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  • 251.
    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.
    Comparison of cellulose nanowhiskers extracted from industrial bio-residue and commercial microcrystalline cellulose2012Inngår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 71, nr 1, s. 28-31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 252.
    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.
    Gas permeability and selectivity of cellulose nanocrystals films (layers) deposited by spin coating2014Inngår i: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 112, s. 494-501Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 253.
    Herrera, Martha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Moisture and Gas Barrier Properties of Cellulose Nanocrystals in Thin Films2014Inngår 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)
  • 254.
    Herrera, Martha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sirviö, Juho A.
    Fibre and Particle Engineering Laboratory, University of Oulu.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Environmental friendly and sustainable gas barrier on porous materials: Nanocellulose coatings prepared using spin- and dip-coating2016Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 93, s. 19-25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 255.
    Herrera Vargas, Natalia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Project: Renewable eco-friendly Poly(Lactic acid) nanocomposites from waste sources2014Annet (Annet (populærvitenskap, debatt, mm))
  • 256.
    Herrera Vargas, Natalia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Singh, Anshu Anjali
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Salaberria, Asier M.
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Faculty of Engineering, Guipúzcoa, University of the Basque Country.
    Labidi, Jalel
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Faculty of Engineering, Guipúzcoa, University of the Basque Country.
    Mathew, Aji P.
    Division of Materials and Environmental Chemistry, Stockholm University.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu.
    Triethyl Citrate (TEC) as a Dispersing Aid in Polylactic Acid/Chitin Nanocomposites Prepared via Liquid-Assisted Extrusion2017Inngår i: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 9, nr 9, artikkel-id 406Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The production of fully bio-based and biodegradable nanocomposites has gained attention during recent years due to environmental reasons; however, the production of these nanocomposites on the large-scale is challenging. Polylactic acid/chitin nanocrystal (PLA/ChNC) nanocomposites with triethyl citrate (TEC) at varied concentrations (2.5, 5.0, and 7.5 wt %) were prepared using liquid-assisted extrusion. The goal was to find the minimum amount of the TEC plasticizer needed to enhance the ChNC dispersion. The microscopy study showed that the dispersion and distribution of the ChNC into PLA improved with the increasing TEC content. Hence, the nanocomposite with the highest plasticizer content (7.5 wt %) showed the highest optical transparency and improved thermal and mechanical properties compared with its counterpart without the ChNC. Gel permeation chromatography confirmed that the water and ethanol used during the extrusion did not degrade PLA. Further, Fourier transform infrared spectroscopy showed improved interaction between PLA and ChNC through hydrogen bonding when TEC was added. All results confirmed that the plasticizer plays an important role as a dispersing aid in the processing of PLA/ChNC nanocomposites.

  • 257.
    Hietala, M.
    et al.
    Fibre and Particle Engineering Research Unit, University of Oulu, Finland.
    Koivuranta, E.
    Fibre and Particle Engineering Research Unit, University of Oulu, Finland.
    Ämmälä, A.
    Fibre and Particle Engineering Research Unit, University of Oulu, Finland.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering Research Unit, University of Oulu, Finland.
    Moisture stability and mechanical durability of peat biocomposites2017Inngår i: ICCM21 Proceedings, ICCM, International Committee on Composite Materials , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Peat, the organic matter formed from incomplete degradation of vegetation in peatlands, was studied as lignocellulosic raw material in manufacture of biocomposites. Peat mosses with varying degree of decomposition, namely slightly decomposed peat (H2) and moderately decomposed peat (H6), were ground into different particle size fractions which were used to prepare peat-polypropylene (PP) composites with 50 wt% peat content using extrusion compounding. The moisture absorption and dimensional stability as well as the mechanical properties and microstructure before and after cyclic freeze-thaw conditioning of the peat-PP composites were analysed and compared to reference wood-plastic composite (WPC). The mechanical properties of peat-PP composites were better than the properties of reference WPC before the freeze-thaw conditioning, and the mechanical permanence of peat-PP composites was better after the cyclic conditioning. Especially when peat with higher decomposition degree was used (H6), the mechanical permanence of peat-PP composites was improved. Likewise, the moisture absorption and the dimensional stability properties were improved the more decomposed the used peat was. The particle size did not affect the composite properties as much as the decomposition degree of peat, though the dimensional stability of peat-PP composite with moderately decomposed peat was better with smaller particle size peat.

  • 258.
    Hietala, Maiju
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Extrusion processing of wood raw materials for use in wood-polymer composites2011Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The interest in wood-polymer composites and their use in different applications has been growing over the last 10-15 years. Environmental issues and demands on lower material costs are the driving forces behind the increasing use of renewable materials such as wood and other natural fibres as reinforcement in polymer composites. Wood flour consisting of small wood particles is currently used as the main wood raw material in commercial wood-polymer composites. However, the reinforcing potential of wood flour is limited. A better reinforcement could be achieved by using wood fibres with a higher aspect ratio as raw material, but individual fibres are seldom used in composite manufacturing due to processing problems and high cost. Therefore, the objective of the work was to study the possibility to use wood chips as raw material and separate individual fibres with higher aspect ratios from the wood chips during the composite manufacturing process. First, the effect of the extrusion process only on wood raw material was studied without a matrix polymer, and then composites using polypropylene as matrix were made. The main goal was to produce wood particles/fibres with high aspect ratio during the manufacturing of wood polymer composites. The effects of extrusion parameters, different screw configurations, raw materials and raw material pre-treatments were evaluated. The size of the separated wood particles and fibres was measured using optical fibre analysis methods. Microstructure of wood particles as well as the fractured surfaces of prepared composites were examined using electron microscopy. The mechanical properties of the composites were measured using flexural and impact testing. The results showed that wood chips can be used as raw material in a one-step manufacturing process of wood-polymer composites. Also, individual fibres with a higher aspect ratio than wood flour were separated from the wood chips with suitable processing conditions

  • 259.
    Hietala, Maiju
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Extrusion processing of wood-based biocomposites2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Interest in biocomposite materials and their use in various applications has been growing steadily over the past 10-15 years. Increasing environmental awareness and lower material costs are the main driving forces for using renewable materials, such as wood and cellulose fibers, as reinforcement in polymer composites. In addition to the materials used in the composite preparation, the processing has a large impact on the final properties of the composite. Therefore, the main thrust of this work has been on processing of wood-based biocomposite materials using twin-screw extrusion.In the first part of the work (Papers I, II and III), wood-plastic composites were manufactured using twin-screw extrusion. Currently, wood flour consisting of small wood particles with low aspect ratio is used as the main wood raw material in commercial woodplastic composites. A better reinforcement is achieved by using wood fibers with a higher aspect ratio, but individual fibers are seldom used in composite manufacturing due to processing problems and higher cost. Therefore, the objective of the first part of this work was to study the use of wood chips as raw material in wood-plastic composites and the possibility to separate individual fibers from the wood chips during the composite manufacturing process. The effect of extrusion parameters and raw materials on the aspect ratio of the wood particles/fibers and on the mechanical properties of the composites was evaluated. The study showed that wood chips can be used as raw material in a one-step process for manufacturing wood-plastic composites, and that it is possible to separate individual fibers with a higher aspect ratio than wood flour from the wood chips under suitable processing conditions. The second part of the work (Papers IV and V) focused on the twin-screw extrusion of cellulose nanocomposites. The use of nanosized cellulose fibers to reinforce polymer matrices has many benefits over the macrosized fibers, such as the high surface area and large aspect ratio. However, the preparation of cellulose nanocomposites is more complicated due to the high hydrophilicity and aggregation tendency of nanocellulose, meaning that drying of the nanofibers is not recommended when good dispersion of nanofibers is needed. Therefore, the aim was to study the processing of green cellulose nanocomposites with twin-screw extrusion using thermoplastic starch as the matrix polymer and cellulose nanofibers with high water content as the reinforcement (Paper IV). In addition, the effect of twin-screw extrusion on separating micro/nanoscale fibers from cellulose fibers during the compounding of biocomposites was studied (Paper V). The fibrillation of nanocellulose is a highly energy intensive process; therefore, it would be very beneficial if it could be done at the same step as the compounding of the composites. The preparation of thermoplastic starch and composite compounding was performed in one step, and the effects of extrusion compounding on the dispersion of the cellulose nanofibers, on the micro/nanofibrillation of cellulose fibers, and on the composites’ mechanical, optical and moisture absorption properties were studied. The results showed that some aggregation of cellulose nanofibers occurred during the extrusion process, but that the addition of cellulose nanofibers had a positive effect on the properties of the prepared bionanocomposites. Nanofibrillation of cellulose was not accomplished using the selected processing conditions; however, dispersion of the fibers was enhanced.

  • 260. Hietala, Maiju
    et al.
    Grubbström, Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Use of wood chips in extrusion of wood plastics composites2009Konferansepaper (Annet vitenskapelig)
  • 261.
    Hietala, Maiju
    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.
    Bionanocomposites of thermoplastic starch and cellulose nanofibers manufactured using twin-screw extrusion2013Inngår i: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 49, nr 4, s. 950-956Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 262. Hietala, Maiju
    et al.
    Niinimäki, Jouko
    University of Oulu.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Processing of wood chip-plastic composites: effect on wood particle size, microstructure and mechanical properties2011Inngår i: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 40, nr 2, s. 49-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wood chips were used as raw material in extrusion of wood-plastic composites. Wood-plastic composites with similar to 50 wt-% wood content were manufactured by using two different compounding methods. Dried and undried wood chips were used to investigate the effect of wood moisture content on the wood particle size and whether the drying process could be carried out in the same step. Wood particle properties were measured using optical fibre analysis. Microscopical methods were used to examine the microstructure of wood particles. Furthermore, the prepared composites' mechanical properties were studied. The particle size of wood chips was significantly reduced during extrusion in both processing methods. The undried wood chips had higher aspect ratios in comparison with the dried wood chips after extrusion. Despite the higher aspect ratio, the mechanical properties of composites manufactured with undried wood chips were not better than the properties of composites with dried wood chips

  • 263.
    Hietala, Maiju
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Niinimäki, Jouko
    University of Oulu.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    The use of twin-screw extrusion in processing of wood: The effect of processing parameter and pretreatment2011Inngår i: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 6, nr 4, s. 4615-4625Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study the effect of processing parameters on different types of wood raw material in extrusion was examined. The study consisted of two parts: the first part was to break and separate individual fibers from wood chips during the extrusion process; in the second part the effect of chemical pre-treatment and screw elements on wood raw material was evaluated. Statistical analysis was performed to evaluate the most important factors affecting wood particle size in extrusion. The statistical analysis showed that the screw speed is the main factor affecting wood fiber length in twin-screw extrusion of wood chips. This study showed that a twin-screw extruder can be used to separate individual fibers from wood chips, and the separated fibers have higher aspect ratios than the wood flour particles typically used in wood-polymer composites. When more fibrous and chemically softened wood raw material was used, fibers with even higher aspect ratios were obtained.

  • 264. Hietala, Maiju
    et al.
    Niinimäki, Jouko
    University of Oulu.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wood chips as raw material in wood plastic composites2010Inngår i: 11th International Conference on Biocomposites: Transition to Green Materials: May 2-4, 2010, Toronto, 2010Konferansepaper (Fagfellevurdert)
  • 265.
    Hietala, Maiju
    et al.
    Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu.
    Pelletized cellulose fibres used in twin-screw extrusion for biocomposite manufacturing: Fibre breakage and dispersion2018Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 109, s. 538-545Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pelletizing is effective in compacting cellulose fibres, but it also causes fibre breakage and poor dispersion due to increased hydrogen bonding. This study investigated whether fibre dispersion and length could be improved by the addition of a lubricant, a commonly used composite processing aid, into cellulose pellets, or by using pelletized fibres that have not been completely dried to reduce hydrogen bonding. Cellulose pellets with different lubricant and moisture contents were prepared and compounded using twin-screw extrusion with polypropylene with 5 wt% fibre and 50 wt% fibre contents. The fibre dispersion, morphology and mechanical properties of the prepared composites were analysed. Dispersion and composite strength were improved with the addition of 4–6 wt% of lubricant while moisture had a negative effect on both properties. This study demonstrated that pelletization in the presence of a lubricant is a promising way to compact cellulose fibres and enable their continuous processing into biocomposites with improved mechanical properties.

  • 266. Hietala, Maiju
    et al.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Technologies for Separation of Cellulose Nanofibers2014Inngår 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)
  • 267. Hietala, Maiju
    et al.
    Rollo, Pierre
    LTU.
    Kekäläinen, Kaarina
    Fibre and Particle Engineering Laboratory, Department of Process and Environmental Engineering, University of Oulu.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Extrusion processing of green biocomposites: Compounding, fibrillation efficiency, and fiber dispersion2014Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 131, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The efficiency of twin-screw extrusion process to fibrillate cellulose fibers into micro/nanosize in the same step as the compounding of green bionanocomposites of thermoplastic starch (TPS) with 10 wt % fibers was examined. The effect of the processing setup on micro/nanofibrillation and fiber dispersion/distribution in starch was studied using two types of cellulose fibers: bleached wood fibers and TEMPO-oxidized cellulose fibers. A composite with cellulose nanofibers was prepared to examine the nanofiber distribution and dispersion in the starch and to compare the properties with the composites containing cellulose fibers. Optical microscopy, scanning electron microscopy, and UV/Vis spectroscopy showed that fibers were not nanofibrillated in the extrusion, but good dispersion and distribution of fibers in the starch matrix was obtained. The addition of cellulose fibers enhanced the mechanical properties of the TPS. Moisture uptake study revealed that the material containing TEMPO-oxidized fibers had higher moisture absorption than the other composites

  • 268.
    Hietala, Maiju
    et al.
    Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu.
    Sain, Sunanda
    Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu.
    Highly redispersible sugar beet nanofibers as reinforcement in bionanocomposites2017Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 5, s. 2177-2189Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A simple method for preparing redispersible nanofibers from sugar beet residue and their use as a well-dispersed reinforcement for a polyvinyl alcohol (PVA) matrix is reported. It is known that the redispersion of dried cellulose nanofibers is difficult because of the formation of strong hydrogen bonds between the nanofibers. The results show that the properties of the initial sugar beet nanofiber suspension can be recovered without the use of chemical modification or additives with higher pectin and hemicellulose content. Undried and redispersed nanofibers with and without pectin were used as nanocomposite reinforcement with PVA. The redispersed nanofibers were as good reinforcements as the undried nanofibers. The tensile strength and elastic modulus of the nanocomposites with the redispersed sugar beet nanofibers were as good as those of the nanocomposites with undried nanofibers. Interestingly, the nanofiber dispersion in the PVA matrix was better when sugar beet nanofibers containing pectin and hemicellulose were used as reinforcements.

  • 269.
    Hietala, Maiju
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Samuelsson, Erik
    Luleå University of Technology.
    Niinimäki, Jouko
    University of Oulu.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    The effect of pre-softened wood chips on wood fibre aspect ratio and mechanical properties of wood-polymer composites2011Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, nr 12, s. 2110-2116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of this work was to study the effect of chemical pre-treatment and moisture content of wood chips on the wood particle aspect ratio after compounding in a twin-screw extruder and on the mechanical properties of wood-polymer composites (WPC). Composites with 50 wt% wood content were manufactured using pre-treated and untreated wood chips. The effect of wood moisture content on composite properties was studied by using dried and undried wood chips. The mechanical properties and fracture surfaces of the composites as well as the microstructure and aspect ratio of wood particles after compounding were studied. The highest wood particle aspect ratio after extrusion was achieved by using pre-treated, undried wood chips as raw material. The chemical pre-treatment was found to enhance the defibration of wood chips as well as the mechanical properties of the composites.

  • 270.
    Hietala, Maiju
    et al.
    Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu, Oulu, Finland.
    Varrio, Kalle
    Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu, Oulu, Finland.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Soini, Jaakko
    Fortum Recycling and Waste Solutions, Oulu, Finland.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu, Oulu, Finland.
    Potential of municipal solid waste paper as raw material for production of cellulose nanofibres2018Inngår i: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 80, s. 319-326Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When aiming for higher resource efficiency, greater utilization of waste streams is needed. In this work, waste paper separated from mixed municipal solid waste (MSW) was studied as a potential starting material for the production of cellulose nanofibres (CNFs). The waste paper was treated using three different techniques, namely pulping, flotation and washing, after which it was subjected to an ultrafine grinding process to produce CNFs. The energy consumption of the nanofibrillation and nanofibre morphology, as well as properties of the prepared nanofibers, were analysed. Despite the varying amounts of impurities in the waste fibres, all samples could be fibrillated into nanoscale fibres. The tensile strengths of the CNF networks ranged from 70 to 100 MPa, while the stiffness was ∼7 GPa; thus, their mechanical strength can be adequate for applications in which high purity is not required. The contact angles of the CNF networks varied depending on the used treatment method: the flotation-treated networks were more hydrophilic (contact angle 52.5°) and the washed networks were more hydrophobic (contact angle 72.6°).

  • 271.
    Hooshmand, Saleh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Process and properties of continuous fibers based on cellulose nanocrystals and nanofibers2014Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In recent years, composites made from natural fibers based on cellulose have received increasing attention since they have a low environmental impact and good mechanical properties. However, these fibers are short and discontinuous and the conventional spinning techniques used for these fibers results in continuous yarns with mechanical properties considerably lower than that of the single fibers. The aim of this work was to prepare continuous fibers where nano-sized cellulose crystals and cellulose nanofibers were used to improve the fiber properties. Two different strategies have been used to reach this aim. In the first study, bio-based fibers of cellulose acetate butyrate (CAB) and cellulose nanocrystals (CNC) using triethyl citrate (TEC) as plasticizer were prepared by melt spinning. Two different dispersion techniques were studied. In the first technique, the water content of the CNC suspension was reduced and exchanged to ethanol using centrifugation. In the second, the water in the CNC suspension was completely exchanged to ethanol by a sol-gel process. Results showed that tensile modulus and tensile strength of the nanocomposite fibers produced with the first technique were lower than CAB-TEC fibers, but the fibers produced by the sol-gel process showed an increase in the tensile modulus and had no decrease in the strength. Optical microscopy of the fibers indicated less aggregations in the sol-gel prepared materials. The results indicate that the sol-gel process is enhancing the dispersion of cellulose nanocrystals and can be a suitable way to prepare nanocomposite fibers. The second study is an extension of the first study. Here the effect of weight concentration of CNC and fiber drawing was studied. The microscopy studies showed that the addition of CNC in CAB resulted in defect-free and smooth fiber surfaces. An addition of 10 wt% CNC enhanced the storage modulus and increased the tensile strength and Young’s modulus. Fiber drawing improved the mechanical properties further. In addition, a micromechanical model of the composite material was used to estimate the stiffness and showed that theoretical values were exceeded for the lower concentration of CNC but not reached for the higher concentration. In conclusion, this dispersion technique combined with melt spinning can be used to produce all-cellulose nanocomposites fibers and that both the increase in CNC volume fraction and the fiber drawing increased the mechanical performance. In the third study a different strategy was used. Here low cost and environmentally friendly continuous fibers of native cellulose were prepared by dry spinning an aqueous suspension of cellulose nanofibers (CNF). The CNF were extracted from banana rachis, a bio-residue from banana cultivation in Columbia. The effect of spinning rate and CNF concentration on the mechanical properties of the fibers were investigated. The results showed that there was a relationship between the spinning rate and concentration. The modulus of the fibers was increased from 7.7 to 12.6 GPa and the strength increased from 131 to 222 MPa when the lowest concentration and highest speed was used. This improvement is believed to be due to an increased orientation of the CNF in the fiber. A minimum concentration of 6.5 wt% was required for continuous fiber spinning. However, this relatively high concentration is thought to limit the orientation of the CNF in the fiber. The process used in this last study has a good potential for up-scaling providing a continuous fiber production with well-controlled speed but further work is required to increase the orientation and subsequently the mechanical properties.The results from these three studies shows that it is possible to spin continuous fibers where nanocellulose is used as a reinforcing agent. It is also shown that the dispersion and alignment of the nanocellulose plays a key role in improving the mechanical properties.

  • 272.
    Hooshmand, Saleh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Processing of continuous fibers based on nanocellulose: Influence of dispersion and orientation on mechanical properties2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The aim of the work was to prepare continuous bio-based fibers where nano-sized cellulose was used to improve the mechanical properties. Two different strategies were used to reach this aim, melt-spinning of thermoplastic fibers reinforced with nanocellulose and dry-spinning of cellulose nanofibers without solvent or chemicals. In the first strategy, melt-spun fibers were reinforced with cellulose nanocrystals. First, nanocomposite fibers of cellulose acetate butyrate (CAB) reinforced with cellulose nanocrystals (CNC) and plasticized with triethyl citrate (TEC) were prepared. Two different techniques for dispersing CNC were compared: a process of solvent exchange of the aqueous CNC suspension to ethanol by centrifugation and sol-gel process. The mechanical properties and microscopy results indicated that the sol-gel process enhanced the dispersion. Subsequently the effect of CNC concentration and solid-state drawing (SSD) was studied. The results were defect-free and smooth fiber surfaces, in which an addition of 10 wt% CNC and drawing increased the tensile strength and Young’s modulus by 43% and 134% compared to the as-spun unreinforced fibers. This melt spinning process was also used to process melt-spun nanocomposite fibers of polylactic acid (PLA) and CNC. In this study the effect of surface modification of the CNC as well as the melt draw ratio (MDR) was investigated. The results showed that the increased MDR together with the surface modification resulted in better mechanical properties. In the second strategy, continuous fibers of native cellulose nanofibers (CNF) were prepared by dry-spinning. First, the effect of the spinning rate and the CNF concentration on the mechanical properties were investigated. The highest orientation and mechanical properties were achieved by combining a low CNF concentration with a high spin rate. The modulus of the fibers increased from 7.7 to 12.6 GPa and the strength form 131 to 222 MPa. After this, to further improve the orientation of the CNF, a small amount of hydroxyethylene cellulose (HEC) was used as a binder and the fibers were cold drawn after the spinning. The results showed that the addition of the binder and cold drawing increased the modulus and strength by 76% and 73% being 15 GPa and 260 MPa respectively. The results also confirmed that dry-spinning has potential for up-scaling, providing a continuous fiber production with well-controlled speed.These studies demonstrated that the dispersion and alignment of nanocellulose in spun fibers play key roles in improving the mechanical properties of these continuous bio-based fibers.

  • 273.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Berglund, Linn
    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.
    Enhanced alignment and mechanical properties through the use of hydroxyethyl cellulose in solvent-free native cellulose spun filaments2017Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 150, s. 79-86Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 274.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    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.
    Dry-spinning of continuous cellulose fibers using only nanofibers from a bio-residue2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 275.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    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.
    Exploiting the self-assembly of cellulose nanofibers in wet and dry spun fibers2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 276.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    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.
    Influence of Matrix and Cold-drawing on Dry Spun Filaments of Cellulose Nanofibers2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 277.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Norberg, Nicholas
    PANalytical.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dry-Spun Single-Filament Fibers Comprising Solely Cellulose Nanofibers from Bioresidue2015Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, nr 23, s. 13022-13028Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 278.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Skrifvars, Mikael
    School of Engineering, University of Borås.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    All-cellulose nanocomposite fibers produced by melt spinning cellulose acetate butyrate and cellulose nanocrystals2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 4, s. 2665-2678Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 279.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    cho, Sung-woo
    University of Borås.
    Skrifvars, Mikael
    University of Borås.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Melt spinning of cellulose acetate butyrate (CAB) nanocomposite fibers reinforced by cellulose nanowhiskers (CNW)2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 280.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Cho, Sung-Woo
    University of Borås.
    Skrifvars, Mikael
    University of Borås.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Melt spun cellulose nanocomposite fibres: comparison of two dispersion techniques2014Inngår i: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 43, nr 1, s. 15-24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 281.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Cho, Sung-Woo
    University of Borås.
    Skrifvars, Mikael
    University of Borås.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Preparation of bio-composite fibers by melt spinning of cellulose acetate butyrate (CAB) and cellulose nanowhiskers (CNW)2012Konferansepaper (Annet vitenskapelig)
  • 282.
    Hooshmand, Saleh
    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.
    Manufacturing and characterization of melt spun and wet spun bionanocomposite fibers2012Konferansepaper (Annet vitenskapelig)
  • 283.
    Huuhilo, Tiina
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Martikka, Ossi
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Butylina, Svetlana
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Impact of mineral fillers to the moisture resistance of wood-plastic composites2010Inngår i: Baltic Forestry, ISSN 1392-1355, E-ISSN 2029-9230, Vol. 16, nr 1, s. 126-131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The impact of mineral fillers to the moisture resistance of the wood-plastic composites (WPC) is studied. Five inorganic fillers were tested for the wood-plastic composites calcium carbonate, two different types of wollastonite, soapstone and talc. The amount of polypropylene, wood and mineral was held constant, only the mineral type was changed during the tests. The studied composites were also compared with a reference sample, which was manufactured without any mineral addition. All added minerals decreased the swelling and moisture absorption of the wood-plastic composite considerably. Also the density of the wood-plastic composites increased when minerals were added. Without any added mineral, clear openings could be seen in the composite structure in scanning electron microscope (SEM) pictures. These openings could work as pathways for water into the inner parts of the WPC and increase swelling. It could also be seen in the SEM pictures that when mineral was added, these pathways for moisture were closed. After three weeks soak/freeze/dry cycles, the bending strength of the reference sample decreased considerably more than the bending strength of the samples with added minerals. Of the studied minerals, talc was the most effective.

  • 284.
    Huuhilo, Tiina
    et al.
    Lappeenranta University of Technology, Department of Mechanical Engineering.
    Martikka, Ossi
    Lappeenranta University of Technology, Department of Mechanical Engineering.
    Butylina, Svetlana
    Lappeenranta University of Technology, Department of Mechanical Engineering.
    Kärki, Timo
    Lappeenranta University of Technology, Department of Mechanical Engineering.
    Mineral fillers for wood-plastic composites2010Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, nr 1, s. 34-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Five mineral fillers were tested for wood-plastic composites (WPCs): calcium carbonate, two different types of wollastonite, soapstone and talc. The impact of the fillers on the mechanical properties of the composites was studied. The experiments included bending tests, tensile tests, Brinell hardness and scanning electron microscopy experiments. The amount of wood, mineral and plastic (polypropylene) was kept steady. Only the mineral type was changed during the tests. A control sample without any mineral added was also manufactured. The mineral addition improved the tensile strength of the WPCs. The hardness of the composite was also improved when the minerals were added, and along with the increasing mineral hardness, the hardness of the composite increased. The wollastonite acicular shape was crushed during the manufacturing process, so the phase of the process in which the minerals are added requires careful consideration.

  • 285.
    Hyvärinen, Marko
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Väntsi, Olli
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Butylina, Svetlana
    Department of LUT Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Ultraviolet light protection of wood-plastic composites a review of the current situation2013Inngår i: Advanced Science Letters, ISSN 1936-6612, E-ISSN 1936-7317, s. 320-324Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wood-plastic composites (WPCs) have several exterior applications where they are easily exposed to ultraviolet (UV) radiation. The paper presents the current situation in a field of UV protection of WPCs, including the most commonly used protective agents and methods, such as UV absorbers and hindered amine light stabilizers (HALS). Surface dressing methods, such as painting, coating and film coating are not included. The focus of the paper is on the ways of how to integrate UV protection comprehensively over the material. The work is a literature review and practical experiments are not included.

  • 286.
    Hägg, Linus
    et al.
    SP Technical Research Institute of Sweden, Wood Technology.
    Johansson, Dennis
    SP Technical Research Institute of Sweden, Wood Technology.
    Vikberg, Tommy
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Influence of Fan Speed on Airflow distribution in a Scandinavian Drying Kiln2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    From the beginning of the 90’s the development of drying kilns in Scandinavia has been focusing on increased drying capacity and also making the kilns more flexible in terms of handling differences in dimensions and initial moisture content. In order to facilitate the demand of higher airflows there has been an increase in circulation fan capacity. In a sawmill with modern kilns the fan capacity in a single batch kiln can be over 90 kW, making the drying kiln fans the single biggest consumer of electric power.Today, more and more sawmills are reviewing their consumption of electric power due to increasing prices. One way of reducing the consumption is to reduce the fan speed when the moisture content is so low that the drying rate is mainly limited by the diffusion properties of the wood and not the airflow. Since modern kilns are designed for high capacity fans there is a lack of knowledge of how a reduced fan speed affects the airflow distribution. This poses a risk of getting reduced quality of the final product due to increased moisture content variation in a batch.In this study the airflow has been measured inside an industrial drying kiln. For this study two experiments were done with 20 airflow gauges placed inside a kiln. During both experiments the kiln was fully loaded with pre dried Scotts pine (Pinus sylvestris) boards with a thickness of 50 mm. The reason for using pre-dried boards was simply that the gauge was not able to withstand the climate produced during a real process. In order to cover as much of the kiln as possible the gauges were distributed differently for the two experiments.The results show that about 30 % of the total airflow passes through the bolster spaces which are only about 20 % of the total flow area. This means that a notable volume of air might not be participating in drying of the boards.The results show also that the relative airflow distribution between the middle and the side of board stacks becomes more heterogeneous at a low fan speed. This trend is also seen for the relative distribution of airflow between bolster and sticker spaces.

  • 287.
    Isarankura Na Ayutthaya, Siriorn
    et al.
    Division of Materials Technology, School of Energy, Environment and Materials, King Mongkut's University of Technology Thonburi.
    Tanpichai, Supachok
    Nanotec-KMUTT Center of Excellence on Hybrid Nanomaterials for Alternative Energy, King Mongkut's University of Technology (KMUTT)Thonburi, Bangkok .
    Sangkhun, Weradesh
    Nanotec-KMUTT Center of Excellence on Hybrid Nanomaterials for Alternative Energy (HyNAE), School of Energy, Environment and Materials, King Mongkut's University of Technology Thonburi, Bangkok.
    Wootthikanokkhan, Jatuphorn
    Nanotec-KMUTT Center of Excellence on Hybrid Nanomaterials for Alternative Energy, King Mongkut's University of Technology (KMUTT)Thonburi, Bangkok .
    Effect of clay content on morphology and processability of electrospun keratin/poly(lactic acid) nanofiber2016Inngår i: International Journal of Biological Macromolecules, ISSN 0141-8130, E-ISSN 1879-0003, Vol. 85, s. 585-595Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This research work has concerned the development of volatile organic compounds (VOCs) removal filters from biomaterials, based on keratin extracted from chicken feather waste and poly(lactic acid) (PLA) (50/50%w/w) blend. Clay (Na-montmorillonite) was also added to the blend solution prior to carrying out an electro-spinning process. The aim of this study was to investigate the effect of clay content on viscosity, conductivity, and morphology of the electrospun fibers. Scanning electron micrographs showed that smooth and bead-free fibers were obtained when clay content used was below 2 pph. XRD patterns of the electrospun fibers indicated that the clay was intercalated and exfoliated within the polymers matrix. Percentage crystallinity of keratin in the blend increased after adding the clay, as evidenced from FTIR spectra and DSC thermograms. Transmission electron micrographs revealed a kind of core-shell structure with clay being predominately resided within the keratin rich shell and at the interfacial region. Filtration performance of the electrospun keratin/PLA fibers, described in terms of pressure drop and its capability of removing methylene blue, were also explored. Overall, our results demonstrated that it was possible to improve process-ability, morphology and filtration efficiency of the electrospun keratin fibers by adding a suitable amount of clay.

  • 288.
    Isarankura Na Ayutthaya, Siriorn
    et al.
    Division of Materials Technology, School of Energy, Environment and Materials, King Mongkut’s University of Technology Thonburi, Bangkok.
    Tanpichai, Supachok
    Learning Institute, King Mongkut’s University of Technology Thonburi, Bangkok, .
    Wootthikanokkhan, Jatuphorn
    Division of Materials Technology, School of Energy, Environment and Materials, King Mongkut’s University of Technology Thonburi, Bangkok.
    Keratin Extracted from Chicken Feather Waste: Extraction, Preparation, and Structural Characterization of the Keratin and Keratin/Biopolymer Films and Electrospuns2015Inngår i: Journal of polymers and the environment, ISSN 1064-7546, E-ISSN 1572-8900, Vol. 23, nr 4, s. 506-516Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, keratin was extracted from chicken feather waste via an environment-friendly method, sulphitolysis method, by using various sodium metabisulphite contents (0.0–0.5 M). Percentage yield and molecular weight of the extracted keratin were characterized by gravimetry and gel electrophoresis (SDS-PAGE), respectively. It was found that the yield increased, with the increase of sodium meta-bisulphite content, to the maximum value of 87.6 % yield, by using sodium meta-bisulphite content at 0.2 M. Molecular weight range of the product also decreased with the increase of the sodium meta-bisulphite content. The extracted keratin, with highest molecular weight ranged between 12 and 20 kDa, was further used for fabricating into fibers by using the electrospinning process. It was found that pure keratin solution could not be electrospun into fiber. However, by blending keratin with more than 10 wt% PLA, the fibers can be prepared. Results from FTIR and DSC also reveal that the crystal structure of the keratin changed from the β-sheet structure (rigid and small displacement characteristic) to the α-helix structure (elastic and large displacement characteristic) after keratin/PLA blends (10–50 wt% keratin) were prepared by the electrospinning method.

  • 289. Jackson-Etang, Ayuk
    et al.
    Mathew, Aji P.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    The effect of plasticizer and cellulose nanowhisker content on the dispersion and properties of cellulose acetate butyrate nanocomposites2009Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 114, nr 5, s. 2723-2730Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 290.
    Jacobs, Valencia
    et al.
    CSIR Materials Science and Manufacturing, Fibres and Textiles Competence Area, Port Elizabeth.
    Anandjiwala, Rajesh D.
    CSIR Materials Science and Manufacturing, Fibres and Textiles Competence Area, Port Elizabeth.
    John, Maya
    CSIR Materials Science and Manufacturing, Fibres and Textiles Competence Area, Port Elizabeth.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Studies on electrospun chitosan based nanofibres reinforced with cellulose and chitin nanowhiskers2011Konferansepaper (Fagfellevurdert)
  • 291.
    Jalvo, Blanca
    et al.
    Department of Chemical Engineering, University of Alcalá.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rosal, Roberto
    Department of Chemical Engineering, University of Alcalá.
    Coaxial poly(lactic acid) electrospun composite membranes incorporating cellulose and chitin nanocrystals2017Inngår i: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 544, s. 261-271Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 292.
    Jaruttrakool, R.
    et al.
    Center of Excellence in Textiles, Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok.
    Tanpichai, Supachok
    Center of Excellence in Textiles, Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok.
    Pentrakoon, Duanghathai
    Center of Excellence in Textiles, Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok .
    Potiyaraj, Pranut
    Center of Excellence in Textiles, Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok.
    Reactive blending of thermoplastic polyurethane and polypropylene2010Inngår i: International polymer processing, ISSN 0930-777X, E-ISSN 2195-8602, Vol. 25, nr 5, s. 327-333Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this research, reactive blending of thermoplastic polyurethane(TPU) and polypropylene (PP) was studied. Grafting of maleic anhydride (MAH) onto TPU/PP blends was performed by a twin-screw extruder in the presence of dicumyl peroxide (DCP). Mechanical properties and morphology of the blends were investigated by tensile testing and scanning electron microscopy (SEM), respectively. Thermal properties of the blends were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The obtained results were compared with those of the uncompatibilized blends and the blends compatibilized with a commercial maleic anhydride grafted polypropylene (PP-g-MA). The results from the uncompatibilized blends clearly indicate that the TPU and PP are immiscible resulting in undesirable properties of the blends. These properties were improved significantly when TPU and PP were reactive-blended in the presence of MAH and DCP. When comparing with the blends compatibilized with PP-g-MA, the blends prepared by the reactive blending technique possessed better mechanical properties.

  • 293. Johansson, Dennis
    Drying and heat treatment of wood: influences on internal checking2005Inngår i: Proceedings of the 3rd Nordic Drying Conference, NDC 2005: June 15th to 17th 2005, Karlstad, Sweden / [ed] Trygve M. Eikevik, Trondheim: sintef akademisk forlag, 2005Konferansepaper (Annet vitenskapelig)
  • 294.
    Johansson, Dennis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Heat treatment of solid wood: effects on absorption, strength and colour2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Wood is a useful construction material, but it has less desirable properties such as poor durability and poor dimensional stability. These problems can be reduced by using various chemical treatments. Increased environmental awareness has raised the demand for more environmentally friendly methods. Heat treatment is an alternative method for improving these properties with no use of chemical additives. When wood is heated, chemical changes start to take place inside the wood structure. These changes result in increased durability and dimensional stability. In this thesis, a method developed in Finland called ThermoWood has been used in which wood is heated in an atmosphere of superheated steam that serves as a shielding gas. Various property changes due to heat treatment have been studied in this thesis: Colour and strength (Paper I), internal checking (Papers II & III) and capillary absorption (Papers IV-VII). Some smaller unpublished studies are also presented. Paper I focuses on colour and strength response of birch to heat treatment. A method for measuring colour heterogeneity was devised. The results show that there is measurable colour heterogeneity present in birch after heat treatment. Paper I also examines the possibility of using colour for predicting mechanical strength in heat-treated birch, but it is concluded that it is not a suitable method. Impact testing did not give any clear results in strength loss, but it showed significant changes in mechanical failure mechanisms; it showed that heat treatment increased the mechanical failures between fibres in birch. When heat-treating boards thicker than 50 mm, there is a risk of internal checking, especially in spruce. The results show that internal checking in heat-treated spruce is caused by both thermal degradation and drying, but drying has the greatest influence on crack formation. One of the main reasons for heat-treating wood is to reduce the hydroscopic properties. Heat-treated wood has lower equilibrium moisture content and lower wettability as demonstrated by contact angle measurement. Increased water uptake has been discovered when Scots pine treated at around 170°C is subjected to free water in such way that capillary absorption is possible. The results in Paper VII indicate that extractives are a contributing factor to this increased absorption. The results also show that extraction by water soaking causes capillary water absorption in Scots pine to decrease in samples dried at 60°C and cause an increase in samples treated at 200°C. After extraction by water soaking, the reducing effect of heat treatment on capillary water absorption had disappeared.

  • 295.
    Johansson, Dennis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Influences of drying on internal checking of spruce (Picea abies L.) heat-treated at 212°C2006Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 60, nr 5, s. 558-560Artikkel i tidsskrift (Fagfellevurdert)
  • 296. Johansson, Dennis
    Strength and colour response of solid wood to heat treatment2005Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Heat treatment is a method for improving the durability and dimensional stability of wood. The treatment method used in this work is called Thermo Wood and is industrially applied in Finland. In 2004 production was 31146 m3. The method involves heating wood in a steam atmosphere where the heat causes chemical changes in the structure of the wood. The present work was done in order to improve the quality of the treated timber both by predicting strength through colour measurement and by understanding the mechanisms behind the internal checking in heat-treated wood. Besides the published papers there are some smaller unpublished studies presented in the thesis. In paper I the connection between colour and the strength reduction caused by the heat treatment is studied. The results show that colour measurements are not a good way of predicting strength loss on an industrial scale. However, they also show that on an experimental level it is an effective way to study the changes that occur in the wood during treatment. There is a problem with internal checking when heat treatment is performed on boards with dimensions greater than about 50 mm. In paper II the connection between internal checking and both mass loss and drying was investigated. The results showed that both mass loss and drying influence the development of internal checking. Paper III focuses on the effects of drying on internal checking. From studying the results from papers II and III together with the results of some of the unpublished studies, the conclusion is that drying stress is the main cause for internal checking in heat-treated wood.

  • 297. Johansson, Dennis
    et al.
    Morén, Tom
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    The potential of colour measurement for strength prediction of thermally treated wood2006Inngår i: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 64, nr 2, s. 104-110Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the effects of thermal treatment of birch with respect to colour and strength. Birch wood was treated at 175 °C and 200 °C for 0 h, 1 h, 3 h and 10 h. In bending-strength experiments, treatment was also performed at 185 °C for 2 h. Both static bending strength and impact bending strength were investigated using multivariate statistics (PLS) for correlation to process parameters, density, EMC, position in board, modulus of elasticity (only in static bending), colour and dimensions of samples. In static bending, two PLS models were designed, one based on process parameters and the other based on colour and EMC. From these models it was concluded that colour is not a useful parameter for prediction of strength. In impacted bending, the correlation was too small to give useful results. One test of static bending strength with matched samples was performed, and it showed a strength reduction of 43% when treatment was conducted at 200 °C for 3 h. Measurement of colour homogeneity of the treated boards showed that the colour is not homogeneous.

  • 298. Johansson, Dennis
    et al.
    Sehlstedt-Persson, Margot
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Morén, Tom
    Effect of heat treatment on capillary water absorption of heat-treated pine, spruce and birch2006Inngår i: Wood structure and properties '06: [proceedings of the 5th IUFRO Symposium Wood Structure and Properties '06 held on September 3-6, 2006 in Sliač - Sielnica, Slovakia] / [ed] R. Lagana; S. Kurjatko; J. Kudela, Zvolen, Slovakia: Arbora Publishers , 2006, s. 251-255Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Longitudinal absorption of water in matched heat-treated and untreated boards was studied. The boards are from three different species. Scots pine (Pious sylvestris), Norway spruce (Picea abies) and birch (Betula pubescens). The heat treatment was performed according to the Thermowood process at two different temperature levels (170 degrees C and 200 degrees C) for all three species. Computer tomography (CT) scanning was used to intermittently monitor the ascent of the water front. The use of CT scanning enables a study of the liquid water ascent in three dimensions over time. This means that it is possible to determine the influence of different treatment temperatures and species as well as the difference between heartwood and sapwood on capillary action.The results show that longitudinal water absorption in pine sapwood was substantially lamer when heat-treated at 170 degrees C compared to untreated pine sapwood. In pine heartwood, the ascent of water was low in heat-treated as well as in untreated boards. Spruce boards showed low water absorption in sap- and heartwood in heat-treated as well as in untreated boards. Birch showed a decreasing uptake of water with increasing treatment temperature

  • 299.
    John, Maya Jacob
    et al.
    CSIR, Materials Science and Manufacturing, Polymers and Composites, Port Elizabeth.
    Anandjiwala, Rajesh
    CSIR, Materials Science and Manufacturing, Polymers and Composites, Port Elizabeth.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Melt-spun polylactic acid fibers: Effect of cellulose nanowhiskers on processing and properties2013Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 127, nr 1, s. 274-281Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 300.
    Jonasson, Simon
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bünder, Anne
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Niittylä, Totte
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu, Oulu, Finland. Mechanical and Industrial Engineering, University of Toronto, Toronto, Canada.
    Isolation and characterization of cellulose nanofibers from aspen wood using derivatizing and non-derivatizing pretreatments2019Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882XArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The link between wood and corresponding cellulose nanofiber (CNF) behavior is complex owing the multiple chemical pretreatments required for successful preparation. In this study we apply a few pretreatments on aspen wood and compare the final CNF behavior in order to rationalize quantitative studies of CNFs derived from aspen wood with variable properties. This is relevant for efforts to improve the properties of woody biomass through tree breeding. Three different types of pretreatments were applied prior to disintegration (microfluidizer) after a mild pulping step; derivatizing TEMPO-oxidation, carboxymethylation and non-derivatizing soaking in deep-eutectic solvents. TEMPO-oxidation was also performed directly on the plain wood powder without pulping. Obtained CNFs (44–55% yield) had hemicellulose content between 8 and 26 wt% and were characterized primarily by fine (height ≈ 2 nm) and coarser (2 nm < height < 100 nm) grade CNFs from the derivatizing and non-derivatizing treatments, respectively. Nanopapers from non-derivatized CNFs had higher thermal stability (280 °C) compared to carboxymethylated (260 °C) and TEMPO-oxidized (220 °C). Stiffness of nanopapers made from non-derivatized treatments was higher whilst having less tensile strength and elongation-at-break than those made from derivatized CNFs. The direct TEMPO-oxidized CNFs and nanopapers were furthermore morphologically and mechanically indistinguishable from those that also underwent a pulping step. The results show that utilizing both derivatizing and non-derivatizing pretreatments can facilitate studies of the relationship between wood properties and final CNF behavior. This can be valuable when studying engineered trees for the purpose of decreasing resource consumption when isolation cellulose nanomaterials.

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