose nanofibres (CNF) and cellulose acetate butyrate (CAB) were prepared using a resin impregnation technique. Porous nanofibre networks together with a low viscosity thermoplastic resin were the key elements in the processing. SEM images of the network before the impregnation showed high porosity and after the impregnation indicated impregnated fibre network. A significant improvement in the visible light transmittance was observed for the nanocomposite compared to the nanofibre network, which is explained on the filling of the pores with a transparent matrix. The tensile tests showed an increase of 364% and 145% for stiffness and strength respectively for nanocomposites with 60 wt.% CNF when compared to CAB. Dynamic mechanical properties showed a good interaction between the CAB and cellulose nanofibres. These results show that CAB impregnated cellulose nanofibre networks are promising biocomposite that could be used in applications where transparency and good mechanical properties are of interest.

  • 32.
    Kusano, Yukihiro
    et al.
    Department of Wind Energy, Section of Composites and Materials Mechanics, Technical University of Denmark, Risø Campus, Roskilde.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Madsen, Bo
    Technical University of Denmark, Department of Wind Energy, Risø Campus.
    Gliding arc surface modification of carrot nanofibre coating: Perspective for composite processing2016In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 139, article id 012027Article in journal (Refereed)
    Abstract [en]

    Surfaces of carrot nanofibre coatings were modified by a gliding arc in atmospheric pressure air. The treatment strengthened wetting of deionized water and glycerol, increased an oxygen content, C-O and C=O, and moderately roughened the surfaces. In the perspective of composite materials, these changes to the nanofibres can potentially improve their processability when they are to be impregnated with a polymeric matrix. However, longer exposure to the gliding arc reduced oxidation and roughness of the surface, and thus there exists an optimum condition to achieve good wetting to solvents

  • 33.
    Kusano, Yukihiro
    et al.
    Department of Wind Energy, Section of Composites and Materials Mechanics, Technical University of Denmark, Roskilde.
    Madsen, Bo
    Technical University of Denmark, Department of Wind Energy, Risø Campus.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dielectric barrier discharge plasma treatment of cellulose nanofibre surfaces2018In: Surface Engineering, ISSN 0267-0844, E-ISSN 1743-2944, Vol. 34, no 11, p. 825-831Article in journal (Refereed)
    Abstract [en]

    Dielectric barrier discharge plasma treatment was applied to modify cellulose nanofibre (CNF) surfaces with and without ultrasonic irradiation. The plasma treatment improved the wetting by deionised water and glycerol, and increased the contents of oxygen, carbonyl group, and carboxyl group on the nanofibre surface. Ultrasonic irradiation further enhanced the wetting and oxidation of the nanofibre coating. Scanning electron microscopic observations showed skeleton-like features on the plasma-treated surface, indicating preferential etching of weaker domains, such as low-molecular weight domains and amorphous phases. Ultrasonic irradiation also improved the uniformity of the treatment. Altogether, it is demonstrated that atmospheric pressure plasma treatment is a promising technique to modify the CNF surface before composite processing.

  • 34.
    Lee, Koon-Yang
    et al.
    Department of Chemical Engineering, University College London.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Lars A.
    Wallenberg Wood Science Centre, Royal Institute of Technology.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bismarck, Alexander
    Vienna University of Technology, Polymer & Composite Engineering (PaCE) Group, Department of Chemical Engineering, Imperial College London, South Kensington Campus.
    On the use of nanocellulose as reinforcement in polymer matrix composites2014In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 105, p. 15-27Article in journal (Refereed)
    Abstract [en]

    Nanocellulose is often being regarded as the next generation renewable reinforcement for the production of high performance biocomposites. This feature article reviews the various nanocellulose reinforced polymer composites reported in literature and discusses the potential of nanocellulose as reinforcement for the production of renewable high performance polymer nanocomposites. The theoretical and experimentally determined tensile properties of nanocellulose are also reviewed. In addition to this, the reinforcing ability of BC and NFC is juxtaposed. In order to analyse the various cellulose-reinforced polymer nanocomposites reported in literature, Cox-Krenchel and rule-of-mixture models have been used to elucidate the potential of nanocellulose in composite applications. There may be potential for improvement since the tensile modulus and strength of most cellulose nanocomposites reported in literature scale linearly with the tensile modulus and strength of the cellulose nanopaper structures. Better dispersion of individual cellulose nanofibres in the polymer matrix may improve composite properties

  • 35.
    Lee, Koon-Yang
    et al.
    UCL, Department of Chemical Engineering, London.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Lars
    Kungliga tekniska högskolan, KTH, Luleå tekniska universitet, Wallenberg Wood Science Centre, Royal Institute of Technology.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bismarck, Alexander
    Vienna University of Technology, Polymer & Composite Engineering (PaCE) Group, Department of Chemical Engineering, Imperial College London, South Kensington Campus.
    Utilising the full potential of bacterial cellulose in composite materials: Can it be done?2014In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 247Article in journal (Refereed)
  • 36.
    Löfqvist, Torbjörn
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Niemi, Jan
    Aitomäki, Yvonne
    Ultrasonic methods in determining elastic material properties of fibres in suspension2008In: 2007 IEEE Ultrasonics Symposium proceedings: New York City, NY, USA, 28 - 31 October 2007, Piscataway, NJ: IEEE Communications Society, 2008, p. 46-49Conference paper (Refereed)
    Abstract [en]

    The presented study concerns the application of the pulse-echo ultrasound measurement technique in determining the elastic properties of fibres suspended in water. The two kinds of fibre materials are investigated, nylon 6/6 fibres and softwood pulp fibres. The fibre mass fraction was 0.5% for nylon and ranges from 0% up to 1% for softwood pulp. The ultrasonic measurements are performed in the frequency range of 2-11 MHz. It is shown that the velocity dispersion of the ultrasound is small for each suspension sample. In obtaining the fibres longitudinal Young's modulus two methods are used, one based on phase velocity and one based on acoustic attenuation. It is found that both methods gives reasonable estimates of the longitudinal Young's modulus for nylon 6/6. For pulp fibres the determined Young's modulus is overestimated in comparison with earlier findings.

  • 37. Niemi, Jan
    et al.
    Aitomäki, Yvonne
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ultrasonic measurements and modelling of attenuation and phase velocity in pulp suspensions2005In: 2005 IEEE Ultrasonics Symposium: 18 - 21 September 2005, Rotterdam, the Netherlands, Piscataway, NJ: IEEE Communications Society, 2005, Vol. 2, p. 775-779Conference paper (Refereed)
    Abstract [en]

    In the manufacturing process of paper the mass fraction and material properties of the fibres in the pulp suspension are important for the quality of the finished product. This study presents two different methods of pulp characterisation. The first is based on phase velocity, which we use to investigate the composition of the pulp. Here a method is presented where the optimal number of circular shifts within the sampling window of the signal is determined which gives, in a weakly dispersive medium, a continuous phase spectrum and minimizes the likelihood of discontinuities within the bandwidth. Hence, the ambiguity in phase unwrapping is avoided. The results from phase velocity measurements show that the phase velocity weakly increases with increasing amount of fines in the suspension. The dispersion is caused by the fibres and it correlates with fibre mass fraction. The second method is based on attenuation and is used to characterise the wood fibres. The results of the attenuation experiments show that it is possible to inversely calculate wood fibre properties by fitting the model to the experimental data, if the fibre diameter distribution is known. However, the accuracy of these calculation is difficult to determined and more work in this area is required.

  • 38.
    Oksman, Kristiina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Liquid Composite Molding2014In: Handbook of Green Materials: Processing Technologies, Properties and Applications, Singapore: World Scientific and Engineering Academy and Society, 2014Chapter in book (Refereed)
  • 39.
    Oksman, Kristiina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Siquiera, Gilberto
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Zhou, Qi
    School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, Stockholm.
    Butylina, Svetlana
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tanpichai, Supachok
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zhou, Xiaojian
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hooshmand, Saleh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Review of the recent developments in cellulose nanocomposite processing2016In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 83, p. 2-18Article in journal (Refereed)
    Abstract [en]

    This review addresses the recent developments of the processing of cellulose nanocomposites, focusing on the most used techniques, including solution casting, melt-processing of thermoplastic cellulose nanocomposites and resin impregnation of cellulose nanopapers using thermoset resins. Important techniques, such as partially dissolved cellulose nanocomposites, nanocomposite foams reinforced with nanocellulose, as well as long continuous fibers or filaments, are also addressed. It is shown how the research on cellulose nanocomposites has rapidly increased during the last 10 years, and manufacturing techniques have been developed from simple casting to these more sophisticated methods. To produce cellulose nanocomposites for commercial use, the processing of these materials must be developed from laboratory to industrially viable methods.

  • 40.
    Oksman, Kristiina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jonoobi, Mehdi
    Siqueira, Gilberto
    Hietala, Maiju
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Cellulose nanofiber isolated from industrial side-streams2013In: Production and Applications of Cellulose Nanomaterials, TAPPI Press, 2013, p. 187-190Chapter in book (Refereed)
    Abstract [en]

    Isolation of cellulose nanofibers from industrial side-streams as raw material is interesting from several reasons; it will not only result in lower overall cost of the nanofibers but also add value for many different processes and products. We have used sludge, a residue from pulp production, carrot residue from juice production, and several agricultural waste products as the starting material to isolate nanofibers. The isolation process was made using a Masuko ultra fine friction grinder and our aim have been to optimize the processing parameters for the lowest energy consumption. In addition to developing the isolation process, the isolated nanofibers structure and properties were characterized. Typically, the isolated nanofibers are bundles with diameters lower than 100 nm. In particular, we found that carrot nanofibers have a uniform fiber size less than 50 nm. Scanning electron microscopy studies showed entangled nanofiber networks and the mechanical properties of nanofiber networks demonstrated a positive impact on modulus and strength when compared to networks with microsized fibers. The improvement is increased with decreased fiber size indicating more efficient fibrillation. From these studies, we have shown that industrial side-streams are excellent raw material sources for nanofiber preparation, being cheaper than other raw materials and consuming less energy for isolation while showing good properties.

  • 41.
    Zhou, Xiaojian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sethi, Jatin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Frisk, Nikolina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sain, Mohini
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dispersion and reinforcing effect of carrot nanofibers on biopolyurethane foams2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 110, p. 526-531Article in journal (Refereed)
    Abstract [en]

    In this study, carrot nanofibers (CNF) were used to enhance the performance of biobased castor oil polyol polyurethane nanocomposite foams. A method of dispersing CNF in the polyol was developed and the foam characteristics and CNF reinforcing effect were studied. Co-solvent-assisted mixing resulted in well-dispersed CNF in the polyol, and foams with 0.25, 0.5 and 1 phr CNF content were prepared. The reinforced nanocomposite foams displayed a narrow cell size distribution and the compressive strength and modulus were significantly elevated and the best compressive strength and modulus were reached with 0.5 phr CNF. Similarly, the modulus of the solid material was also significantly increased based on theoretical calculations. When comparing the foam performance, compressive strength and stiffness as a function of the density, the nanocomposite foams performs as commercial rigid PU foam with a closed cell structure. These results are very promising and we believe that these foams are excellent core materials for lightweight sandwich composites.

1 - 41 of 41
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf