Endre søk
Begrens søket
1234567 151 - 200 of 757
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 151.
    Elustondo, Diego
    et al.
    FPInnovations-Wood Products, Vancouver, British Columbia.
    Oliveira, Luiz C De S
    FPInnovations-Wood Products, Vancouver, British Columbia.
    Comparing weight and capacitance for sorting lumbe before drying2012Konferansepaper (Fagfellevurdert)
  • 152.
    Elustondo, Diego
    et al.
    FPInnovations-Wood Products, Vancouver, British Columbia.
    Oliveira, Luiz C De S
    FPInnovations-Wood Products, Vancouver, British Columbia.
    New methodology to optimize sorting in wood drying2010Inngår i: Proceedings, 11th International IUFRO Wood Drying Conference: [... in Skellefteå, Sweden, January 18 - 22, 2010 ... the theme of the conference was "Recent Advances in the Field of Wood Drying"] / [ed] Tom Morén; Lena Antti; Margot Sehlstedt-Persson, Luleå: Luleå tekniska universitet, 2010Konferansepaper (Fagfellevurdert)
  • 153.
    Elustondo, Diego
    et al.
    Forintek Canada Corporation, Western Laboratory, Vancouver, BC.
    Oliveira, Luiz C De S
    Forintek Canada Corporation, Western Laboratory, Vancouver, BC.
    Strategies to reduce energy consumption in kiln drying2007Inngår i: Proceedings: 10th International IUFRO Division 5 Wood Drying Conference, August 26-30, 2007, Orono, Maine, U.S.A. : Understanding and modeling the theoretical and practical aspects of solid wood and wood based materials / [ed] Robert W. Rice, Orno, Maine: University of Maine Press, 2007Konferansepaper (Fagfellevurdert)
  • 154.
    Elustondo, Diego
    et al.
    Department of Wood Science, University of British Columbia, Vancouver.
    Oliveira, Luiz C De S
    Forintek Canada Corporation, Western Laboratory, Vancouver, BC.
    Avramidis, Stavros H.
    University of British Columbia, Department of Wood Science.
    Evaluation of three semi-empirical models for superheated steam vacuum drying of timbers2003Inngår i: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 21, nr 5, s. 875-893Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Superheated steam drying at sub-atmospheric pressure (SSV) has been successfully employed in Europe and Asia for drying some types of timbers, showing that drying time could be reduced by 50% with respect to conventional drying without significant losses in the quality of the final product. This reduction is the consequence of a different heat and mass transfer control mechanism. Since SSV drying is carried out in absence of gaseous air, diffusion of the generated vapor is not a limiting factor and drying rate becomes more dependent on heat transference. Therefore, classical interpretation of timber drying as a process based on moisture migration control is not applicable to SSV. This work is targeting the development and validation of a simplified semi-empirical model for SSV drying of timbers. Mathematical representation of the proposed model is uncomplicated and straightforward to apply, and the comparison between model predicted and experimental data showed a high degree of agreement under variable drying conditions.

  • 155.
    Ericson, Mats
    et al.
    Luleå tekniska universitet.
    Lindberg, Henrik
    Luleå tekniska universitet.
    A method to quantify energy dissipation during crack propagation on the nanometer scale in polymers1994Inngår i: Preprint papers / Polymat '94, 19 - 22 September 1994, Imperial College, London, UK: eight major international conferences within: diffusion in polymers-IV, polymers in extreme environments-II, modelling of polymers structure and properties, reactive polymer processing, polymer technologies for electronics, polymer properties for CAD/CAM-II, polymer blends-II, toughening of plastics-III / [ed] John Hodgkinson, London: Institute of Materials , 1994, s. 614-617Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An ultramicrotome was used in order to measure the work to section, W sub s , during sectioning of polymers (PS, PC, PMMA, epoxy). W sub s was measured as a function of section thickness for five different amorphous polymers in the glassy state. W sub s was found to increase with increasing section thickness and varied from approx15-100 J/m exp 2 depending on the material and section thickness. It is believed that this technique is applicable for quantification of energy dissipation at a very local level in polymers. The reason is that the sections are very thin (as thin as 60 nm) and therefore only a very small volume of material is believed to be activated during the crack propagation. This is supported by the fact that W sub s approaches the smallest possible value, the intrinsic fracture energy, G sub 0 , for very small section thicknesses

  • 156. Eriksson, John
    et al.
    Johansson, Håkan
    Danvind, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    A mass-transport model for drying wood under isothermal conditions2005Inngår i: Proceedings: 9th International IUFRO Wood Drying Conference, Nanjing Forestry University , 2005Konferansepaper (Fagfellevurdert)
  • 157.
    Eriksson, John
    et al.
    Chalmers University of Technology.
    Johansson, Håkan
    Danvind, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Numerical determination of diffusion coefficients in wood using data from CT-scanning2006Inngår i: Wood and Fiber Science, ISSN 0735-6161, Vol. 38, nr 2, s. 334-344Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The radial moisture diffusion coefficient in Fick's law for a sample of Norway spruce (Picea abies) under isothermal drying conditions was determined in a parameterization of Arrhenius' equation type. Using X-ray CT-scanning, the wood density and moisture content distributions were obtained in the radial direction for the wood sample. An optimization scheme, based on finite element computation, was then applied to find the parameter values such that the difference between observed and computed moisture content was minimized. The combined numerical and experimental technique was developed to reduce known disadvantages of similar approaches, and a specific algorithm to determine diffusion coefficients was presented. A comparison of the calibrated diffusion coefficient with those given in the literature showed a good fit. The computed moisture content based on the obtained diffusion coefficient and the observed moisture content agreed well. Finally, the effect of measurement errors on the computed material parameter was found to be small

  • 158.
    Eslah, Farnaz
    et al.
    Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran.
    Jonoobi, Mehdi
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
    Faezipour, Mehdi
    Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran.
    Ashori, Alireza
    Department of Chemical Technologies, Iranian Research Organization for Science and Technology (IROST), Tehran.
    Chemical modification of soybean flour-based adhesives using acetylated cellulose nanocrystals2018Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 39, nr 10, s. 3618-3625Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, two types of new bioadhesives formulated from abundant and renewable soybean flour (SF), acetylated soybean flour based adhesive (ASF), and soybean flour-based adhesive, were modified with acetylated cellulose nanocrystal (ACNC). The apparent viscosity and morphology of the adhesive formulations were characterized. The chemical composition of the formulations was evaluated by FT-IR spectroscopy and the effect of polyethilenimine (PEI) on the formulations was investigated using the proton nuclear magnetic resonance (1H NMR) spectra. Moreover, water resistance of produced plywood composites bonded with the bioadhesives was measured. The results of FT-IR and 1H NMR confirmed that chemical modifications of the SF occurred. The scanning electron microscopy (SEM) images showed less holes and cracks on the cross section of the ASF/PEI/NaOH and SF/PEI/NaOH/ACNC formulations. The results showed that the plywood specimens bonded with formulations of the ASF/PEI/NaOH (with a dry weight ratio of ASF/PEI: 5/1 and 6/1), and SF/PEI/NaOH/ACNC had good resistance to water. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

  • 159.
    Esmaeili, Chakavak
    et al.
    School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi.
    Abdi, Mahnaz M.
    University Putra Malaysia, Department of Chemistry, Faculty of Science, University Putra Malaysia.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Jonoobi, Mehdi
    Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rezayi, Majid
    Chemistry Department, Faculty of Science, University Malaya.
    Synergy Effect of Nanocrystalline Cellulose for the Biosensing Detection of Glucose2015Inngår i: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 15, nr 10, s. 24681-24697Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Integrating polypyrrole-cellulose nanocrystal-based composites with glucose oxidase (GOx) as a new sensing regime was investigated. Polypyrrole-cellulose nanocrystal (PPy-CNC)-based composite as a novel immobilization membrane with unique physicochemical properties was found to enhance biosensor performance. Field emission scanning electron microscopy (FESEM) images showed that fibers were nanosized and porous, which is appropriate for accommodating enzymes and increasing electron transfer kinetics. The voltammetric results showed that the native structure and biocatalytic activity of GOx immobilized on the PPy-CNC nanocomposite remained and exhibited a high sensitivity (ca. 0.73 μA·mM(-1)), with a high dynamic response ranging from 1.0 to 20 mM glucose. The modified glucose biosensor exhibits a limit of detection (LOD) of (50 ± 10) µM and also excludes interfering species, such as ascorbic acid, uric acid, and cholesterol, which makes this sensor suitable for glucose determination in real samples. This sensor displays an acceptable reproducibility and stability over time. The current response was maintained over 95% of the initial value after 17 days, and the current difference measurement obtained using different electrodes provided a relative standard deviation (RSD) of 4.47%.

  • 160. Esping, Björn
    et al.
    Morén, Tom
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Program för svensk trätorkningsforskning 1983-19861983Rapport (Annet vitenskapelig)
  • 161. Esping, Björn
    et al.
    Morén, Tom
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Program för svensk trätorkningsforskning 1983-19861983Rapport (Annet vitenskapelig)
  • 162.
    Eyholzer, Christian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dried nanofibrillated cellulose and its bionanocomposites2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    During the past decade there has been a growing interest in the reinforcement of synthetic polymers with cellulose nanowhiskers and nanofibrillated cellulose (NFC) obtained from plants or bacteria. Their beneficial mechanical properties like high stiffness and strength, in combination with their low mass allowed successful reinforcement of water based polymer dispersions (latexes) for the production of solution cast composite films. However, the production of fully degradable or biocompatible nanocomposites containing NFC with high aspect ratio and diameters below 100 nm is still a challenging task. One of the main issues to overcome is irreversible agglomeration (hornification) of NFC. Hornification can occur during drying of aqueous NFC suspensions or during compounding of NFC with hydrophobic polymers and it can be explained with the formation of a large number of hydrogen bonds between the hydroxyl groups of adjacent nanofibrils. This process is accompanied by a considerable decrease of the NFC aspect ratio and consequently results in the complete loss of its beneficial properties. Therefore, the objective of this PhD work was to chemically functionalize NFC in order to prevent hornification during drying and to develop novel bionanocomposites with well dispersed NFC, displaying improved properties compared to the neat polymers. Successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In this study, a method for the preparation of water-redispersible NFC in powder form was developed, comprising carboxymethylation and mechanical disintegration of refined, bleached beech pulp (RBP). The powders formed stable gels when dispersed in water and SEM images confirmed that carboxymethylation had successfully prevented hornification of NFC during drying. Dynamic mechanical analysis (DMA) of poly(vinyl acetate) latex composites showed that carboxymethylation did not negatively influence the reinforcing potential of NFC. Consistently, the reinforcing potential of c-NFC was not altered by the drying procedure, as was shown by DMA experiments and tensile tests of hydroxypropyl cellulose composites containing dried and never-dried c-NFC. In a subsequent study, bionanocomposites were developed by UV-photopolymerization of N-vinyl-2-pyrrolidone in presence of a trimethacrylate crosslinker and water-redispersed c-NFC powder to yield a biocompatible hydrogel for the replacement of degenerated human Nucleus Pulposus (NP) in intervertebral discs. The native structure and function of the NP was mimicked by the randomly oriented c-NFC fibrils in the hydrogel matrix. The biocomposite hydrogels showed similar values for swelling ratio and modulus of elasticity in compression, compared to native NP. A final study focused on the feasibility of an industrial up-scaling of poly(lactic acid) composites containing compatibilized c-NFC using extrusion.

  • 163.
    Eyholzer, Christian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Preparation and properties of dried nanfibrillated cellulose and its nanocomposites2010Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The production of fully degradable nanocomposites with biopolymers as matrix and cellulose nanofibrils with high aspect ratios as reinforcement is still a challenging task. Also, due to the large amount of hydroxyl groups on the surface of these nanofibrils, they tend to irreversibly agglomerate during drying. This process, known as hornification, decreases the aspect ratio of the nanofibrils. Consequently, their reinforcing potential in nanocomposites is lowered. Thus, the objective of this PhD project is to produce novel biopolymer composites that are reinforced by functionalised cellulose nanofibrils in powder form. A successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In order to induce an optimal compounding of the fibrils with different biopolymers, good fibril/matrix embedding is required. Therefore, the cellulose nanofibrils have to be modified appropriately to match the hydrophilic or hydrophobic nature of the polymer matrix.The production of fully degradable nanocomposites with biopolymers as matrix and cellulose nanofibrils with high aspect ratios as reinforcement is still a challenging task. Also, due to the large amount of hydroxyl groups on the surface of these nanofibrils, they tend to irreversibly agglomerate during drying. This process, known as hornification, decreases the aspect ratio of the nanofibrils. Consequently, their reinforcing potential in nanocomposites is lowered. Thus, the objective of this PhD project is to produce novel biopolymer composites that are reinforced by functionalised cellulose nanofibrils in powder form. A successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In order to induce an optimal compounding of the fibrils with different biopolymers, good fibril/matrix embedding is required. Therefore, the cellulose nanofibrils have to be modified appropriately to match the hydrophilic or hydrophobic nature of the polymer matrix. In the first study, water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by carboxymethylation and mechanical disintegration. The sequence of the treatments influenced the stability of the final products in water. When carboxymethylation was applied first, enhanced disintegration of RBP into its sub-structural elements was observed. The prepared powder of this route formed a stable gel in water without sedimentation after 20 h. SEM images affirmed a significant reduction of cellulose nanofibrils agglomeration compared to unmodified NFC. The results suggest that NFC in dry form could be used as an alternative to conventional NFC in aqueous suspensions used as starting material for derivatization and compounding with biopolymers.

  • 164.
    Eyholzer, Christian
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bordeanu, Nico
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Lopez-Suevos, F
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Rentsch, D
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Zimmermann, Tanja
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Preparation and characterization of water-redispersible nanofibrillated cellulose in powder form2010Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 17, nr 1, s. 19-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by carboxymethylation (c) and mechanical disintegration (m). Two routes were examined by altering the sequence of the chemical and mechanical treatment, leading to four different products: RBP-m and RBP-mc (route 1), and RBP-c and RBP-cm (route 2). The occurrence of the carboxymethylation reaction was confirmed by FT-IR spectrometry and 13C solid state NMR (13C CP-MAS) spectroscopy with the appearance of characteristic signals for the carboxylate group at 1,595 cm-1 and 180 ppm, respectively. The chemical modification reduced the crystallinity of the products, especially for those of route 2, as shown by XRD experiments. Also, TGA showed a decrease in the thermal stability of the carboxymethylated products. However, sedimentation tests revealed that carboxymethylation was critical to obtain water-redispersible powders: the products of route 2 were easier to redisperse in water and their aqueous suspensions were more stable and transparent than those from route 1. SEM images of freeze-dried suspensions from redispersed RBP powders confirmed that carboxymethylation prevented irreversible agglomeration of cellulose fibrils during drying. These results suggest that carboxymethylated and mechanically disintegrated RBP in dry form is a very attractive alternative to conventional NFC aqueous suspensions as starting material for derivatization and compounding with (bio)polymers.

  • 165. Eyholzer, Christian
    et al.
    Couraça, A. Borges de
    Laboratoire de Technologie des Composites et Polymères (LTC) Ecole Polytechnique Fédérale de Lausanne.
    Duc, F.
    Laboratoire de Technologie des Composites et Polymères (LTC) Ecole Polytechnique Fédérale de Lausanne.
    Bourban, P.E.
    Laboratoire de Technologie des Composites et Polymères (LTC) Ecole Polytechnique Fédérale de Lausanne.
    Zimmerman, T.
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Tingaut, P.
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Månsson, J.A.E.
    Laboratoire de Technologie des Composites et Polymères (LTC) Ecole Polytechnique Fédérale de Lausanne.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Biocomposite hydrogels with carboxymethylated, nanofibrillated cellulose powder for replacement of the nucleus pulposus2011Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, nr 5, s. 1419-1427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Biocomposite hydrogels with carboxymethylated, nanofibrillated cellulose (c-NFC) powder were prepared by UV polymerization of N-vinyl-2-pyrrolidone with Tween 20 trimethacrylate as a crosslinking agent for replacement of the native, human nucleus pulposus (NP) in intervertebral discs. The swelling ratios and the moduli of elasticity in compression of neat and biocomposite hydrogels were evaluated in dependence of c-NFC concentration (ranging from 0 to 1.6% v/v) and degree of substitution (DS, ranging from 0 to 0.23). The viscoelastic properties in shear and the material relaxation behavior in compression were measured for neat and biocomposite hydrogels containing 0.4% v/v of fibrils (DS ranging from 0 to 0.23) and their morphologies were characterized by cryo-scanning electron microscopy (cryo-SEM). The obtained results show that the biocomposite hydrogels can successfully mimic the mechanical and swelling behavior of the NP. In addition, the presence of the c-NFC show lower strain values after cyclic compression tests and consequently create improved material relaxation properties, compared to neat hydrogels. Among the tested samples, the biocomposite hydrogel containing 0.4% v/v of c-NFC with a DS of 0.17 shows the closest behavior to native NP. Further investigation should focus on evaluation and improvement of the long-term relaxation behavior.

  • 166. Eyholzer, Christian
    et al.
    Lopez-Suevos, F
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Tingaut, P
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Zimmermann, Tanja
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Reinforcing effect of carboxymethylated nanofibrillated cellulose powder on hydroxypropyl cellulose2010Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 17, nr 4, s. 793-802Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bionanocomposites of hydroxypropyl cellulose (HPC) and nanofibrillated cellulose (NFC) were prepared by solution casting. The various NFC were in form of powders and were prepared from refined, bleached beech pulp (RBP) by mechanical disintegration, optionally combined with a pre- or post mechanical carboxymethylation. Dynamic mechanical analysis (DMA) and tensile tests were performed to compare the reinforcing effects of the NFC powders to those of their never-dried analogues. For unmodified NFC powders an inferior reinforcing potential in HPC was observed that was ascribed to severe hornification and reagglomeration of NFC. In contrast, the composites with carboxymethylated NFC showed similar behaviors, regardless of the NFC suspensions being dried or not prior to composite preparation. SEM characterization confirmed a homogeneous dispersion of dried, carboxymethylated NFC within the HPC matrix. These results clearly demonstrate that drying of carboxymethylated NFC to a powder does not decrease its reinforcing potential in (bio)nanocomposites.

  • 167.
    Eyholzer, Christian
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lopez-Suevos, Francisco
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Bordeanu, Nico
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Zimmermann, Tanja
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Structure and properties of functional cellulose fibrils-based nanocomposites2008Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 235, nr 24Artikkel i tidsskrift (Annet vitenskapelig)
  • 168.
    Eyholzer, Christian
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tingaut, P.
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Zimmermann, T.
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dispersion and reinforcing potential of carboxymethylated nanofibrillated cellulose powders modified with 1-hexanol in extruded poly(lactic acid) (PLA) composites2012Inngår i: Journal of polymers and the environment, ISSN 1566-2543, E-ISSN 1572-8919, Vol. 29, nr 4, s. 1052-1062Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bionanocomposites of poly(lactic acid) (PLA) and chemically modified, nanofibrillated cellulose (NFC) powders were prepared by extrusion, followed by injection molding. The chemically modified NFC powders were prepared by carboxymethylation and mechanical disintegration of refined, bleached beech pulp (c-NFC), and subsequent esterification with 1-hexanol (c-NFC-hex). A solvent mix was then prepared by precipitating a suspension of c-NFC-hex and acetone-dissolved PLA in ice-cold isopropanol (c-NFC-hex sm), extruded with PLA into pellets at different polymer/fiber ratios, and finally injection molded. Dynamic mechanical analysis and tensile tests were performed to study the reinforcing potential of dried and chemically modified NFC powders for PLA composite applications. The results showed a faint increase in modulus of elasticity of 10 % for composites with a loading of 7.5 % w/w of fibrils, irrespective of the type of chemically modified NFC powder. The increase in stiffness was accompanied by a slight decrease in tensile strength for all samples, as compared with neat PLA. The viscoelastic properties of the composites were essentially identical to neat PLA. The absence of a clear reinforcement of the polymer matrix was attributed to poor interactions with PLA and insufficient dispersion of the chemically modified NFC powders in the composite, as observed from scanning electron microscope images. Further explanation was found in the decrease of the thermal stability and crystallinity of the cellulose upon carboxymethylation

  • 169.
    Eyholzer, Christian
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Zimmerman, Tanja
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Water-redispersible, nanofibrillated cellulose powders for polymer reinforcement2010Konferansepaper (Fagfellevurdert)
  • 170.
    Fadel, Shaimaa M
    et al.
    Cellulose and Paper Department, National Research Center, Cairo.
    Hassan, Mohammad L
    Cellulose and Paper Department, National Research Center, Cairo.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Improving tensile strength and moisture barrier properties of gelatin using microfibrillated cellulose2013Inngår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 47, nr 16, s. 1977-1985Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microfibrillated cellulose isolated from bagasse was used to prepare novel nanocomposites using cross-linked gelatin as a biodegradable polymer matrix. Microfibrillated cellulose loadings up to 25% (weight percent) were used. The prepared nanocomposites were characterized regarding their wet and dry tensile strength, water sorption, and water vapor permeability. Nanocomposites’ surfaces were examined by scanning electron microscopy; the scanning electron microscopy images indicated homogeneous distribution of microfibrillated cellulose in the gelatin matrix. Microfibrillated cellulose improved wet and dry maximum tensile stress and modulus of cross-linked gelatin but resulted in a decrease of its strain at break. Microfibrillated cellulose did not affect the water absorption of cross-linked gelatin but significantly improved its moisture barrier property.

  • 171.
    Farid, Touaiti
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Chemical Engineering Department, Faculty of Science and Technology, University of Ghardaia.
    Herrera Vargas, Natalia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Investigation of crystalline structure of plasticized poly (lactic acid)/Banana nanofibers composites2018Inngår i: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 369, artikkel-id 012031Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polylactic acid (PLA) is a promising biodegradable candidate to replace synthetic commodity plastics in many applications. However, this polymer shows high brittleness, slow rate and lower degree of crystallization. The addition of plasticizing agents can enhance the toughness, but its effects on the crystallization behavior remain inconclusive. Therefore, this research is aiming to cast light on this area. Using differential scanning calorimetry (DSC) at a 2°C/min cooling rate, extruded neat PLA samples showed lower degree of crystallinity and thermal stability. This material shows cold crystallization upon heating and does recrystallize prior melting. These results indicate a clear instability in the crystalline state are confirmed by the crystallographic results by the X-ray diffractions (XRD) pattern and atomic force microscopic imagery. The addition of around 20 wt% of glycerol triacetate (GTA) with 1wt% of banana nanofibers (BNF) almost doubled the crystallinity. This modification is believed to occur through a dilution mechanism in order to increase crystallization rate yielding a more stable crystalline structure as shown by the XRD. However, the dynamic mechanical thermal analysis (DMTA) showed a 30 to 50% reduction in the room temperature storage modulus (stiffness) is in plasticized samples when compared to neat 100% PLA. Although these results shows the possibility to enhance the crystallization through a combination of plasticizing and nanoreinforcing effects, further studies is still needed to optimize the material formulation in order to find the best ratios to secure both a good crystallization and mechanical properties. This will definitively result in a new material that can be used for current and futuristic applications.

  • 172.
    Fatima, Nowshir
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Degradation mechanism of water contaminated automatic transmission fluid (ATF) in wet clutch system2013Konferansepaper (Fagfellevurdert)
  • 173. Fatima, Nowshir
    et al.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Wet Clutch Friction Interfaces under Water Contaminated Lubricant Conditions2016Inngår i: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 59, nr 3, s. 441-450Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The performance of wet clutches used for automatic transmissions or other applications usually includes the desired positive friction characteristics and a shudder-free torque generation. Changes in the operating variables such as the lubricant conditions influence the formation of tribofilm, friction characteristics and can alter the degradation of the friction interfaces. In this work, the friction characteristics and degradation of the paper-steel friction interfaces were monitored when a commercial fully-formulated automatic transmission fluid (ATF) was contaminated with water. It was found that water in ATF influenced the clutch stability by increasing the mean coefficient of friction (µ) and the negative friction-velocity slope. Surface studies of the post-test friction interfaces clearly indicated reduced surface porosity and permeability, increased wettability and changed elemental composition on the contacting surfaces after tested with water- contaminated ATF. Moreover, water-contaminated paper-liners’ thermal decomposition shifted to a lower temperature compared to an uncontaminated liner during thermal analyses. These results displayed faster degradation and reduced service life of the clutch friction interfaces for water contamination. The resultant surface condition can be associated with the observed unstable friction and negative friction-velocity slopes.

  • 174.
    Ferraz, Natalia
    et al.
    Uppsala University, Department of Engineering Science.
    Mihranyan, Albert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Is there a future for electrochemically assisted hemodialysis?: focus on the application of polypyrrole-nanocellulose composites2014Inngår i: Nanomedicine, ISSN 1743-5889, E-ISSN 1748-6963, Vol. 9, nr 7, s. 1095-1110Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work summarizes the various aspects of using electrochemically assisted solute removal techniques in hemodialysis with a focus on blood electrodialysis and electrochemically controlled uremic retention solute removal using polypyrrole. In particular, the feasibility of using highly porous conductive polypyrrole-Cladophora cellulose membranes for hemodialysis are overviewed as a part of our dedicated research efforts during the past 4 years. The potential benefits and the current limitations associated with using the electrochemically controlled uremic retention solute removal techniques are discussed in detail.

  • 175.
    Frisk, Nikolina
    et al.
    Luleå tekniska universitet. Centre for Biocomposites and Biomaterials Processing, Faculty of Forestry, University of Toronto, Toronto, Canada.
    Sain, Mohini
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Centre for Biocomposites and Biomaterials Processing, Faculty of Forestry, University of Toronto, Toronto, Canada.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Centre for Biocomposites and Biomaterials Processing, Faculty of Forestry, University of Toronto, Toronto, Canada.
    Nanocellulose reinforced bio-polyurethane foams as core in sandwich composite panels2017Inngår i: ICCM21 Proceedings, ICCM, International Committee on Composite Materials , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of this work was to reinforce bio-polyurethane (BPU) with cellulose nanofibers (CNF) to develop foams suitable for use as core in lightweight composite panels. The nanofibers were prepared using mechanical grinding of bleached carrot juice residue, a cheap and energy efficient process. The prepared foam properties were studied and compared to neat BPU foam properties. The results showed that the CNF reinforced foam had better mechanical properties compared to the neat bio-PU foams and the addition of cellulose nanofibers deceased the cell size and open cell content. Then the foam suitability for composite use was evaluated by manufacturing lightweight sandwich panels using vacuum infusion process with CNF reinforced BPU foam core. Kraft paper was used as a skin and epoxy resin was used as adhesive resin and the composite laminates were prepared using vacuum infusion technique. These nanofiber reinforced core materials resulted in sandwich panels with improved mechanical properties. X-ray tomography showed that the resin did not penetrate into the core but only the foam surface layer. Moreover, the results were evaluated in a material selection process by means of minimizing merit indices. A trend in the behaviour of compressive properties of the foam and flexural properties of the sandwich panels could be established. The addition of small amount of cellulose nanofibers to BPU based foams is leading to a foam which have similar properties as commercial rigid PU foams. © 2017 International Committee on Composite Materials. 

  • 176.
    Frisk, Nikolina
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sain, Mohini
    University of Toronto.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Novel Applications of Nanocellulose: Lightweight Sandwich Composites for Transportation2015Inngår i: Reference module in materials science and materials engineering / [ed] Saleem Hashmi, Amsterdam: Elsevier, 2015Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    This chapter is focusing on improvement of the mechanical properties of bio-polyurethane (PU) foam by reinforcing the pre-resin with cellulose nanofibers (CNF). The prepared foam performance was evaluated by manufacturing lightweight sandwich panels using vacuum infusion process with CNF-reinforced bio-PU foam core. Cellulose fiber network (kraft paper) was used as a skin and epoxy resin was used as adhesive resin. The sandwich was tested and compared to a non-reinforced PU foam core sandwich in terms of compressive, flexural, and structural properties. The results showed that the CNF-reinforced foam resulted in sandwich panel with improved mechanical properties, and to foam with smaller cell size and lower open cell content. Moreover, the results were evaluated in a material selection process by means of minimizing merit indices. A trend in the behavior of compressive properties of the foam and flexural properties of the sandwich panels could be established. Overall, the results indicated that the mechanical properties of bio-PU foam was improved by reinforcing the pre-resin with small amounts of wet carrot CNF.

    Ultimately, this work shows a positive trend suggesting CNF-reinforced bio-PU foam has a great potential for use in commercialized products or structural components in future constructions.

  • 177.
    García Vogel, Andres
    et al.
    Luleå tekniska universitet. Fiber and Particle Engineering, University of Oulu, Finland.
    Hooshmand, Saleh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fiber and Particle Engineering, University of Oulu, Finland.
    All-cellulose composites based on wet-spun cellulose fibers reinforced with cellulose nanocrystals and halloysite nanoclay2017Inngår i: ICCM21 Proceedings, ICCM, International Committee on Composite Materials , 2017, artikkel-id 3751Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of the study was to develop biobased and lightweight composites with unidirectional cellulose fibers without a matrix polymer, so called all-cellulose composites with excellent mechanical properties. Continuous cellulose fibers are currently gaining interest for composite applications and if these fibers can be welded together without using a polymer resin it would result in an environmental friendly composite material. The regenerated fibers were prepared using wet spinning of DMAc/LiCl dissolved cellulose where cellulose nanocrystals (CNC) and halloysitenanotubes (HNT) were used as reinforcements. The loading of the nanomaterials into the dissolved cellulose was between 2 to 20 %. The preliminary results showed that the addition of both CNC and HNT improved the mechanical properties of the regenerated cellulose fibers. It was also seen that low concentration of the nanomaterials was more effective reinforcement than high concentration. Also, the HNT showed slightly better improvement compared to the CNC). The spun nanocomposite fibers were directly wound to a roll after the wet spinning, compression molded to compositesheet and dried. The all-cellulose composites mechanical properties as well as microstructure including nanomaterials orientation in the spun fibers were studied and composites mechanical properties are compared with theoretical models. 

  • 178.
    Geng, Shiyu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Cellulose-based Nanocomposites – The Relationship between Structure and Properties2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Nanocellulose materials extracted from various types of biomass have recently attracted significant attention. Due to their remarkable mechanical properties, large surface area and biodegradability, they can be promising reinforcements in nanocomposites. Cellulose-based nanocomposites constitutive of nanocellulose reinforcements and biodegradable polymer matrices have great potential to be used in environmentally friendly applications to replace fossil-based materials. However, the challenge of controlling their nanoscale structure, especially achieving good dispersion of nanocellulose in hydrophobic polymer matrices, still poses significant obstacles to producing high-performance nanocomposites. Therefore, this thesis reports several methods for structural modification of cellulose-based nanocomposites toward the objectives of improving the dispersion of nanocellulose and enhancing the properties of the nanocomposites. The methods include in situ emulsion polymerization in the presence of nanocellulose, crosslinking of polymer matrix, grafting of polymer brushes to nanocellulose and drawing of nanocomposites to obtain aligned structures. The resulting mechanical, thermal and other related properties are investigated, and the relationship between structure and properties of the nanocomposites are discussed.

    To address the challenge of achieving good dispersion of nanocellulose in hydrophobic matrices, in situ emulsion polymerization of vinyl acetate monomer in the presence of cellulose nanocrystals has been developed. Microscopy results show that the in situ method improves the compatibility between nanocellulose and hydrophobic polymers, which consequently improves the dispersion of nanocellulose in the nanocomposites. Compared with direct mixed polymer/nanocellulose composites, the in situ synthesized nanocomposites exhibit higher stiffness and strength arising from their superior interphase volume, which is confirmed theoretically and experimentally. Crosslinking of partially hydrolyzed poly(vinyl acetate) by borate additives under different pH conditions has been studied to further enhance mechanical properties of the nanocomposites. Moreover, the “grafting to” modification method also helps to overcome this challenge. It is revealed that poly(ethylene glycol)-grafted cellulose nanofibers disperse better in poly(lactic acid) matrix than unmodified cellulose nanofibers, which is attributed to the improved compatibility and steric effect provided by the covalently grafted poly(ethylene glycol) brushes.

    To substantially enhance the unidirectional mechanical properties of cellulose-based nanocomposites, a highly aligned structure in the materials is obtained through the drawing process. Drawing conditions including temperature, speed and draw ratio show considerable effects on the mechanical and thermal properties of the nanocomposites. Furthermore, the aligned nanocomposites consisting of poly(lactic acid) matrix and ultra-low weight fraction of poly(ethylene glycol)-grafted cellulose nanofibers demonstrate competitive strength, superb toughness and interesting optical behaviors compared with other aligned nanocellulose-based materials reported in the literature, indicating their potential to be further developed for large-scale environmentally friendly applications.

  • 179.
    Geng, Shiyu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    High-strength, High-toughness Aligned Polymer-based Nanocomposite Reinforced with Ultra-low Weight Fraction of Functionalized NanocelluloseManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Multifunctional lightweight, flexible, yet strong polymer-based nanocomposites are highly desired for specific applications. However, the control of orientation and dispersion of reinforcing nanoparticles and the optimization of the interfacial interaction still pose substantial challenges in nanocellulose-reinforced polymer composites. In this study, poly(ethylene glycol)-grafted nanocellulose fibers (TOCNF-g-PEG) has demonstrated much better dispersion in a poly(lactic acid) (PLA) matrix as compared to unmodified nanocellulose fibers. Through a uniaxial drawing method, aligned PLA/nanocellulose nanocomposites with high strength, high toughness, and unique optical behavior are obtained. With the incorporation of only 0.1 wt% of TOCNF-g-PEG in PLA, the ultimate strength of the nanocomposite reaches 343 MPa, which is significantly higher than that of other aligned PLA-based nanocomposites reported previously. Compared with the aligned nanocomposite reinforced with unmodified nanocellulose, the ultimate strength and toughness are enhanced by 39% and 70%, respectively. Moreover, the aligned nanocomposite film is highly transparent and possesses an anisotropic light scattering effect, revealing its significant potential for optical applications.

  • 180.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Haque, MD Minhaz Ul
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Crosslinked polyvinyl acetate (PVAc) reinforced with cellulose nanocrystals (CNC) – structure and mechanical properties2016Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 126, s. 35-42Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structure of cellulose-based nanocomposites significantly influences their final mechanical properties. However, obtaining a good dispersion of hydrophilic nanocellulose materials in a hydrophobic polymer matrix is challenging. In this study, two unique methods were developed to improve the dispersion of cellulose nanocrystals (CNC) in a poly(vinyl acetate) (PVAc) matrix. One method was the crosslinking of PVAc by sodium tetraborate (borax), which is expected to prevent agglomeration of CNCs during the drying process, and the other method was the in-situ polymerization of vinyl acetate in the presence of CNCs to generate good compatibility between CNC and PVAc. The results showed that the crosslinking degree of PVAc could be varied by tuning the pH. The atomic force microscopy images illustrate that after drying, the in-situ polymerized PVAc/CNC composite was much better dispersed than the composite produced using mechanical mixing. The mechanical and thermo-mechanical characterizations indicate that the in-situ nanocomposite with 10 wt% of CNC had a higher strength and storage modulus compared with the mixed composite with the same CNC concentration. Further investigations of the restriction effect caused by the crosslinker are required.

  • 181.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Haque, MD Minhaz Ul
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Crosslinked polyvinyl acetate reinforced with cellulose nanocrystals –: Characterization of structure and mechanical properties2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The structure of cellulose based nanocomposites influences their final mechanical properties significantly. Obtaining good dispersion of hydrophilic nanocellulose materials in hydrophobic polymer matrix is challenging. Here two unique methods were developed to improve the dispersion of cellulose nanocrystals (CNC) in polyvinyl acetate (PVAc) matrix. One is in-situ polymerization of vinyl acetate in the presence of CNCs, and the other one is crosslinking of PVAc by sodium tetraborate (Borax), which restricts the movement of CNCs during the drying process. The results from atomic force microscopy (AFM) show that the in-situ CNC/PVAc emulsion has much better dispersion than the one produced by stirring. Moreover, the mechanical characterization indicates that the in-situ composite with 10 wt% CNC has higher strength compared to the stirred composite with the same CNC concentration. The mechanical properties of crosslinked PVAc materials can be varied by changing the pH and may be attributed to differences of the crosslinking degree. Further investigations of the restriction effect caused by borax are needed.

  • 182.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Harila, Maria
    Luleå tekniska universitet.
    Yao, Kun
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Zhou, Qi
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Grafting polyethylene glycol on nanocellulose toward biodegradable polymer nanocomposites2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we investigated the effects of grafting polyethylene glycol on nanocellulose on microstructure, mechanical properties and thermal behaviors of the polylactic acid/nanocellulose composites.

  • 183.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Noël, Maxime
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Liu, Peng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Cellulose-based nanocomposites with outstanding dispersion produced by in-situ polymerization2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cellulose-based nanocomposites are promising materials to replace the fossil-based polymers since they are biodegradable and produced from renewable resources. However, achieving good dispersion of nanocellulose in the matrix is one of the main obstacles because nanomaterials tend to form aggregates and lose their merits. In this study we developed an in-situ polymerization method to produce cellulose nanocrystals reinforced polyvinyl acetate, and the method of direct mechanical mixing was used as reference. The stability of in-situ and mixed nanocomposite aqueous dispersions was investigated by zeta potential measurements, and the results show that both of them were electrostatic stable at pH 4. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the dispersion of cellulose nanocrystals in the in-situ and mixed nanocomposites after drying, and better dispersion could be seen in the in-situ samples compared with the mixed ones. Tensile testing showed that the in-situ nanocomposites with same cellulose content had higher strength and longer elongation at break compared to the mixed nanocomposites. Furthermore, crosslinking the cellulose and partially hydrolyzed polyvinyl acetate with sodium tetraborate was also performed to further improved the reinforcing efficiency. The results from Raman spectroscopy illustrate that the heavy atoms (CC and CO) in cellulose experienced more stretching in the crosslinked nanocomposites, and the tensile testing indicated the elastic modulus and ultimate strength of them were increased significantly than those without crosslinking.

  • 184.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Noël, Maxime
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Liu, Peng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Single-step method for producing cellulose based nanocomposites with outstanding dispersion2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cellulose nanomaterials are promising as reinforcement in composites, which is attributed to high mechanical properties, generating large interfacial area and biodegradable ability, etc. However, obtaining good dispersion is a main challenge of large-scale industrial applications since nanomaterials tend to form aggregates and lose their merits. In this study we developed a single-step method that is in-situ polymerization to produce cellulose nanocrystals reinforced polyvinyl acetate with good dispersion. Compared to normal composites prepared by direct mechanical mixing, better dispersion of cellulose nanocrystals by using in-situ polymerization has been confirmed by atomic force microscopy. Mechanical testing shown that the in-situ nanocomposites with same cellulose content had higher strength and longer elongation at break compared to direct mixed composites. Moreover, crosslinks between cellulose and partially hydrolysed polyvinyl acetate could be formed by tetrahydroborate ions in aqueous dispersion, which further improved the reinforcing efficiency. The cellulose based nanocomposites produced by in-situ polymerization are potential materials to replace fossil based polymers used in packaging and coating applications.

  • 185.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Shah, Faiz Ullah
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Liu, Peng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antzutkin, Oleg
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Plasticizing and crosslinking effects of borate additives on the structure and properties of poly(vinyl acetate)2017Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, nr 13, s. 7483-7491Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As an environmentally friendly, low-cost and widely used polymer, poly(vinyl acetate) (PVAc) is worth modifying to achieve better properties. Here, we report on the influence of borate additives on the structure and properties of partially hydrolysed PVAc. In addition to the general crosslinking function of borate additives, an extraordinary plasticizing effect was found. By controlling the pH from 4 to 11 during sample preparation, the plasticizing and crosslinking effects can be shifted. In alkaline conditions, the degree of crosslinking in the PVAc/borate sample is increased; however, this increase declines gradually with an increase in the borate additive content, which impacts the morphology of the PVAc latex particles, as well as the mechanical and thermal properties of the PVAc/borate films. In contrast, in acidic conditions, the PVAc/borate films are plasticized by borate additives; thus, their ultimate mechanical strength, elastic moduli and thermal stabilities decrease, while the water diffusivities increase.

  • 186.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wei, Jiayuan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Noël, Maxime
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. 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-nanocomposites2018Inngår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, nr 25, s. 11797-11807Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 187.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wei, Jiayuan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Jonasson, Simon
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hedlund, Jonas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Multifunctional Carbon Aerogels with Hierarchical Anisotropic Structure Derived from Lignin and Cellulose Nanofibers for CO2 Capture and Energy Storage2020Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In current times, CO2 capture and light-weight energy storage are receiving significant attention and will be vital functions in next-generation materials. Porous carbonaceous materials have great potential in these areas, whereas most of the developed carbon materials still have significant limitations, such as non-renewable resources, complex and costly processing or the absence of tailorable structure. In this study, a new strategy is developed for using the currently under-utilized lignin and cellulose nanofibers, which can be extracted from renewable resources to produce high-performance multifunctional carbon aerogels with a tailorable, anisotropic pore structure. Both the macro- and microstructure of the carbon aerogels can be simultaneously controlled by discreetly tuning the weight ratio of lignin to cellulose nanofibers in the carbon aerogel precursors, which considerably influences their final porosity and surface area. The designed carbon aerogels demonstrate excellent performance in both CO2 capture and capacitive energy storage, and the best results exhibit a CO2 adsorption capacity of 5.23 mmol g-1 at 273 K and 100 kPa, and a specific electrical double layer capacitance of 124 F g-1 at a current density of 0.2 A g-1, indicating that they have great future potential in the relevant applications.

  • 188.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yao, Kun
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Harila, Maria
    Luleå tekniska universitet.
    Noël, Maxime
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Zhou, Qi
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aligned biodegradable cellulose-reinforced nanocomposites with high strength and toughness2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cellulose, as the most abundant component in wood, has attracted a lot of attention for utilizing it in environmentally-friendly applications to replace the fossil-based materials. Nanocellulose materials with high stiffness and strength, large surface area and biodegradability, are promising reinforcement in polymers. However, the energy consumption of nano-scale isolation of cellulose and the dispersion of nanocellulose materials in the polymers are still challenging for obtaining low-cost and ultra-strong nanocomposites. To overcome these, we focus on investigating the aligned nanocomposites reinforced by a very low cellulose nanofibers (CNF) content (0.1 wt%), and grafting polyethylene glycol (PEG) on CNF was performed to improve the dispersion of them. We found that the alignment can improve mechanical properties of the polylactic acid (PLA)/CNF composites dramatically. With a draw ratio of 8, the strength of the aligned composite reached 320 MPa and the toughness was 30 times enhanced compared to the isotropic material. Much better dispersion of the CNF grafted with PEG in PLA matrix was confirmed by scanning electron microscopy (SEM) compared to the ungrafted CNF, and further supported by the mechanical testing results. Furthermore, the aligned nanocomposites exhibited light scattering behavior indicating they have the potential to be used in optical applications.

  • 189.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yao, Kun
    Royal Institute of Technology, School of Biotechnology, Stockholm.
    Harila, Maria
    Luleå tekniska universitet.
    Zhou, Qi
    Royal Institute of Technology, School of Biotechnology, Stockholm.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu, Finland.
    Grafting polyethylene glycol on nanocellulose toward biodegradable polymer nanocomposites2017Inngår i: ICCM21 Proceedings, ICCM, International Committee on Composite Materials , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The reinforcing effect of a small amount of nanocellulose materials on biodegradable and polymer-based nanocomposites remains challenging because of the poor dispersion of the nanomaterials and inefficient interaction between the nanocellulose and the polymer matrix. To improve this, we grafted polyethylene glycol (PEG) on nanocellulose and produced composites of 0.1 wt% nanocellulose materials and polylactic acid (PLA) matrix. Here, two types of PEG grafted nanocellulose including TEMPO-oxidized cellulose nanocrystals (TOCNCs) and cellulose nanofibers (TOCNFs), with different lengths and diameters were used as reinforcements, respectively. We investigated the effects of grafting PEG on microstructure, mechanical properties and thermal behaviors of the PLA/nanocellulose composites. It is found that the PEG grafted nanocellulose dispersed better compared to the unmodified nanocellulose in the PLA matrix, and provides higher reinforcing effect that improves the elastic modulus of the nanocomposites compared to the composites with unmodified nanocellulose and ungrafted PEG. However, the glass transition temperature of the nanocomposites was not improved by grafting PEG significantly. We also found that the nanocomposites reinforced by TOCNF exhibited enhanced mechanical and thermal properties compared to those with TOCNCs, which is caused by the higher aspect ratio of the TOCNFs.

  • 190.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yao, Kun
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Zhou, Qi
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aligned polylactic acid based nanocomposite reinforced using a tiny amount of functionalized cellulose nanofibers2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Due to the challenges of the cost of nanocellulose materials and the dispersion of them in polymer matrix, small amount and well-dispersed nanocellulose materials are desired as reinforcement to achieve environmentally-friendly nanocomposites with high performance. In this study, an aligned polylactic acid (PLA) based nanocomposite reinforced by 0.1 wt% of functionalized cellulose nanofibers (CNFs) was investigated. The CNFs were covalently grafted by polyethylene glycol (PEG), which improves the dispersion of the CNFs in the PLA significantly compared to the native CNFs. The improved dispersion was examined by scanning electron microscopy (SEM), polarized optical microscopy (POM) and mechanical testing. Furthermore, it was found that the alignment can improve mechanical properties of the nanocomposite dramatically. The strength of the aligned nanocomposite reaches 343 MPa with a draw ratio of 8, meanwhile the toughness is about 30 times enhanced compared to the isotropic material. The aligned nanocomposite also exhibits light scattering behavior, indicating that it has the potential to be used in optical applications.

  • 191.
    Geng, Shiyu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Yao, Kun
    Division of Glycoscience, Department of Chemistry, KTH Royal Institute of Technology.
    Zhou, Qi
    Division of Glycoscience, Department of Chemistry, KTH Royal Institute of Technology.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu.
    High-strength, High-toughness Aligned Polymer-based Nanocomposite Reinforced with Ultra-low Weight Fraction of Functionalized Nanocellulose2018Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, nr 10, s. 4075-4083Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multifunctional lightweight, flexible, yet strong polymer-based nanocomposites are highly desired for specific applications. However, the control of orientation and dispersion of reinforcing nanoparticles and the optimization of the interfacial interaction still pose substantial challenges in nanocellulose-reinforced polymer composites. In this study, poly(ethylene glycol)-grafted nanocellulose fibers (TOCNF-g-PEG) has demonstrated much better dispersion in a poly(lactic acid) (PLA) matrix as compared to unmodified nanocellulose fibers. Through a uniaxial drawing method, aligned PLA/nanocellulose nanocomposites with high strength, high toughness, and unique optical behavior are obtained. With the incorporation of only 0.1 wt% of TOCNF-g-PEG in PLA, the ultimate strength of the nanocomposite reaches 343 MPa, which is significantly higher than that of other aligned PLA-based nanocomposites reported previously. Compared with the aligned nanocomposite reinforced with unmodified nanocellulose, the ultimate strength and toughness are enhanced by 39% and 70%, respectively. Moreover, the aligned nanocomposite film is highly transparent and possesses an anisotropic light scattering effect, revealing its significant potential for optical applications.

  • 192.
    Ghafari, Robab
    et al.
    Department of Wood and Paper Sciences and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
    Jonoobi, Mehdi
    Department of Wood and Paper Sciences and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
    Mohammadi Amirabad, Leila
    Marquette University, School of Dentistry, Milwaukee, WI, USA.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Taheri, Ahmad Reza
    Department of Plastic Surgery, Imam Khomeini Hospital, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
    Fabrication and characterization of novel bilayer scaffold from nanocellulose based aerogel for skin tissue engineering applications2019Inngår i: International Journal of Biological Macromolecules, ISSN 0141-8130, E-ISSN 1879-0003, Vol. 136, s. 796-803Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to fabricate a novel bilayer scaffold containing cellulose nanofiber/poly (vinyl) alcohol (CNF/PVA) to evaluate its potential use in skin tissue engineering. Here, the scaffolds were fabricated using a novel one-step freeze-drying technique with two different concentrations of the aforementioned polymers. FE-SEM analysis indicated that the fabricated scaffolds had interconnected pores with two defined pore size in each layer of the bilayer scaffolds that can recapitulate the two layers of the dermis and epidermis of the skin. Lower concentration of polymers causes higher porosity with larger pore size and increased water uptake and decreased mechanical strength. FTIR proved the presence of functional groups and strong hydrogen bonding between the molecules of CNF/PVA and the efficient crosslinking. The MTT assay showed that these nanofibrous scaffolds meet the requirement as a biocompatible material for skin repair. Here, for the first time, we fabricated bilayer scaffold using a novel one-step freeze-drying technique only by controlling the polymer concentration with spending less time and energy.

  • 193.
    Goetz, Lee
    et al.
    Institute of Paper Science and Technology, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta.
    Folston, Marcus
    Institute of Paper Science and Technology, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ragauskas, Arthur J.
    Institute of Paper Science and Technology, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta.
    Poly(methyl vinyl ether-co-maleic acid)-Polyethylene glycol nanocomposites cross-linked in situ with cellulose nanowhiskers2010Inngår i: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, nr 10, s. 2660-2666Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanocomposites were developed by cross-linking cellulose nanowhiskers with poly(methyl vinyl ether-co-maleic acid) and polyethylene glycol. Nuclear magnetic resonance (NMR) studies showed cross-linking occurs between the matrix and cellulose nanowhiskers via an esterification reaction. Proton NMR T 2 relaxation experiments provided information on the mobility of the polymer chains within the matrix, which can be related to the structure of the cross-linked nanocomposite. The nanocomposite was found to consist of mobile chain portions between cross-linked junction points and immobilized chain segments near or at those junction points, whose relative fraction increased upon further incorporation of cellulose nanowhiskers. Atomic force microscopy images showed a homogeneous dispersion of nanowhiskers in the matrix even at high nanowhisker content, which can be attributed to cross-linking of the nanowhiskers in the matrix. Relative humidity conditions were found to affect the mechanical properties of the composites negatively while the nanowhiskers content had a positive effect. It is expected that the cross-links between the matrix and the cellulose nanowhiskers trap the nanowhiskers in the cross-linked network, preventing nanowhisker aggregation subsequently producing cellulose nanocomposites with unique mechanical behaviors. The results show that in situ cross-linking of cellulose nanowhiskers with a matrix polymer is a promising route to obtain nanocomposites with well dispersed nanowhiskers, tailored nanostructure, and mechanical performance

  • 194.
    Goetz, Lee
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Jalvo, Bianca
    Department of Chemical Engineering, University of Alcalá.
    Rosal, Roberto
    Department of Chemical Engineering, University of Alcalá.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Superhydrophilic anti-fouling electrospun cellulose acetate membranes coated with chitin nanocrystals for water filtration2016Inngår i: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 510, s. 238-248Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrospun cellulose acetate (CA) random mats were prepared and surface coated with chitin nanocrystals (ChNC) to obtain water filtration membranes with tailored surface characteristics. Chitin nanocrystals self-assembled on the surface of CA fibers into homogenous nanostructured networks during drying that stabilized via hydrogen bonding and formed webbed film-structures at the junctions of the electrospun fibers. Coating of CA random mats using 5% chitin nanocrystals increased the strength by 131% and stiffness by 340% accompanied by a decrease in strain. The flux through these membranes was as high as 14217 L m−2 h−1 at 0.5 bar. The chitin nanocrystal surface coating significantly impacted the surface properties of the membranes, producing a superhydrophilic membrane (contact angle 0°) from the original hydrophobic CA mats (contact angle 132°). The coated membranes also showed significant reduction in biofouling and biofilm formation as well as demonstrated improved resistance to fouling with bovine serum albumin and humic acid fouling solutions. The current approach opens up an easy, environmental friendly and efficient route to produce highly hydrophilic membranes with high water flux and low fouling for microfiltration water purification process wash water from food industry for biological contaminants.

  • 195.
    Goetz, Lee
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Karim, Zoheb
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effect of micropatterned cellulose acetate membranes impregnated with cellulose and chitin nanocrystals on water filtration membrane behavior2016Manuskript (preprint) (Annet vitenskapelig)
  • 196.
    Goetz, Lee
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gatenholm, Paul
    Chalmers University of Technology.
    Ragauskas, Art
    Georgia Institute of Technology.
    A novel nanocomposite film prepared from crosslinked cellulosic whiskers2009Inngår i: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 75, nr 1, s. 85-89Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cellulose whiskers are increasingly being used as a reinforcing phase in polymer systems and their use is a growing area of importance in bionanocomposite research. Although the reinforcing effect of cellulose whiskers has been studied in various polymers, the impact of crosslinking cellulose whiskers has not been explored so far. This work deals with the development of novel cellulose nanocomposites, wherein the cellulose nanowhiskers are crosslinked with poly(methyl vinyl ether-co-maleic acid) and poly(ethylene glycol). The morphology of the nanocomposite was studied using atomic force microscopy (AFM), which revealed a network structure embedded in a continuous phase. The water sorption studies demonstrated that the crosslinked nanocomposites are capable of absorbing up to ~ 900% water and have potential to be used as hydrogels.

  • 197.
    Goetz, Lee
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ragauskas, Arthur J.
    Thermal gravimetric analysis of in-situ crosslinked nanocellulose whiskers - poly(methyl vinyl ether-co-maleic acid) - polyethylene glycol2011Inngår i: TAPPI Journal, ISSN 0734-1415, Vol. 10, nr 4, s. 29-33Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal stability and decomposition of in-situ crosslinked nanocellulose whiskers – poly(methyl vinyl ether-co-maleic acid) – polyethylene glycol formulations (PMVEMA-PEG), (25%, 50%, and 75% whiskers) – were investigated using thermal gravimetric analysis (TGA) methods. The thermal degradation behavior of the films varied according to the percent cellulose whiskers in each formulation. The presence of cellulose whiskers increased the thermal stability of the PMVEMA-PEG matrix. Application: It is possible to develop novel material properties by cross-linking cellulose whiskers in which the final physical properties are derived from the cross-linking reagents and cross-linking density. This study examines the thermal properties of cross-linking sulfuric acid derived cellulose whiskers with PMVEMA-PEG, which will be a key property as these tunable hydrogels are utilized for value-added packaging applications.

  • 198.
    Goetz, Lee
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Naseri, Narges
    Department of Materials and Environmental Chemistry, Stockholm University.
    Nair, Santhosh S.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Karim, Zoheb
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials and Environmental Chemistry, Stockholm University.
    All cellulose electrospun water purification membranes nanotextured using cellulose nanocrystals2018Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, nr 5, s. 3011-3023Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cellulose acetate (CA) fibers were electrospun on a mesh template to create specific surface and pore structures for membrane applications. The mesh template CA fiber mats were impregnated with cellulose nanocrystals at varying weight percentages. The membranes showed nanotextured surfaces and improved mechanical properties post impregnation. More importantly, the hydrophilicity of the original CA fibers was increased from a hydrophobic contact angle of 102°–0° thereby creating an anti-fouling membrane surface structure. The membranes showed rejection of 20–56% for particles of 0.5–2.0 μm, indicating potential of these membranes in rejecting microorganisms from water. Furthermore, high rejection of dyes (80–99%) by adsorption and potential application as highly functional affinity membranes was demonstrated. These membranes can therefore be utilized as all-cellulose, green, scalable and low cost high flux membranes (> 20,000 LMH) for water cleaning applications in food industry where microorganisms and charged contaminants are to be removed.

  • 199.
    Goetz, Lee
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ragauskas, Art J.
    Georgia Institute of Technology.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tying cellulose whiskers together2008Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 235, nr 229Artikkel i tidsskrift (Annet vitenskapelig)
  • 200. Gong, Guan
    et al.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Strong aqueous gels of cellulose nanofibers and nanowhiskers isolated from softwood flour2011Inngår i: TAPPI Journal, ISSN 0734-1415, Vol. 10, nr 2, s. 42565-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two nanocelluloses (cellulose nanofibers [CNF] and nanowhiskers [CNW]) were extracted from softwood flour using chemical refining followed either by mechanical fibrillation or acid hydrolysis. The CNF slurry formed an opaque gel that exhibited highly coiled and entangled long fibers with widths between 10 and 20 nm when studied using atomic force microscopy (AFM). The aqueous suspension of the CNW formed a transparent gel with unique morphology of rigid and uniform, whiskerlike structures with widths as low as 1.5-3 nm and lengths in micrometer levels. The viscoelastic properties of these hydrogels with solids content of 0.2 wt% were measured using dynamic rheology experiments. The elastic modulus (G') and viscous modulus (G '') were frequency independent in the low-frequency region. Furthermore, G' was almost 10-fold higher than G '', showing a typical elastic gel behavior. The lower crystallinity obtained from X-ray analysis indicated that the unique structure of CNW from wood could be attributed to the native cellulose being partly dissolved and regenerated during acid hydrolysis

1234567 151 - 200 of 757
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf