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  • 201.
    Gong, Guan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Toughening effect of cellulose nanowhiskers on polyvinyl acetate: Fracture toughness and viscoelastic analysis2011Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 32, nr 10, s. 1492-1498Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 202.
    Gong, Guan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pyo, Jinkyung
    Luleå tekniska universitet.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tensile behavior, morphology and viscoelastic analysis of cellulose nanofiber-reinforced (CNF) polyvinyl acetate (PVAc)2011Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, nr 9, s. 1275-1282Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 203.
    Grubbström, Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Processing and properties of silane crosslinked wood-polyethylene composites2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Utilizing wood as filler and reinforcement in thermoplastic polymer-matrix composites, has gained interest during the last decades, mainly as profile extruded exterior building products such as deck boards, railings, and door- and window frame components. This thesis deals with silane-crosslinking of wood-polyethylene composites through reactiveextrusion. The reactive-extrusion aims to graft silanes to the polyethylene in the moltenphase using peroxide as initiator, and a subsequent curing in high humidity and elevated temperature results in crosslinking of the wood-composite. The goal of using this method is to increase the materials strength, toughness and resistance to creep. Long-term mechanical performance is an issue for wood composites of commonly used thermoplastic matrices and improvements of properties may make these composites applicable as primary load-bearing members in structures. The extrusion process, whereonly grafting of silanes should take place, has earlier shown to be difficult for a wood composite, leading to unintentional crosslinking (scorch) in the melt and thereby poor processability of the composite. The objective for this study was to investigate how to control this reactive-extrusion process for wood-polyethylene composites, by studying process-structure relations, and furthermore to understand the relationship between structure and properties of the composites. The process was investigated by use of different material compositions (papers I-III), curing modes (papers I-III) and extrudersettings (paper IV). The structure-properties relations were studied by use of various test and analysis methods (papers I-V). It was found that the process can be controlled such that scorch was suppressed, and the efficiency of curing was increased. Significant differences on the results were shown for extruder-variables like barrel heat, screw speed and screw configurations. The peroxideload in the grafting step also showed a strong effect. Consequently, a composite not scorched and effectively cured could be obtained, and it was concluded that the complexity of this process, in comparison to the silane-crosslinking of a neat polyethylene, is due to the hydrophilic wood present in the process. All crosslinked composites in this study have improved in strength, toughness and creep resistance, compared to a non-crosslinked counterpart. Not scorched composites showed highest strength, toughness and resistance to creep, despite a lower degree of crosslinking in the matrix after curing, compared to highly scorched samples. To investigate the mechanisms leading to properties improvement, dynamic-mechanical analysis and adhesion tests were employed. It showed that direct chemical bonding between wood and matrix polymer is plausible, but do not describe the mechanism for improvements. A model of interphase for silane-crosslinked wood-polyethylene composites was presented, where it was suggested that the wood particles become surface-treated in the extrusion process, leading to an interphase of more efficient stress transfer. Nothing proves that pure chemical bonding between the wood and polyethylene answers to the strength improvements of the silane-crosslinked composites. It was suggested that future work in this field, in terms of processing, should address the use of ethylene-vinyl-silane copolymers (EVS) or blends of polyethylene and EVS, to obviate the silane-grafting step in the process. However, since the bonds of this crosslinking (-Si-O-Si-) are reversible hydrolysable, the long-term stability should be evaluated. For only stabilizing the matrix polymer, crosslinking by use of peroxides only, may be a better option.

  • 204.
    Grubbström, Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Reactive extrusion of wood-thermoplastic composites2009Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The interest in Wood-thermoplastic composites (WPCs) has increased during the last decades. WPCs are commonly used as building material for decking and railing because of its low need of maintenance. Wood is a renewable resource of good mechanical properties and this make wood fibers interesting to use as reinforcement in a thermoplastic composite. A drawback with this type of composite is the poor long-term mechanical properties which limit its field of applications. The objective of this work was to optimize the process and understand structure-property relations of silane-crosslinked WPCs produced in a one-step reactive extrusion. The specific goal of crosslinking the composite was to improve the interfacial strength and stabilize the polymer matrix in order to improve these composites long-term mechanical properties.Silane-crosslinked WPC was produced by adding wood flour, polyethylene and a silane-peroxide solution to a compounding extruder. The composites were thereafter conditioned in different environments to promote the formation of silane-crosslinks. Parameters like wood flour moisture content, amount/composition of silane-peroxide solution and different general types of polyethylene was studied and related to the efficiency of the process.It was found that silane-technology applied to WPCs can be optimized in terms of processability and achieved property improvements. All crosslinked composites in this study have improved in strength, toughness and creep resistance but it was shown that the tested parameters have affect on both processing and properties. A gentle use of peroxides in the process was concluded to be positive for both processability and resulting property improvements. The unintentional crosslinking in the extrusion process is a drawback but was limited by lower peroxide concentrations. The use of low density polyethylene as polymer matrix lead to twice as high crosslinking rate compared to a high density polyethylene matrix. However, too excessive moisture uptake in the composites appears to lower the efficiency of crosslinking. Future studies should evaluate long-term load behavior more thoroughly and also investigate the conditioning step more carefully.

  • 205.
    Grubbström, Göran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Silane-crosslinking of recycled low-density polyethylene/wood composites2010Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 41, nr 5, s. 678-683Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this work was to study silane-crosslinking of recycled low-density polyethylene wood composites and its effect on composites properties. The composites were produced in a one-step twin-screw extrusion process and the silane-peroxide solution was pumped into the extruder. Degree of crosslinking, mechanical properties, short-term creep, fractured surfaces and nature of crosslinking were studied to understand the relationship between composite structure and properties. The results showed that crosslinked composite strength, toughness and creep resistance were improved compared to uncrosslinked composites. The flexural strength was doubled compared to uncrosslinked samples and the creep strain was reduced. The crosslinked composites stored under room conditions showed the highest strength, whereas storage in a sauna resulted in a higher degree of crosslinking. The Fourier transform infrared spectroscopy indicated formation of silane-bridges between wood and polyethylene, accordingly improving the interfacial adhesion between the wood and LDPE. The low concentration of peroxide in the silane-solution was shown to be a preferred composition to limit unintentional crosslinking during the process.

  • 206. Grubbström, Göran
    et al.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Influence of wood flour moisture content on the degree of silane-crosslinking and its relationship to structure property relations of wood-thermoplastic composites2009Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, nr 7-8, s. 1045-1050Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of this work was to examine how the moisture content of wood flour affects the degree of crosslinking when producing silane-crosslinked wood-thermoplastic composites. Crosslinked composites were produced by adding a silane solution to the compounding process of wood flour and polyethylene. Crosslinked composites of pre-dried as well as non-dried wood flour were prepared and their degree of crosslinking at various storage conditions was determined. Mechanical properties and the creep response of the crosslinked composites were tested in order to establish structure-properties relations. The results showed that all crosslinked composites displayed higher strengths and lower creep responses compared with non-crosslinked control samples. However, the degree and rate of crosslinking proved to be lower when a larger amount of moisture was present in the compounding process. It was concluded that the silane-grafting yield was lower when wood flour of a higher moisture content was used.

  • 207. Grubbström, Göran
    et al.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Silane-crosslinking efficiency in wood-polyethylene composites: study of different polyethylenes2010Inngår i: 10th International Conference on Wood & Biofiber Plastic Composites and Cellulose NanoComposites Symposium, Forest Products Society, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The objective of this work was to examine how the moisture content of wood flour affects the degree of crosslinking during the fabrication of silane-crosslinked wood-thermoplastic composites. Crosslinked composites were produced by adding a silane solution to the compounding process of wood flour and polyethylene. Crosslinked composites of pre-dried as well as non-dried wood flour were prepared and their degree of crosslinking at various storage conditions was determined. Mechanical properties and the creep response of the crosslinked composites were tested in order to establish structure-properties relations. The results showed that all crosslinked composites displayed higher strengths and significantly lower creep responses as opposed a non-crosslinked control sample. However, the degree and rate of crosslinking proved to be lower when a larger amount of moisture was present in the compounding process. It was concluded that the silane-grafting yield was lower when wood flour of a higher moisture content was used, and a possible reason for this was that the radicals necessary for grafting the silanes to the polyethylene had been consumed in the process.

  • 208.
    Gürdağ, Gülten
    et al.
    Faculty of Engineering, Department of Chemical Engineering, Istanbul University.
    Sarmad, Shokat
    Faculty of Engineering, Department of Chemical Engineering, Istanbul University.
    Cellulose Graft Copolymers: Synthesis, Properties, and Applications2013Inngår i: Polysaccharide based Graft Copolymers / [ed] Susheel Kalia and M.W. Sabaa, Berlin: Springer, 2013, s. 15-57Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Grafting of vinyl monomers onto cellulose is an important tool for the modification of cellulose. Depending on the monomer grafted onto cellulose, it gains new properties. The grafting can be performed in heterogeneous or homogeneous medium. In the grafting performed in heterogeneous medium, the reaction is carried out in aqueous medium using a suitable initiator. As initiator, the radiation or chemical initiators such as ceric ammonium nitrate (CAN), various persulfates, azobisisobutyronitrile (AIBN), and Fenton reagent (Fe(II)–H2O2) are mostly used. In case of CAN initiator, the grafting should be performed in acidic medium in order to prevent its hydrolysis. In the homogeneous grafting reactions, either a water-soluble cellulose derivative is used in the grafting or cellulose is dissolved in a suitable solvent, and then the grafting is performed. Higher number of grafts per cellulose chain is obtained in homogeneous grafting than those in heterogeneous medium

  • 209. Hafrén, J.
    et al.
    Westermark, Ulla
    Lennholm, U.
    Terashima, N.
    Formation of specifically C-13 enriched DHP in lignifying tissue1999Konferansepaper (Annet vitenskapelig)
  • 210. Hafrén, Johan
    et al.
    Westermark, Ulla
    Distribution of acidic and esterified polygalacturonans in sapwood of spruce, birch and aspen2001Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 16, nr 4, s. 284-290Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The distribution and degree of esterification of polygalacturonans have been studied in spruce, birch and aspen using immunolocalization. Monoclonal antibodies against acidic and methyl esterified polygalacturonan were localized by fluorescence- and transmission electron microscopy.

  • 211.
    Hafrén, Jonas
    et al.
    Swedish Pulp and Paper Research Institute.
    Daniel, Geoffrey
    Sveriges Lantbruksuniversitet.
    Westermark, Ulla
    The distribution of acidic and esterified pectin in cambium, developing xylem and mature xylem of Pinus sylvestris2000Inngår i: IAWA Journal, ISSN 0928-1541, Vol. 21, nr 2, s. 157-168Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Homogalacturonans with low and high degree of methyl esterification have been immuno-localised in the cambium, differentiating xylem and mature xylem of Pinus sylvestris, by monoclonal antibodies JIM5 and JIM7. In the unlignified cambial tissue the antibodies revealed a similar distribution for acidic and esterified pectin in the compound middle lamella, ray cell walls and pit membranes. In the lignified xylem tissue, pectin was also found in the compound middle lamella, although dominantly in the methylesterified form. Lignification seemed to coincide with a decrease in the presence of acidic pectin in the compound middle lamella. Both antibodies indicated labelling in pit membranes and ray cell walls in partially and fully lignified wood fibres.

  • 212.
    Hafrén, Jonas
    et al.
    Swedish Pulp and Paper Research Institute, Stockholm.
    Fujino, Takeshi
    Wood Research Institute, Kyoto University,.
    Itoh, Takao
    Wood Research Institute, Kyoto University,.
    Westermark, Ulla
    Terashima, Noritsugu
    Swedish Pulp and Paper Research Institute, Stockholm.
    Ultrastructural changes in the compound middle lamella of Pinus thunbergii during lignification and lignin removal2000Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 54, nr 3, s. 234-240Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structure of the middle lamella in Pinus thunbergii has been studied by the rapid-freeze deep-etching (RFDE) technique in combination with transmission electron microscopy (TEM). The ultrastructure of the compound middle lamella was studied in the early phases of the development of woody tissue in the cambial and differentiating xylem, before the heavy incrustation with lignin had occurred. Lignified middle lamella in the xylem was studied both directly and after delignification. It was found that the structure of the unlignified middle lamella in the cambium/developing xylem consists of a fine irregular network probably containing pectin and hemicellulose. As a result of lignin incrustation, the middle lamella becomes increasingly dense and the surface structure of the fully lignified middle lamella appeared to be compact and partly covered with globular structures. After delignification of the lignified middle lamella a thin network with a different structure was revealed. This network probably mainly consists of hemicellulose. No microfibrils of the type that occurs in the primary and secondary walls were found in the middle lamella.

  • 213.
    Hafrén, Jonas
    et al.
    STFI, Stockholm.
    Westermark, Ulla
    Lennholm, Helena
    Royal Institute of Technology.
    Terashima, Noritsugu
    STFI, Stockholm.
    Formation of 13C-enriched cell-wall DHP using isolated soft xylem from Picea abies2002Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 56, nr 6, s. 585-591Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cell-wall dehydrogenation polymers (CW-DHP) were prepared by incubating a mixture of soft xylem (differentiating xylem) from Picea abies, coniferin 13C-enriched at the side-chain β-carbon and unenriched coniferin, both with and without the addition of β-glucosidase and glucose oxidase, which causes an in situ polymerisation of the coniferyl alcohol in the cell wall. From difference solid state 13C-NMR spectra between 13C-enriched CW-DHP and unenriched CW-DHP, the bond frequencies involving specifically 13C-enriched carbon can be quantitatively determined. The sub-structures in CW-DHP prepared without the addition of β-glucosidase and glucose oxidase showed more similarity to protolignin than CW-DHP prepared with the addition of extraneous enzymes. The CW-DHP obtained without the addition of enzymes contained 36% β-O-4-derived sub-structures, 44% combined β-β, β-5 and β-1 sub-structures and 20% coniferyl alcohol/coniferaldehyd end groups. After acetone/water extraction of the CW-DHP, the content of β-β, β-5 and β-1 structures decreased by 4%, and the β-O-4 dominating peak increased by 4%. The 13C-enriched CW-DHP material can be used to study lignin reactions in a solid wood matrix, and is also a powerful system for detailed studies on in vivo lignification mechanisms and the effects on lignification conditions on lignin structure

  • 214.
    Hagstrand, P.-O.
    et al.
    Chalmers University of Technology.
    Oksman, Kristiina
    Mechanical properties and morphology of flax fiber reinforced melamine-formaldehyde composites2001Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 22, nr 4, s. 568-578Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber-matrix interface. In contrast, melamine-formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this Paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM), it is found that microcracking takes place mainly in the fiber cell walls and not at the fiber-matrix interface. This suggests that the fiber-matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements

  • 215.
    Hansson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Controlling microwave heating and its effect on the properties of wood2003Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Drying wood with microwave energy is not so common, but could be a complement to conventional air circulation drying due to the possibility of drying wood faster than with conventional drying methods with preserved quality. An industrial-scale, on-line microwave drier for wood components is under development at the Division of Wood Physics. This drier will be mainly used for demonstrations, product testing and for students? laboratory work. The purpose of the present work was to study the drying of wood by microwave heating and to investigate whether the method affects the properties of wood. The aim was also to ascertain how to adjust the design of a microwave construction for industrial use. Testing of the mechanical properties of the wood showed no difference in bending strength in comparison with the conventional air-circulation method. Nor did testing of wood hardness (Janka) show any significant difference between the drying methods and the temperature level during microwave drying. Furthermore, when using the microwave drying method, the infrared (IR) images showed that it is very important to control microwave heating and to move the components during the drying process in order to achieve more uniform heating and avoid thermal runaway at the end of the process. This runaway effect can negatively affect the mechanical properties of the wood.

  • 216.
    Hansson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Microwave treatment of wood2007Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Drying wood using microwave energy is not very common, but could be a complement to conventional air-circulation drying due to the possibility to dry wood faster than the conventional drying methods with preserved quality. Furthermore, this technique could be used to condition boards with too high moisture content gradient. In this study, an industrial-scale, online microwave drier for wood components has been used and adapted to wood treatment. The aim of the present work was to investigate if the microwave drying method itself affects such wood properties as bending strength, hardness and colour change. Another aim was to explain, with finite element model simulations, the interaction between microwaves and wood during heating and drying and to a lesser extent also during microwave scanning of wood. Tests of the mechanical properties of wood showed no difference in bending strength in comparison with the conventional air circulation method. Nor was there any significant difference in wood hardness (Janka) perpendicular to the grain between the drying methods or between different temperature levels during the microwave drying. However, the results showed that there is a significant difference in wood hardness parallel to the grain between the methods when drying progressed to relatively lower levels of moisture content; i.e. wood hardness becomes higher during microwave drying. The developed multiphysics finite element model is a powerful evaluation tool for understanding the interaction between wood and microwaves during heating and drying as well as scanning. The model can be used for simulation of different microwave treatments of wood.

  • 217.
    Hansson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Styrprogram för temperaturhållning av last i mikrovågsugn2002Rapport (Annet vitenskapelig)
    Abstract [sv]

    För att kunna studera hur trä påverkas om det torkas med hjälp av mikrovågor vid olika temperaturer, har avdelning för träfysik Institutionen i Skellefteå använt sig av bl a en vanlig hushållsmikrovågsugn. Mätningen av temperaturen har skett med en fiberoptisk termometer. Torkningarna kan vara relativt tidsödande, och eftersom termometern och mikrovågsugnen inte har varit sammankopplade så har det hitintills varit så att den som utfört torkningen alltid fått närvara vid denna process. Syftet med detta projekt var att göra en styrning som fungerar som en automatisk temperaturstyrning av processen och inte som tidigare en manuell temperatur övervakning. Resultatet visar att med detta nya styrprogram så reduceras behovet av den manuella övervakningen till att endast se till så att träbitarna uppnår önskad fuktkvot

  • 218.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    Design and performance of an industrial microwave drier for on-line drying of wood components2003Inngår i: Proceedings of the 8th IUFRO International Wood Drying Conference: Improvement and innovation in wood drying : a major issue for a renewable material : 24-29 August 2003, Brasov, Romania / [ed] Mihai Ispas; Sergiu T Chiriacescu, Brasov: Transilvania University of Brasov, Faculty of Wood Industry , 2003, s. 156-158Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The most common industrial method for drying wood is by air circulation. However, an alternative method - microwave drying-has been investigated at the Division of Wood Physics, Luleå University of Technology in Skellefteå, Sweden. The use of microwave energy to dry wood is not very common, but it could be advantageous due to the possibility of heating and drying wood much faster than conventional methods and with preserved quality. The objective of the investigation is to install an on-line microwave drier for wood components and, furthermore, to integrate this drying process into the total production. The purpose of this paper is to briefly describe the design and performance of this on-line microwave drier, its advantages and its limitations.

  • 219.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    Modeling microwave heating and moisture redistribution in wood2008Inngår i: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 26, nr 5, s. 552-559Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A finite element model was developed to describe and explain microwave heating of wood and the following moisture redistribution in wood. Dielectric and thermal properties are of great importance, since they are continuously affected during the process by moisture content, density, grain direction, temperature, and more. Computer tomography was used to detect wood density and moisture content. Heat distribution was verified by fiber-optic temperature sensors. The tests were performed in a designed microwave dryer based on 1-kW generators, 2.45GHz. The results show that finite element modeling is a powerful tool to simulate heat and mass transfer in wood, providing the material is well described.

  • 220.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    The effect of drying method and temperature level on the hardness of wood2006Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 171, nr 3, s. 467-470Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of the present work was to investigate whether wood hardness is affected by temperature level during microwave (MW) drying and whether the response is different from that of conventionally dried wood. Matched samples of Norway spruce (Picea abies) were therefore dried from green state to different moisture content (mc) at different temperature levels, both conventionally by air circulation and by MW. The results show that specimens dried by any of the two methods at a temperature level of 100 or 60°C there is a significant difference in wood hardness parallel to the grain between the methods when drying progresses to relatively lower level of moisture content, i.e. wood hardness becomes higher during MW drying. Temperature level in the range 60-110°C during MW drying has no significant influence on wood hardness. Variables such as density and mc have a greater influence on wood hardness than does the drying method or the drying temperature. Since wood is a biological material, its strength varies within the specimens as well as between different samples. For this reason it is important to use matched samples when performing this type of comparative investigation.

  • 221.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    The effect of microwave drying on Norway spruce woods strength: a comparison with conventional drying2003Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 141, nr 1, s. 41-50Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of the present work was to investigate whether the drying method itself affects strength of wood apart from fibre direction, density, temperature in the wood, moisture content and with which angle the microfibril is placed in the middle layer at the secondary cell wall S2. The drying methods compared were microwave drying and conventional air-circulation drying, and the species tested was Norway spruce. The result shows that it is not possible to demonstrate any difference between the two drying methods with respect to the strength of the wood. What affects wood strength are such variables as moisture content, number of annual rings and the density properties weight, width and thickness

  • 222.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    Lundgren, Nils
    Hagman, Olle
    Finite element modeling (FEM) simulation of interactions between wood and microwaves2006Inngår i: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 52, nr 5, s. 406-410Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to use finite element modeling (FEM) as a tool to analyze microwave scattering in wood and to verify the model by measurements with a microwave scanner. A medical computed tomography scanner was used to measure distribution of density and moisture content in a piece of Scots pine (Pinus sylvestris). Dielectric properties were calculated from measured values for cross sections from the piece and used in the model. Images describing the distribution of the electric field and phase shift were obtained from the FEM simulation. The model was verified by measurements with a scanner based on a microwave sensor. The results show that simulated values correspond well to measured values. Furthermore, discontinuities in the material caused scattering in both the measured and the simulated values. The greater the discontinuity in the material, the greater was the need for computational power in the simulation.

  • 223.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    Morén, Tom
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    IR- och HFV-teknik för virkestorkning2002Rapport (Annet vitenskapelig)
    Abstract [sv]

    Syftet med föreliggande arbete är att presentera några relativt nya virkestorkningsmetoder. Tanken är att visa på metodernas möjligheter och begränsningar för den svenska träbranschen. De metoder som valts ut är torkning med hjälp av infraröd strålning och högfrekvens/vakuum-torkning. Studien baseras på fysikaliska förutsättningar, litteraturinventering, intervjuer med metodutvecklare och i IR-fallet på medverkan vid praktiska kvalitetsmätningar av det torkade virket. Resultatet visar att teknologin som bygger på infraröd teknik möjligen kan minska torkningstiden, men detta antagande bygger endast på den grundläggande fysiken bakom teknologin. De som har investerat i denna teknologi vill ej ge ut information kring tekniken innan den grundligt har testats. Därför finns en del obesvarade frågeställningar, såsom hur mycket tid som kan tjänas vid torkningen, energiåtgångens storlek samt vilken torkningskvalitet som erhålls med denna torkningsmetod. Det sistnämnda undersöks för närvarande av Trätek. Högfrekvens/vakuumtekniken som beskrivs här är utvecklad i Kanada och används industriellt där, än så länge dock i liten skala. Träslag som på senare tid undersökts och torkas med denna metod är företrädesvis nordamerikanskt barrvirke. Metoden lämpar sig ur ekonomiskt perspektiv (i Kanada) framför allt för torkning av grövre dimensioner, men också för att fuktutjämna konventionellt torkat virke. Fördelarna med metoden jämfört med konventionell teknik är kortare torkningstid, mindre förekomst av ytsprickor, inre spänningar och fläckvis missfärgning förekommer inte alls och dessutom uppnås en jämn slutfuktkvot i hela lasten. Virket behöver inte ströläggas då den huvudsakliga fukttransporten sker i fiberriktningen. Svårigheter med torkstyrningen i form av övertorkning och kollaps har numera minimerats genom den senaste generationen högfrekvens-/vakuumtorkar. Metoden kräver tillgång till elenergi och energiförbrukningen uppges till 1.2 kWh per kg bortfört vatten.

  • 224.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Cherepanova, Ekaterina
    Determination of wood moisture properties using a CT-scanner in a controlled high-temperature environment2012Inngår i: Journal of Civil Engineering and Architecture, ISSN 1934-7359, E-ISSN 1934-7367, Vol. 6, nr 3, s. 372-378Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of the present work was to analyze moisture flow and moisture content data for high-temperature drying by using an advanced image- processing algorithm.Since wood starts to shrink below the fibre saturation point during drying, the size and shape of wood will change. The dry wood image was thoroughly transformed to the shape of the wet wood image prior to calculating the dry weight moisture content. The use of the image- processing algorithm for the dry weight moisture content on density data from the CT-scanning during drying in a controlled high-temperature environment showed that this method is a powerful tool for analyzing the moisture flow inside the wood piece. Furthermore, the new CT-scanner together with the climate chamber gave unique results, as it has not been possible to study high-temperature drying with this method before.

  • 225.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Cherepanova, Ekaterina
    Luleå tekniska universitet.
    Determination of wood moisture properties using a CT-scanner in a controlled low-temperature environment2012Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, nr 2, s. 87-92Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of the present work was to examine an advanced image-processing algorithm for moisture content (mc) calculation and also to use this algorithm to analyse moisture loss data for low temperature drying. Since wood starts to shrink below the fibre saturation point during drying, the geometrical shape of the wood piece will change. The dry wood image was thoroughly transformed to the shape of the wet wood image prior to calculating the dry weight mc. The results show that the algorithm for the dry weight mc on density data from the CT-scanning during low-temperature drying in the climate chamber is a powerful tool for analysing the moisture loss inside the wood piece. This method can make it possible to get a higher quality on the product

  • 226.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Cherepanova, Ekaterina
    Morén, Tom
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    CT-scanning during heat treatment of wood2011Inngår i: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 7, nr 4, s. 11-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Earlier experiences from industrial heat treatment of wood with the ThermoWood® process show that more or less extensive internal cracking may occur for thicker dimensions. This type of timber damage is particularly troublesome because these cracks do not reach the surface and are thus not visible on unprocessed timber. After resawing or planing the boards, cracks can appear, resulting in costly downgrading of the material. The ThermoWood® heat treatment process can be divided into six periods. The first period, the heating period, is when saturated steam is injected into the kiln, the second period is the drying step, which can be either high or low temperature drying, the third period is when the final heating and drying take place, the fourth period is when the temperature is kept constant for about 2–4 hours, the fifth period is the cooling regime, the sixth period is the conditioning regime for remoistening the material, and the last period is the cooling one. At the Division of Wood Physics at Luleå University of Technology in Skellefteå a climate chamber has recently been installed. This climate chamber together with a CTscanner makes it possible to study wood density changes in different climates. As the maximum temperature that can be reached in the climate chamber is 220 °C, it is also possible to study the heat treatment process, besides conventional air circulation drying. The aim of this study was to use the CT-scanning (CT) technique during heat treatment of wood in order to investigate whether it is possible to detect internal checking in situ during the treatment.

  • 227.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Fjellner, Bengt-Arne
    Luleå tekniska universitet, Verksamhetsstöd, VSS Support.
    Wood shrinkage coefficient and dry weight moisture content estimations from CT-images2013Inngår i: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 9, nr 4, s. 557-561Artikkel i tidsskrift (Fagfellevurdert)
  • 228.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Lundgren, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Antti, Lena
    Hagman, Olle
    FEM simulation of heating wood in an industrial microwave applicator2005Inngår i: 10th International Conference on Microwave and High Frequency Heating : Modena, Italy, September 12 - 15, 2005 / [ed] Cristina Leonelli, 2005Konferansepaper (Fagfellevurdert)
  • 229.
    Hansson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Lundgren, Nils
    Antti, Lena
    Hagman, Olle
    Microwave penetration in wood using imaging sensor2005Inngår i: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 38, nr 1, s. 15-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is possible to determine properties of wood using microwave scanning techniques. The purpose of this study was to verify the measured values from a microwave imaging sensor. Attenuation and phase shift of an electromagnetic wave transmitted through birch wood were measured and compared with theoretical calculated values. A test piece with varying thickness was measured with a scanner based on a microwave sensor (Satimo 9.375GHz) at different temperatures and moisture contents. The density distribution of the test piece was determined by computer tomography scanning. The result showed good correspondence between measured and theoretical values. The proportion of noise was higher at low moisture content due to lower attenuation. There is more noise in attenuation measurement than in measurement of phase shift. A reason for this could be that wood is an inhomogeneous material in which reflections and scattering affect attenuation more than phase shift. The microwave scanner has to be calibrated to a known dielectric to quantify the error in the measurement

  • 230.
    Haque, MD Minhaz Ul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Semi-IPN of biopolyurethane, benzyl starch, and cellulose nanofibers: Structure, thermal and mechanical properties2016Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 133, nr 45, artikkel-id 43726Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to develop bionanocomposites of biopolyurethane (PU), benzyl starch (BS), and cellulose nanofibers (CNF) with semi-interpenetrating polymer network (S-IPN) structure of improved properties. Morphology, thermal and mechanical properties of S-IPN blends and nanocomposites were studied and compared with the neat polymers. Microscopy study showed that PU and BS were partially miscible as well as CNF were dispersed in both PU and BS phases in the nanocomposites. Dynamic mechanic thermal analysis demonstrated that BS decreased the tan δ peak of the PU while CNF increased it. The positive shifting of tan δ peak in the S-IPN nanocomposite also indicated the presence of CNF in the PU phase. It was also noticed that S-IPN nanocomposite displayed two tan δ peaks at higher temperature, indicating molecular interaction among BS, PU, and CNF. Furthermore, the S-IPN nanocomposites displayed significantly higher E-modulus and tensile strength compared with the neat PU

  • 231.
    Haque, Md. Minhaz-Ul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Herrera, Natalia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Geng, Shiyu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu, Finland.
    Melt compounded nanocomposites with semi-interpenetrated network structure based on natural rubber, polyethylene, and carrot nanofibers2018Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 135, nr 10, artikkel-id 45961Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present study deals with the processing and characterization of cellulose nanocomposites natural rubber (NR), low-density polyethylene (LDPE) reinforced with carrot nanofibers (CNF) with the semi-interpenetrated network (S-IPN) structure. The nanocomposites were compounded using a co-rotating twin-screw extruder where a master-batch of NR and CNF was fed to the LDPE melt, and the NR phase was crosslinked with dicumyl peroxide. The prepared S-IPN nanocomposites exhibited a significant improvement in tensile modulus and yield strength with 5 wt % CNF content. These improvements are due to a better phase dispersion in the S-IPN nanocomposites compared with the normal blend materials, as demonstrated by optical microscopy, electron microscopy and ultraviolet–visible spectroscopy. The S-IPN nanocomposite also displayed an improved crystallinity and higher thermal resistance compared with NR, CNF, and the normal blend materials.

  • 232.
    Hassan, Enas A.
    et al.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Hassan, Mohammad L.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Abou-zeid, Ragab Esmail
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Use of bacterial cellulose and crosslinked cellulose nanofibers membranes for removal of oil from oil-in-water emulsions2017Inngår i: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 9, nr 9, artikkel-id 388Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Never-dried bacterial cellulose (BC) and crosslinked cellulose nanofibers (CNF) were used for the removal of oil from stabilized and non-stabilized oil-in-water emulsions with droplet sizes less than 1 µm. The CNF membranes were exchanged with isopropyl alcohol before drying. The microscopic structure of the prepared membranes was evaluated using scanning electron microscopy (SEM); the water flux and the rejection of oil were evaluated using a dead-end filtration cell. BC harvested after different incubation time periods (2 to 10 days) did not show a change in the width of the nanofibers, but only the thickness of the membranes was increased. Pure water flux was not affected as a result of increasing thicknesses of BC membranes harvested after 4–10 days while BC harvested after two days had significantly higher water flux than the others. BC showed a higher flux and efficiency in removing oil from oil emulsions than CNF membranes. Removal of oil by the different membranes from the non-stabilized oil emulsion was more efficient than from the stabilized one.

  • 233.
    Hassan, Enas A.
    et al.
    National Research Center, Cellulose & Paper Department, Cairo.
    Hassan, Mohammad L.
    National Research Center, Cellulose & Paper Department, Cairo.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Improving bagasse pulp paper sheet properties with microfibrillated cellulose isolated from xylanase-treated bagasse2011Inngår i: Wood and Fiber Science, ISSN 0735-6161, Vol. 43, nr 1, s. 76-82Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To improve the properties of paper sheets, microfibrillated cellulose (MFC) was isolated from bleached bagasse pulp pretreated with xylanase enzymes and returned to the pulp in varying amounts. The standard hand sheet paper-making method was used. The effect of adding different amounts of MFC on tensile strength (wet and dry), tear resistance, burst strength, opacity, and porosity of paper sheets was studied. Adding MFC to bagasse pulp improved wet and dry tensile strength, but tear resistance and burst strength decreased with increasing amounts of MFC. Also, adding MFC to bagasse pulp did not significantly affect opacity, slightly decreased porosity, and tightened the texture of the paper sheets as observed from scanning electron microscopy images. The strength properties of paper sheets made from bagasse and MFC were compared with those of paper sheets made from bagasse and softwood fibers. Paper sheets containing MFC had higher tensile strength (wet and dry) than those containing softwood fibers, but the later had higher tear resistance and burst strength.

  • 234.
    Hassan, Mohammad
    et al.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Giza, Egypt; Egypt Nanotechnology Centre, Cairo University, 6th October City, Egypt.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Abou-Zeid, Ragab
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Giza , Egypt.
    Hassan, Enas
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Giza , Egypt.
    Abou-Elseoud, Wafaa
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Giza , Egypt.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu, Oulu, Finland.
    Nanocomposite Film Based on Cellulose Acetate and Lignin-Rich Rice Straw Nanofibers2019Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 4, artikkel-id 595Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanofibers isolated from unbleached neutral sulfite rice straw pulp were used to prepare transparent films without the need to modify the isolated rice straw nanofibers (RSNF). RSNF with loading from 1.25 to 10 wt.% were mixed with cellulose acetate (CA) solution in acetone and films were formed by casting. The films were characterized regarding their transparency and light transmittance, microstructure, mechanical properties, crystallinity, water contact angle, porosity, water vapor permeability, and thermal properties. The results showed good dispersion of RSNF in CA matrix and films with good transparency and homogeneity could be prepared at RSNF loadings of less than 5%. As shown from contact angle and atomic force microscopy (AFM) measurements, the RSNF resulted in increased hydrophilic nature and roughness of the films. No significant improvement in tensile strength and Young’s modulus was recorded as a result of adding RSNF to CA. Addition of the RSNF did not significantly affect the porosity, crystallinity and melting temperature of CA, but slightly increased its glass transition temperature

  • 235.
    Hassan, Mohammad
    et al.
    Cellulose and Paper Department, Centre of Excellence for Advanced Sciences, National Research Centre, Giza, Egypt. Egypt Nanotechnology Centre, Cairo University, El-Sheikh Zayed, City, Egypt.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hassan, Enas
    Cellulose and Paper Department, Centre of Excellence for Advanced Sciences, National Research Centre, Giza, Egypt.
    Abou-Zeid, Ragab
    Cellulose and Paper Department, Centre of Excellence for Advanced Sciences, National Research Centre, Giza, Egypt.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu, Oulu, Finland.
    Effect of xylanase pretreatment of rice straw unbleached soda and neutral sulfite pulps on isolation of nanofibers and their properties2018Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 35, nr 5, s. 2939-2953Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There is a recent interest in producing cellulose nanofibers with different surface properties from unbleached cellulose pulps for economic and environmental reasons. In the current study we investigated the use of xylanase pretreatment on two types of unbleached rice straw pulps, namely, soda and neutral sulfite, and their fibrillation to nanofibers using ultrafine grinding. The effect of xylanase pretreatment on the fibrillation progress, energy consumption, and nanofiber dimensions was studied. In addition, mechanical properties, water contact angle, water absorption, and roughness of produced nanopapers were studied. Although very thin nanofibers with a homogenous width could be isolated from both xylanase-treated and untreated pulps, the xylanase pretreatment resulted in faster fibrillation. In addition, nanopapers prepared from xylanase-treated nanofibers had better mechanical properties than those isolated from the untreated pulps. The energy consumption during fibrillation depended on the type of pulp; a slightly lower energy consumption (~ 8%) was recorded for xylanase-treated soda pulp while a higher energy consumption (~ 21%) was recorded for xylanase-treated neutral sulfite pulp compared to the untreated pulps.

  • 236.
    Hassan, Mohammad L.
    et al.
    Cellulose and Paper Department, National Research Center, Dokki.
    Fadel, Shaimaa M.
    Cellulose and Paper Department, National Research Center, Dokki.
    El-Wakil, Nahla A.
    Cellulose and Paper Department, National Research Center, Dokki.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Chitosan/rice straw nanofibers nanocomposites: preparation, mechanical, and dynamic thermomechanical properties2012Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 125, nr Suppl. 2, s. E216-E222Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanofibers were isolated from rice straw pulp using ultrahigh friction grinding and high-pressure homogenization. Chitosan nanocomposites were prepared using the isolated nanofibers at fiber loading from 2.5 to 20% by solution casting and evaporation technique. The effect of nanofiber loading on dry and wet tensile strength, dynamic mechanical thermal properties, and cyrstallinity of chitosan were studied using tensile testing, thermogravimetric analysis, dynamic mechanical thermal analysis, and X-ray diffraction. Addition of rice straw nanofibers (RSNF) to chitosan resulted in significant improvement in wet and dry tensile strength, and shift of glass transition temperature (Tg) of chitosan matrix to higher values. Chitosan nanocomposites prepared using RSNF (CRSNF) had remarkable wet and dry tensile strength, which could be attributed to presence of both nanofibers and nanosilica particles originally present in rice straw fibers. Addition of RSNF to chitosan did not affect its onset thermal degradation temperature

  • 237.
    Hassan, Mohammad L.
    et al.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Abou-zeid, Ragab Esmail
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Hassan, Enas A.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Membranes based on cellulose nanofibers and activated carbon for removal of Escherichia coli bacteria from water2017Inngår i: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 9, nr 8, artikkel-id 335Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 238.
    Hassan, Mohammad L.
    et al.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Hassan, Enas A.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Fadel, Shaimaa M.
    Cellulose and Paper Department and Centre of Excellence for Advanced Sciences, National Research Centre, Giza.
    Abou-zeid, Ragab Esmail
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, Faculty of Technology, University of Oulu.
    Metallo-Terpyridine-Modified Cellulose Nanofiber Membranes for Papermaking Wastewater Purification2018Inngår i: Journal of Inorganic and Organometallic Polymers, ISSN 1053-0495, E-ISSN 1572-8870, Vol. 28, nr 2, s. 439-447Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Metallo-terpyridine compounds and polymers exhibit unique optical, electrical, magnetic and antimicrobial properties. Recently, metallo-terpyridine-modified cellulosic films with interesting porous structure, that exhibit these properties, have been prepared. Herein we report the use of Cu-terpyridine-modified oxidized cellulose nanofibers (OXCNF-Cu-Tpy) as membranes for treatment of effluents of paper mills to produce re-usable water. The OXCNF-Cu-Tpy was prepared by modification of TEMPO-oxidized CNF (OXCNF) using copper(II) complex of 4′-Chloro [2,2′:6′,2″] terpyridine. The modification was proven by elemental analysis and Fourier transform infrared spectroscopy. The prepared OXCNF-Cu-Tpy was also characterized using X-ray diffraction and transmission electron microscopy. The prepared membranes were evaluated regarding their microscopic structure using scanning electron microscopy, atomic force microscopy, contact angle measurement, water flux and rejection of sub-micron size suspended particles in papermaking wastewater effluent. Chemical modification of OXCNF with the Cu-Tpy groups significantly increased pure water flux of the membranes by about 52 and 194% depending on pressure used during filtration (0.5 and 1 MPa, respectively). Although both OXCNF and OXCNF-Cu-Tpy exhibited high efficiency in removing the sub-micron size suspended particles from wastewater effluent, OXCNF-Cu-Tpy membranes showed about 30% higher flux rate than OXCNF membranes.

  • 239.
    Hassan, Mohammad L.
    et al.
    Cellulose and Paper Department, National Research Center, Dokki.
    Hassan, Enas A.
    Cellulose and Paper Department, National Research Center, Dokki.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effect of pretreatment of bagasse fibers on the properties of chitosan/microfibrillated cellulose nanocomposites2011Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 46, nr 6, s. 1732-1740Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bleached bagasse pulp was pretreated with dilute alkali and xylanase enzymes before isolation of microfibrillated cellulose using ultra-high friction grinding and high-pressure homogenization. The isolated nanofibers were used with chitosan polymer to prepare chitosan nanocomposites by solution casting at nanofiber loading from 2.5 to 20%. The effect of nanofibers loading on moisture sorption, dry and wet tensile strength, crystallinity, thermal stability, and dynamic mechanical thermal properties was studied using tensile testing, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA). Nanocomposites with good transparency were obtained at the different nanofibers loadings. Chitosan nanocomposites made using nanofibers isolated from bagasse fibers treated with xylanase or alkali showed higher dry and wet tensile strength than those made using nanofibers isolated from untreated bagasse pulp. DMTA results showed higher storage modulus and indicated higher glass transition temperature for the chitosan nanocomposites than that of neat chitosan. XRD patterns showed that, at low nanofibers loading, addition of bagasse nanofibers to chitosan matrix increased ordering of chitosan chains upon drying the nanocomposites films.

  • 240.
    Hassan, Mohammad L.
    et al.
    National Research Centre.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hassan, Enas A.
    National Research Centre.
    Fadel, Shiamaa M
    National Research Centre.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Improving cellulose/polypropylene nanocomposites properties with chemical modified bagasse nanofibers and maleated polypropylene2014Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 33, nr 1, s. 26-36Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 241.
    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 tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effect of pretreatment of bagasse pulp on properties of isolated nanofibers and nanopaper sheets2010Inngår i: Wood and Fiber Science, ISSN 0735-6161, Vol. 42, nr 3, s. 362-376Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 242.
    Hassan, Mohammad
    et al.
    National Research Centre.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hassan, Enas
    National Research Centre.
    El-Wakil, Nahla
    National Research Centre.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nanofibers from bagasse and rice straw: process optimization and properties2012Inngår i: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, nr 1-3, s. 193-205Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 243.
    Hassan, Mohammad
    et al.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Dokki, Giza, Egypt. Egypt Nanotechnology Centre, Cairo University, 6th October City, Egypt.
    Zeid, Ragab E. Abou
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Dokki, Giza, Egypt.
    Abou-Elseoud, Wafaa S.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Dokki, Giza, Egypt.
    Hassan, Enas
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Dokki, Giza, Egypt.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON, Canada.
    Effect of Unbleached Rice Straw Cellulose Nanofibers on the Properties of Polysulfone Membranes2019Inngår i: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 11, nr 6, artikkel-id 938Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In addition to their lower cost and more environmentally friendly nature, cellulose nanofibers isolated from unbleached pulps offer different surface properties and functionality than those isolated from bleached pulps. At the same time, nanofibers isolated from unbleached pulps keep interesting properties such as hydrophilicity and mechanical strength, close to those isolated from bleached pulps. In the current work, rice straw nanofibers (RSNF) isolated from unbleached neutral sulfite pulp (lignin content 14%) were used with polysulfone (PSF) polymer to make membrane via phase inversion. The effect of RSNF on microstructure, porosity, hydrophilicity, mechanical properties, water flux, and fouling of PSF membranes was studied. In addition, the prepared membranes were tested to remove lime nanoparticles, an example of medium-size nanoparticles. The results showed that using RSNF at loadings from 0.5 to 2 wt.% can significantly increase hydrophilicity, porosity, water flux, and antifouling properties of PSF. RSNF also brought about an increase in rejection of lime nanoparticles (up to 98% rejection) from their aqueous suspension, and at the same time, with increasing flux across the membranes. Tensile strength of the membranes improved by ~29% with addition of RSNF and the maximum improvement was obtained on using 0.5% of RSNF, while Young’s modulus improved by ~40% at the same RSNF loading. As compared to previous published results on using cellulose nanofibers isolated from bleached pulps, the obtained results in the current work showed potential application of nanofibers isolated from unbleached pulps for improving important properties of PSF membranes, such as hydrophilicity, water flux, rejection, and antifouling properties

  • 244.
    Hedmark, Per G.
    et al.
    Kungliga tekniska högskolan, KTH.
    Jansson, Jan-Fredrik
    Kungliga tekniska högskolan, KTH.
    Hult, Anders
    Kungliga tekniska högskolan, KTH.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Gedde, Ulf W.
    Luleå tekniska universitet.
    Selective etching of thermotropic liquid crystalline polyesters1987Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 34, nr 2, s. 743-762Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    DSC, IR, ESCA, macroscopic etching rate measurements, analysis of etchant solution, and electron microscopy conclusively show that n-alkylamines (ethylamine, n-propylamine, n-butylamine, and n-pentylamine) and NaOH selectively degrade (etch) the ethylene terephthalate (ET)-rich phase in glassy liquid crystalline poly(p-hydroxybenzoic acid-co-ethylene terephthalate) [P(HBA-ET)] with molar compositions 0.60:0.40 and 0.80:0.20. ESCA demonstrates the excellent selectivity of the n-alkylamine etchants in the 0.60:0.40 copolymer. The 50 Å top layer of the etched samples contains 95 mol% HBA. Treatment with H2SO4 and NH3 gives ambiguous results, and these compounds are not suitable as etchants. It is demonstrated by electron microscopy on the 0.60:0.40 copolymer, in accordance with earlier reports by Joseph et al.,5-8 that the ET-rich phase is discontinuous (1-2 m spheres) and surrounded by an HBA-rich matrix. SEM is a useful tool for characterization of this morphology. However, both phases have a substracture which is revealed only by TEM. The morphology of the 0.80:0.20 copolymer is fine-textured, which means that SEM is a less suitable method for the characterization of etched samples.

  • 245.
    Hemmilä, Venla
    et al.
    Linnéuniversitetet.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Modified Wood-Protein Adhesive Bondline Strength Development during Curing2014Inngår i: The seventh European Conference on Wood Modification: Book of Abstracts / [ed] Lina Nunes; Dennis Jones; Callum Hill; Holger Militz, Lissabon, 2014, s. 134-137Konferansepaper (Fagfellevurdert)
  • 246.
    Herrera, Martha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Preparation and characterization of nanocellulose films and coatings from industrial bio-residues2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The aim of this work has been to study cellulose nanocrystals (CNC) from bio-residues and their use as green coating materials. In the first part of this work, physical and chemical properties of different types of cellulose nanocrystals, from different raw material sources and different treatments were compared. It was found that all CNC suspensions had similar flow birefringence behavior, and similar diameters of the crystals. The mechanically isolated CNC from bio-ethanol residue had lower crystallinity but higher thermal stability compared chemically isolated CNC. Also the surface charge of these nanocrystals was different, being lower for the mechanically isolated CNC.In the second part, nanocrystals with lower and higher surface charges, were used to spin-coat films. The films were prepared with two different configurations: one with alternating layering of an anchoring polymer and CNC and the other with a single polymer layer coated with multilayers of CNC. The CNC with higher surface charge resulted in a smoother surface and the surface charge impacted the films’ hydrophobicity, being highest for CNC with lower surface charge. The gas permeability coefficient was dependent primarily on the surface charge of the CNC and secondly on the film configuration. The films with lower surface charge CNC were gas barriers for nitrogen and oxygen, and showed gas selectivity with some gas combinations while the films with higher surface charge CNC did not show gas selectivity.In the third part, coatings of CNC were prepared using spin- and dip-coating methods, on porous cellulose substrates. Microscopy studies showed that spin coating technique was suitable for the substrate with smaller pore size, while dip coating was suitable for the substrate with the larger pore size. The coating thickness ranged from some hundreds of nanometers for the spin-coated samples, to some micrometers for the dip-coated ones. The contact angle increased with the coating thickness and roughness. Additionally, the samples showed low oxygen permeability at 23% of relative humidity (RH). It was also seen that eight months storing reduced the barrier properties of the coatings when compared with fresh materials.In the last study, a new coating design as well as sorbitol plasticizer and citric acid crosslinker were used to improve the barrier and mechanical properties. This resulted in a dramatic improvement of the barrier properties and decreased water vapor permeability of more than 60%. Oxygen permeability value as low as 0.7 mL*μm/(m2*day*kPa) at 49% RH was reached when sorbitol was used. Overall, it was seen that the addition of sorbitol increased the thermal stability, barrier properties, and maximum strength of the CNC coatings.This work has demonstrated that nanocellulose films and coating from bio-residues can potentially be used to produce functional barrier coatings, thereby increasing the value of the forest resources.

  • 247.
    Herrera, Martha A.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Barrier and mechanical properties of plasticized and cross-linked nanocellulose coatings for paper packaging applications2017Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 9, s. 3969-3980Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 248.
    Herrera, Martha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Jackson-Etang, Ayuk
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Novel biorefinery: A residue from wood bioethanol production converted into cellulose nanocrystals2010Inngår i: International Conference on Nanotechnology for the Forest Products Industry 2010: Otaniemi, Espoo, Finland, 27-29 September 2010, Norcross, GA: TAPPI Press, 2010, s. 1241-1266Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of the work was to use an industrial bio-residue as a raw material for the production of cellulose nanocrystals. The used residue, obtained from a bioethanol pilot plant, was purified using chemical extraction and whitening, and separated to nanocrystals by mechanical and chemical treatments such as ultrasonication, high-pressure homogenization and hydrolization. The chemical compositions and characteristics of the bio-residue were studied before and after purification using a TAPPI standard, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The morphology of the isolated nanocrystals was characterized using atomic force microscope (AFM). The chemical composition of the used bio-residue was found to be 49.5 wt-% cellulose, 42.1 wt-% lignin and 8.4 wt-% extractives. The crystallinity of the bio-residue was 14.5% and it increased to more than 73% after the purification process. The AFM study showed that a simple ultrasonication and homogenization processes resulted in nanosized crystals with diameters in the 10-20 nm range.

  • 249.
    Herrera, Martha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Cellulose nanocrystals: extraction from bio-residues2013Inngår i: Production and Applications of Cellulose Nanomaterials, TAPPI Press, 2013, s. 13-16Kapittel i bok, del av antologi (Fagfellevurdert)
    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.

  • 250.
    Herrera, Martha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Characterization of cellulose nanowhiskers: a comparison of two industrial bio-residues2012Inngår i: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Konferansepaper (Fagfellevurdert)
    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.

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