Change search
Refine search result
1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 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.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Cellulose-based Nanocomposites – The Relationship between Structure and Properties2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nanocellulose materials extracted from various types of biomass have recently attracted significant attention. Due to their remarkable mechanical properties, large surface area and biodegradability, they can be promising reinforcements in nanocomposites. Cellulose-based nanocomposites constitutive of nanocellulose reinforcements and biodegradable polymer matrices have great potential to be used in environmentally friendly applications to replace fossil-based materials. However, the challenge of controlling their nanoscale structure, especially achieving good dispersion of nanocellulose in hydrophobic polymer matrices, still poses significant obstacles to producing high-performance nanocomposites. Therefore, this thesis reports several methods for structural modification of cellulose-based nanocomposites toward the objectives of improving the dispersion of nanocellulose and enhancing the properties of the nanocomposites. The methods include in situ emulsion polymerization in the presence of nanocellulose, crosslinking of polymer matrix, grafting of polymer brushes to nanocellulose and drawing of nanocomposites to obtain aligned structures. The resulting mechanical, thermal and other related properties are investigated, and the relationship between structure and properties of the nanocomposites are discussed.

    To address the challenge of achieving good dispersion of nanocellulose in hydrophobic matrices, in situ emulsion polymerization of vinyl acetate monomer in the presence of cellulose nanocrystals has been developed. Microscopy results show that the in situ method improves the compatibility between nanocellulose and hydrophobic polymers, which consequently improves the dispersion of nanocellulose in the nanocomposites. Compared with direct mixed polymer/nanocellulose composites, the in situ synthesized nanocomposites exhibit higher stiffness and strength arising from their superior interphase volume, which is confirmed theoretically and experimentally. Crosslinking of partially hydrolyzed poly(vinyl acetate) by borate additives under different pH conditions has been studied to further enhance mechanical properties of the nanocomposites. Moreover, the “grafting to” modification method also helps to overcome this challenge. It is revealed that poly(ethylene glycol)-grafted cellulose nanofibers disperse better in poly(lactic acid) matrix than unmodified cellulose nanofibers, which is attributed to the improved compatibility and steric effect provided by the covalently grafted poly(ethylene glycol) brushes.

    To substantially enhance the unidirectional mechanical properties of cellulose-based nanocomposites, a highly aligned structure in the materials is obtained through the drawing process. Drawing conditions including temperature, speed and draw ratio show considerable effects on the mechanical and thermal properties of the nanocomposites. Furthermore, the aligned nanocomposites consisting of poly(lactic acid) matrix and ultra-low weight fraction of poly(ethylene glycol)-grafted cellulose nanofibers demonstrate competitive strength, superb toughness and interesting optical behaviors compared with other aligned nanocellulose-based materials reported in the literature, indicating their potential to be further developed for large-scale environmentally friendly applications.

  • 3.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    High-strength, High-toughness Aligned Polymer-based Nanocomposite Reinforced with Ultra-low Weight Fraction of Functionalized NanocelluloseManuscript (preprint) (Other academic)
    Abstract [en]

    Multifunctional lightweight, flexible, yet strong polymer-based nanocomposites are highly desired for specific applications. However, the control of orientation and dispersion of reinforcing nanoparticles and the optimization of the interfacial interaction still pose substantial challenges in nanocellulose-reinforced polymer composites. In this study, poly(ethylene glycol)-grafted nanocellulose fibers (TOCNF-g-PEG) has demonstrated much better dispersion in a poly(lactic acid) (PLA) matrix as compared to unmodified nanocellulose fibers. Through a uniaxial drawing method, aligned PLA/nanocellulose nanocomposites with high strength, high toughness, and unique optical behavior are obtained. With the incorporation of only 0.1 wt% of TOCNF-g-PEG in PLA, the ultimate strength of the nanocomposite reaches 343 MPa, which is significantly higher than that of other aligned PLA-based nanocomposites reported previously. Compared with the aligned nanocomposite reinforced with unmodified nanocellulose, the ultimate strength and toughness are enhanced by 39% and 70%, respectively. Moreover, the aligned nanocomposite film is highly transparent and possesses an anisotropic light scattering effect, revealing its significant potential for optical applications.

  • 4.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Haque, MD Minhaz Ul
    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.
    Crosslinked polyvinyl acetate (PVAc) reinforced with cellulose nanocrystals (CNC) – structure and mechanical properties2016In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 126, p. 35-42Article in journal (Refereed)
    Abstract [en]

    The structure of cellulose-based nanocomposites significantly influences their final mechanical properties. However, obtaining a good dispersion of hydrophilic nanocellulose materials in a hydrophobic polymer matrix is challenging. In this study, two unique methods were developed to improve the dispersion of cellulose nanocrystals (CNC) in a poly(vinyl acetate) (PVAc) matrix. One method was the crosslinking of PVAc by sodium tetraborate (borax), which is expected to prevent agglomeration of CNCs during the drying process, and the other method was the in-situ polymerization of vinyl acetate in the presence of CNCs to generate good compatibility between CNC and PVAc. The results showed that the crosslinking degree of PVAc could be varied by tuning the pH. The atomic force microscopy images illustrate that after drying, the in-situ polymerized PVAc/CNC composite was much better dispersed than the composite produced using mechanical mixing. The mechanical and thermo-mechanical characterizations indicate that the in-situ nanocomposite with 10 wt% of CNC had a higher strength and storage modulus compared with the mixed composite with the same CNC concentration. Further investigations of the restriction effect caused by the crosslinker are required.

  • 5.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Haque, MD Minhaz Ul
    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.
    Crosslinked polyvinyl acetate reinforced with cellulose nanocrystals –: Characterization of structure and mechanical properties2015Conference paper (Refereed)
    Abstract [en]

    The structure of cellulose based nanocomposites influences their final mechanical properties significantly. Obtaining good dispersion of hydrophilic nanocellulose materials in hydrophobic polymer matrix is challenging. Here two unique methods were developed to improve the dispersion of cellulose nanocrystals (CNC) in polyvinyl acetate (PVAc) matrix. One is in-situ polymerization of vinyl acetate in the presence of CNCs, and the other one is crosslinking of PVAc by sodium tetraborate (Borax), which restricts the movement of CNCs during the drying process. The results from atomic force microscopy (AFM) show that the in-situ CNC/PVAc emulsion has much better dispersion than the one produced by stirring. Moreover, the mechanical characterization indicates that the in-situ composite with 10 wt% CNC has higher strength compared to the stirred composite with the same CNC concentration. The mechanical properties of crosslinked PVAc materials can be varied by changing the pH and may be attributed to differences of the crosslinking degree. Further investigations of the restriction effect caused by borax are needed.

  • 6.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Harila, Maria
    Luleå University of Technology.
    Yao, Kun
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Zhou, Qi
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Grafting polyethylene glycol on nanocellulose toward biodegradable polymer nanocomposites2017Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigated the effects of grafting polyethylene glycol on nanocellulose on microstructure, mechanical properties and thermal behaviors of the polylactic acid/nanocellulose composites.

  • 7.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Liu, Peng
    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.
    Cellulose-based nanocomposites with outstanding dispersion produced by in-situ polymerization2016Conference paper (Refereed)
    Abstract [en]

    Cellulose-based nanocomposites are promising materials to replace the fossil-based polymers since they are biodegradable and produced from renewable resources. However, achieving good dispersion of nanocellulose in the matrix is one of the main obstacles because nanomaterials tend to form aggregates and lose their merits. In this study we developed an in-situ polymerization method to produce cellulose nanocrystals reinforced polyvinyl acetate, and the method of direct mechanical mixing was used as reference. The stability of in-situ and mixed nanocomposite aqueous dispersions was investigated by zeta potential measurements, and the results show that both of them were electrostatic stable at pH 4. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the dispersion of cellulose nanocrystals in the in-situ and mixed nanocomposites after drying, and better dispersion could be seen in the in-situ samples compared with the mixed ones. Tensile testing showed that the in-situ nanocomposites with same cellulose content had higher strength and longer elongation at break compared to the mixed nanocomposites. Furthermore, crosslinking the cellulose and partially hydrolyzed polyvinyl acetate with sodium tetraborate was also performed to further improved the reinforcing efficiency. The results from Raman spectroscopy illustrate that the heavy atoms (CC and CO) in cellulose experienced more stretching in the crosslinked nanocomposites, and the tensile testing indicated the elastic modulus and ultimate strength of them were increased significantly than those without crosslinking.

  • 8.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Liu, Peng
    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.
    Single-step method for producing cellulose based nanocomposites with outstanding dispersion2015Conference paper (Refereed)
    Abstract [en]

    Cellulose nanomaterials are promising as reinforcement in composites, which is attributed to high mechanical properties, generating large interfacial area and biodegradable ability, etc. However, obtaining good dispersion is a main challenge of large-scale industrial applications since nanomaterials tend to form aggregates and lose their merits. In this study we developed a single-step method that is in-situ polymerization to produce cellulose nanocrystals reinforced polyvinyl acetate with good dispersion. Compared to normal composites prepared by direct mechanical mixing, better dispersion of cellulose nanocrystals by using in-situ polymerization has been confirmed by atomic force microscopy. Mechanical testing shown that the in-situ nanocomposites with same cellulose content had higher strength and longer elongation at break compared to direct mixed composites. Moreover, crosslinks between cellulose and partially hydrolysed polyvinyl acetate could be formed by tetrahydroborate ions in aqueous dispersion, which further improved the reinforcing efficiency. The cellulose based nanocomposites produced by in-situ polymerization are potential materials to replace fossil based polymers used in packaging and coating applications.

  • 9.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Shah, Faiz Ullah
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Liu, Peng
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Plasticizing and crosslinking effects of borate additives on the structure and properties of poly(vinyl acetate)2017In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 13, p. 7483-7491Article in journal (Refereed)
    Abstract [en]

    As an environmentally friendly, low-cost and widely used polymer, poly(vinyl acetate) (PVAc) is worth modifying to achieve better properties. Here, we report on the influence of borate additives on the structure and properties of partially hydrolysed PVAc. In addition to the general crosslinking function of borate additives, an extraordinary plasticizing effect was found. By controlling the pH from 4 to 11 during sample preparation, the plasticizing and crosslinking effects can be shifted. In alkaline conditions, the degree of crosslinking in the PVAc/borate sample is increased; however, this increase declines gradually with an increase in the borate additive content, which impacts the morphology of the PVAc latex particles, as well as the mechanical and thermal properties of the PVAc/borate films. In contrast, in acidic conditions, the PVAc/borate films are plasticized by borate additives; thus, their ultimate mechanical strength, elastic moduli and thermal stabilities decrease, while the water diffusivities increase.

  • 10.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wei, Jiayuan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    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. Fibre and Particle Engineering, University of Oulu, Oulu, Finland .
    Well-dispersed cellulose nanocrystals in hydrophobic polymers by in situ polymerization for synthesizing highly reinforced bio-nanocomposites2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 25, p. 11797-11807Article in journal (Refereed)
    Abstract [en]

    In nanocomposites, dispersing hydrophilic nanomaterials in a hydrophobic matrix using simple and environmentally friendly methods remains challenging. Herein, we report a method based on in situ polymerization to synthesize nanocomposites of well-dispersed cellulose nanocrystals (CNCs) and poly(vinyl acetate) (PVAc). We have also shown that by blending this PVAc/CNC nanocomposite with poly(lactic acid) (PLA), a good dispersion of the CNCs can be reached in PLA. The outstanding dispersion of CNCs in both PVAc and PLA/PVAc matrices was shown by different microscopy techniques and was further supported by the mechanical and rheological properties of the composites. The in situ PVAc/CNC nanocomposites exhibit enhanced mechanical properties compared to the materials produced by mechanical mixing, and a theoretical model based on the interphase effect and dispersion that reflects this behavior was developed. Comparison of the rheological and thermal behaviors of the mixed and in situ PVAc/CNC also confirmed the great improvement in the dispersion of nanocellulose in the latter. Furthermore, a synergistic effect was observed with only 0.1 wt% CNCs when the in situ PVAc/CNC was blended with PLA, as demonstrated by significant increases in elastic modulus, yield strength, elongation to break and glass transition temperature compared to the PLA/PVAc only material.

  • 11.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yao, Kun
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Harila, Maria
    Luleå University of Technology.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zhou, Qi
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aligned biodegradable cellulose-reinforced nanocomposites with high strength and toughness2017Conference paper (Refereed)
    Abstract [en]

    Cellulose, as the most abundant component in wood, has attracted a lot of attention for utilizing it in environmentally-friendly applications to replace the fossil-based materials. Nanocellulose materials with high stiffness and strength, large surface area and biodegradability, are promising reinforcement in polymers. However, the energy consumption of nano-scale isolation of cellulose and the dispersion of nanocellulose materials in the polymers are still challenging for obtaining low-cost and ultra-strong nanocomposites. To overcome these, we focus on investigating the aligned nanocomposites reinforced by a very low cellulose nanofibers (CNF) content (0.1 wt%), and grafting polyethylene glycol (PEG) on CNF was performed to improve the dispersion of them. We found that the alignment can improve mechanical properties of the polylactic acid (PLA)/CNF composites dramatically. With a draw ratio of 8, the strength of the aligned composite reached 320 MPa and the toughness was 30 times enhanced compared to the isotropic material. Much better dispersion of the CNF grafted with PEG in PLA matrix was confirmed by scanning electron microscopy (SEM) compared to the ungrafted CNF, and further supported by the mechanical testing results. Furthermore, the aligned nanocomposites exhibited light scattering behavior indicating they have the potential to be used in optical applications.

  • 12.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yao, Kun
    Royal Institute of Technology, School of Biotechnology, Stockholm.
    Harila, Maria
    Luleå University of Technology.
    Zhou, Qi
    Royal Institute of Technology, School of Biotechnology, Stockholm.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu, Finland.
    Grafting polyethylene glycol on nanocellulose toward biodegradable polymer nanocomposites2017In: ICCM21 Proceedings, ICCM, International Committee on Composite Materials , 2017Conference paper (Refereed)
    Abstract [en]

    The reinforcing effect of a small amount of nanocellulose materials on biodegradable and polymer-based nanocomposites remains challenging because of the poor dispersion of the nanomaterials and inefficient interaction between the nanocellulose and the polymer matrix. To improve this, we grafted polyethylene glycol (PEG) on nanocellulose and produced composites of 0.1 wt% nanocellulose materials and polylactic acid (PLA) matrix. Here, two types of PEG grafted nanocellulose including TEMPO-oxidized cellulose nanocrystals (TOCNCs) and cellulose nanofibers (TOCNFs), with different lengths and diameters were used as reinforcements, respectively. We investigated the effects of grafting PEG on microstructure, mechanical properties and thermal behaviors of the PLA/nanocellulose composites. It is found that the PEG grafted nanocellulose dispersed better compared to the unmodified nanocellulose in the PLA matrix, and provides higher reinforcing effect that improves the elastic modulus of the nanocomposites compared to the composites with unmodified nanocellulose and ungrafted PEG. However, the glass transition temperature of the nanocomposites was not improved by grafting PEG significantly. We also found that the nanocomposites reinforced by TOCNF exhibited enhanced mechanical and thermal properties compared to those with TOCNCs, which is caused by the higher aspect ratio of the TOCNFs.

  • 13.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yao, Kun
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Zhou, Qi
    Division of Glycoscience, School of Biotechnology, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aligned polylactic acid based nanocomposite reinforced using a tiny amount of functionalized cellulose nanofibers2018Conference paper (Refereed)
    Abstract [en]

    Due to the challenges of the cost of nanocellulose materials and the dispersion of them in polymer matrix, small amount and well-dispersed nanocellulose materials are desired as reinforcement to achieve environmentally-friendly nanocomposites with high performance. In this study, an aligned polylactic acid (PLA) based nanocomposite reinforced by 0.1 wt% of functionalized cellulose nanofibers (CNFs) was investigated. The CNFs were covalently grafted by polyethylene glycol (PEG), which improves the dispersion of the CNFs in the PLA significantly compared to the native CNFs. The improved dispersion was examined by scanning electron microscopy (SEM), polarized optical microscopy (POM) and mechanical testing. Furthermore, it was found that the alignment can improve mechanical properties of the nanocomposite dramatically. The strength of the aligned nanocomposite reaches 343 MPa with a draw ratio of 8, meanwhile the toughness is about 30 times enhanced compared to the isotropic material. The aligned nanocomposite also exhibits light scattering behavior, indicating that it has the potential to be used in optical applications.

  • 14.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yao, Kun
    Division of Glycoscience, Department of Chemistry, KTH Royal Institute of Technology.
    Zhou, Qi
    Division of Glycoscience, Department of Chemistry, KTH Royal Institute of Technology.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu.
    High-strength, High-toughness Aligned Polymer-based Nanocomposite Reinforced with Ultra-low Weight Fraction of Functionalized Nanocellulose2018In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, no 10, p. 4075-4083Article in journal (Refereed)
    Abstract [en]

    Multifunctional lightweight, flexible, yet strong polymer-based nanocomposites are highly desired for specific applications. However, the control of orientation and dispersion of reinforcing nanoparticles and the optimization of the interfacial interaction still pose substantial challenges in nanocellulose-reinforced polymer composites. In this study, poly(ethylene glycol)-grafted nanocellulose fibers (TOCNF-g-PEG) has demonstrated much better dispersion in a poly(lactic acid) (PLA) matrix as compared to unmodified nanocellulose fibers. Through a uniaxial drawing method, aligned PLA/nanocellulose nanocomposites with high strength, high toughness, and unique optical behavior are obtained. With the incorporation of only 0.1 wt% of TOCNF-g-PEG in PLA, the ultimate strength of the nanocomposite reaches 343 MPa, which is significantly higher than that of other aligned PLA-based nanocomposites reported previously. Compared with the aligned nanocomposite reinforced with unmodified nanocellulose, the ultimate strength and toughness are enhanced by 39% and 70%, respectively. Moreover, the aligned nanocomposite film is highly transparent and possesses an anisotropic light scattering effect, revealing its significant potential for optical applications.

  • 15.
    Haque, Md. Minhaz-Ul
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Herrera, Natalia
    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. Fibre and Particle Engineering, University of Oulu, Finland.
    Melt compounded nanocomposites with semi-interpenetrated network structure based on natural rubber, polyethylene, and carrot nanofibers2018In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 135, no 10, article id 45961Article in journal (Refereed)
    Abstract [en]

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

  • 16.
    Moberg, Tobias
    et al.
    Department of Materials and Manufacturing Technology, Chalmers University of Technology .
    Sahlin, Karin
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology.
    Yao, Kun
    School of Biotechnology, Royal Institute of Technology, Stockholm.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Westman, Gunnar
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology.
    Zhou, Qi
    School of Biotechnology, Royal Institute of Technology, Stockholm.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rigdahl, Mikael
    Department of Materials and Manufacturing Technology, Chalmers University of Technology.
    Rheological properties of nanocellulose suspensions: effects of fibril/particle dimensions and surface characteristics2017In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, no 6, p. 2499-2510Article in journal (Refereed)
    Abstract [en]

    The rheological properties of aqueous suspensions based on three different nanocelluloses were compared. One system was obtained via acid hydrolysis (thus yielding crystalline nanocellulose, CNC) and the other two from mechanical shearing, but from different origins and subjected to different pretreatments. Of the latter two, one was considered to be a rather typical cellulose nanofibril (CNF) suspension whereas the other was a kind of intermediate between CNF and CNC. All three nanocellulose elements differed in dimensions as evident from transmission electron microscopy and atomic force microscopy. With regard to the length of the fibrils/particles, the three nanocelluloses formed three distinct groups with lengths between 200 and slightly more than 800 nm. The three cellulosic elements were also subjected to a TEMPO-mediated oxidation yielding a similar carboxylate content in the three systems. Furthermore, the TEMPO-oxidized elements were grafted with poly(ethylene glycol) (PEG). The amount of grafted PEG was about 35 wt%. The shear viscosity, the storage modulus and the loss modulus of suspensions of the unmodified, the TEMPO-oxidized and the grafted nanocelluloses were determined at room temperature and the solids content of the suspensions was varied between 0.7 and 2.0 wt%. It was concluded that the rheological properties varied significantly between the suspensions depending on the dimensions of the cellulosic elements and their surface characteristics. In this context, the length (or the aspect ratio) of the particles played a very important role.

  • 17.
    Singh, Anshu A.
    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.
    Herrera Vargas, Natalia
    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.
    Aligned plasticized polylactic acid cellulose nanocomposite tapes: Effect of drawing conditions2018In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 104, p. 101-107Article in journal (Refereed)
    Abstract [en]

    Aligned nanocomposite tapes based on plasticized polylactic acid (PLA) and 1 wt.% cellulose nanofibers (CNF) were prepared using uniaxial solid-state drawing, and the effects of drawing conditions including temperature, speed and draw ratio on the material were studied. Microscopy studies confirmed alignment and the formation of ‘shish-kebab’ morphology in the drawn tape. Mechanical properties demonstrate that the solid-state drawing is a very effective way to produce stronger and tougher PLA nanocomposites, and the toughness can be improved 60 times compared to the undrawn tape. Additionally, the thermal properties, i.e. storage modulus, glass transition temperature and degree of crystallinity were improved. These improvements are expected due to the synergistic effect of CNF in the nanocomposite and orientations induced by the solid-state drawing.

  • 18.
    Singh, Anshu A.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wei, Jiayuan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vargas, Natalia Herrera
    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. Fibre and Particle Engineering, University of Oulu.
    Synergistic effect of chitin nanocrystals and orientations induced by solid-state drawing on PLA-based nanocomposite tapes2018In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 162, p. 140-145Article in journal (Refereed)
    Abstract [en]

    Uniaxial solid-state drawing was used to orientate plasticized polylactic acid (PLA) and its nanocomposite tapes with 1 and 5 wt% chitin nanocrystals (ChNC). Microscopy studies confirmed the orientation and formation of a ‘shish-kebab’ morphology in the drawn tapes. The mechanical properties demonstrated that the drawing led to stronger and tougher nanocomposites compared to plasticized PLA. The tensile strength increased from 41 MPa to 71 MPa, and the elongation at break increased from 5% to 60% for the nanocomposite with 5 wt% ChNC and a draw ratio of 3. The ChNC had a positive effect on the thermomechanical properties; the tan delta peak shifted to a higher temperature with an increasing ChNC content. These improvements in the mechanical and thermal properties are expected synergistic effects of both the ChNC in the nanocomposite and the alignment of the ChNC together with the polymer chains induced by the solid-state drawing.

  • 19.
    Wei, Jiayuan
    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.
    Pitkänen, Olli
    University of Oulu.
    Järvinen, Topias
    University of Oulu.
    Kordas, Krisztian
    University of Oulu.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Biomass-derived electrospun carbon nanofiber networks for high-performance supercapacitors2019Conference paper (Refereed)
  • 20.
    Wei, Jiayuan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Pitkänen, Olli
    Microelectronics research group, University of Oulu, FI-90570, Oulu, Finland.
    Järvinen, Topias
    Microelectronics research group, University of Oulu, FI-90570, Oulu, Finland.
    Kordas, Krisztian
    Microelectronics research group, University of Oulu, FI-90570, Oulu, Finland.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lignin-based carbon mats – promising electrodes of supercapacitors from wood2018Conference paper (Refereed)
    Abstract [en]

    Lignin is one of the major renewable sources which can be obtained from the forest, however, about 98% of lignin from pulping and papermaking industry has been wasted or simply burnt. Recent studies show that lignin can be spun and converted to carbon fibers of high quality due to its abundant phenolic structure. Moreover, electrospinning as a state-of-art process can be applied to produced lignin-based nanofiber mats, which gives the fiber mats significantly high specific surface area. Together with carbonization process, the lignin-based carbon mats are attractive to be used as electrodes in supercapacitors for energy saving and storage. In this study, lignin/poly(vinyl alcohol)-based fiber mats with very high lignin content (75 wt%) are prepared via electrospinning and the as-spun mats are carbonized at different temperatures up to 1400 °C. The fiber networks obtained from electrospinning remains intact after the carbonization process, which guarantees their outstanding specific surface areas as high as 1700 m2/g. Furthermore, the electrochemical measurements of the carbonized mats indicate that a superior specific capacitance of 241 F/g are reached compared with most of the literature-reported values, which shows that the lignin-based carbon mats have great potential to replace electrodes from fossil-based and/or unrenewable materials.

  • 21.
    Wei, Jiayuan
    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.
    Pitkänen, Olli
    University of Oulu.
    Järvinen, Topias
    University of Oulu.
    Kordas, Krisztian
    University of Oulu.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Making good use of lignin – from a low-value biopolymer to energy storage devices2019Conference paper (Refereed)
  • 22.
    Wei, Jiayuan
    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.
    Sarmad, Shokat
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Adsorption of Carbon Dioxide on Cellulose Nanofiber-Based Monolithic Cryogels Impregnated with Acetylated Cellulose Nanocrystals2018Conference paper (Refereed)
    Abstract [en]

    Nanocellulose materials with large surface area are prospective as substrates to obtain low-carbon-footprint CO2 adsorbents. In this study, ice-templating was conducted to prepare cellulose nanofibers (CNFs) based cryogels with monolithic structure, which can provide a good mass flow during the adsorption process. Furthermore, since acetyl groups have shown relatively high CO2 affinity, cellulose nanocrystals (CNCs) were acetylated and then impregnated into the cryogel to improve its CO2 capacity. Meanwhile, different amounts of cellulose acetate (CA) were impregnated and characterized as references. The success of the acetylation of CNCs was confirmed by Fourier-transform infrared spectroscopy (FTIR) and the degree of substitution was determined by titration. Results from the scanning electron microscopy (SEM) demonstrated that the monolithic structure was maintained after the impregnation. According to the breakthrough test, the cryogel impregnated with 0.1g of acetylated CNCs exhibits a much higher CO2 capacity with a value of 1.49 mmol/g compared to the CA impregnated ones. The mechanical properties of the cryogels were also evaluated by compression testing, revealing the outstanding reinforcing effect of acetylated CNCs.

  • 23.
    Zhou, Xiaojian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sethi, Jatin
    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.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Frisk, Nikolina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    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.
    Dispersion and reinforcing effect of carrot nanofibers on biopolyurethane foams2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 110, p. 526-531Article in journal (Refereed)
    Abstract [en]

    In this study, carrot nanofibers (CNF) were used to enhance the performance of biobased castor oil polyol polyurethane nanocomposite foams. A method of dispersing CNF in the polyol was developed and the foam characteristics and CNF reinforcing effect were studied. Co-solvent-assisted mixing resulted in well-dispersed CNF in the polyol, and foams with 0.25, 0.5 and 1 phr CNF content were prepared. The reinforced nanocomposite foams displayed a narrow cell size distribution and the compressive strength and modulus were significantly elevated and the best compressive strength and modulus were reached with 0.5 phr CNF. Similarly, the modulus of the solid material was also significantly increased based on theoretical calculations. When comparing the foam performance, compressive strength and stiffness as a function of the density, the nanocomposite foams performs as commercial rigid PU foam with a closed cell structure. These results are very promising and we believe that these foams are excellent core materials for lightweight sandwich composites.

1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf