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  • 51.
    Awoyemi, Lawrence
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Influence of prefreezing on the fibre saturation point, sorption and swelling properties of birch (Betula pubescens) wood2006Inngår i: International Wood Products Journal, ISSN 0020-3203, Vol. 17, nr 4, s. 225-227Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Matched samples were obtained from green birch (Betula pubescens) wood. Prefreezing was done at -20°C for 72hours. Both the prefrozen and unfrozen samples were dried and soaked in water for the determination of sorption behavior, swelling properties and fibre saturation point. Prefreezing resulted in 6.7 to 666.7% increase in rate of adsorption, 0 to 13.3% decrease in the rate of desorption, 2.2% decrease in volumetric swelling coefficient and 0.8% decrease in fibre saturation point. However only the change in the rate of water adsorption is statistically significant at 95% confidence level. Since these results were obtained from samples taken from a typical board, more results are required in order to characterise the effects of prefreezing on available stock of Birch wood

  • 52.
    Awoyemi, Lawrence
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Mechanical behaviour of birch (Betula Pubescens) wood under high temperature drying2009Inngår i: International Wood Products Journal, ISSN 0020-3203, Vol. 19, nr 1, s. 27-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High temperature drying is employed to reduce the drying time of sawn wood. However the deterioration in mechanical properties associated with it seems to be a major limitation of its use in the seasoning of some wood species. As in conventional drying, both the modulus of elasticity and modulus of rupture increase with decreasing moisture content. High temperature drying does not seem to constitute a meaningful threat to the mechanical properties of this species and hence its use is strongly recommended. The low effect of high temperature drying on this species strongly reinforces the results of the previous studies on other species that the effect of this technique is both species and property dependent.

  • 53.
    Awoyemi, Lawrence
    Luleå tekniska universitet.
    Reversibility of dimensional changes in birch (Betula pubescens) and Scots pine (Pinus sylvestris L.) wood2004Inngår i: Taiwan Linye Kexue, ISSN 1026-4469, Vol. 19, nr 2, s. 97-101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The reversibility of wood shrinkage through swelling of birch (Betula pubescens) and Scots pine (Pinus sylvestris L.) as a measure of their response to changing conditions of adsorption and desorption during service was determined. Virtually all dimensional changes that occurred in the form of shrinkage during drying at both conventional and high temperatures were recovered during swelling in both species. It is suggested that minor changes in the equilibrium moisture content, which commonly occur during the life span of wood, will not result in significant dimensional changes in either species except in the tangential direction of Scots pine. Significant differences between shrinkage and swelling in the tangential direction in Scots pine where swelling was greater than shrinkage implies a higher stability of Scots pine during shrinkage compared to swelling. Hence it is expected that in the tangential direction, this species will be more stable during desorption than adsorption

  • 54.
    Baby, Thomas
    et al.
    Kuriakose Gregorios College, Pampady, Kottayam, Kerala, India.
    Jose E, Tomlal
    St Berchmans College, Changanachery, Kottayam, Kerala, India.
    George, Gejo
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varkey, Vinitha
    Kuriakose Gregorios College, Pampady, Kottayam, Kerala, India.
    Cherian, Shijo K.
    St Berchmans College, Changanachery, Kottayam, Kerala, India.
    A new approach for the shaping up of very fine and beadless UV light absorbing polycarbonate fibers by electrospinning2019Inngår i: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 80, artikkel-id 106103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An innovation will be recognized as successful only if it satisfies all phases of product development; i.e. from the specification to mass production. Therefore, a cost-effective production by keeping the best possible characteristics is vital in any Industry. Large scale production of polymer fibers with ultrafine morphology is such a challenge to in the field of nanotechnology. The idea proposed here utilizes the versatile electrospinning technology for the preparation of uniform, beadless and ultraviolet light absorbing polycarbonate (PC) nanofibers. The average diameter limits to 114 nm and that too by using most convenient and comparatively less toxic solvent mixture. This method is simple and so far, it is not reported elsewhere. For THF-DMF system a PC concentration of 17 w/v% and for DCM-DMF system a PC concentration of 15 w/v% was found to be the optimum polymer concentration. The average fiber diameter and bead density were very much influenced by the viscosity, conductivity and concentration of the solution used for electrospinning. The PC fibers (PC concentration of 15 w/v % in DCM-DMF system) with lowest average diameter of 114 nm shows excellent ultraviolet absorption, semicrystalline nature, enhanced glass transition temperature and thermal stability.

  • 55.
    Backman, Anna
    Luleå tekniska universitet.
    Interaction and adhesion at the interface between wood and paint, glue, lacquer measured with DMTA and SEM2000Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The aim of the present thesis was to study the interface between wood (Pinus sylvestis) and synthetic polymers such as glue, lacquer and paint. The weakest part of these interfaces is always the bond. The long-term properties of bonds between wood and an adherend are those which are interesting. If a good bond is achieved, the surface between wood and an adherend would be less susceptible to degradation. To achieve a good bond, the wood polymers and the adhering polymers must be compatible. The contact area between the substrate and an adherend should be as large as possible to give a high quantity of bonds. A large contact area also gives the possibility of adhesion through mechanical interlocking. The interaction between wood and glue and lacquer was studied with Dynamic Mechanical Thermal Analysis. The interaction was correlated with adhesion properties observed with Scanning Electron Microscopy (SEM) fractography. Dynamic mechanical properties of untreated wood in the tangential and radial direction was studied to have a knowledge of the wood polymers behaviour. The properties of the wood polymers was needed for evaluating the change in behaviour when wood was combined with glue and lacquer. It was shown that polymers interacting with the wood polymers experienced a higher free volume in contact with wood, thus decreasing the glass transition temperature of the synthetic polymers. This decrease was considered most probably to be due to the polymers being subjected to tensile forces developed during drying. The high level of interaction was correlated to high adhesion on the wood cell wall level. Two similar commercial polyurethane-alkyd lacquers showed interaction with wood, but a commercial polyvinyl acetate glue showed poor interaction and poor adhesion. The fracture surface between wood and paint in a 50-year-old window was studied with SEM, using backscattered electron image. The method makes it possible to analyse fracture surfaces and determine where the fracture occurrs. It could be used, as an indication of whether the weakest link in different paint/wood systems is the interface.

  • 56.
    Baillif, Marie Le
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    The effect of processing on fiber dispersion, fiber length and thermal degradation of bleached sulfite cellulose fiber polypropylene composites2009Inngår i: Journal of Thermoplastic Composite Materials, ISSN 0892-7057, E-ISSN 1530-7980, Vol. 22, nr 2, s. 115-133Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The goal of this study was to examine how the extrusion process affects the dispersion, length and thermal degradation of cellulose fibers (CF) in polypropylene (PP) composites. Bleached sulfite cellulose fibers were pelletized and then compounded (20 and 30 wt%) in a co-rotating twin screw extruder. The pelletizing process of cellulose fibers was found to cause extensive fiber breakage. The fiber length was decreased from an initial 1.7 to 0.8 mm. The results showed that higher screw speed, higher fiber content and two extrusions increased the shear energy, resulting in improved fiber dispersion but also caused fiber breakage and thermal degradation. The composites mechanical properties were not improved with better fiber dispersion and the reason for this might be the extensive fiber breakage and thermal degradation. Moreover, it was found that the PP polymer was also slightly degraded during the compounding process.

  • 57.
    Bajraktari, Agron
    et al.
    Prishtina University, Faculty of Technical Applied Sciences.
    Korkut, Süleyman
    Duzce University, Faculty of Forestry, Department of Forest Industrial Engineering.
    Elustondo, Diego
    Duzce University, Faculty of Forestry, Department of Forest Industrial Engineering.
    Cukaj, Kushtrim
    Prishtina University, Faculty of Technical Applied Sciences.
    Thac, Bashkim
    Prishtina University, Faculty of Technical Applied Sciences.
    Weathering protection for beech wood in Kosovo2013Inngår i: International Journal of Current Engineering and Technology, ISSN 2277-4106, Vol. 3, nr 2, s. 331-333Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Beech wood (Fagus sylvatica L.) is one of the most important timber species produced in Kosovo. About 33% of the trees in our country are beech and most of the wood products are from this kind of timber. The color difference between red heart wood and white wood of the beech is significant. Adequate protection against weathering (snow, rain and low temperature) and leaching of preservative components into the environment are the main problems faced by wood companies in Kosovo as coatings defects may become apparent after only one year of outside exposure. The aim of this study was to assess the best way to protect beech wood products from weathering with available types of commercial wood coatings: film forming, non film forming, transparent stain and semi transparent penetrating stain. We concluded that the film forming and semitransparent penetrating stain are the best painting methods for beech woodproducts protection, according to weathering performance and coating properties.

  • 58.
    Bekin, Seda
    et al.
    Department of Chemical Engineering, Faculty of Engineering, Istanbul University.
    Sarmad, Shokat
    Department of Chemical Engineering, Faculty of Engineering, Istanbul University.
    Gürkan, Koray
    Department of Electrical and Electronics Engineering, Faculty of Engineering, Istanbul University.
    Keçeli, Gönül
    Department of Chemistry, Faculty of Engineering, Istanbul University.
    Gürdağ, Gülten
    Department of Chemical Engineering, Faculty of Engineering, Istanbul University.
    Synthesis, characterization and bending behavior of electroresponsive sodium alginate / poly (acrylic acid) interpenetrating network films in an electric stimulus2014Inngår i: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 202, s. 878-892Artikkel i tidsskrift (Fagfellevurdert)
  • 59.
    Bekin, Seda
    et al.
    Department of Chemical Engineering, Faculty of Engineering, Istanbul University.
    Sarmad, Shokat
    Department of Chemical Engineering, Faculty of Engineering, Istanbul University.
    Gürkan, Koray
    Department of Electrical and Electronics Engineering, Faculty of Engineering, Istanbul University.
    Yenici, Gökcen
    Department of Chemical Engineering, Faculty of Engineering, Istanbul University, Avcilar.
    Keceli, Gönül
    Department of Chemistry, Faculty of Engineering, Istanbul University.
    Gürdag, Gülten
    Department of Chemical Engineering, Faculty of Engineering, Istanbul University.
    Dielectric, thermal, and swelling properties of calcium ion crosslinked sodium alginate film2014Inngår i: Polymer Engineering and Science, ISSN 0032-3888, E-ISSN 1548-2634, Vol. 54, nr 6, s. 1372-1382Artikkel i tidsskrift (Fagfellevurdert)
  • 60.
    Bengtsson, Magnus
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Gatenholm, Paul
    CTH.
    Oksman, Kristiina
    The effect of crosslinking on the properties of polyethylene/wood flour composites2005Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 65, nr 10, s. 1468-1479Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the possibility of using silane technology in crosslinking composites of wood flour and polyethylene has been investigated. Composites of vinyltrimethoxy silane grafted high density polyethylene and wood flour were produced by compounding in a twin-screw extruder. Gel content analysis with p-xylene extraction revealed higher gel content in the samples where wood flour was added compared to neat crosslinked matrix. Mechanical analysis of the crosslinked composites showed increased tensile strength with increasing amount of wood flour, which might be an indication of improved adhesion between the matrix and the wood flour. The stiffness increased with increasing amount of wood flour with accompanied decrease in strain at break. Dynamic mechanical thermal analysis of crosslinked plastics and composites showed no significant shift in the γ-transition towards higher temperature for the composites compared to neat plastic. Short-term creep experiments showed reduced creep deformation with increasing amount of wood flour. Crosslinking of the composites reduced the creep deformation further. A boiling test in water followed by tensile testing showed that the crosslinked composites were less susceptible to water uptake compared to the non-crosslinked. Moreover, the decrease in tensile strength of the crosslinked composites was not as significant as for the non-crosslinked composites. Scanning electron microscopy revealed good compatibility and adhesion between the plastic and the wood flour for crosslinked composites.

  • 61.
    Bengtsson, Magnus
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    LeBaillif, Marie
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Extrusion and mechanical properties of highly filled cellulose fibre-polypropylene composites2007Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 38, nr 8, s. 1922-1931Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study focused on manufacturing of highly filled cellulose fibre-polypropylene composites and evaluation of the mechanical properties of the composites. Cellulose fibre reinforced polypropylene composites with up to 60 wt-% of fibres with and without coupling agent were manufactured by extrusion. In order to achieve consistent feeding of the fibres into the extruder a pelletization technique was used where the fibres were pressed into pellets. Two commercial grades of cellulose fibres were used in the study, bleached sulfite and bleached kraft fibres. Fibre dimension measurements showed that the pelletization process and extrusion at high fibre loading caused the most severe fibre breakage. Flexural testing showed that increased fibre loading made the composites stiffer but reduced the toughness. Addition of maleic anhydride grafted coupling agent increased the stiffness and strength of the composites significantly. In general, there was no significant difference in the mechanical properties between the composites with kraft and sulfite fibres. Scanning electron microscopy showed that addition of coupling agent improved the interfacial adhesion between the fibres and polypropylene matrix.

  • 62.
    Bengtsson, Magnus
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Crosslinked wood-thermoplastic composites: profile extrusion & mechanical properties2006Inngår i: Proceedings of the International Conference on Progress in Wood and Bio-Fibre Plastic Composites, Centre for Materials and Manufacturing , 2006Konferansepaper (Fagfellevurdert)
  • 63. Bengtsson, Magnus
    et al.
    Oksman, Kristiina
    Optimization of silane crosslinkling technology for use in polyethylene-wood flour composites2005Inngår i: 8th International Conference on Woodfiber-Plastic Composites (and Other Natural Fibers): May 23 - 25, 2005, Monona Terrace Community & Convention Center, Madison, Wisconsin, USA, Forest Products Society, 2005Konferansepaper (Fagfellevurdert)
  • 64.
    Bengtsson, Magnus
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Silane crosslinked wood plastic composites: Processing and properties2006Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 66, nr 13, s. 2177-2186Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The focus of the study has been to produce silane crosslinked wood plastic composites in a compounding process. Silane crosslinking is one way to improve the mechanical and long-term properties of wood plastic composites. Silane crosslinked composites with different amounts of vinyltrimethoxy silane were produced in a compounding process using a co-rotating twin-screw extruder. The composites were stored in a sauna and at room temperature to study the effect of humidity on the degree of crosslinking. Gel content and swelling experiments showed that the highest degree of crosslinking was found in the composites stored in a sauna. The crosslinked composites showed toughness, impact strength and creep properties superior to those composites to which no silane was added. The flexural modulus, on the other hand, was lower in the crosslinked samples than in the non-crosslinked ones. Differential scanning calorimetry measurements of the composites showed a lower crystallinity in the crosslinked samples than in the non-crosslinked.

  • 65. Bengtsson, Magnus
    et al.
    Oksman, Kristiina
    The Effect of Crosslinking on the Properties of Polyethylene/Wood Flour Composites2004Inngår i: Conference proceedings: Progress in Woodfibre-Plastic Composites Conference 2004 : May 10 - 11, 2004, Toronto, Canada, Toronto, 2004Konferansepaper (Fagfellevurdert)
  • 66.
    Bengtsson, Magnus
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    The use of silane technology in crosslinking polyethylene/wood flour composites2006Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 37, nr 5, s. 752-765Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the use of silane technology in crosslinking polyethylene-wood flour composites have been investigated. Composites were produced in a one-step process using a co-rotating twin-screw extruder. The composites were stored in a sauna and at room temperature to study the effect of humidity on the degree of crosslinking. Crosslinked composites showed improved toughness and creep properties compared to non-crosslinked composites. The flexural modulus, on the other hand, was lower in the crosslinked samples than in the non-crosslinked ones. FTIR was used to study the crosslinking reaction in the samples. X-ray mapping of the silicon signal was also performed to locate the silane in the composites. This study provides a basis for proposing, that part of the silane is grafted onto polyethylene and wood thereby creating a crosslinked network in the matrix with chemical bonds (covalent and hydrogen bonding) to wood. The other part of the silane remains un-reacted and blends into the system.

  • 67.
    Bengtsson, Magnus
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Stark, Nicole
    Forest Products Laboratory.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Durability and mechanical properties of silane cross-linkedwood thermoplastic composites2007Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 67, nr 13, s. 2728-2738Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, silane cross-linked wood-polyethylene composite profiles were manufactured by reactive extrusion. These composites were evaluated regarding their durability and mechanical properties in comparison with two non-cross-linked wood-polyethylene composites. An addition of only 2% w/w of silane solution during manufacturing was enough to achieve almost 60% degree of cross-linking after curing. The cross-linked composites showed flexural toughness superior to the non-cross-linked composites. The cross-linked composites also absorbed less moisture during a boiling test in water and this was an indirect evidence of improved interfacial adhesion. After accelerated weathering for 1000-3000 h the general trend was a decrease in flexural modulus and strength of both the non-cross-linked and cross-linked composites. The decrease in modulus seemed to be lower for the cross-linked composites while the decrease in strength seemed to be higher compared to the non-cross-linked composites. Weathering also resulted in a considerable colour fading of the composites. Water absorption-freeze-thaw cycling decreased the flexural modulus of non-cross-linked composites considerably while there was no statistical decrease in modulus for the cross-linked composites. There was only an insignificant decrease in strength for the composites after the water absorption-freeze-thaw cycling.

  • 68.
    Bengtsson, Magnus
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Stark, Nicole
    Forest Products Laboratory.
    Oksman, Kristiina
    Profile Extrusion and Mechanical Properties of Crosslinked Wood-Thermoplastic Composites2006Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 27, nr 2, s. 184-194Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Challenges for wood-thermoplastic composites to be utilized in structural applications are to lower product weight and to improve the long-term load performance. Silane crosslinking of the composites is one way to reduce the creep during long-term loading and to improve the mechanical properties. In this study, silane crosslinked wood-polyethylene composites were produced by reactive extrusion and subsequently manufactured into rectangular profiles. The silane crosslinked composites were stored in a sauna at 90 °C to increase the degree of crosslinking. The toughness of the silane crosslinked composites was significantly higher than for the non-crosslinked composites. Improved adhesion between the wood and polyethylene phases is most likely the reason for the improved toughness of the crosslinked composites. There was no significant difference in flexural modulus between the crosslinked and non-crosslinked composites. In addition, impact testing showed that the impact strength of the crosslinked composites was considerable higher (at least double) than the non-crosslinked. The effect of temperature on the impact strength of the composites indicated slightly higher impact strength at _30 °C than at 0° and at 25 °C, and then an incrase in impact strength at 60 °C. Crosslinking also reduced the creep response during short-term loading. Moreover, scanning electron microscopy on the fracture surface of the crosslinked composites revealed good adhesion between the polyethylene and wood phases.

  • 69.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    From bio-based residues to nanofibers using mechanical fibrillation for functional biomaterials2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Bio-based resource utilization in different forms has been driven by societal, industrial and academic research interests towards the development of “green”, sustainable materials from renewable sources. Within this context, exploiting biomass from different industrial residues is further advantageous from an environmental and economic point of view, leading to minimization of residues by means of waste treatment and to the development of high-addedvalue- products. Breaking down the cell wall structure to its smallest structural components is one means of turning bio-based residues into high-value products, leaving us with nanofibers. The aim of this work has been to understand how these nanofibers can be liberated from various cellulosic sources using mechanical fibrillation and how they can be assembled into functional hydrogels.

    The production of bio-based nanofibers as a sustainable bio-based material is in the early stages of commercialization and considerable research has been devoted to explore different methods of reaching nanoscale. However, the extraction process by chemical and/or mechanical means is still associated with a relatively high energy demand and/or cost. These are key obstacles for use of the material in a wide range of applications. Another challenge is that methods to characterize nanofiber dimensions are still being developed, with few options available as online measurements for assessing the degree of fibrillation. Allowing for assessment during the fibrillation process would enable not only optimization towards a more energy efficient fibrillation, but also matching of the nanofiber quality to its intended function, since different applications will require widely different nanofiber qualities. Energy-efficient fibrillation and scalability from industrial residues were explored using upscalable ultrafine grinding processes.

    Nanofibers from various industrial bio-residues and wood were prepared and characterized, including the development of a method for evaluation of the fibrillation process online via viscosity measurements as an indication of the degree of fibrillation down to nanoscale. Furthermore, the correlation of viscosity to that of the strength of the nanopapers (dried fiber networks) was evaluated for the different raw materials.

    Switchable ionic liquids (SIL) were tested as a green pretreatment for delignification, without bleaching of wood prior to fibrillation, with the aim to preserve the low environmental impact that the raw material source offers.

    In order to employ the hydrophilic nature and strong network formation ability of the fibrillated nanofibers, they were utilized in the preparation of functional biomaterials in the form of hydrogels. Firstly, brewer’s spent grain nanofibers were used to promote and reinforce hydrogel formation of lignin-containing arabinoxylan, resulting in a hydrogel completely derived from barley residues. In addition, alginate-rich seaweed nanofibers from the stipe (stem-like part of the seaweed) were used directly after fibrillation as an ink and hydrogels were formed via 3D printing.

  • 70.
    Berglund, Linn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Anugwom, Ikenna
    Technical Chemistry, Department of Chemistry, Chemical-Biological Centre, Umeå University .
    Hedenström, Mattias
    Technical Chemistry, Department of Chemistry, Chemical-Biological Centre, Umeå University .
    Aitomäki, Yvonne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mikkola, Jyri-Pekka
    Technical Chemistry, Department of Chemistry, Chemical-Biological Centre, Umeå University.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu.
    Switchable ionic liquids enable efficient nanofibrillation of wood pulp2017Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 8, s. 3265-3279Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 71.
    Berglund, Linn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonoobi, Mehdi
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu, Oulu, Finland.
    Promoted hydrogel formation of lignin-containing arabinoxylan aerogel using cellulose nanofibers as a functional biomaterial2018Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 8, nr 67, s. 38219-38228Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, three-dimensional (3D) aerogels and hydrogels based on lignin-containing arabinoxylan (AX) and cellulose nanofibers (CNF) were prepared. The effects of the CNF and the crosslinking with citric acid (CA) of various contents (1, 3, 5 wt%) were evaluated. All the aerogels possessed highly porous (above 98%) and lightweight structures. The AX-CNF hydrogel with a CA content of 1 wt% revealed a favorable network structure with respect to the swelling ratio; nanofiber addition resulted in a five-fold increase in the degree of swelling (68 g of water per g). The compressive properties were improved when the higher CA content (5 wt%) was used; when combined with CNF, there was a seven-fold enhancement in the compressive strength. The AX-CNF hydrogels were prepared using a green and straightforward method that utilizes sustainable resources efficiently. Therefore, such natural hydrogels could find application potential, for example in the field of soft tissue engineering.

  • 72.
    Berglund, Linn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Noël, Maxime
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Öman, Tommy
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Production potential of cellulose nanofibers from industrial residues: Efficiency and nanofiber characteristics2016Inngår i: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 92, s. 84-92Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 73.
    Bismarck, Alexander
    et al.
    Vienna University of Technology.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bionanocomposites: Processing Methods, Characterization, and Properties2014Inngår i: Handbook of Green Materials: Processing Technologies, Properties and Applications, Singapore: World Scientific and Engineering Academy and Society, 2014Kapittel i bok, del av antologi (Fagfellevurdert)
  • 74.
    Blumer, Hartwig
    et al.
    Luleå tekniska universitet.
    Johansson, Ingvar
    Luleå tekniska universitet.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Träkompositer: forskning, utveckling, tillverkning1993Rapport (Annet vitenskapelig)
  • 75.
    Blumer, Hartwig
    et al.
    Luleå tekniska universitet.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Johansson, Ingvar
    Luleå tekniska universitet.
    Träkompositer: kunskapsöversikt och forskningsbehov1992Rapport (Annet vitenskapelig)
  • 76. Bondeson, Daniel
    et al.
    Kvien, Ingvild
    Oksman, Kristiina
    Bio-nanocomposites based on cellulose whiskers2006Inngår i: 6th Global Wood and Natural Fibre Composites Symposium: April 05 - 06, 2006 ; scientific presentations / [ed] Andrzej K. Bledzki, Lehrstuhl Kunststoff- und Recyclingtechnik , 2006Konferansepaper (Fagfellevurdert)
  • 77.
    Bondeson, Daniel
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Kvien, Ingvild
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Strategies for preparation of cellulose whiskers from microcrystalline cellulose as reinforcement in nanocomposites2006Inngår i: Cellulose Nanocomposites: Processing, characterization and Properties, Washington: American Chemical Society (ACS), 2006, s. 10-25Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 78.
    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 Hydrolysis2006Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 13, nr 2, s. 171-180Artikkel i tidsskrift (Fagfellevurdert)
    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).

  • 79.
    Bondeson, Daniel
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dispersion and characteristics of surfactant modified cellulose whiskers nanocomposites2007Inngår i: Composite interfaces (Print), ISSN 0927-6440, E-ISSN 1568-5543, Vol. 14, nr 7-9, s. 617-630Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Biodegradable nanocomposites based on 5 wt% cellulose nanowhiskers (CNW) and polylactic acid (PLA) were prepared using an extrusion process. An anionic surfactant (5, 10, and 20 wt%) was used to improve the dispersion of the CNW in the PLA matrix. The results showed that increased surfactant content resulted in improved dispersion but at the same time degraded the PLA matrix. The results from mechanical testing showed a maximum modulus for the composite with 5 wt% surfactant and as the surfactant content increased, the CNW dispersion improved and the tensile strength and elongation at break was improved compared to its unreinforced counterpart.

  • 80. Bondeson, Daniel
    et al.
    Oksman, Kristiina
    Optimization of the preparation of nano crystals from microcrystalline cellulose in aqueous suspensions2005Inngår i: Abstracts of papers, 229th ACS national meeting : San Diego, CA, March 13 - 17, 2005, Washington, DC: American Chemical Society (ACS), 2005Konferansepaper (Fagfellevurdert)
  • 81.
    Bondeson, Daniel
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Polylactic acid/cellulose whisker nanocomposites modified by polyvinyl alcohol2007Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 38, nr 12, s. 2486-2492Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to produce biodegradable polylactic acid/cellulose whisker nanocomposites by compounding extrusion and investigate the possibility to use polyvinyl alcohol to improve the dispersion of whiskers in the matrix. Two feeding methods of polyvinyl alcohol and cellulose nanowhiskers were used and evaluated, dry-mixing with polylactic acid prior extrusion or pumping as suspension directly into the extruder. Various microscopic techniques, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposites. Due to immiscibility of the polymers, phase separation occurred with a continuous polylactic acid phase and a discontinuous polyvinyl alcohol phase. The whiskers were primarily located in the polyvinyl alcohol phase and only a negligible amount was located in the polylactic acid phase. This inadequate dispersion of whiskers in the polylactic acid phase was probably the reason why no improvements in thermal properties were seen for the nanocomposites. The relative small improvements in tensile modulus, tensile strength, and elongation to break for the nanocomposites also indicated that it was principally the polyvinyl alcohol phase that was reinforced with whiskers but not the polylactic acid phase.

  • 82.
    Bondeson, Daniel
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Syre, Peder
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    All cellulose nanocomposites produced by compounding extrusion2007Inngår i: Journal of Biobased Materials and Bioenergy, ISSN 1556-6560, E-ISSN 1556-6579, Vol. 1, nr 3, s. 367-371Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A transparent biobased nanocomposite of 5 wt% cellulose nanowhiskers (CNW) and cellulose acetate butyrate (CAB), plasticized by triethyl citrate (TEC), was produced by melt extrusion. The cellulose nanowhiskers were prepared from commercially available microcrystalline cellulose (MCC) by hydrochloric acid hydrolysis. The plasticizer, TEC, was solved in the whisker suspension and this suspension was pumped into the extruder during the compounding process. Scanning electron microscopy, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposite. The tensile modulus and strength indicated an improvement with 300% and 100%, respectively, compared to neat CAB but the elongation at break was decreased. Further more, the softening temperature of CAB was extended for the nanocomposite. Results from DMTA showed that the tanδ peak temperature was shifted by 31 °C, from 117 °C to 148 °C with addition of CNW in CAB. The extrusion process with liquid feeding was shown to be successful for this material combination. AbstractA transparent biobased nanocomposite of 5 wt% cellulose nanowhiskers (CNW) and cellulose acetate butyrate (CAB), plasticized by triethyl citrate (TEC), was produced by extrusion compounding. The cellulose nanowhiskers were prepared from commercially available microcrystalline cellulose (MCC) by hydrochloric acid hydrolysis. The plasticizer, TEC, was solved in the whisker suspension and this suspension was pumped into the extruder during the compounding process. Scanning electron microscopy, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposite. The tensile modulus and strength were improved with 300% and 100%, respectively, compared to neat CAB but the elongation at break was decreased. Further more, the softening temperature of CAB was extended for the nanocomposite. Results from DMTA showed that the tan d peak temperature was shifted by 31 ˚C, from 117 °C to 148 ˚C with addition of CNW in CAB.

  • 83.
    Borges, Ana C.
    et al.
    École Polytechnique Fédérale de Lausanne.
    Eyholzer, Christian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Duc, Fabien
    École Polytechnique Fédérale de Lausanne.
    Bourban, Pierre-Etienne
    École Polytechnique Fédérale de Lausanne.
    Tingaut, Philippe
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Zimmermann, Tanja
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Pioletti, Dominique P.
    École Polytechnique Fédérale de Lausanne.
    Månson, Jan-Anders E.
    École Polytechnique Fédérale de Lausanne.
    Nanofibrillated cellulose composite hydrogel for the replacement of the Nucleus Pulposus2011Inngår i: Acta Biomaterialia, ISSN 1742-7061, E-ISSN 1878-7568, Vol. 7, nr 9, s. 3412-3421Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The swelling and compressive mechanical behavior as well as the morphology and biocompatibility of composite hydrogels based on Tween® 20 trimethacrylate (T3), N-vinyl-2-pyrrolidone (NVP) and nanofibrillated cellulose (NFC) were assessed in the present study. The chemical structure of T3 was verified by FTIR and 1H NMR and the degree of substitution (DS) was found to be around 3. Swelling ratios of neat hydrogels composed of different concentrations of T3 and NVP were found to range from 1.5 to 5.7 with decreasing concentration of T3. Various concentrations of cellulose nanofibrils (0.2 to 1.6 wt%) were then used to produce composite hydrogels that showed lower swelling ratios than neat ones for a given T3 concentration. Neat and composite hydrogels exhibited typical non-linear response under compression. All composite hydrogels showed an increase in elastic modulus compared to neat hydrogel of about 3 to 8-fold, reaching 18 kPa at 0% strain and 62 kPa at 20% strain for the hydrogel with the highest NFC content. All hydrogels presented a porous and homogeneous structure, with interconnected pore cells of around 100 nm in diameter. The hydrogels are biocompatible. The results of this study demonstrate that composite hydrogels reinforced with NFC may be viable as nucleus pulposus implant due to their adequate swelling ratio that may restore annulus fibrosus loading and their increased mechanical properties that could possibly restore the height of intervertebral discs.

  • 84.
    Bozic, Mojca
    et al.
    Faculty of Mechanical Engineering, Institute for Engineering Materials and Design, University of Maribor.
    Liu, Peng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    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 nanoparticles2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 4, s. 2713-2726Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 85.
    Brunow, G.
    et al.
    University of Helsinki.
    Karlsson, Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Lundquist, K.
    Chalmers University of Technology.
    Sipilä, J.
    University of Helsinki.
    On the distribution of the diastereomers of the structural elements in lignins: the steric course of reactions mimicking lignin biosynthesis1993Inngår i: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 27, nr 4, s. 281-286Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stereochemical studies on the formation of the diastereomers of arylglycerol-β-aryl ether structures during lignin biosynthesis have been carried out with model compounds. The addition of water to quinone methides of the β-syringyl ether type gives arylglycerol β-syringyl ethers with a predominance of the erythro isomer when the pH of the medium is low. Since erythro forms of arylglycerol β-syringyl ethers are prevalent in hardwood lignins, this indicates that the pH of the medium in which lignin biosynthesis occurs is lower than has been assumed until now. Equilibration studies with non-phenolic model compounds of the arylglycerolβ-guaiacyl ether and β-syringyl ether types under acidolysis conditions indicate that the erythro predominance observed in the syringyl ethers in lignins does not correspond to equilibrium conditions. A remarkable resistance to acidolysis is observed in the model compounds of etherified syringylglycerol β-syringyl ether type.

  • 86.
    Bulota, Mindaugas
    et al.
    Department of Forest Products Technology, School of Chemical Technology, Aalto University.
    Tanpichai, Supachok
    Materials Science Centre, School of Materials, School of Materials, University of Manchester.
    Hughes, Mark R.
    Department of Forest Products Technology, School of Chemical Technology, Aalto University.
    Eichhorn, Stephen J.
    College of Engineering, Mathematics and Physical Sciences, University of Exeter.
    Micromechanics of TEMPO-oxidized fibrillated cellulose composites2012Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, nr 1, s. 331-337Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Composites of poly(lactic) acid (PLA) reinforced with TEMPO-oxidized fibrillated cellulose (TOFC) were prepared to 15, 20, 25, and 30% fiber weight fractions. To aid dispersion and to improve stress transfer, we acetylated the TOFC prior to the fabrication of TOFC-PLA composite films. Raman spectroscopy was employed to study the deformation micromechanics in these systems. Microtensile specimens were prepared from the films and deformed in tension with Raman spectra being collected simultaneously during deformation. A shift in a Raman peak initially located at ∼1095 cm -1, assigned to C-O-C stretching of the cellulose backbone, was observed upon deformation, indicating stress transfer from the matrix to the TOFC reinforcement. The highest band shift rate, with respect to strain, was observed in composites having a 30% weight fraction of TOFC. These composites also displayed a significantly higher strain to failure compared to pure acetylated TOFC film, and to the composites having lower weight fractions of TOFC. The stress-transfer processes that occur in microfibrillated cellulose composites are discussed with reference to the micromechanical data presented. It is shown that these TOFC-based composite materials are progressively dominated by the mechanics of the networks, and a shear-lag type stress transfer between fibers.

  • 87.
    Butylina, Svetlana
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Polypropylene (PP)-Based Hybrid Biocomposites and Bionanocomposites2018Inngår i: Polypropylene-Based Biocomposites and Bionanocomposites / [ed] P. M. Visakh, Matheus Poletto, NJ, USA.: John Wiley & Sons, 2018, s. 113-144Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Hybrid biocomposites and particularly hybrid bionanocomposites are relatively recent additions to the composite family. Biocomposites are composite materials which include parts of biological origin. Hybridization is very useful because it makes it possible to tailor the composite properties according to the desired structure. This chapter deals with the preparation methods applied for PP-based hybrid biocomposites and bionanocomposites. The mechanical and thermal properties as well as the weathering properties and fire performance of various hybrid composites are summarized. The properties of hybrid biocomposites depend on the nature, size and loading of the filler and its interaction with the PP matrix. In most cases, commercial use of biocomposites has been limited to nonstructural or semistructural applications due to low stiffness, impact and thermal properties. Hybridization helps to overcome these problems. Nanofillers can improve the thermal stability, flame retardancy and durability, and therefore give rise to new applications and extend the existing applications of PP-based biocomposites

  • 88.
    Butylina, Svetlana
    et al.
    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.
    Properties of as-prepared and freeze-dried hydrogels made from poly(vinyl alcohol) and cellulose nanocrystals using freeze-thaw technique2016Inngår i: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 81, s. 386-396Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Poly(vinyl alcohol), PVA hydrogels are potential materials for biomedical and biotechnogical applications. However, their low mechanical properties restrict their use. In this study, the effect of PVA concentration, addition of nanocrystalline cellulose, CNC, number of freeze-thaw cycles and freeze-drying stage on properties of resulting hydrogels were investigated. The results showed that increase in PVA concentration and the addition of CNC improved the compressive properties of the hydrogels. Overall, increase in number of freeze-thaw cycles from 3 to 5 did not show any improvements in properties of hydrogels. Concentration of PVA had great effect on morphology of freeze-dried hydrogels. The CNC reduced crystallinity of PVA/CNC hydrogels as compared to PVA hydrogels. Rehydrated PVA and PVA/CNC hydrogels had higher compressive characteristics than their as-prepared analogues. In general, an improvement of compressive properties of hydrogels was achieved via reduction of their water content. In case of 5% PVA hydrogel, an addition of CNC was found to be beneficial because it increased degree of swelling and water content on rehydration.

  • 89.
    Butylina, Svetlana
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Hyvärinen, Marko
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    A study of surface changes of wood-polypropylene composites as the result of exterior weathering2012Inngår i: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 97, nr 3, s. 337-345Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Outdoor applications of composites raised questions about their durability. In this study, the effects of outdoor weathering on the properties of wood-polypropylene composites with and without pigments were examined. The composites were placed outdoors for one year, and their colour changes were evaluated after 1, 3, 6, 9 and 12 months of weathering. The weathering resulted in considerable colour fading of the composites. Composites containing darker colour pigments had better colour stability. Scanning electron microscopy analysis revealed that surface cracks caused by weathering in a wood-polypropylene composite having a higher polypropylene content were less abundant, and the deterioration of the surface layer was lower compared to composites containing less polymer. Measurements of melting temperatures by differential scanning calorimetry gave a consistent picture of polypropylene degradation in the surface layer. After weathering, a decrease in Charpy impact strength was found for composites characterised by higher moisture absorption.

  • 90.
    Butylina, Svetlana
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Hyvärinen, Marko
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Accelerated weathering of wood-polypropylene composites containing minerals2012Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 43, nr 11, s. 2087-2094Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Accelerated weathering tests were carried out on wood-polypropylene composites containing minerals. Three different mineral fillers were studied: calcium carbonate, wollastonite and talc. Colour changes were evaluated after distinct periods; the total time of exposure of the composites to UV irradiation was 2000 h. The weathering resulted in significant colour fading of the composites. The composites containing mineral fillers had higher changes of colour (lightness) than the reference composite. Scanning electron microscopy analysis revealed deterioration of the polymer surface layer in all weathered composites. Exposure of the reference composite to UV irradiation resulted in the disappearance of the polypropylene surface layer and disclosure of wood fibres, which led to a higher drop in the lignin content of this composite compared to mineral-containing composites. A substitution of part of the wood with mineral fillers resulted in decreased water absorption and thickness swelling of mineral-containing composites, compared to the reference composite. Exposure to water immersion-freeze-thaw cyclic treatment and UV irradiation led to a decrease in the Charpy impact strength of the composites, except for the composite containing talc

  • 91.
    Butylina, Svetlana
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Mechanical Engineering, Lappeenranta University of Technology .
    Hyvärinen, Marko
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Weathering of wood-polypropylene and wood-wollastonite-polypropylene composites containing pigments in Finnish climatic conditions2015Inngår i: Pigment & Resin Technology, ISSN 0369-9420, E-ISSN 1758-6941, Vol. 44, nr 5, s. 313-321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose The purpose of this paper is to study the resistance of wood-polypropylene and wood-wollastonite-polypropylene composites containing pigments to natural weathering. Design/methodology/approach Natural weathering of composites was conducted in Finnish climatic conditions for one year. The colour of the composites was determined with a spectrophotometer, the morphology of the composite surface was analysed by scanning electron microscopy (SEM), and the changes in the polymer structure in surface layer of the composites were analysed with differential scanning calorimetry (DSC). Charpy impact strength was determined with an impact tester. Findings The pigments used in this study reduced the colour change of the composites exposed to outdoor weathering as compared with the un-coloured composite. The carbon black pigment was more effective than the iron oxide pigment. Moreover, only the carbon black pigment was found to reduce the degradation of the surface layer of the composites. The addition of the carbon black pigment had a positive effect on the dimensional stability of the composites in a water absorption test. Only the combination of the carbon black pigment and wollastonite resulted in a composite which was capable to retain its Charpy impact strength both after one year of outdoor weathering and cyclic treatment. Research limitations/implications This study is a part of continuous research on the development of wood-polymer composites (WPUs) suitable for outdoor applications in Finnish climatic conditions. The first part of the study, which has been published earlier, showed the results of weathering of composites in accelerated tests in comparison with 1,000 hours outdoor exposure during summer time (June and July). Outdoor weathering limited to 1,000 hours cannot give an objective view on the weathering behaviour of composites in Finnish climatic conditions. The results of the current study were obtained from one-year outdoor exposure of composites. Originality/value The wood-polypropylene composite made with the combination of the carbon black pigment and wollastonite can be recommended for outdoor applications. The study provides useful information on the resistance of wood-polypropylene composites to weathering in Finnish climatic conditions.

  • 92.
    Butylina, Svetlana
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Mechanical Engineering, Lappeenranta University of Technology.
    Hyvärinen, Marko
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Weathering of wood-polypropylene composites containing pigments2012Inngår i: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 70, nr 5, s. 719-726Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Outdoor applications of composites have raised questions about their durability. In this study, the effects of outdoor weathering on the properties of wood-polypropylene composites with and without pigments were examined. The composites were placed outdoors for one year, and their colour changes were evaluated after 1, 3, 6, 9 and 12 months of weathering. The durability of the composites was assessed by testing flexural strength and density. Scanning electron microscopy was applied to evaluate the surface degradation of the composites. The weathering resulted in considerable colour fading of the composites. The composites containing darker colour pigments had better colour stability. After weathering, the general trend was a decrease of the flexural strength and density of the composites. The decrease in flexural strength was found to be lower for the composites having higher density.

  • 93.
    Butylina, Svetlana
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology, Finland.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology, Finland.
    Resistance to weathering of wood-polypropylene and wood-wollastonite-polypropylene composites made with and without carbon black2014Inngår i: Pigment & Resin Technology, ISSN 0369-9420, E-ISSN 1758-6941, Vol. 43, nr 4, s. 185-193Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose - The purpose of this paper is to study natural and accelerated weathering of wood-polypropylene (WF-PP) and wood-wollastonite-polypropylene composites made with and without carbon black.

    Design/methodology/approach - Natural weathering was conducted in Ruokolahti, Finland in the time of year when solar radiation was maximal. The accelerated weathering tests included exposure to a xenon-arc source with and without spray, and a cyclic test consisting of water immersion-freeze-thaw stages.

    Findings - Both the type of weathering and the formulation of the composite determined the degree of change in their properties. Weathering, including xenon-arc exposure with spray resulted in much higher changes of colour of non-pigmented composites compared to natural weathering or xenon-arc weathering without spray. Both UV irradiation and moisture had an adverse effect on the Charpy impact strength of non-pigmented composites. Carbon black containing composites performed better than non-pigmented composites.

    Research limitations/implications - This study is a part of an ongoing research on the development of wood-polymer composites (WPCs) suitable for outdoor applications in Finnish climatic conditions. Outdoor weathering limited to 1,000 h cannot be used for the prediction of the service life of composites and was used here solely for comparative purposes.

    Originality/value - This paper will help to understand the effect of different weathering factors on the behaviour of WF-PP and wood-wollastonite-polypropylene composites made with and without carbon black (as UV stabiliser). The study demonstrated that while accelerated weathering tests provided useful information on the resistance of WF-PP composites to different weathering factors, they cannot be used alone to predict the behaviour of WPCs meant for outdoor application

  • 94.
    Butylina, Svetlana
    et al.
    Department of Chemical Technology, Lappeenranta University of Technology.
    Luque, Susana
    bDepartment of Chemical and Environmental Engineering, University of Oviedo.
    Nyström, Marianne
    Department of Chemical Technology, Lappeenranta University of Technology.
    Fractionation of whey-derived peptides using a combination of ultrafiltration and nanofiltration2006Inngår i: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 280, nr 1-2, s. 418-426Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes the fractionation and further isolation and characterisation of peptides and proteins present in sweet whey by means of ultrafiltration using a regenerated cellulose membrane with a nominal molar mass cut-off value of 10 kg/mol and nanofiltration through sulphonated polyether sulphone membrane with a cut-off of 1 kg/mol. The concentration of whey proteins was done below the critical flux. The sieving coefficients for the whey components (proteins, lactose and salts) were estimated. Whey proteins were completely rejected by the ultrafiltration membrane. Size exclusion chromatography (SEC) and matrix-assisted laser desorption ionisation time-of-flight (MALDI-TOF) mass spectrometry were used to evaluate the molar masses of the peptide fractions that were present in the whey permeates. Nanofiltration of whey permeates obtained after ultrafiltration was conducted at two pH values (9.5 and 3.0) that corresponded to the different charged states of the membrane and of the peptides. The transmission of peptides, amino acids and lactose was found to be mainly affected by the permeability of the fouling layer. The selectivity of the nanofiltration membranes toward peptides compared to lactose was calculated as 0.82 and 6.81 at pH 9.5 and 3.0, respectively.

  • 95.
    Butylina, Svetlana
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Martikka, Ossi
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Comparison of water absorption and mechanical properties of wood-plastic composites made from polypropylene and polylactic acid2010Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, nr 3-4, s. 220-228Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study focuses on the water absorption and mechanical properties of composites made from softwood sawdust and plastics, such as virgin and recycled polypropylene and polylactic acid (PLA). The composites were processed by extrusion, and their properties were investigated by a water immersion test, mechanical tests and a cyclic test for moisture resistance. Scanning electron microscopy was used to study the morphology of the fracture surfaces of the composites. The composites made with recycled polypropylene had the lowest water absorption and thickness swelling of the studied composites. The PLA composites made with heat-treated sawdust showed the highest flexural strength. Of the polypropylene based composites, virgin polypropylene resulted in composites with higher flexural strength. The Charpy impact strength of the composites was found to have an inverse trend compared to flexural strength. Cyclic treatment of the studied composites resulted in 20-60% loss of flexural strength, depending on type of composite.

  • 96.
    Butylina, Svetlana
    et al.
    Mechanical Engineering, Lappeenranta University of Technology.
    Martikka, Ossi
    Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Mechanical Engineering, Lappeenranta University of Technology.
    Effects of water immersion-freeze-thaw cycling on the properties of wood-polypropylene composites containing pigments2011Inngår i: Pigment & Resin Technology, ISSN 0369-9420, E-ISSN 1758-6941, Vol. 40, nr 6, s. 386-392Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose - The purpose of this paper is to study the effects of water immersion-freeze-thaw treatment on the physical properties, flexural strength (FS) and morphology of wood-polypropylene composites containing pigments. Design/methodology/approach - Wood-polypropylene composites containing brown, green and grey pigments were compounded in a conical twinscrew extruder. A composite manufactured without any pigment addition was used as a reference. The amount of pelletized wood, polypropylene and coupling agent (MAPP) was kept constant. The moisture content, thickness swelling (TS), FS and surface colour of the composites were measured before and after water immersion-freeze-thaw cycling. Scanning electron microscopy (SEM) was used to study the morphology of the composites. Findings - FS and dimensional stability were reduced after exposure to water immersion-freeze-thaw cycling for all composites. The surface properties (colour and roughness) of the composites also changed after exposure to water immersion-freeze-thaw cycling. The degree of change depended on the presence of pigment and the type of polypropylene (neat or recycled), however. Research limitations/implications - This study is a part of an ongoing study on weathering of wood-polymer composites (WPC) containing different additives. The results of this study were obtained from accelerated laboratory experiments. Practical implications - Inorganic pigments are widely used as additives in plastics, because they have an excellent UV absorption, good IR-reflective properties and heat stability. The research revealed that metal-containing pigments had an effect on degradation in quality of wood-polypropylene composites exposed to water immersion-freeze-thaw cyclic treatment. The addition of metal-containing pigments to composite formulation resulted in a higher susceptibility of wood-polypropylene composites to water absorption, and as a consequence to a higher drop of FS compared to composites made without pigment. The polymer matrix plays an important role in the protection of WPC against weathering. Originality/value - This paper will help in understanding possible problems in the durability of wood-polypropylene composites compounded with metal-based pigments when they are exposed to water immersion-freeze-thaw cyclic treatment.

  • 97.
    Butylina, Svetlana
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Martikka, Ossi
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Physical and mechanical properties of wood-polypropylene composites made with virgin and/or recycled polypropylene2011Inngår i: Polymer-plastics technology and engineering (Softcover ed.), ISSN 0360-2559, E-ISSN 1525-6111, Vol. 50, nr 10, s. 1040-1046Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The physical and mechanical properties of wood-polymer composites made with virgin or recycled polypropylene, or a mixture of these were studied. The composites made with recycled polypropylene had higher density, lower porosity, and higher dimensional stability compared to the composites made with virgin polypropylene. Although the composites made with recycled polypropylene exhibited lower tensile strength than those made with virgin polypropylene, they had higher Charpy impact strength. Scanning electron microscopy analysis of the fractured surfaces of the composites showed no significant differences in the fracture mechanisms of the studied composites. The degree of crystallinity was estimated to be higher for the virgin polypropylene than for the recycled one.

  • 98.
    Butylina, Svetlana
    et al.
    Lappeenranta University of Technology.
    Martikka, Ossi
    Lappeenranta University of Technology.
    Kärki, Timo
    Lappeenranta University of Technology.
    Properties of wood fibre-polypropylene composites: Effect of wood fibre source2011Inngår i: Applied Composite Materials, ISSN 0929-189X, E-ISSN 1573-4897Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study examined the effect of type of wood fibre source on the physical and mechanical properties of wood fibre-polypropylene composites. Wood flour, fibres of heattreated wood and pellets were used as sources of wood fibres in the manufacturing process. All studied wood fibre-polypropylene composites were made from 75% wood, 22% recycled polypropylene (PP) and 3% maleated polypropylene (MAPP). Wood fibrepolypropylene composites were compounded in a conical twin-screw extruder. Water absorption and thickness swelling were studied. Mechanical properties of the composites were characterised by tensile, flexural, and impact testing. Micromechanical deformation processes were investigated using scanning electron microscopy done on the fractured surfaces of broken samples. The durability of composites exposed to three accelerated cycles of water immersion, freezing and thawing was examined. The results showed that the density of the composites was a key factor governing water absorption and thickness swelling. A significant improvement in tensile strength, flexural strength, and Charpy impact strength was observed for composites reinforced with heat-treated fibre compared to composites reinforced with pellets and especially to wood flour reinforced composites. The flexural strength and dimensional stability performance reduced after exposure to freezethaw cycling for all composites, but the degree of these changes was dependent on the wood fibre source.

  • 99.
    Butylina, Svetlana
    et al.
    Lappeenranta University of Technology.
    Martikka, Ossi
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Thermal performance and optical properties of wood-polymer composites2013Inngår i: Journal of Thermoplastic Composite Materials, ISSN 0892-7057, E-ISSN 1530-7980, Vol. 26, nr 1, s. 60-73Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal performance and optical properties of wood-polypropylene composites made from untreated wood material with and without metal-containing pigments, and composites made from heat-treated wood material were studied. The thermal heat buildup and linear shrinkage were determined. The impact of the optical properties of the surface of the composites on the heat buildup was analysed. The wood-polypropylene composites made from untreated wood without pigment were found to have the lowest heat buildup; a similar composite containing grey pigment had the highest heat buildup. The linear shrinkage of the studied wood-polypropylene composites was in the range 0.05-0.16%

  • 100.
    Butylina, Svetlana
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Martikka, Ossi
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Weathering properties of coextruded polypropylene-based composites containing inorganic pigments2015Inngår i: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 120, s. 10-16Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study concerns the weathering properties of coextruded polypropylene-based composites containing pigments. Three different pigments were incorporated in the shell layer of the composites: iron oxide, titanium dioxide and zinc oxide. The surface colour, surface gloss and tensile properties were tested. In addition, the weathered surfaces were studied by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The surfaces of the composites containing inorganic pigments were found to have fewer cracks after 500 h of weathering than the surface of the reference composite. The results revealed that the composites containing titanium oxide pigment exhibited better colour stability than the composites made with the other pigments. In spite of its high colour stability in weathering, the tensile properties (strength, Young's modulus and elongation at break) of the composite containing titanium oxide were reduced by weathering. The FTIR analysis revealed that the composite containing zinc oxide had a stabilising effect on polypropylene photo-degradation, which correlates well with the results of mechanical testing, showing that this composite retained its mechanical properties after weathering

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