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Publications (10 of 16) Show all publications
Wei, J., Geng, S., Sarmad, S., Hedlund, J. & Oksman, K. (2018). Adsorption of Carbon Dioxide on Cellulose Nanofiber-Based Monolithic Cryogels Impregnated with Acetylated Cellulose Nanocrystals. In: : . Paper presented at 72nd Forest Products Society (FPS) International Convention, Madison, Wisconsin, USA, June 11–14, 2018.
Open this publication in new window or tab >>Adsorption of Carbon Dioxide on Cellulose Nanofiber-Based Monolithic Cryogels Impregnated with Acetylated Cellulose Nanocrystals
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2018 (English)Conference paper, Poster (with or without abstract) (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.

Keywords
Nanocellulose, cryogel, adsorption, carbon dioxide, acetylation
National Category
Chemical Process Engineering Bio Materials
Research subject
Wood and Bionanocomposites; Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-71083 (URN)
Conference
72nd Forest Products Society (FPS) International Convention, Madison, Wisconsin, USA, June 11–14, 2018
Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2019-01-16Bibliographically approved
Singh, A. A., Geng, S., Herrera Vargas, N. & Oksman, K. (2018). Aligned plasticized polylactic acid cellulose nanocomposite tapes: Effect of drawing conditions. Composites. Part A, Applied science and manufacturing, 104, 101-107
Open this publication in new window or tab >>Aligned plasticized polylactic acid cellulose nanocomposite tapes: Effect of drawing conditions
2018 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 104, p. 101-107Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Nanocomposites; Mechanical properties; Thermal properties; Microstructural analysis
National Category
Composite Science and Engineering Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-64862 (URN)10.1016/j.compositesa.2017.10.019 (DOI)000418966900010 ()2-s2.0-85032722515 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-11-14 (andbra)

Available from: 2017-07-13 Created: 2017-07-13 Last updated: 2018-08-15Bibliographically approved
Geng, S. (2018). Cellulose-based Nanocomposites – The Relationship between Structure and Properties. (Doctoral dissertation). Luleå: Luleå University of Technology
Open this publication in new window or tab >>Cellulose-based Nanocomposites – The Relationship between Structure and Properties
2018 (English)Doctoral 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.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Nanocellulose; Nanocomposite; Dispersion; Poly(vinyl acetate); Poly(lactic acid); Alignment; Mechanical characteristics
National Category
Composite Science and Engineering Nano Technology Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-70411 (URN)978-91-7790-182-2 (ISBN)978-91-7790-183-9 (ISBN)
Public defence
2018-09-19, E632, Luleå, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg FoundationBio4Energy
Available from: 2018-08-16 Created: 2018-08-15 Last updated: 2018-09-04Bibliographically approved
Geng, S., Yao, K., Zhou, Q. & Oksman, K. (2018). High-strength, High-toughness Aligned Polymer-based Nanocomposite Reinforced with Ultra-low Weight Fraction of Functionalized Nanocellulose. Biomacromolecules, 19(10), 4075-4083
Open this publication in new window or tab >>High-strength, High-toughness Aligned Polymer-based Nanocomposite Reinforced with Ultra-low Weight Fraction of Functionalized Nanocellulose
2018 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, no 10, p. 4075-4083Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
Keywords
nanocellulose, nanocomposite, alignment, mechanical characteristics, light scattering
National Category
Composite Science and Engineering Nano Technology Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-70591 (URN)10.1021/acs.biomac.8b01086 (DOI)000447118500018 ()2-s2.0-85053301832 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationBio4Energy
Note

Validerad;2018;Nivå 2;2018-10-29 (johcin) 

Available from: 2018-08-27 Created: 2018-08-27 Last updated: 2018-10-29Bibliographically approved
Singh, A. A., Wei, J., Vargas, N. H., Geng, S. & Oksman, K. (2018). Synergistic effect of chitin nanocrystals and orientations induced by solid-state drawing on PLA-based nanocomposite tapes. Composites Science And Technology, 162, 140-145
Open this publication in new window or tab >>Synergistic effect of chitin nanocrystals and orientations induced by solid-state drawing on PLA-based nanocomposite tapes
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2018 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 162, p. 140-145Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-68545 (URN)10.1016/j.compscitech.2018.04.034 (DOI)000438180500017 ()2-s2.0-85046361270 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-05-03 (andbra)

Available from: 2018-04-30 Created: 2018-04-30 Last updated: 2018-08-09Bibliographically approved
Geng, S., Wei, J., Aitomäki, Y., Noël, M. & Oksman, K. (2018). Well-dispersed cellulose nanocrystals in hydrophobic polymers by in situ polymerization for synthesizing highly reinforced bio-nanocomposites. Nanoscale, 10(25), 11797-11807
Open this publication in new window or tab >>Well-dispersed cellulose nanocrystals in hydrophobic polymers by in situ polymerization for synthesizing highly reinforced bio-nanocomposites
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2018 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 25, p. 11797-11807Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Composite Science and Engineering Biomaterials Science Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-68465 (URN)10.1039/C7NR09080C (DOI)000437761500010 ()29675528 (PubMedID)2-s2.0-85049520332 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-07 (rokbeg)

Available from: 2018-04-23 Created: 2018-04-23 Last updated: 2018-08-15Bibliographically approved
Geng, S., Yao, K., Harila, M., Zhou, Q. & Oksman, K. (2017). Grafting polyethylene glycol on nanocellulose toward biodegradable polymer nanocomposites. In: ICCM21 Proceedings: . Paper presented at 21st International Conference on Composites Materials, August 20-24, 2017, Xi’an, China. ICCM, International Committee on Composite Materials
Open this publication in new window or tab >>Grafting polyethylene glycol on nanocellulose toward biodegradable polymer nanocomposites
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2017 (English)In: ICCM21 Proceedings, ICCM, International Committee on Composite Materials , 2017Conference paper, Published 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.

Place, publisher, year, edition, pages
ICCM, International Committee on Composite Materials, 2017
Keywords
Nanocellulose, Grafting, Dispersion, Mechanical property, Thermal property
National Category
Composite Science and Engineering Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-72436 (URN)2-s2.0-85053118470 (Scopus ID)
Conference
21st International Conference on Composites Materials, August 20-24, 2017, Xi’an, China
Available from: 2019-01-04 Created: 2019-01-04 Last updated: 2019-01-04Bibliographically approved
Geng, S., Shah, F. U., Liu, P., Antzutkin, O. & Oksman, K. (2017). Plasticizing and crosslinking effects of borate additives on the structure and properties of poly(vinyl acetate). RSC Advances, 7(13), 7483-7491
Open this publication in new window or tab >>Plasticizing and crosslinking effects of borate additives on the structure and properties of poly(vinyl acetate)
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2017 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 13, p. 7483-7491Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Physical Chemistry Bio Materials
Research subject
Wood and Bionanocomposites; Chemistry of Interfaces
Identifiers
urn:nbn:se:ltu:diva-61616 (URN)10.1039/C6RA28574K (DOI)000393757100006 ()2-s2.0-85010648470 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-02-13 (andbra)

Available from: 2017-01-24 Created: 2017-01-24 Last updated: 2018-11-16Bibliographically approved
Moberg, T., Sahlin, K., Yao, K., Geng, S., Westman, G., Zhou, Q., . . . Rigdahl, M. (2017). Rheological properties of nanocellulose suspensions: effects of fibril/particle dimensions and surface characteristics. Cellulose (London), 24(6), 2499-2510
Open this publication in new window or tab >>Rheological properties of nanocellulose suspensions: effects of fibril/particle dimensions and surface characteristics
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2017 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, no 6, p. 2499-2510Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-63027 (URN)10.1007/s10570-017-1283-0 (DOI)000400851800012 ()2-s2.0-85017431715 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-05-30 (rokbeg)

Available from: 2017-04-13 Created: 2017-04-13 Last updated: 2018-07-10Bibliographically approved
Geng, S., Noël, M., Liu, P. & Oksman, K. (2016). Cellulose-based nanocomposites with outstanding dispersion produced by in-situ polymerization (ed.). Paper presented at American Chemical Society (ACS) National Meeting & Exposition : 13/03/2016 - 17/03/2016. Paper presented at American Chemical Society (ACS) National Meeting & Exposition : 13/03/2016 - 17/03/2016.
Open this publication in new window or tab >>Cellulose-based nanocomposites with outstanding dispersion produced by in-situ polymerization
2016 (English)Conference paper, Oral presentation only (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.

National Category
Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
urn:nbn:se:ltu:diva-31334 (URN)57c1b390-8309-46a3-8ce8-3ce137323856 (Local ID)57c1b390-8309-46a3-8ce8-3ce137323856 (Archive number)57c1b390-8309-46a3-8ce8-3ce137323856 (OAI)
Conference
American Chemical Society (ACS) National Meeting & Exposition : 13/03/2016 - 17/03/2016
Note
Godkänd; 2016; 20160331 (shigen)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1776-2725

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