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  • 1.
    Butylina, Svetlana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Properties of as-prepared and freeze-dried hydrogels made from poly(vinyl alcohol) and cellulose nanocrystals using freeze-thaw technique2016In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 81, p. 386-396Article in journal (Refereed)
    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.
    Hietala, Maiju
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bionanocomposites of thermoplastic starch and cellulose nanofibers manufactured using twin-screw extrusion2013In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 49, no 4, p. 950-956Article in journal (Refereed)
    Abstract [en]

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

  • 3.
    Liu, Xiaohui
    et al.
    Luleå tekniska universitet.
    Wu, Qiuju
    Luleå tekniska universitet.
    Non-isothermal crystallization behaviors of polyamide 6/clay nanocomposites2002In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 38, no 7, p. 1383-1389Article in journal (Refereed)
    Abstract [en]

    The non-isothermal crystallization behaviors of polyamide 6/clay nanocomposite (PA6CN) were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). DSC results showed that the nanometric silicate layers in PA6CN acted as effective nucleation agents. The addition of silicate layers influenced the mechanism of nucleation and the growth of PA6 crystallites. The DSC results also implied an unusual phenomenon, in contrast to PA6, the crystallinity degree of PA6CN increased with increasing cooling rate. XRD results verified this phenomenon and indicated that the addition of silicate layers favored the formation of the γ crystalline form.

  • 4.
    Ma, Xiaofeng
    et al.
    College of Science, Nanjing Forestry University, Nanjing, P. R. China. Institute of Polymer Materials, Nanjing Forestry University, Nanjing, P. R. China..
    Lan, Xiaoyu
    College of Science, Nanjing Forestry University, Nanjing, P. R. China.
    Wu, Linlin
    College of Materials Science and Engineering, Nanjing Tech University, Nanjing, P. R. China.
    Wang, Lei
    Institute of Polymer Materials, Nanjing Forestry University, Nanjing, P. R. China.
    Gu, Qun
    Chemistry Department, Edinboro University of Pennsylvania, Edinboro PA, USA.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gu, Xiaoli
    College of Chemical Engineering, Nanjing Forestry University, Nanjing, P. R. China.
    Luo, Zhenyang
    College of Science, Nanjing Forestry University, Nanjing, P. R. China. Institute of Polymer Materials, Nanjing Forestry University, Nanjing, P. R. China..
    Photo-induced Actuator using Temperature and Light Dual Responsive Azobenzene Containing Ion Gel in Ionic Liquid2020In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 123, article id 109446Article in journal (Refereed)
    Abstract [en]

    A series of well-defined random copolymers comprising butyl acrylate (BA) and 4-phenylazophenylmethacrylate (AzoMA) (P(AzoMA-r-BA)) are prepared successfully by reversible addition fragmentation chain transfer (RAFT) polymerization. P(AzoMA-r-BA)s show LCST-type phase transition in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfone)amide ([C4mim][NTf2]). LCST depends on the photoisomerization state of azobenzene, as well as on the AzoMA composition in the random copolymers. LCST of (P(cis-AzoMA-r-BA) is significantly higher than that of P(trans-AzoMA-r-BA), because cis-AzoMA and trans-AzoMA behave as solvato-philic and solvato-phobic comonomer, respectively. At a bistable temperature, photo-induced phase separation is completely reversible. Secondly, based on this phenomenon, a thermo- / photo- responsive ion gel (BA-AzoMA ion gel) can be prepared by free radical polymerization of BA and AzoMA using ethylene glycol dimethacrylate (EGDMA) as crosslinker in [C4mim][NTf2]. BA-AzoMA ion gel shows high temperature contraction and low temperature expansion behavior, due to LCST-type phase behavior of polymer system consisting of AzoMA and BA. Contraction temperature of BA-AzoMA ion gel depends on photoisomerization state of the azobenzene group in polymers. At a bistable temperature, photo-induced expansion-contraction is reversible. Finally, a Photo-induced actuator can be realized using BA-AzoMA ion gel at suitable temperatures, featuring reversible bending by alternate irradiating with visible and UV light. The bending behavior is also demonstrated.

  • 5. Mathew, Aji P.
    et al.
    Packirisamy, S.
    Mahatma Gandhi University.
    Radusch, H.J.
    Martin Luther Universität.
    Thomas, Sabu
    Effect of initiating system, blend ratio and crosslink density on the mechanical properties and failure topography of nano-structured full-interpenetrating polymer networks from natural rubber and polystyrene2001In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 37, no 9, p. 1921-1934Article in journal (Refereed)
    Abstract [en]

    The mechanical performance of full-interpenetrating polymer networks (IPNs) based on natural rubber/polystyrene (NR/PS) system has been studied in detail. The IPNs were prepared using different initiators viz., benzoyl peroxide (BPO), azo-bis-isobutyronitrile (AIBN), and dicumyl peroxide (DCP) and the effect of initiating systems on the properties was studied. It was observed that in all cases the IPNs initiated using DCP showed a superior property compared to BPO and AIBN initiated ones. The crosslink density of the IPN was varied by varying the percent of divinyl benzene (crosslinking agent of PS) and the effect of crosslink density on the properties has been studied. The stress-strain behaviour, tensile strength, Young's modulus, elongation at break, tear strength, tension set and tensile set were determined. The effects of strain rate on tensile properties were analysed. The studies on the morphology using scanning electron microscopy showed an increase in phase mixing on increasing the PS content and PS crosslinking. However, high level of PS content and PS crosslinking lead to a decrease in phase mixing. The morphology studies using TEM revealed the interesting fact that NR/PS IPN system was nano-structured. The fracture surfaces of tensile and tear specimens were studied using scanning electron microscopy, to get a clear picture of the mechanism of failure.

  • 6.
    Sethi, Jatin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Illikainen, Mirja
    Fiber and Particle engineering, University of Oulu.
    Sain, Mohini
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Polylactic acid/polyurethane blend reinforced with cellulose nanocrystals with semi-interpenetrating polymer network (S-IPN) structure2017In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 86, p. 188-199Article in journal (Refereed)
    Abstract [en]

    The aim of the current work was to prepare and characterize a cellulose nanocrystal reinforced semi-interpenetrated network (SIPN) derived from polylactic acid (PLA) and polyurethane (PU) polymers. SIPN films were prepared using solvent casting from 1,4-dioxane solution. The morphology, mechanical and thermal properties of the neat SIPN and its nanocomposite were characterized. A novel dispersion method was used, for the first time, to disperse the CNCs into the polyol. This method led to well dispersed CNCs in the SIPN, and at 1 wt% CNC concentration, the elastic modulus of the nanocomposite was improved by 54% over an unreinforced SIPN. Additionally, the results indicated that the toughness of PLA, which is the main polymer phase, was improved. However, in the nanocomposite, CNCs formed a strong network and reinforced the PU phase, which resulted in a lower toughness of the final material. The storage modulus of the SIPN nanocomposite was higher than that of the neat PLA at temperatures higher than 55 °C up to 100 °C. This increase in thermomechanical properties indicates that the reinforced PU network in the PLA matrix can enhance the thermal behavior of material.

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