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  • 1.
    Butylina, Svetlana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratory of Computational and Process Engineering, Lappeenranta-Lahti University of Technology, Lappeenranta, Finland.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Laatikainen, Katri
    Laboratory of Computational and Process Engineering, Lappeenranta-Lahti University of Technology, Lappeenranta, Finland.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON, Canada.
    Cellulose Nanocomposite Hydrogels: From Formulation to Material Properties2020In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 8, article id 655Article in journal (Refereed)
    Abstract [en]

    Poly(vinyl alcohol) (PVA) hydrogels produced using the freeze-thaw method have attracted attention for a long time since their first preparation in 1975. Due to the importance of polymer intrinsic features and the advantages associated with them, they are very suitable for biomedical applications such as tissue engineering and drug delivery systems. On the other hand, there is an increasing interest in the use of biobased additives such as cellulose nanocrystals, CNC. This study focused on composite hydrogels which were produced by using different concentrations of PVA (5 and 10%) and CNC (1 and 10 wt.%), also, pure PVA hydrogels were used as references. The main goal was to determine the impact of both components on mechanical, thermal, and water absorption properties of composite hydrogels as well as on morphology and initial water content. It was found that PVA had a dominating effect on all hydrogels. The effect of the CNC addition was both concentration-dependent and case-dependent. As a general trend, addition of CNC decreased the water content of the prepared hydrogels, decreased the crystallinity of the PVA, and increased the hydrogels compression modulus and strength to some extent. The performance of composite hydrogels in a cyclic compression test was studied; the hydrogel with low PVA (5) and high CNC (10) content showed totally reversible behavior after 10 cycles.

  • 2.
    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.

  • 3.
    El Ouardi, Youssef
    et al.
    Lappeenranta-Lahti University of Technology LUT, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Lamsayah, Morad
    Laboratory of Applied and Environmental Chemistry (LCAE), Faculty of Science, University Mohammed First, 60 000, Oujda, Morocco.
    Butylina, Svetlana
    Lappeenranta-Lahti University of Technology LUT, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Esmaeili, Mohammadamin
    Lappeenranta-Lahti University of Technology LUT, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Giove, Alessio
    Lappeenranta-Lahti University of Technology LUT, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland; Université de Toulon, MAPIEM, Toulon, France.
    Massima Mouele, Emile S.
    Lappeenranta-Lahti University of Technology LUT, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Virolainen, Sami
    Lappeenranta-Lahti University of Technology LUT, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    El Barkany, Soufian
    Laboratory of Molecular Chemistry, Materials and Environment (LMCME), Department of Chemistry, Faculty Multidisciplinary Nador, Mohamed 1st University, P. B. 300, Nador 62700, Morocco.
    Ouammou, Abdelkrim
    LIMOME Laboratory, Dhar El Mehraz Faculty of Sciences, Sidi Mohamed Ben Abdellah University, B.P. 1796, Atlas, Fes 30000, Morocco.
    Repo, Eveliina
    Lappeenranta-Lahti University of Technology LUT, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Laatikainen, Katri
    Lappeenranta-Lahti University of Technology LUT, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Sustainable composite material based on glutenin biopolymeric-clay for efficient separation of rare earth elements2022In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 440, article id 135959Article in journal (Refereed)
    Abstract [en]

    Rare earth metals (REEs) are crucial for modern industries and technological development. Their extraction from non-renewable primary sources has almost reached its threshold due to excessive global demand. An effectual approach for REEs recovery is recycling secondary sources governed by separation materials. In this work, a novel glutenin-based Na-bentonite (Gle@Na_Bex:y) composite was produced via the in-situ hydrothermal route followed by a subsequent freeze-drying process. Additionally, a possible production route for the composites was proposed. The novel Gle@Na_Bex:y composites were characterized with Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface area, and zeta potential (ZP) measurements. FTIR results complemented with SEM images and XRD measurements confirmed the successful incorporation of glutenin into the Na-bentonite clay. The separation of REEs from aqueous solution was used as a model system to demonstrate the material’s ability for selective metal recovery. The best conditions (T, pH, time) for REE sorption were assessed using equilibrium batch adsorption experiments. The kinetics of REE adsorption were effectively explained by a pseudo-second-order model; all the adsorption equilibrium data followed the Langmuir model. Thermodynamic investigations revealed that the adsorption is endothermic and spontaneous, and the adsorption of REEs occurred through a chemisorption process. The sorption mechanism of REE ions was investigated using molecular modelling. The results of this study demonstrate the feasibility of utilizing Gle@Na_Be50:50 composite as an efficient material for REEs removal. The maximum adsorption capacities of Y3+, La3+, and Nd3+ achieved with Gle@Na_Be50:50, were 76.87, 56.71, and 74.61 mg/g, respectively. This work offers a new route for engineering, valuable composite materials for the separation of REEs from diverse sources.

  • 4.
    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.

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  • 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 (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.

  • 6.
    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.

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  • 7.
    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.

  • 8.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Maennlein, Alexis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yu, Liang
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    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. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON, M5S 3G8, Canada.
    Monolithic carbon aerogels from bioresources and their application for CO2 adsorption2021In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 323, article id 111236Article in journal (Refereed)
    Abstract [en]

    Monolithic binder-free CO2 adsorbents with high adsorption capacity, selectivity, adsorption-desorption kinetics, and regenerability are highly desired to both reduce the environmental impact of anthropogenic CO2 emissions and purify valuable gases from CO2. Herein, we report a strategy to prepare monolithic carbonaceous CO2 adsorbents from low-cost and underutilized bioresources, which enabled the formation of a delicate anisotropic, hierarchical porous structure. With optimized material composition and processing conditions, the biobased carbon adsorbent demonstrated a CO2 adsorption capacity of 4.49 mmol g-1 at 298 K and 100 kPa, relatively weak adsorbent-adsorbate affinity, good CO2/N2 selectivity, and advantageous hydrophobicity against water vapor. Moreover, the unique anisotropic porous structure provided high stiffness and good flexibility to the adsorbent in the axial and radial directions, respectively. We confirmed that this type of carbon adsorbent could be packed in a column for dynamic CO2 capture independent of any binders, indicating its promising future for further development toward widespread utilization.

  • 9.
    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.

  • 10.
    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.

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    FULLTEXT01
  • 11.
    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, 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.

  • 12.
    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.

  • 13.
    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.
    Jonasson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material 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. Fibre and Particle Engineering, University of Oulu. Mechanical & Industrial Engineering (MIE), University of Toronto.
    Multifunctional Carbon Aerogels with Hierarchical Anisotropic Structure Derived from Lignin and Cellulose Nanofibers for CO2 Capture and Energy Storage2020In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 12, no 6, p. 7432-7441Article in journal (Refereed)
    Abstract [en]

    In current times, CO2 capture and light-weight energy storage are receiving significant attention and will be vital functions in next-generation materials. Porous carbonaceous materials have great potential in these areas, whereas most of the developed carbon materials still have significant limitations, such as non-renewable resources, complex and costly processing or the absence of tailorable structure. In this study, a new strategy is developed for using the currently under-utilized lignin and cellulose nanofibers, which can be extracted from renewable resources to produce high-performance multifunctional carbon aerogels with a tailorable, anisotropic pore structure. Both the macro- and microstructure of the carbon aerogels can be simultaneously controlled by discreetly tuning the weight ratio of lignin to cellulose nanofibers in the carbon aerogel precursors, which considerably influences their final porosity and surface area. The designed carbon aerogels demonstrate excellent performance in both CO2 capture and capacitive energy storage, and the best results exhibit a CO2 adsorption capacity of 5.23 mmol g-1 at 273 K and 100 kPa, and a specific electrical double layer capacitance of 124 F g-1 at a current density of 0.2 A g-1, indicating that they have great future potential in the relevant applications.

  • 14.
    Geng, Shiyu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wloch, Daniela
    Luleå University of Technology.
    Herrera, 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. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON, M5S 3G8, Canada.
    Large-scale manufacturing of ultra-strong, strain-responsive poly(lactic acid)-based nanocomposites reinforced with cellulose nanocrystals2020In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 194, article id 108144Article in journal (Refereed)
    Abstract [en]

    Developing materials from renewable resources to produce nanocomposites with satisfactory mechanical properties is a vital progress in today's society, and meanwhile, the widespread use of these nanocomposites needs to be enabled through large-scale manufacturing. Herein, ultra-strong nanocomposites with an aligned structure that consisted of bio-based, biodegradable poly(lactic acid) (PLA) and cellulose nanocrystals are demonstrated, and these nanocomposites can be manufactured at a large scale through surface modification of the nanocrystals, liquid-assisted extrusion, and solid-state drawing. An ultimate strength of 353 MPa and a toughness of 107 MJ/m3 can be achieved by these nanocomposites, which are superior compared to the values of many other thermoplastic materials. The mechanism that explains the high toughness of these nanocomposites has been extensively investigated, revealing that sliding of the PLA crystallites present in the materials is the main factor. Moreover, these nanocomposites possess relatively high glass transition temperature and exhibit strain-responsive birefringence behavior, which indicates their great potential in not only structural applications, but also optical strain sensing areas.

  • 15.
    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.

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  • 16.
    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.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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.

  • 20.
    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, 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.

  • 21.
    Nissilä, Tuukka
    et al.
    Fibre and Particle Engineering Research Unit, Faculty of Technology, University of Oulu, FI-90014 Oulu, Finland.
    Wei, Jiayuan
    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.
    Teleman, Anita
    RISE Research Institutes of Sweden, SE-11428 Stockholm, Sweden.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON M5S 3G8, Canada.
    Ice-Templated Cellulose Nanofiber Filaments as a Reinforcement Material in Epoxy Composites2021In: Nanomaterials, E-ISSN 2079-4991, Vol. 11, no 2, article id 490Article in journal (Refereed)
    Abstract [en]

    Finding renewable alternatives to the commonly used reinforcement materials in composites is attracting a significant amount of research interest. Nanocellulose is a promising candidate owing to its wide availability and favorable properties such as high Young’s modulus. This study addressed the major problems inherent to cellulose nanocomposites, namely, controlling the fiber structure and obtaining a sufficient interfacial adhesion between nanocellulose and a non-hydrophilic matrix. Unidirectionally aligned cellulose nanofiber filament mats were obtained via ice-templating, and chemical vapor deposition was used to cover the filament surfaces with an aminosilane before impregnating the mats with a bio-epoxy resin. The process resulted in cellulose nanocomposites with an oriented structure and a strong fiber–matrix interface. Diffuse reflectance infrared Fourier transform and X-ray photoelectron spectroscopy studies revealed the presence of silane on the filaments. The improved interface, resulting from the surface treatment, was observable in electron microscopy images and was further confirmed by the significant increase in the tan delta peak temperature. The storage modulus of the matrix could be improved up to 2.5-fold with 18 wt% filament content and was significantly higher in the filament direction. Wide-angle X-ray scattering was used to study the orientation of cellulose nanofibers in the filament mats and the composites, and the corresponding orientation indices were 0.6 and 0.53, respectively, indicating a significant level of alignment.

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  • 22.
    Oliver-Ortega, Helena
    et al.
    Group LEPAMAP, Department of Chemical Engineering, University of Girona, EPS. Ed. PI. C/ Maria Aurelia Capmany 61, 17003 Girona, Spain.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Espinach, Francesc Xavier
    Design, Development and Product Innovation, Department Organization, Business Management and Product Design, University of Girona, C/ Maria Aurelia Capmany 61, 17003 Girona, Spain.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON M5S 3G8, Canada.
    Vilaseca, Fabiola
    Engineering Materials, Industrial and Materials Science, Chalmers University of Technology, SE 41296 Göteborg, Sweden. BIMATEC, Department of Chemical Engineering, University of Girona, EPS. Ed. PI. C/ Maria Aurelia Capmany 61, 17003 Girona, Spain.
    Bacterial Cellulose Network from Kombucha Fermentation Impregnated with Emulsion-Polymerized Poly(methyl methacrylate) to Form Nanocomposite2021In: Polymers, E-ISSN 2073-4360, Vol. 13, no 4, article id 664Article in journal (Refereed)
    Abstract [en]

    The use of bio-based residues is one of the key indicators towards sustainable development goals. In this work, bacterial cellulose, a residue from the fermentation of kombucha tea, was tested as a reinforcing nanofiber network in an emulsion-polymerized poly(methyl methacrylate) (PMMA) matrix. The use of the nanofiber network is facilitating the formation of nanocomposites with well-dispersed nanofibers without using organic solvents or expensive methodologies. Moreover, the bacterial cellulose network structure can serve as a template for the emulsion polymerization of PMMA. The morphology, size, crystallinity, water uptake, and mechanical properties of the kombucha bacterial cellulose (KBC) network were studied. The results showed that KBC nanofibril diameters were ranging between 20–40 nm and the KBC was highly crystalline, >90%. The 3D network was lightweight and porous material, having a density of only 0.014 g/cm3. Furthermore, the compressed KBC network had very good mechanical properties, the E-modulus was 8 GPa, and the tensile strength was 172 MPa. The prepared nanocomposites with a KBC concentration of 8 wt.% were translucent with uniform structure confirmed with scanning electron microscopy study, and furthermore, the KBC network was homogeneously impregnated with the PMMA matrix. The mechanical testing of the nanocomposite showed high stiffness compared to the neat PMMA. A simple simulation of the tensile strength was used to understand the limited strain and strength given by the bacterial cellulose network. The excellent properties of the final material demonstrate the capability of a residue of kombucha fermentation as an excellent nanofiber template for use in polymer nanocomposites.

  • 23.
    Patel, Mitul Kumar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hansson, Freja
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pitkänen, Olli
    Microelectronics Research Unit, Faculty of Information Technology and Electrical Engineering, University of Oulu, 90570 Oulu, Finland.
    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. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, Ontario M5S 3G8, Canada; Wallenberg Wood Science Center (WWSC).
    Biopolymer Blends of Poly(lactic acid) and Poly(hydroxybutyrate) and Their Functionalization with Glycerol Triacetate and Chitin Nanocrystals for Food Packaging Applications2022In: ACS Applied Polymer Materials, E-ISSN 2637-6105, Vol. 4, no 9, p. 6592-6601Article in journal (Refereed)
    Abstract [en]

    Polylactic acid (PLA) is a biopolymer that has potential for use in food packaging applications; however, its low crystallinity and poor gas barrier properties limit its use. This study aimed to increase the understanding of the structure property relation of biopolymer blends and their nanocomposites. The crystallinity of the final materials and their effect on barrier properties was studied. Two strategies were performed: first, different concentrations of poly(hydroxybutyrate) (PHB; 10, 25, and 50 wt %) were compounded with PLA to facilitate the PHB spherulite development, and then, for further increase of the overall crystallinity, glycerol triacetate (GTA) functionalized chitin nano crystals (ChNCs) were added. The PLA:PHB blend with 25 wt % PHB showed the formation of many very small PHB spherulites with the highest PHB crystallinity among the examined compositions and was selected as the matrix for the ChNC nanocomposites. Then, ChNCs with different concentrations (0.5, 1, and 2 wt %) were added to the 75:25 PLA:PHB blend using the liquid-assisted extrusion process in the presence of GTA. The addition of the ChNCs resulted in an improvement in the crystallization rate and degree of PHB crystallinity as well as mechanical properties. The nanocomposite with the highest crystallinity resulted in greatly decreased oxygen (O) and carbon dioxide (CO2) permeability and increased the overall mechanical properties compared to the blend with GTA. This study shows that the addition ChNCs in PLA:PHB can be a possible way to reach suitable gas barrier properties for food packaging films.

  • 24.
    Patel, Mitul Kumar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Schwendemann, Daniel
    Institute for Material Engineering and Plastics Processing, University of Applied Sciences Eastern Switzerland, CH-8640 Rapperswil, Switzerland.
    Spigno, Giorgia
    Department for Sustainable Food Process (DiSTAS), Università Cattolica del Sacro Cuore, Via Emilia Parmense 84, 29122 Piacenza, Italy.
    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.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering, University of Toronto, Toronto, ON M5S 3BS, Canada.
    Functional Nanocomposite Films of Poly(Lactic Acid) with Well-Dispersed Chitin Nanocrystals Achieved Using a Dispersing Agent and Liquid-Assisted Extrusion Process2021In: Molecules, ISSN 1431-5157, E-ISSN 1420-3049, Vol. 26, no 15, article id 4557Article in journal (Refereed)
    Abstract [en]

    The development of bio-based nanocomposites is of high scientific and industrial interest, since they offer excellent advantages in creating functional materials. However, dispersion and distribution of the nanomaterials inside the polymer matrix is a key challenge to achieve high-performance functional nanocomposites. In this context, for better dispersion, biobased triethyl citrate (TEC) as a dispersing agent in a liquid-assisted extrusion process was used to prepare the nanocomposites of poly (lactic acid) (PLA) and chitin nanocrystals (ChNCs). The aim was to identify the effect of the TEC content on the dispersion of ChNCs in the PLA matrix and the manufacturing of a functional nanocomposite. The nanocomposite film’s optical properties; microstructure; migration of the additive and nanocomposites’ thermal, mechanical and rheological properties, all influenced by the ChNC dispersion, were studied. The microscopy study confirmed that the dispersion of the ChNCs was improved with the increasing TEC content, and the best dispersion was found in the nanocomposite prepared with 15 wt% TEC. Additionally, the nanocomposite with the highest TEC content (15 wt%) resembled the mechanical properties of commonly used polymers like polyethylene and polypropylene. The addition of ChNCs in PLA-TEC15 enhanced the melt viscosity, as well as melt strength, of the polymer and demonstrated antibacterial activity.

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  • 25.
    Patel, Mitulkumar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Schwendemann, Daniel
    Institute of Material Technology and Plastics Processing, University of Applied Sciences Eastern, Switzerland, 8640 Rapperswil, Switzerland – Switzerland.
    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. Mechanical Industrial Engineering (MIE) University of Toronto, Toronto, ON, Canada – Canada. Fibre and Particle Engineering, University of Oulu, FIN-90014 Oulu, Finland – Finland.
    Dispersion of chitin nanocrystal in Polylactic acid nanocomposites prepared via liquid assisted extrusion by triethyl citrate2019In: 6th EPNOE International Polysaccharide Conference: Book of Abstracts, European Polysaccharide Network of Excellence (EPNOE) , 2019, p. 289-289, article id 2019:278282Conference paper (Other academic)
    Abstract [en]

    Efforts to replace petroleum-based polymers with environmental-friendly biopolymers have been intensified during recent years. Presently, polylactic acid (PLA) is one of the most developed biopolymers and chitin nanocrystals (ChNCs), a nano-reinforcement extracted from chitin in crustacean waste, can provide enhanced structural, barrier and bioactive properties to PLA. Hence, the PLA/ChNC combination is promising to produce nanocomposite films for sustainable packaging applications. In this work, PLA/ChNC nanocomposites wereprepared by a novel liquid-assisted extrusion method. To improve the compatibility between ChNCs and PLA matrix, triethyl citrate (TEC), a bio-based plasticizer, was added to the nanocomposites with different concentrations (7.5%-15%). The main objective here is to identify the minimum amount of TEC needed to improve the ChNC dispersion and toughness of the nanocomposites. The plasticized PLA/ChNC nanocomposites were investigated by microcopy techniques to determine the dispersion of ChNCs in PLA. Moreover, their transparency, mechanical performance and thermal behaviors were characterized. All results reveal that TEC plays an important role as a dispersant in the processing of PLA/ChNC nanocomposites and significant toughening effect was obtained when the TEC concentration exceeds 12.5 wt%. This project is funded by the Bio-Based Industries Joint Undertaking under the European Union’s Horizon 2020 (Grant No. 792261).

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  • 26.
    Rosenstock Völtz, Luísa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Di Guiseppe, Irangeli
    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.
    The Effect of Recycling on Wood-Fiber Thermoplastic Composites2020In: Polymers, E-ISSN 2073-4360, Vol. 12, no 8, article id 1750Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate the effect of recycling on polypropylene (PP) and wood-fiber thermoplastic composites (WPCs) using a co-rotating twin-screw extruder. After nine extrusion passes microscopy studies confirmed that the fiber length decreased with the increased number of recycling passes but the increased processing time also resulted in excellent dispersion and interfacial adhesion of the wood fibers in the PP matrix. Thermal, rheological, and mechanical properties were studied. The repeated extrusion passes had minimal effect on thermal behavior and the viscosity decreased with an increased number of passes, indicating slight degradation. The recycling processes had an effect on the tensile strength of WPCs while the effect was minor on the PP. However, even after the nine recycling passes the strength of WPC was considerably better (37 MPa) compared to PP (28 MPa). The good degree of property retention after recycling makes this recycling strategy a viable alternative to discarding the materials. Thus, it has been demonstrated that, by following the most commonly used extrusion process, WPCs can be recycled several times and this methodology can be industrially adapted for the manufacturing of recycled products.

  • 27.
    Rosenstock Völtz, Luísa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Wallenberg Wood Science Center (WWSC), Luleå, Sweden.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Wallenberg Wood Science Center (WWSC), Luleå, Sweden.
    Teleman, Anita
    RISE Research Institutes of Sweden, Stockholm, Sweden.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Wallenberg Wood Science Center (WWSC), Luleå University of Technology, SE-97187 Luleå, Sweden; Department of Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON M5S 3G8, Canada.
    Influence of Dispersion and Orientation on Polyamide-6 Cellulose Nanocomposites Manufactured through Liquid-Assisted Extrusion2022In: Nanomaterials, E-ISSN 2079-4991, Vol. 12, no 5, article id 818Article in journal (Refereed)
    Abstract [en]

    In this study, the possibility of adding nanocellulose and its dispersion to polyamide 6 (PA6), a polymer with a high melting temperature, is investigated using melt extrusion. The main challenges of the extrusion of these materials are achieving a homogeneous dispersion and avoiding the thermal degradation of nanocellulose. These challenges are overcome by using an aqueous suspension of never-dried nanocellulose, which is pumped into the molten polymer without any chemical modification or drying. Furthermore, polyethylene glycol is tested as a dispersant for nanocellulose. The dispersion, thermal degradation, and mechanical and viscoelastic properties of the nanocomposites are studied. The results show that the dispersant has a positive impact on the dispersion of nanocellulose and that the liquid-assisted melt compounding does not cause the degradation of nanocellulose. The addition of only 0.5 wt.% nanocellulose increases the stiffness of the neat polyamide 6 from 2 to 2.3 GPa and shifts the tan δ peak toward higher temperatures, indicating an interaction between PA6 and nanocellulose. The addition of the dispersant decreases the strength and modulus but has a significant effect on the elongation and toughness. To further enhance the mechanical properties of the nanocomposites, solid-state drawing is used to create an oriented structure in the polymer and nanocomposites. The orientation greatly improves its mechanical properties, and the oriented nanocomposite with polyethylene glycol as dispersant exhibits the best alignment and properties: with orientation, the strength increases from 52 to 221 MPa, modulus from 1.4 to 2.8 GPa, and toughness 30 to 33 MJ m−3 in a draw ratio of 2.5. This study shows that nanocellulose can be added to PA6 by liquid-assisted extrusion with good dispersion and without degradation and that the orientation of the structure is a highly-effective method for producing thermoplastic nanocomposites with excellent mechanical properties.

  • 28.
    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.

  • 29.
    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.

  • 30.
    Singh, Shikha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Centre Català del Plàstic (CCP)—Universitat Politècnica de Catalunya Barcelona Tech (EEBE-UPC)-ePLASCOM, 08019 Barcelona, Spain.
    Patel, Mitul Kumar
    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.
    Teleman, Anita
    RISE (Research Institutes of Sweden), SE-114 28 Stockholm, Sweden.
    Herrera, Natalia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Schwendemann, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Maspoch, Maria Lluisa
    Centre Català del Plàstic (CCP)—Universitat Politècnica de Catalunya Barcelona Tech (EEBE-UPC)-ePLASCOM, 08019 Barcelona, Spain.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering, University of Toronto, Toronto, ON M5S 3BS, Canada; Wallenberg Wood Science Center (WWSC), Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Orientation of Polylactic Acid–Chitin Nanocomposite Films via Combined Calendering and Uniaxial Drawing: Effect on Structure, Mechanical, and Thermal Properties2021In: Nanomaterials, E-ISSN 2079-4991, Vol. 11, no 12, article id 3308Article in journal (Refereed)
    Abstract [en]

    The orientation of polymer composites is one way to increase the mechanical properties of the material in a desired direction. In this study, the aim was to orient chitin nanocrystal (ChNC)-reinforced poly(lactic acid) (PLA) nanocomposites by combining two techniques: calendering and solid-state drawing. The effect of orientation on thermal properties, crystallinity, degree of orientation, mechanical properties and microstructure was studied. The orientation affected the thermal and structural behavior of the nanocomposites. The degree of crystallinity increased from 8% for the isotropic compression-molded films to 53% for the nanocomposites drawn with the highest draw ratio. The wide-angle X-ray scattering results confirmed an orientation factor of 0.9 for the solid-state drawn nanocomposites. The mechanical properties of the oriented nanocomposite films were significantly improved by the orientation, and the pre-orientation achieved by film calendering showed very positive effects on solid-state drawn nanocomposites: The highest mechanical properties were achieved for pre-oriented nanocomposites. The stiffness increased from 2.3 to 4 GPa, the strength from 37 to 170 MPa, the elongation at break from 3 to 75%, and the work of fracture from 1 to 96 MJ/m3. This study demonstrates that the pre-orientation has positive effect on the orientation of the nanocomposites structure and that it is an extremely efficient means to produce films with high strength and toughness.

  • 31.
    Singh, Shikha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Centre Català del Plàstic (CCP), Universitat Politècnica de Catalunya Barcelona Tech (EEBE-UPC), C/Colom 114, Terrassa 08222, Spain.
    Patel, Mitul
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Schwendemann, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics. IWK Institut für Werkstofftechnik und Kunststoffverarbeitung, CH-8640 Rapperswil, Switzerland.
    Zaccone, Marta
    Proplast, Via Roberto di Ferro 86, 15122 Alessandria, Italy.
    Geng, Shiyu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Maspoch, Maria Lluisa
    Centre Català del Plàstic (CCP), Universitat Politècnica de Catalunya Barcelona Tech (EEBE-UPC), C/Colom 114, Terrassa 08222, Spain.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering, University of Toronto, Toronto, ON M5S 3BS, Canada.
    Effect of Chitin Nanocrystals on Crystallization and Properties of Poly(lactic acid)-Based Nanocomposites2020In: Polymers, E-ISSN 2073-4360, Vol. 12, no 3, article id 726Article in journal (Refereed)
    Abstract [en]

    The crystalline phase of poly(lactic acid) (PLA) has crucial eects on its own propertiesand nanocomposites. In this study, the isothermal crystallization of PLA, triethyl citrate-plasticizedPLA (PLA–TEC), and its nanocomposite with chitin nanocrystals (PLA–TEC–ChNC) at dierenttemperatures and times was investigated, and the resulting properties of the materials werecharacterized. Both PLA and PLA–TEC showed extremely low crystallinity at isothermal temperaturesof 135, 130, 125 ºC and times of 5 or 15 min. In contrast, the addition of 1 wt % of ChNCs significantlyimproved the crystallinity of PLA under the same conditions owing to the nucleation eect ofthe ChNCs. The samples were also crystallized at 110 ºC to reach their maximal crystallinity,and PLA–TEC–ChNC achieved 48% crystallinity within 5 min, while PLA and PLA–TEC required 40 min to reach a similar level. Moreover, X-ray diffraction analysis showed that the addition ofChNCs resulted in smaller crystallite sizes, which further influenced the barrier properties and hydrolytic degradation of the PLA. The nanocomposites had considerably lower barrier propertiesand underwent faster degradation compared to PLA–TEC110. These results confirm that the additionof ChNCs in PLA leads to promising properties for packaging applications.

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  • 32.
    Thomas, Bony
    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.
    Sain, Mohini
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON M5S 3G8, Canada.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON M5S 3G8, Canada.
    Hetero-Porous, High-Surface Area Green Carbon Aerogels for the Next-Generation Energy Storage Applications2021In: Nanomaterials, E-ISSN 2079-4991, Vol. 11, no 3, article id 653Article in journal (Refereed)
    Abstract [en]

    Various carbon materials have been developed for energy storage applications to address the increasing energy demand in the world. However, the environmentally friendly, renewable, and nontoxic bio-based carbon resources have not been extensively investigated towards high-performance energy storage materials. Here, we report an anisotropic, hetero-porous, high-surface area carbon aerogel prepared from renewable resources achieving an excellent electrical double-layer capacitance. Two different green, abundant, and carbon-rich lignins which can be extracted from various biomasses, have been selected as raw materials, i.e., kraft and soda lignins, resulting in clearly distinct physical, structural as well as electrochemical characteristics of the carbon aerogels after carbonization. The obtained green carbon aerogel based on kraft lignin not only demonstrates a competitive specific capacitance as high as 163 F g−1 and energy density of 5.67 Wh kg−1 at a power density of 50 W kg−1 when assembled as a two-electrode symmetric supercapacitor, but also shows outstanding compressive mechanical properties. This reveals the great potential of the carbon aerogels developed in this study for the next-generation energy storage applications requiring green and renewable resources, lightweight, robust storage ability, and reliable mechanical integrity.

  • 33.
    Thomas, Bony
    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.
    Wei, Jiayuan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sain, Mohini
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, Ontario M5S 3G8, Canada.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, Ontario M5S 3G8, Canada; Wallenberg Wood Science Center (WWSC), Stockholm, Sweden.
    Ice-Templating of Lignin and Cellulose Nanofiber-Based Carbon Aerogels: Implications for Energy Storage Applications2022In: ACS Applied Nano Materials, E-ISSN 2574-0970, Vol. 5, no 6, p. 7954-7966Article in journal (Refereed)
    Abstract [en]

    Hierarchically porous carbon aerogels (CAs) were synthesized by following a green, facile preparation route involving ice-templating and lyophilization followed by carbonization. For the first time, we report CAs prepared with a cooling rate of 7.5 K/min, demonstrating a very high specific surface area (SSA) of 1260 m2 g–1 without any physical or chemical activation steps, and the electrode prepared using the latter aerogel showed superior electrochemical performance with a specific capacitance of 410 F g–1 at 2 m V s–1 with a cyclic stability of 94% after 4500 charge–discharge cycles. The effects of the ice-templating cooling rate and the solid content of lignin and cellulose nanofibers (CNFs) in the suspension on the structure and electrochemical performance of the CAs were investigated. The ice-templating process and the cooling rate were found to have a large effect on the generation of the nanoporous structure and the specific surface area of carbon aerogels, while the solid content of the lignin-nanocellulose suspension showed negligible effects. When assembled as a supercapacitor (SC), a remarkable specific capacitance of 240 F g–1 at 0.1 A g–1 was achieved. The relaxation time constant for the prepared SC was 1.3 s, which shows the fast response of these SCs. In addition, an energy density of 4.3 Wh kg–1 was also obtained at a power density of 500 W kg–1. Thus, this study opens new perspectives for the preparation of green, environment-friendly, free-standing, high-performance CA electrodes for future energy storage applications.

  • 34.
    Thomas, Bony
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    George, Gejo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Landström, Anton
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Concina, Isabella
    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.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, 30172 Venezia Mestre, Italy.
    Sain, Mohini
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, Ontario M5S 3G8, Canada.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, Ontario M5S 3G8, Canada.
    Electrochemical Properties of Biobased Carbon Aerogels Decorated with Graphene Dots Synthesized from Biochar2021In: ACS Applied Electronic Materials, E-ISSN 2637-6113, Vol. 3, no 11, p. 4699-4710Article in journal (Refereed)
    Abstract [en]

    Carbon aerogels prepared from low-cost renewable resources are promising electrode materials for future energy storage applications. However, their electrochemical properties must be significantly improved to match the commercially used high-carbon petroleum products. This paper presents a facile method for the green synthesis of carbon aerogels (CAs) from lignocellulosic materials and graphene dots (GDs) from commercially available biochar. The produced carbon aerogels exhibited a hierarchical porous structure, which facilitates energy storage by forming an electrical double-layer capacitance. Surprisingly, the electrochemical analyses of the GD-doped carbon aerogels revealed that in comparison to pristine carbon aerogels, the surface doping of GDs enhanced the electrochemical performance of carbon aerogels, which can be attributed to the combined effect from both double-layer capacitance and pseudocapacitance. Herein, we designed and demonstrated the efficacy of a supercapacitor device using our green carbon electrode as a sustainable option. These green carbon aerogels have opened a window for their practical use in designing sustainable energy storage devices. 

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  • 35.
    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.
    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. Fibre and Particle Engineering, University of Oulu, Finland. Mechanical and Industrial Engineering (MIE), University of Toronto, Toronto, Canada.
    Lightweight, flexible, and multifunctional anisotropic nanocellulose-based aerogels for CO2 adsorption2020In: Cellulose, ISSN 0969-0239, E-ISSN 1572-882X, Vol. 27, no 5, p. 2695-2707Article in journal (Refereed)
    Abstract [en]

    CO2 adsorption is a promising strategy to reduce costs and energy use for CO2 separation. In this study, we developed CO2 adsorbents based on lightweight and flexible cellulose nanofiber aerogels with monolithic structures prepared via freeze-casting, and cellulose acetate or acetylated cellulose nanocrystals (a-CNCs) were introduced into the aerogels as functional materials using an impregnation method to provide CO2 affinity. The microstructure of the adsorbent was examined using scanning electron microscopy, and compression tests were performed to analyze the mechanical properties of the adsorbents. The CO2 adsorption behavior was studied by recording the adsorption isotherms and performing column breakthrough experiments. The samples showed excellent mechanical performance and had a CO2 adsorption capacity of up to 1.14 mmol/g at 101 kPa and 273 K. Compared to the adsorbent which contains cellulose acetate, the one impregnated with a-CNCs had better CO2 adsorption capacity and axial mechanical properties owing to the building of a nanoscale scaffold on the surface of the adsorbent. Although the CO2 adsorption capacity could be improved further, this paper reports a potential CO2 adsorbent that uses all cellulose-based materials, which is beneficial for the environment from both resource and function perspectives. Moreover, the interesting impregnation process provides a new method to attach functional materials to aerogels, which have potential for use in many other applications.

  • 36.
    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.
    Kumar, Manish
    Fibre and Particle Engineering Research Unit, University of Oulu, Oulu, Finland.
    Pitkänen, Olli
    Microelectronics Research Group, University of Oulu, Oulu, Finland.
    Hietala, Maiju
    Fibre and Particle Engineering Research Unit, University of Oulu, Oulu, Finland.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Investigation of Structure and Chemical Composition of Carbon Nanofibers Developed From Renewable Precursor2019In: Frontiers in Materials, E-ISSN 2296-8016, Vol. 6, article id 334Article in journal (Refereed)
    Abstract [en]

    In this study, lignin-based carbon nanofibers were prepared by electrospinning, followed by carbonization at four different temperatures (800, 1,000, 1,200, and 1,400°C). The surface and bulk elemental compositions were analyzed by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, respectively. In addition, the structure of the prepared carbon nanofibers was characterized by scanning electron microscopy, transmission electron microscopy, focused ion beam microscopy, and Raman spectroscopy. Results showed that all carbon nanofibers, irrespective of the carbonization temperature, had continuous and homogeneous structures. They were dense and no phase separation was observed. Moreover, the nanofibers carbonized at 800°C or 1,000°C predominately contained amorphous carbon and some non-carbon elements. When the carbonization was performed at a higher temperature (1,200°C or 1,400°C), non-carbon elements were effectively removed and nanocrystalline graphite was formed, indicating that high temperature carbonization facilitated the formation of ordered carbon structures.

  • 37.
    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, O.
    Microelectronics Research Group, University of Oulu, Oulu, Finland.
    Järvinen, Topias
    Microelectronics Research Group, University of Oulu, Oulu, Finland.
    Kordas, Krisztian
    Microelectronics Research Group, University of Oulu, Oulu, Finland.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering Research Group, University of Oulu, Finland.
    Biomass-derived electrospun carbon nanofiber networks for high-performance supercapacitors2019Conference paper (Refereed)
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  • 38.
    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
    Microelectronics Research Group, University of Oulu, FI-90570 Oulu, Finland.
    Jarvinen, 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, Material Science. Fibre and Particle Engineering Research Group, University of Oulu, FI-90570 Oulu, Finland. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON, M5S 3G8, Canada.
    Green carbon nanofiber networks for advanced energy storage2020In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 3, no 4, p. 3530-3540Article in journal (Refereed)
    Abstract [en]

    Energy storage devices such as supercapacitors of high-performance are in great need due to the continuous expansion of digitalization and related devices for mobile electronics, autonomous sensors and vehicles of different kinds. However, the non-renewable resources and often complex preparation processes associated with electrode materials and structure pose limited scale-up in production and difficulties in versatile utilization of the devices. Here, free-standing and flexible carbon nanofiber networks derived from renewable and abundant bio-resources are demonstrated. By a simple optimization of carbonization, the carbon nanofiber networks reach a large surface area of 1670 m2 g-1 and excellent specific gravimetric capacitance of ~240 F g-1, outperforming many other nanostructured carbon, activated carbon and even those decorated with metal oxides. The remarkable electrochemical performance and flexibility of the green carbon networks enable an all-solid-state supercapacitor device, which displays a device capacitance of 60.4 F g-1 with a corresponding gravimetric energy density of 8.4 Wh kg-1 while maintaining good mechanical properties.

  • 39.
    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
    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, Material Science. Fibre and Particle Engineering Research Group, University of Oulu, Finland.
    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.

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  • 40.
    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
    Microelectronics Research Group, University of Oulu, Oulu, Finland.
    Järvinen, Topias
    Microelectronics Research Group, University of Oulu, Oulu, Finland.
    Kordas, Krisztian
    Microelectronics Research Group, University of Oulu, Oulu, Finland.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering Research Group, University of Oulu, Finland.
    Making good use of lignin – from a low-value biopolymer to energy storage devices2019In: Nordic Polymer Days 2019: Book of Abstracts / [ed] Rita de Sousa Dias; Sulalit Bandyopadhyay, Norwegian University of Science and Technology , 2019, p. 48-48, article id 04.3Conference paper (Refereed)
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  • 41.
    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
    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, Material Science. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON M5S 3G8, Canada.
    Lignin: From underutilized biopolymer to high-performance energy storage materials2021Conference paper (Refereed)
    Abstract [en]

    Lignin, second only to cellulose in natural abundance, is believed to be a promising precursor for porous renewable carbon, which has great potentials in energy storage applications. However, the development of lignin-based carbon materials is still at a very early stage and needs to be intensively analyzed. In this study, alkali lignin has been electrospun with poly(vinyl alcohol) to form nanofiber mats. The as-spun fiber mats are carbonized at 800, 1000, 1200 and 1400 °C respectively to prepare the carbon nanofiber mats (CFMs). The obtained free-standing and flexible CFMs show excellent electrochemical performance when used as electrodes in supercapacitors. The highest specific gravimetric capacitance reaches 241 F g-1, which outperforms many other reported carbon electrodes. In addition, an all-solid-state supercapacitor device made of selected CFMs displays a device capacitance of 60.4 F g-1 and a gravimetric energy density of 8.4 Wh kg-1. Good retention after harsh bending of the all-solid-state supercapacitor indicates that this device can be integrated in a wearable device with further optimization.

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  • 42.
    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.

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  • 43.
    Wei, Jiayuan
    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.
    Johansson Carne, Lisa
    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.
    Antzutkin, Oleg N.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Sain, Mohini
    Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON M5S 3G8, Canada.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Mechanical & Industrial Engineering (MIE), University of Toronto, Toronto, ON M5S 3G8, Canada.
    Oriented Carbon Fiber Networks by Design from Renewables for Electrochemical Applications2021In: ACS Sustainable Chemistry and Engineering, E-ISSN 2168-0485, Vol. 9, no 36, p. 12142-12154Article in journal (Refereed)
    Abstract [en]

    With the explosion of global demands for electrified mobility systems and a surge in rural energy transport mechanisms augmented by the scarcity of key metals, carbon by design has become a transformational pathway to fill the gap as an energy material of choice. The development of functional carbon from renewables with outstanding electrostatic double-layer capacitance is still in its infancy, as there is a significant gap in understanding the relationship between the tunable structure and properties of the bioresources both before and after their controlled carbonization. Herein, we report carbon fiber networks (CFNs) with highly controllable intact structure manufactured from four functional lignins originating from different types of processing residues, demonstrating excellent electrochemical efficacies, which makes them promising self-standing electrodes in supercapacitors. This study also underpins the feasibility and importance of preparing CFNs with highly oriented structure, which endows superior specific capacitance and cycle stability compared to the CFNs with randomly oriented fibers. The randomly oriented CFNs reached a specific capacitance value of 456 F g–1 under current densities of 1 A g–1 and a cycle stability of 73.6%, while the CFNs with an orientation factor of 0.87 exhibited significant improvement of the specific capacitance by approximately 15% (529 F g–1) and the cycle stability reached 95% after 10 000 charge–discharge cycles. The high specific capacitance and excellent overall electrochemical properties of the highly oriented CFNs make them a cost-effective and greener material of choice for energy storage devices. 

  • 44.
    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.

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