| 1. |
- Aitomäki, Yvonne, et al.
(författare)
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Impregnation of cellulose nanofibre networks with a thermoplastic polymer
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Bozic, Mojca, et al.
(författare)
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Enzymatic phosphorylation of cellulose nanofibers to new highly-ions adsorbing, flame-retardant and hydroxyapatite-growth induced natural nanoparticles
- 2014
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 21:4, s. 2713-2726
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Tidskriftsartikel (refereegranskat)abstract
- This study confirms the enzyme-mediated phosphorylation of cellulose nanofibers (CNF) by using hexokinase and adenosine-5’-triphosphate (ATP) in the presence of Mg-ions, resulting in a phosphate group’s creation predominantly at C-6-O positioned hydroxyl groups of cellulose monomer rings. A proof-of-concept is provided using 12C CPMAS, 31P MAS NMR, ATR-FTIR and XPS analyzing methods. The degree of substitution is determined for the first time by ATR-FTIR spectroscopy being in a correlation with XPS and potentiometric titration results. From the thermal degradation measurements using TGA, the C-6-O phosphorylation was found to noticeably prevent the CNF derivatives from weight loss in the pyrolysis process, thus, providing them flame-resistance functionality. Furthermore, phosphorylation significantly enhanced adsorption capacity of Fe3+ ions making them interesting for fabrication of biobased filters and membranes. Finally, the biomimetic growth of Ca-P crystals (hydroxyapatite) in simulated body fluid was characterized by SEM and showing further practicability for biomedical materials.
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| 3. |
- Colic, Miodrag, et al.
(författare)
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Cytocompatibility and immunomodulatory properties of wood based nanofibrillated cellulose
- 2015
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 22:1, s. 763-778
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibrils (CNFs), unique and promising natural materials have gained significant attention recently for biomedical applications, due to their special biomechanical characteristics, surface chemistry, good biocompatibility and low toxicity. However, their long bio-persistence within organisms may provoke chronic immune reactions and this aspect of CNFs has not been studied to date. Therefore, the aim of this work was to examine and compare the biocompatibility and immunomodulatory properties of CNFs in vitro. CNFs (diameters of 10-70nm; lengths of a few microns) were prepared from Norway spruce (Picea abies) by mechanical fibrillation and high pressure homogenisation. L929 cells, rat thymocytes or human peripheral blood mononuclear cells (PBMNCs) were cultivated with CNFs. None of the six concentrations of CNFs (31.25µg/ml – 1mg/ml) induced cytotoxicity and oxidative stress in the L929 cells, nor induced necrosis and apoptosis of the thymocytes and PBMNCs. Higher concentrations (250µg/ml – 1mg/ml) slightly inhibited the metabolic activities of the L929 cells as a consequence of inhibited proliferation. The same concentrations of CNFs suppressed the proliferation of PBMNCs to phytohemaglutinine, a T-cell mitogen, and the process was followed by down-regulation of interleukin-2 (IL-2) and interferon-γ (IFN-γ) production. The highest concentration of CNFs inhibited IL-17A but increased IL-10 and IL-6 production. The secretions of the inflammatory cytokines, IL-1β and the tumor necrosis factor-α (TNF-α) as well as Th2 cytokine (IL-4), remained unaltered. In conclusion, the results suggest that these CNFs are biocompatible, non-inflammatory and non-immunogenic nanomaterial. Higher concentrations seem to be tollerogenic to the immune system, a characteristic very desirable for implantable biomaterials.
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| 4. |
- Deepa, B., et al.
(författare)
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Utilization of various lignocellulosic biomass for the production of nanocellulose : a comparative study
- 2015
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 22:2, s. 1075-1090
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Tidskriftsartikel (refereegranskat)abstract
- Nanocellulose was successfully extracted from five different lignocellulosic biomass sources viz. banana rachis, sisal, kapok, pineapple leaf and coir using a combination of chemical treatments such as alkaline treatment, bleaching and acid hydrolysis. The shape, size and surface properties of the nanocellulose generally depend on the source and hydrolysis conditions. A comparative study of the fundamental properties of raw material, bleached and nanocellulose was carried out by means of Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, birefringence, X-ray diffraction, inverse gas chromatography and thermogravimetric analysis. Through the characterization of the nanocellulose obtained from different sources, the isolated nanocellulose showed an average diameter in the range of 10–25 nm, high crystallinity, high thermal stability and a great potential to be used with acid coupling agents due to a predominantly basic surface. This work provides an insight into the effective utilization of a variety of plant biomass as a potential source for nanocellulose extraction.
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| 5. |
- Deepalakshmi, P, et al.
(författare)
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Advances in elastomers : Their composites and nanocomposites: State of art, new challenges and opportunities
- 2013
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Ingår i: Advances in elastomers II. - Berlin : Encyclopedia of Global Archaeology/Springer Verlag. - 9783642209277 - 9783642209284 ; , s. 1-9
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Bokkapitel (refereegranskat)abstract
- The field of elastomers, their composites and nanocomposites has gained a lot of interest in recent years. These composite materials have great significance both from the fundamental and application point of view. Since this field is growing at a faster rate, it is always necessary to address the structure, properties and applicability of such materials. The present chapter gives a brief account on various elastomer systems, their composites and nanocomposites. Various topics such as elastomer based macrocomposites, nanocomposites, interphase modification, compatiblisation of rubber based nanocomposites, fully green elastomer nanocomposites, elastomeric micro and nanocomposites for tyre applications, elastomer based bionanocomposites, bio-medical applications of elastomeric composites and nanocomposites have been very briefly discussed. Finally the applications, new challenges and opportunities of these composites and nanocomposites are also discussed.
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| 6. |
- Dobryden, Illia
(författare)
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Surface characterization and force measurements applied to industrial materials with atomic force microscopy
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis focuses on the application of force measurements with atomic force microscopy (AFM) on materials with a few surface contacts/asperities and chemically modified surfaces. The technique allows measurements of ultra-small intermolecular and surface forces, down to the piconewton level. The force measurements between surfaces of well-defined geometry are often used to measure and model the interaction between different systems of charged and neutral surfaces in various environments. However, detailed knowledge of the contacting surface profile geometry and surface properties is required to model the fundamental forces involved in the interaction. The preparation of such well-defined and idealized surfaces is often time consuming and the surfaces may not possess the behavior and properties of a source material in real processes, such as in industry. Moreover, external factors such as magnetic fields, ionic strengths and pH-values in a solution, may further complicate the evaluation. Hence, it is desirable to explore and develop techniques for trustable measurements of forces between “real” surfaces. These are often a complex composition of various force interactions and multiple surface contacts.The AFM probe technique was explored to measure force interactions between “real” particle surfaces. The work shows the applicability of the AFM technique to study the interaction forces despite the forecasted difficulties with the roughness of the particles.A technique to measure the adhesion and work of adhesion from AFM force curves was implemented and used. The thermal tune method was implemented in our commercial NT-MDT microscope to determine cantilever spring constants. The force interactions between natural microsize (m-s) magnetite particles and synthetic nanosize (n-s) magnetite particles were studied in calcium solution with concentrations of 1, 10, 100 mM and at pH values 4, 6 and 10. The changes in force interactions, due to variations in calcium concentration and pH were investigated. The adhesion force change with the concentration and pH was similar for m-s/m-s and m-s/n-s systems, and the adhesion force increased with the concentration at pH 6, except for the highest calcium concentration of 100 mM at pH 10. It was found that the magnetite surface modification could appear at the highest calcium concentration at pH 10. Moreover, the thesis contains preliminary results of the force interaction study between natural and synthetic bentonite-magnetite particles in calcium solution with concentrations of 1, 10 and 100 mM at pH 6.The influence of roughness on the calculation of contact mechanics parameters were studied with AFM and Vertical Scanning Interferometry (VSI). This is important for future development of a model to describe and characterize the force interaction between samples with multiple surface contacts. It was found that the optical artifacts, induced by VSI, have a large influence on all the roughness parameters calculated on the calibration grids, which represent extreme surface topographies.
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| 7. |
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| 8. |
- Esmaeili, Chakavak, et al.
(författare)
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Synergy Effect of Nanocrystalline Cellulose for the Biosensing Detection of Glucose
- 2015
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 15:10, s. 24681-24697
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Tidskriftsartikel (refereegranskat)abstract
- 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%.
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| 9. |
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| 10. |
- Fatima, Nowshir, et al.
(författare)
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Wet Clutch Friction Interfaces under Water Contaminated Lubricant Conditions
- 2016
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 59:3, s. 441-450
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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