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  • 1.
    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 technique2016Ingår i: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 81, s. 386-396Artikel i tidskrift (Refereegranskat)
    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.

  • 2.
    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 conditions2015Ingår i: Pigment & Resin Technology, ISSN 0369-9420, E-ISSN 1758-6941, Vol. 44, nr 5, s. 313-321Artikel i tidskrift (Refereegranskat)
    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.

  • 3.
    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 black2014Ingår i: Pigment & Resin Technology, ISSN 0369-9420, E-ISSN 1758-6941, Vol. 43, nr 4, s. 185-193Artikel i tidskrift (Refereegranskat)
    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

  • 4.
    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 pigments2015Ingår i: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 120, s. 10-16Artikel i tidskrift (Refereegranskat)
    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

  • 5.
    Keskisaari, Anna
    et al.
    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.
    Use of construction and demolition wastes as mineral fillers in hybrid wood-polymer composites2016Ingår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 133, nr 19, artikel-id 43412Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The recycling of construction materials has been the subject of much research in past years. In this study, the use of construction and demolition wastes (CDWs) as mineral fillers in hybrid wood-polymer composites was studied. Two types of waste materials were used as fillers in the composites: (1) a mixture consisting of waste mineral wool (MW) and plasterboard (PB) and (2) mixed CDWs. The performance of the composites was evaluated from their mechanical properties and water-absorption behavior. We found in the study that the addition of mineral fillers decreased the flexural strength and modulus values of the wood-polypropylene (PP) composites. On the other hand, the exchange of part of the wood with a mineral filler resulted in an increase in the impact strength of the composite. The composite manufactured with the combination of MW and PB had the lowest water absorption. The decrease in wood loading resulted in improved dimensional stability in the hybrid wood-mineral filler-PP composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43412.

  • 6.
    Oksman, Kristiina
    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.
    Siquiera, Gilberto
    Applied Wood Materials Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf.
    Zhou, Qi
    School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, Stockholm.
    Butylina, Svetlana
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tanpichai, Supachok
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Zhou, Xiaojian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hooshmand, Saleh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Review of the recent developments in cellulose nanocomposite processing2016Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 83, s. 2-18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This review addresses the recent developments of the processing of cellulose nanocomposites, focusing on the most used techniques, including solution casting, melt-processing of thermoplastic cellulose nanocomposites and resin impregnation of cellulose nanopapers using thermoset resins. Important techniques, such as partially dissolved cellulose nanocomposites, nanocomposite foams reinforced with nanocellulose, as well as long continuous fibers or filaments, are also addressed. It is shown how the research on cellulose nanocomposites has rapidly increased during the last 10 years, and manufacturing techniques have been developed from simple casting to these more sophisticated methods. To produce cellulose nanocomposites for commercial use, the processing of these materials must be developed from laboratory to industrially viable methods.

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