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  • 1.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jonoobi, Mehdi
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Impregnation of cellulose nanofibre networks with a thermoplastic polymer2013Conference paper (Other academic)
    Abstract [en]

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

  • 2.
    Bondeson, Daniel
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Mathew, Aji P.
    Oksman, Kristiina
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Optimization of the Isolation of Nanocrystals from Microcrystalline Cellulose by Acid Hydrolysis2006In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 13, no 2, p. 171-180Article in journal (Refereed)
    Abstract [en]

    The objective of this work was to find a rapid, high-yield process to obtain an aqueous stable colloid suspension of cellulose nanocrystals/whiskers. Large quantities are required since these whiskers are designed to be extruded into polymers in the production of nano-biocomposites. Microcrystalline cellulose (MCC), derived from Norway spruce (Picea abies), was used as the starting material. The processing parameters have been optimized by using response surface methodology. The factors that varied during the process were the concentration of MCC and sulfuric acid, the hydrolysis time and temperature, and the ultrasonic treatment time. Responses measured were the median size of the cellulose particles/whiskers and yield. The surface charge as calculated from conductometric titration, microscopic examinations (optical and transmission electron microscopy), and observation of birefringence were also investigated in order to determine the outcome (efficiency) of the process. With a sulfuric acid concentration of 63.5% (w/w), it was possible to obtain cellulose nanocrystals/whiskers with a length between 200 and 400 nm and a width less than 10 nm in approximately 2 h with a yield of 30% (of initial weight).

  • 3.
    Bozic, Mojca
    et al.
    Faculty of Mechanical Engineering, Institute for Engineering Materials and Design, University of Maribor.
    Liu, Peng
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kokol, Vanja
    Faculty of Mechanical Engineering, Institute for Engineering Materials and Design, University of Maribor.
    Enzymatic phosphorylation of cellulose nanofibers to new highly-ions adsorbing, flame-retardant and hydroxyapatite-growth induced natural nanoparticles2014In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, no 4, p. 2713-2726Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Colic, Miodrag
    et al.
    Medical Faculty of the Military Medical Academy, University of Defense in Belgrade, Serbia.
    Mihajlovic, Dusan
    Medical Faculty of the Military Medical Academy, University of Defense in Belgrade, Serbia.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Naseri, Narges
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kokol, Vanja
    University of Maribor, Institute for Engineering Materials and Design, Smetanova ul. 17, SI-2000 Maribor, Slovenia.
    Cytocompatibility and immunomodulatory properties of wood based nanofibrillated cellulose2015In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, no 1, p. 763-778Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Deepa, B.
    et al.
    Department of Chemistry, Bishop Moore College, Mavelikara, 690101, Kerala.
    Abraham, Eldho
    Robert H Smith Faculty of Agriculture, Food and Environment, Hebrew University, Jerusalem.
    Cordeiro, Nerida
    Competence Centre in Exact Science and Engineering, University of Madeira.
    Mozetic, Milan
    Department of Surface Engineering, Jozef Stefan Institute.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Faria, Marisa
    Competence Centre in Exact Science and Engineering, University of Madeira.
    Thomas, Sabu
    Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala, Department of Chemistry, C.M.S. College, Kottayam, 686001, Kerala.
    Pothan, Laly A.
    Department of Chemistry, Bishop Moore College, Mavelikara, 690101, Kerala.
    Utilization of various lignocellulosic biomass for the production of nanocellulose: a comparative study2015In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, no 2, p. 1075-1090Article in journal (Refereed)
    Abstract [en]

    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.

  • 6. Deepalakshmi, P
    et al.
    Visakh, P M
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chandra, Arup K.
    Thomas, Sabu
    Advances in elastomers: Their composites and nanocomposites: State of art, new challenges and opportunities2013In: Advances in elastomers II: Composites and nanocomposites, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2013, p. 1-9Chapter in book (Refereed)
    Abstract [en]

    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.

  • 7. Duchemin, Benoit
    et al.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    All-cellulose composites by partial dissolution in the ionic liquid 1-butyl-3-methylimidazolium chloride2009In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 40, no 12, p. 2031-2037Article in journal (Refereed)
    Abstract [en]

    Fully bio-based and biodegradable all-cellulose composites were prepared in the form of films by partial dissolution of two cellulose sources: a commercially available microfibrillated cellulose (MFC) and filter paper (FP). The solvent selected for this work was the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl). Both cellulose sources were partially dissolved at 80 °C and consolidated by partial dissolution, resulting in excellent mechanical properties. X-ray diffraction and electron microscopy demonstrated that partial dissolution was a viable path to transform FP into a continuous paracrystalline matrix reinforced with cellulose I crystallites. In contrast, partially dissolved MFC was not as thoroughly dissolved and large amounts of undissolved material were still visible along the center line of the films after the longest dissolution times. Consequently, partially dissolved MFC retained its initially high crystallinity. The degree of polymerization of the materials after dissolution was significantly reduced.

  • 8. Duchemin, Benoit
    et al.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Green ionic liquids for the production of fully-biobased and biodegradable all-cellulose nanocomposites2010In: 10th International Conference on Wood & Biofiber Plastic Composites and Cellulose NanoComposites Symposium, Forest Products Society, 2010Conference paper (Refereed)
  • 9.
    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 University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jonoobi, Mehdi
    Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rezayi, Majid
    Chemistry Department, Faculty of Science, University Malaya.
    Synergy Effect of Nanocrystalline Cellulose for the Biosensing Detection of Glucose2015In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 15, no 10, p. 24681-24697Article in journal (Refereed)
    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%.

  • 10.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Degradation mechanism of water contaminated automatic transmission fluid (ATF) in wet clutch system2013Conference paper (Refereed)
  • 11. Fatima, Nowshir
    et al.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wet Clutch Friction Interfaces under Water Contaminated Lubricant Conditions2016In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 59, no 3, p. 441-450Article in journal (Refereed)
    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.

  • 12.
    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 University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    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 nanowhiskers2010In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 10, p. 2660-2666Article in journal (Refereed)
    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

  • 13.
    Goetz, Lee
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jalvo, Bianca
    Department of Chemical Engineering, University of Alcalá.
    Rosal, Roberto
    Department of Chemical Engineering, University of Alcalá.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Superhydrophilic anti-fouling electrospun cellulose acetate membranes coated with chitin nanocrystals for water filtration2016In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 510, p. 238-248Article in journal (Refereed)
    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.

  • 14.
    Goetz, Lee
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Karim, Zoheb
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effect of micropatterned cellulose acetate membranes impregnated with cellulose and chitin nanocrystals on water filtration membrane behavior2016Manuscript (preprint) (Other academic)
  • 15.
    Goetz, Lee
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gatenholm, Paul
    Chalmers University of Technology.
    Ragauskas, Art
    Georgia Institute of Technology.
    A novel nanocomposite film prepared from crosslinked cellulosic whiskers2009In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 75, no 1, p. 85-89Article in journal (Refereed)
    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.

  • 16.
    Goetz, Lee
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ragauskas, Arthur J.
    Thermal gravimetric analysis of in-situ crosslinked nanocellulose whiskers - poly(methyl vinyl ether-co-maleic acid) - polyethylene glycol2011In: TAPPI Journal, ISSN 0734-1415, Vol. 10, no 4, p. 29-33Article in journal (Refereed)
    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.

  • 17.
    Goetz, Lee
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Naseri, Narges
    Department of Materials and Environmental Chemistry, Stockholm University.
    Nair, Santhosh S.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Karim, Zoheb
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials and Environmental Chemistry, Stockholm University.
    All cellulose electrospun water purification membranes nanotextured using cellulose nanocrystals2018In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, no 5, p. 3011-3023Article in journal (Refereed)
    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.

  • 18.
    Goetz, Lee
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ragauskas, Art J.
    Georgia Institute of Technology.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tying cellulose whiskers together2008In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 235, no 229Article in journal (Other academic)
  • 19. Gong, Guan
    et al.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Strong aqueous gels of cellulose nanofibers and nanowhiskers isolated from softwood flour2011In: TAPPI Journal, ISSN 0734-1415, Vol. 10, no 2, p. 42565-Article in journal (Refereed)
    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

  • 20.
    Gong, Guan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Toughening effect of cellulose nanowhiskers on polyvinyl acetate: Fracture toughness and viscoelastic analysis2011In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 32, no 10, p. 1492-1498Article in journal (Refereed)
    Abstract [en]

    The toughening effect of cellulose nanowhiskers (CNWs) on modified polyvinyl acetate (PVAc) was analyzed with the help of morphology, relaxation, and creep behavior. The CNWs together with bound moisture at the matrix/whisker interfaces resulted in significant improvement in resistance to crack initiation and propagation. The magnitude of plastic deformation of the nanocomposites was higher than that of the neat PVAc. The relaxation temperature decreased, while the width of the damping peak increased with increasing CNW and moisture contents. The results from creep modeling showed that the instantaneous elastic modulus first increased and then decreased with the addition of CNWs, while the time-dependent elasticity and viscosity decreased. The results suggested that the reinforcing effect of the CNWs was overwhelmed by the plasticizing effect of the bound moisture. Furthermore, low concentrations of CNWs significantly improved the fracture toughness of PVAc at the minor cost of strength, stiffness, and creep resistance. In this article, we present a novel approach to studying the toughening effect of CNWs on polymers using fracture tests and viscoelastic modeling

  • 21.
    Gong, Guan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pyo, Jinkyung
    Luleå tekniska universitet.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tensile behavior, morphology and viscoelastic analysis of cellulose nanofiber-reinforced (CNF) polyvinyl acetate (PVAc)2011In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, no 9, p. 1275-1282Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofiber-reinforced (CNF) polyvinyl acetate (PVAc) composites were prepared using the twin-screw extrusion technique. The influence of CNF content on nanocomposites morphology, tensile, and viscoelastic properties was studied. The tensile modulus and strength increased with increasing CNF content, being 59% and 21% higher in 10 wt% CNF composite compared to neat PVAc. The activation volume at yielding of PVAc was decreased by CNFs, indicating restricted chain mobility. The fracture surfaces of nanocomposites showed bridging of CNFs inside the micro-cracks. The storage modulus increased for all nanocomposites compared to the matrix, being more significant in the rubbery state. Also, the activation energy for the transition increased with increased CNF content. A slight shift and broadening was observed in the tan delta peak for 10 wt% CNFs composite. The creep strain of PVAc was reduced, whereas the creep elasticity and viscosity calculated from Burger’s model were increased by the addition of CNFs.Keywords: A. Polymer-matrix composites (PMCs); B. Creep, Mechanical properties; E. Extrusion

  • 22.
    Hassan, Mohammad L.
    et al.
    National Research Centre.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hassan, Enas A.
    National Research Centre.
    Fadel, Shiamaa M
    National Research Centre.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Improving cellulose/polypropylene nanocomposites properties with chemical modified bagasse nanofibers and maleated polypropylene2014In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, no 1, p. 26-36Article in journal (Refereed)
    Abstract [en]

    The properties of cellulose/polypropylene (PP) nanocomposites with n-octadecyl-modified bagasse nanofibers (MBNF) were compared to those with maleated polypropylene (MAPP) coupling agent. The nanocomposites were prepared by twin-screw extrusion with bagasse nanofiber (BNF) content varying from 2.5 to 10 wt%. The compression molded nanocomposites sheets were characterized regarding their tensile strength properties, dynamic mechanical thermal properties, crystallinity, water absorption, transparency and loss of strength due to composting in soil. As a compatibilizer to improve the tensile strength properties and transparency of PP/cellulose nanofibers nanocomposites, MAPP was more effective than n-octadecyl-modified cellulose nanofibers. The crystallinity of the nanocomposites was lower than that of neat PP except for those prepared using high loading of MBNF. Dynamic mechanical thermal analysis (DMTA) of the prepared materials showed that adding the different nanofibers (treated or untreated) resulted in better mechanical thermal properties above glass transition temperature (Tg) of PP. Water absorption capability in all nanocomposites was weakened while that in PP/MBNF was the lowest. No significant differences were found between the nanocomposites with different kinds of nanofibers regarding the loss of their tensile strength after compositing in soil up to six months.

  • 23.
    Hassan, Mohammad L
    et al.
    National Research Center, Cellulose & Paper Department, Cairo.
    Mathew, Aji P.
    Hassan, Enas A,
    National Research Center, Cellulose & Paper Department, Cairo.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effect of pretreatment of bagasse pulp on properties of isolated nanofibers and nanopaper sheets2010In: Wood and Fiber Science, ISSN 0735-6161, Vol. 42, no 3, p. 362-376Article in journal (Refereed)
    Abstract [en]

    Nanofibers were isolated from bagasse pulp pretreated with dilute hydrochloric acid, dilute sodium hydroxide, cellulase, or xylanase enzymes using high-shear ultrafine grinding and high-pressure homogenization. The effect of the different pretreatments on chemical composition and structure of isolated nanofibers was studied using chemical analyses, X-ray diffraction, and Fourier transform infrared. The dimensions and properties of the isolated nanofibers were followed at the different processing stages using optical microscopy, transmission electron microscopy, atomic force microscopy, and tensile properties (wet and dry). The diameter of the microfibrils was in the range of 7-30 nm for untreated and pretreated bagasse pulps while larger microfibrillar bands (to 150 nm wide) were observed for untreated bagasse pulp than the pretreated pulps (to 90 nm wide). Nanopaper sheets made from nanofibers isolated from alkali- and xylanase-treated pulps showed better wet and dry tensile strength than those made from the other pulps.

  • 24.
    Hassan, Mohammad
    et al.
    National Research Centre.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hassan, Enas
    National Research Centre.
    El-Wakil, Nahla
    National Research Centre.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nanofibers from bagasse and rice straw: process optimization and properties2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, no 1-3, p. 193-205Article in journal (Refereed)
    Abstract [en]

    Nanofibers (NF) were isolated from bleached bagasse and rice straw pulps. The pulps were refined using high-shear ultrafine grinder and then homogenized using high-pressure homogenizer. The efficiency of the used isolation processes was studied by optical microscopy (OM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and testing the tensile properties (wet and dry) of nanopaper sheets made from the nanofibers. In addition, opacity and porosity of nanopaper sheets made after different processing steps were investigated. The microscopy studies showed that the processes used resulted in nanofibers with diameters ranging from 3.5 to 60 nm. The results indicated that main isolation of nanofibers took place during refining using the ultrafine grinding process, while high-pressure homogenization resulted in smaller and more homogeneous size of nanofibers. Nanopaper sheets made from bagasse showed better wet and dry tensile strength properties than those made of rice straw

  • 25.
    Herrera, Martha A.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Barrier and mechanical properties of plasticized and cross-linked nanocellulose coatings for paper packaging applications2017In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, no 9, p. 3969-3980Article in journal (Refereed)
    Abstract [en]

    Barrier, mechanical and thermal properties of porous paper substrates dip-coated with nanocellulose (NC) were studied. Sorbitol plasticizer was used to improve the toughness, and citric acid cross-linker to improve the moisture stability of the coatings. In general, the addition of sorbitol increased the barrier properties, maximum strength and toughness as well as the thermal stability of the samples when compared to the non-modified NC coatings. The barrier properties significantly improved, especially for plasticized NC coating’s, where the oxygen permeability value was as low as 0.7 mL μm day−1 m−2 kPa−1 at 49% RH and the water vapor permeability was reduced by 60%. Furthermore, we found that the cross-linked plasticized NC coating had a smoother surface (50% lower roughness) compared to non-modified ones. This study shows that the environmentally friendly additives sorbitol and citric acid had positive effects on NC coating properties, increasing its potential use in paper-based packaging applications.

  • 26.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Cellulose nanocrystals: extraction from bio-residues2013In: Production and Applications of Cellulose Nanomaterials, TAPPI Press, 2013, p. 13-16Chapter in book (Refereed)
    Abstract [en]

    The aim of this study is to explore the utilization of industrial bio-residues as a source of raw material, for the industrial production of cellulose nanocrystals. For this purpose, cellulose nanocrystals have been isolated from bio-residues from ethanol and specialty cellulose production, to analyze their properties.

  • 27.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Characterization of cellulose nanowhiskers: a comparison of two industrial bio-residues2012In: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Conference paper (Refereed)
    Abstract [en]

    Cellulose nanowhiskers separated from two different industrial residues, sludge from cellulose production (CNWSL) and lignin residue from ethanol production (CNWER), were compared in order to evaluate their characteristics and their potential as a source for the production of cellulose nanowhiskers (CNWs). It was found that CNWSL and CNWER suspensions exhibited flow birefringence when they were studied through cross-polarized filters. Transmission electron microscopy (TEM) study showed that the CNWSL were longer (377 nm) than CNWER (301 nm). It was also demonstrated that most CNWSL had nanowhiskers between 375-449 nm and CNWER between 300-374 nm. The UV/Vis spectroscopy showed a stronger interference in the UV and visible region for the CNWSL films. The crystallinity, obtained by X-ray analysis, was higher for CNWSL (86%) than for CNWER (78%). Finally, the thermal stability appeared to be slightly higher for the CNWER than for CNWSL. Both studied residues seem to be suitable sources for large-scale production of CNWs.

  • 28.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Comparison of cellulose nanowhiskers extracted from industrial bio-residue and commercial microcrystalline cellulose2012In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 71, no 1, p. 28-31Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to compare the physical and chemical properties of cellulose nanowhiskers extracted from industrial bio-residue (CNW-BR) by homogenization, and microcrystalline cellulose (CNW-MCC) by acid hydrolysis. CNW-MCC showed a higher surface charge than CNW-BR when analyzed using conductometric titration. Both CNW-suspensions showed flow birefringence, indicating the presence of individualized whiskers. Morphology study confirmed that the whisker diameters were less than 10 nm for both materials, and atomic force microscope images showed somewhat more aggregated BR nanowhiskers. UV/Vis spectroscopy of the CNW-films showed transparency in visual light. The relative crystallinity obtained from X-ray diffraction was 77% for the CNW-BR, and 85% for the CNW-MCC. It was demonstrated, by thermal analysis, that the CNW-BR was more thermally stable than the CNW-MCC, having a higher degradation onset temperature (218 °C and 155 °C) as well as maximum degradation temperature.

  • 29.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gas permeability and selectivity of cellulose nanocrystals films (layers) deposited by spin coating2014In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 112, p. 494-501Article in journal (Refereed)
    Abstract [en]

    Cellulose nanocrystals (CNC) were extracted from a cellulose residue using two different acid hydrolysis procedures. CNC extracted with sulfuric acid (CNCS) showed higher surface charge (339 μmol/g) compared with crystals extracted with hydrochloric acid (CNCHCl). Spin-coated films with two different configurations were prepared; the first with alternate layers of poly(allylamine hydrochloride) (PAHCl) and CNC, and the second with a single layer of PAHCl coated with multilayers of CNC. Film characteristics such as roughness, thickness, contact angle, orientation, gas permeability and gas selectivity were studied. Optical microscopy showed more homogeneous films of CNCS compared to CNCHCl. The surface charge of the crystals impacted the films’ hydrophobicity, being highest for 25 alternate layers of PAHCl and CNCHCl. The gas permeability coefficient was different for each film, depending primarily on the surface charge of the crystals and secondly on the film configuration. The films made with CNCHCl displayed gas barriers with nitrogen and oxygen, and gas selectivity with some gas combinations. CNCS films did not show gas selectivity. These results indicate that CNC with low surface charge can be further developed for gas separation and barrier applications.

  • 30.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sirviö, Juho A.
    Fibre and Particle Engineering Laboratory, University of Oulu.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Environmental friendly and sustainable gas barrier on porous materials: Nanocellulose coatings prepared using spin- and dip-coating2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 93, p. 19-25Article in journal (Refereed)
    Abstract [en]

    In this study, environmental friendly and sustainable coatings of nanocellulose (NC) were prepared using spin- and dip-coating methods, on two different porous cellulose substrates. Microscopy studies showed that spin-coating technique was suitable for the substrate with smaller pore size, while the dip-coating was suitable for the substrate with larger pore size. The coating thickness ranged from some hundreds of nanometers for the spin-coated layers, to some micrometers for the dip-coated ones. It was also seen that the contact angle increased with the coating thickness and roughness. NC coating resulted in low oxygen permeability (between 0.12 and 24 mL ∗ μm/(m2 ∗ 24 h ∗ kPa)) at 23% RH, but at 50% RH the oxygen permeability was too high to be measured, except for the dip-coated sample with 23 μm thickness. Also, it was seen that eight month storing reduced the barrier properties of the coatings when compared with fresh materials. These results indicate that NC coatings have a great potential as sustainable alternative coating on paperboard.

  • 31.
    Herrera Vargas, Natalia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Project: Renewable eco-friendly Poly(Lactic acid) nanocomposites from waste sources2014Other (Other (popular science, discussion, etc.))
  • 32.
    Hietala, Maiju
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bionanocomposites of thermoplastic starch and cellulose nanofibers manufactured using twin-screw extrusion2013In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 49, no 4, p. 950-956Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate if cellulose nanofiber (CNF) gels with high water contents can be processed to nanocomposites with starch powder using continuous twin-screw extrusion and to improve the mechanical properties and moisture sensitivity of thermoplastic starch. Nanocomposites with 0, 5, 10, 15 and 20 wt% cellulose nanofiber content were prepared. The characterization methods were conventional tensile testing, UV/Vis spectroscopy, scanning electron microscopy and moisture absorption. The cellulose nanofiber gel with high water content was mixed with starch powder, fed to the extruder as powder, performing the gelatinization of starch as well as the mixing of CNF in one step. The microscopy study showed that the CNF aggregated during the process and that the screw configuration needs to be more distributive and dispersive to get homogeneous material. The results showed that the addition of CNF improved the mechanical properties and had a positive effect on moisture uptake of the thermoplastic starch. Also, the translucency of the TPS/CNF composite films remained, even with high CNF content (20 wt%).

  • 33.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Enhanced alignment and mechanical properties through the use of hydroxyethyl cellulose in solvent-free native cellulose spun filaments2017In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 150, p. 79-86Article in journal (Refereed)
    Abstract [en]

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

  • 34.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dry-spinning of continuous cellulose fibers using only nanofibers from a bio-residue2014Conference paper (Refereed)
    Abstract [en]

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

  • 35.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Exploiting the self-assembly of cellulose nanofibers in wet and dry spun fibers2014Conference paper (Refereed)
    Abstract [en]

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

  • 36.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of Matrix and Cold-drawing on Dry Spun Filaments of Cellulose Nanofibers2015Conference paper (Refereed)
    Abstract [en]

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

  • 37.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Norberg, Nicholas
    PANalytical.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dry-Spun Single-Filament Fibers Comprising Solely Cellulose Nanofibers from Bioresidue2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 23, p. 13022-13028Article in journal (Refereed)
    Abstract [en]

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

  • 38.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Skrifvars, Mikael
    School of Engineering, University of Borås.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    All-cellulose nanocomposite fibers produced by melt spinning cellulose acetate butyrate and cellulose nanocrystals2014In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, no 4, p. 2665-2678Article in journal (Refereed)
    Abstract [en]

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

  • 39.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    cho, Sung-woo
    University of Borås.
    Skrifvars, Mikael
    University of Borås.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Melt spinning of cellulose acetate butyrate (CAB) nanocomposite fibers reinforced by cellulose nanowhiskers (CNW)2013Conference paper (Refereed)
    Abstract [en]

    Bio-based continuous fibers were processed by melt spinning of cellulose acetate butyrate (CAB) and cellulose nanowhiskers (CNW) as well as environmental friendly plasticizer, triethyl citrate (TEC). Homogeneous dispersion of the CNW in CAB was achieved by solvent exchange to ethanol using sol-gel process. The appropriate amounts of well dispersed CNW organo-gel (2 and 10 wt%) as well as 15 wt% TEC were compounded with the dissolved CAB in ethanol followed by magnetic string, solution casting and grinding. Melt spinning of compounded CAB/TEC and CAB/TEC/CNW were carried out using a twin-screw micro extruder in continuous mode to decrease the residence time of materials and avoid thermal degradation. Afterwards, the fibers were solid-state drawn to enhance the mechanical properties. The addition of the CNW restricted the drawability of the fibers to a factor of 1.5. The tensile test data showed that 2 wt% CNW had no noticeable effect on modulus and tensile strength of the fibers while 10 wt% CNW increased the modulus and tensile strength by 58% and 36% respectively. Drawing, in general, provided greater stiffness and strength but sacrificed the ductility of the fibers. The microscopy studies showed that the fiber diameters were in the range of 350-450 μm for as-spun fibers and 300-350 μm for drawn fibers and no defect and increased surface roughness could be detected on the surface of the both as-spun and drawn composite fibers. Furthermore, The thermal properties, viscoelastic behavior as well as crystallinity properties of the fibers were characterized by TGA, DMTA and XRD.

  • 40.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Cho, Sung-Woo
    University of Borås.
    Skrifvars, Mikael
    University of Borås.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Melt spun cellulose nanocomposite fibres: comparison of two dispersion techniques2014In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 43, no 1, p. 15-24Article in journal (Refereed)
    Abstract [en]

    Bio-based continuous fibers were processed by melt spinning of cellulose acetate butyrate (CAB) and cellulose nanowhiskers (CNW) as well as environmental friendly plasticizer, triethyl citrate (TEC). Homogeneous dispersion of the CNW in CAB was achieved by solvent exchange to ethanol using sol-gel process. The appropriate amounts of well dispersed CNW organo-gel (2 and 10 wt%) as well as 15 wt% TEC were compounded with the dissolved CAB in ethanol followed by magnetic string, solution casting and grinding. Melt spinning of compounded CAB/TEC and CAB/TEC/CNW were carried out using a twin-screw micro extruder in continuous mode to decrease the residence time of materials and avoid thermal degradation. Afterwards, the fibers were solid-state drawn to enhance the mechanical properties. The addition of the CNW restricted the drawability of the fibers to a factor of 1.5. The tensile test data showed that 2 wt% CNW had no noticeable effect on modulus and tensile strength of the fibers while 10 wt% CNW increased the modulus and tensile strength by 58% and 36% respectively. Drawing, in general, provided greater stiffness and strength but sacrificed the ductility of the fibers. The microscopy studies showed that the fiber diameters were in the range of 350-450 μm for as-spun fibers and 300-350 μm for drawn fibers and no defect and increased surface roughness could be detected on the surface of the both as-spun and drawn composite fibers. Furthermore, The thermal properties, viscoelastic behavior as well as crystallinity properties of the fibers were characterized by TGA, DMTA and XRD.

  • 41.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Cho, Sung-Woo
    University of Borås.
    Skrifvars, Mikael
    University of Borås.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Preparation of bio-composite fibers by melt spinning of cellulose acetate butyrate (CAB) and cellulose nanowhiskers (CNW)2012Conference paper (Other academic)
  • 42.
    Hooshmand, Saleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Manufacturing and characterization of melt spun and wet spun bionanocomposite fibers2012Conference paper (Other academic)
  • 43. Jackson-Etang, Ayuk
    et al.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The effect of plasticizer and cellulose nanowhisker content on the dispersion and properties of cellulose acetate butyrate nanocomposites2009In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 114, no 5, p. 2723-2730Article in journal (Refereed)
    Abstract [en]

    We studied the effects of plasticizer and cellulose nanowhisker content on the dispersion and properties of cellulose acetate butyrate (CAB)-based bionanocomposites. The cellulose nanowhiskers in an aqueous medium were solvent-exchanged to nonaqueous polar solvent (acetone) and used for nanocomposite processing by solution casting. The plasticized and unplasticized nanocomposites with 5 and 10 wt % cellulose nanowhisker content were prepared. Atomic force microscopy indicated nanoscale dispersion of whiskers in the CAB matrix. The dynamic mechanical analysis showed an increase in storage modulus with addition of cellulose nanowhiskers, especially above the glassy-rubbery transition region. Thermogravimetric analysis showed an improvement in thermal stability with increased whisker content for both unplasticized and plasticized nanocomposites. The plasticized nanocomposites showed better transparency than the unplasticized composites, indicating a better dispersion of cellulose nanowhiskers in CAB, in the presence of a plasticizer. The dynamic mechanical properties and thermal stability increased, whereas transparency decreased with increased CNW content.

  • 44.
    Jacobs, Valencia
    et al.
    CSIR Materials Science and Manufacturing, Fibres and Textiles Competence Area, Port Elizabeth.
    Anandjiwala, Rajesh D.
    CSIR Materials Science and Manufacturing, Fibres and Textiles Competence Area, Port Elizabeth.
    John, Maya
    CSIR Materials Science and Manufacturing, Fibres and Textiles Competence Area, Port Elizabeth.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Studies on electrospun chitosan based nanofibres reinforced with cellulose and chitin nanowhiskers2011Conference paper (Refereed)
  • 45.
    Jalvo, Blanca
    et al.
    Department of Chemical Engineering, University of Alcalá.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rosal, Roberto
    Department of Chemical Engineering, University of Alcalá.
    Coaxial poly(lactic acid) electrospun composite membranes incorporating cellulose and chitin nanocrystals2017In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 544, p. 261-271Article in journal (Refereed)
    Abstract [en]

    In this study, we used electrospinning to produce core-shell nanofibers of poly(lactic acid) as core and polyacrylonitrile/cellulose nanocrystals (CNC) or polyacrylonitrile/chitin nanocrystals (ChNC) as shell. Electrospun materials prepared at different nanocrystal concentrations were tested and assayed as microfiltration membranes. The coaxial membranes presented a maximum pore size in the 1.2–2.6 μm range and rejections > 85% for bacterial cells (0.5 × 2.0 μm) and > 99% for fungal spores (> 2 μm). The morphological and mechanical properties and the water permeability of the nanocomposite membranes were studied. The morphological characterization showed random fibers of beadless and well-defined core/shell structured fibers with diameter generally below the micron size with presence of secondary ultrafine nanofibers. Tensile strength and Young's modulus of elasticity improved with respect to coaxial membranes without nanocrystals with best mechanical properties achieved at 5 wt% CNC and 15 wt% ChNC loadings. The enhancement was attributed to the reinforcing effect of the percolating network of cellulose nanocrystals. Water permeability increased for all membranes loaded with nanocrystals with respect to the coaxial fibers without nanocrystals, the highest corresponding to ChNC composites with up to a 240% increase over non-loaded membranes. Composite membranes prepared with CNC in their shell were hydrophilic, in contrast with the hydrophobic PLA core, while coaxial fibers with ChNC were superhydrophilic. CNC membranes were negatively charged but ChNC originated neutral or positively charged membranes due to the contribution of deacetylated chitin structural units. Upon exposure to E. coli cultures, composite membranes containing ChNC showed a high antimicrobial action and were essentially free of bacterial colonization under strong biofilm formation conditions.

  • 46.
    John, Maya Jacob
    et al.
    CSIR, Materials Science and Manufacturing, Polymers and Composites, Port Elizabeth.
    Anandjiwala, Rajesh
    CSIR, Materials Science and Manufacturing, Polymers and Composites, Port Elizabeth.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Melt-spun polylactic acid fibers: Effect of cellulose nanowhiskers on processing and properties2013In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 127, no 1, p. 274-281Article in journal (Refereed)
    Abstract [en]

    Bio-based continuous fibers were processed from polylactic acid (PLA) and cellulose nanowhiskers (CNWs) by melt spinning. Melt compounding of master batches of PLA with 10 wt % CNWs and pure PLA was carried out using a twin-screw extruder in which compounded pellets containing 1 and 3 wt % of CNWs were generated for subsequent melt spinning. The microscopy studies showed that the fiber diameters were in the range of 90-95 µm, and an increased surface roughness and aggregations in the fibers containing CNWs could be detected. The addition of the CNWs restricted the drawability of the fibers to a factor of 2 and did not affect the fiber stiffness or strength, but resulted in a significantly lower strain and slightly increased crystallinity. Furthermore, CNWs increased the thermal stability, creep resistance and reduction in thermal shrinkage of PLA fibers, possibly indicating a restriction of the polymer chain mobility due to the nanoscale additives.

  • 47.
    Jonoobi, Mehdi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Thermoplastic polymer impregnation of cellulose nanofibre networks: Morphology, mechanical and optical properties2014In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 58, p. 30-35Article in journal (Refereed)
    Abstract [en]

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

  • 48.
    Jonoobi, Mehdi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Harun, Jalaluddin
    Institute of Tropical Forestry and Forest Products, University Putra Malaysia, Kuala Lumpur.
    Mathew, Aji P.
    Hussein, Mohd ZB
    Department of Chemistry, Faculty of Science, University Putra Malaysia.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Preparation of cellulose nanofibers with hydrophobic surface characteristics2010In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 27, no 2, p. 299-307Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to develop cellulose nanofibers with hydrophobic surface characteristics using chemical modification. Kenaf fibers were modified using acetic anhydride and cellulose nanofibers were isolated from the acetylated kenaf using mechanical isolation methods. Fourier transform infrared spectroscopy (FTIR) indicated acetylation of the hydroxyl groups of cellulose. The study of the dispersion demonstrated that acetylated cellulose nanofibers formed stable, well-dispersed suspensions in both acetone and ethanol. The contact angle measurements showed that the surface characteristics of nanofibers were changed from hydrophilic to more hydrophobic when acetylated. The microscopy study showed that the acetylation caused a swelling of the kenaf fiber cell wall and that the diameters of isolated nanofibers were between 5 and 50 nm. X-ray analysis showed that the acetylation process reduced the crystallinity of the fibers, whereas mechanical isolation increased it. The method used provides a novel processing route for producing cellulose nanofibers with hydrophobic surfaces.

  • 49.
    Jonoobi, Mehdi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Harun, Jalaluddin
    University Putra Malaysia.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mechanical properties of cellulose nanofiber (CNF) reinforced polylactic acid (PLA) prepared by twin screw extrusion2010In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 70, no 12, p. 1742-1747Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to develop cellulose nanofiber (CNF) reinforced polylactic acid (PLA) by twin screw extrusion. Nanocomposites were prepared by premixing a master batch with high concentration of CNFs in PLA and diluting to final concentrations (1, 3, 5 wt%) during the extrusion. Morphology, mechanical and dynamic mechanical properties (DMA) were studied theoretically and experimentally to see how different CNF concentrations affected the composites' properties. The tensile modulus and strength increased from 2.9 GPa to 3.6 GPa and from 58 MPa to 71 MPa, respectively, for nanocomposites with 5 wt% CNF. The DMA results were also positive; the storage modulus increased for all nanocomposites compared to PLA; being more significant in the high temperature region (70°C). The addition of nanofibers shifted the tan delta peak towards higher temperatures. The tan delta peak of the PLA shifted from 70°C to 76°C for composites with 5 wt% CNF.

  • 50.
    Jonoobi, Mehdi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Abdi, M.M.
    University Putra Malaysia.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Makinejad, M.D.
    University Putra Malaysia.
    A comparison of modified and unmodified cellulose nanofiber reinforced polylactic acid (PLA) prepared by twin screw extrusion2012In: Journal of polymers and the environment, ISSN 1566-2543, E-ISSN 1572-8919, Vol. 20, no 4, p. 991-997Article in journal (Refereed)
    Abstract [en]

    The goal of this work was to evaluate the effect of chemical modification of cellulose nanofibers (CNF) on the properties of polylactic acid (PLA) nanocomposites. Acetylated nanofibers (ACNF), with degree of substitution 1.07, were isolated from acetylated kenaf fibers by mechanical treatments. Acetylated nanofibers showed more hydrophobic properties compared to non-acetylated ones. The results showed that both crystallinity and thermal stability of acetylated nanofibers were lower than non-acetylated ones. The nanocomposites were prepared by premixing two PLA master batches, one with a high concentration of ACNF and the second with CNF. These were diluted to final concentrations (5 wt%) during the extrusion. The morphology studies of PLA and its nanocomposites showed nanofiber aggregates in both materials. The results showed that the tensile and dynamic mechanical properties were enhanced for both acetylated and non-acetylated nanocomposites compared to the neat PLA matrix while no significant improvement was observed for the acetylated nanocomposites compared to non-acetylated ones. However, the storage modulus increased slightly for acetylated nanocomposites compared to non-acetylated ones.

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