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Strong surface treatment effects on reinforcement efficiency in biocomposites based on cellulose nanocrystals in poly(vinyl acetate) matrix
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0001-7870-6327
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0001-9832-027X
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0001-5818-2378
2015 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 12, 3916-3924 p.Article in journal (Refereed) Published
Abstract [en]

In this work, the problem to disperse cellulose nanocrystals (CNC) in hydrophobic polymer matrices has been addressed through application of an environmentally friendly chemical modification approach inspired by clay chemistry. The objective is to compare the effects of unmodified CNC and modified CNC (modCNC) reinforcement, where degree of CNC dispersion is of interest. Hydrophobic functionalization made it possible to disperse wood-based modCNC in organic solvent and cast well-dispersed nanocomposite films of poly(vinyl acetate) (PVAc) with 1-20 wt % CNC. Composite films were studied by infrared spectroscopy (FT-IR), UV-vis spectroscopy, dynamic mechanical thermal analysis (DMTA), tensile testing, and field-emission scanning electron microscopy (FE-SEM). Strongly increased mechanical properties were observed for modCNC nanocomposites. The reinforcement efficiency was much lower in unmodified CNC composites, and specific mechanisms causing the differences are discussed.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2015. Vol. 16, no 12, 3916-3924 p.
National Category
Biochemistry and Molecular Biology Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-131466DOI: 10.1021/acs.biomac.5b01245ISI: 000366616700021Scopus ID: 2-s2.0-84949844757OAI: oai:DiVA.org:kth-131466DiVA: diva2:656542
Note

QC 20160115

Available from: 2013-10-16 Created: 2013-10-16 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Wood Nanocellulose Materials and Effects from Surface Modification of Nanoparticles
Open this publication in new window or tab >>Wood Nanocellulose Materials and Effects from Surface Modification of Nanoparticles
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanocellulose is an interesting natural material thatis gaining interest in the field of materials science, particularly nanocomposites. Depending on the disintegration route, nanocellulose can be isolated either in the form of long and flexible fibres (nanofibrillated cellulose, NFC), or stiff, rod-like crystals (cellulose nanocrystals, CNC). Nanocellulose can be utilized in nanocomposites either as a reinforcement element or as a network matrix due to its ability to form a strong network. In this thesis, nanocellulose based materials are prepared by evaporation of a liquid medium. The key step in this processing route is a good dispersion of the nanoparticles in the selected matrix. Therefore the importance of surface modification in order to ensure favourable nanocellulose dispersion is clarified in avariety of materials systems.

In Paper I, poly(methyl methacrylate) (PMMA) based fibres prepared by electrospinning were reinforced with nanofibrillated cellulose. Native NFC appeared to show a good compatibility with PMMA matrix in the electrospinning solution and resulting fibres. Furthermore, a new method for mechanical testing of mats with random fibre orientation as well as aligned fibres was developed.

In Paper II, commingled nanopaper structures with carbon nanotubes (CNTs) were prepared. Several surfactants were used to disperse hydrophobic CNTs in water. A nonylphenol phosphate ester (NPPE) was found to work well for both dispersing CNTs in water and providing compatibility with NFC through electrostatic repulsion between the phosphate ester groups of the surfactant and the carboxylate groups of NFC.

In Paper III, a new water based route for functionalization of cellulose nanocrystals was developed. In this approach, inspired by organo-modified layered silicates, quaternary ammonium salts were adsorbed. It was demonstrated that different functionalities (alkyl, phenyl, glycidylor diallyl) can be introduced onto the cellulose and the dispersibility in organic solvents was studied. Subsequently, in Paper IV, nanocomposites with poly(vinyl acetate) (PVAc)were prepared. The effect of modification on the degree of dispersion of the CNC within the matrix was studied as well as the strong effects on the properties of the resulting nanocomposites.

In Paper V, taking advantage of the entangled NFC network and the possibility to tailor the pore size and surface chemistry, lubricant-infused slippery films and coatings based on NFC were prepared for the first time.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 55 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:40
Keyword
Nanocellulose, nanoc omposite, dispersion, surface modification, surfa ctant, poly(methyl methacrylate), poly(vinyl acetate), carbon nanotubes, electrospinning, lubricant - infused surfaces
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-131469 (URN)978-91-7501-866-9 (ISBN)
Public defence
2013-11-01, F3, Lindstetsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20131016

Available from: 2013-10-16 Created: 2013-10-16 Last updated: 2013-10-16Bibliographically approved
2. Nanostructured Cellulose Biocomposites: Effects from dispersion, network and interface
Open this publication in new window or tab >>Nanostructured Cellulose Biocomposites: Effects from dispersion, network and interface
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The major load bearing component in native wood, cellulose nanofibrils, are potential candidates for use as reinforcement in polymer matrices. This study is based on nanocellulose composites and attempts to prepare and characterize biocomposites with high nanocellulose content and investigate the influence of nanostructure on macroscopic properties.

In an initial study, effects from cellulose nanocrystal (CNC) dispersion on optical and mechanical properties of CNC composites are studied in a model system using polyvinylacetate (PVAc) as the polymer. CNC surface modification is used as an aid to improve dispersion, and nanocomposites with up to 20 wt% of modified and unmodified CNC are characterized. Strong influence of CNC as reinforcement and on polymer matrix characteristics were observed with well-dispersed CNCs, resulting in nanocomposites with significantly improved mechanical properties.

In the subsequent parts, an impregnation-based processing strategy is used to prepare cellulose nanofibril (CNF) based thermoset (epoxy and unsaturated polyester) composites with high CNF content (15 - 50 vol%). Influence of CNF surface hydroxyls on epoxy curing is discussed. A mono-epoxy compound is used to confirm covalent epoxy/CNF reaction and the implications of this modification on mechanical properties of wet CNF network are illustrated. Mechanical properties of thermoset composites are characterized at different relative humidities to evaluate their hygromechanical stability. The role of the CNF-thermoset interface is investigated by comparing composites with epoxy and unsaturated polyester matrices. Unique effects due to the nanostructure of composites are discussed with respect to CNF dispersion, CNF network characteristics and CNF/matrix interface. Additionally, pulp fiber composites, where the fiber wall itself is impregnated with resin, are designed and differences between nanocellulose (nanoscale network) and pulp fibers (microscale diameter) as reinforcements are analyzed.

Abstract [sv]

Trä och träbaserade material erbjuder ett hållbart alternativ till petroleumbaserade material. Mikrofibriller, eller som de också kallas i materialsammanhang, nanofibriller från cellulosa (CNF) är den huvudsakliga lastbärande komponenten i trä. Den har stor potential som förstärkande tillsats i polymerer. Denna studie handlar om kompositer baserade på nanocellulosa. Biokompositer med företrädesvis hög andel nanocellulosa framställs och karakteriseras. Huvudsyftet är att förklara inverkan av nanostruktur på makroskopiska egenskaper.

I en första studie används polyvinylacetat (PVAc) som modellpolymer för att undersöka effekten av dispergeringgrad hos cellulosa-nanokristaller (CNC) för optiska och mekaniska egenskaper. En miljövänlig form av modifiering av CNC används för att förbättra dispergeringsgraden. Nanokompositer med upp till 20 vikts-% modifierad eller icke modifierad CNC studerades. Nanokompositer med väldispergerad CNC visade dramatiskt förbättrade egenskaper, eftersom nanopartiklarna kraftigt påskyndade fysikalisk åldring av PVAc så att den fick högre E-modul och hållfasthet.

I avhandlingens andra del framställdes härdplastkompositer genom harts-impregnering av porösa CNF-nätverk, följt av härdning. Epoxi (EP) och omättade polyester (UP) användes som härdplaster. Volymsfraktionen CNF var mellan 15-50%. Reaktionshastigheten under härdning ökade kraftigt i närvaro av nanocellulosa med hög specifik yta. Troligen reagerade epoxigrupper med hydroxylgrupper på cellulosaytan, under förutsättning att katalytiska aminföreningar fanns tillgängliga. Hypotesen fick ytterligare stöd i en studie av monoepoxi + nanocellulosa. Den modifieringen visade sig också göra CNF-nätverket mindre hygroskopiskt, så att de hygromekaniska egenskaperna förbättrades. Mekaniska egenskaper hos EP- och UP-kompositer bestämdes med hjälp av dragprov vid olika luftfuktighet. EP-kompositerna visade bättre egenskaper vid hög fuktighet, främst pga de kovalenta bindningarna mellan EP och CNF. Effekter av CNF-Dispergering, CNF-nätverkets egenskaper och gränsytan CNF-härdplast analyserades. Slutligen jämfördes EP-kompositer baserade på CNF med kompositer från blekta massafibrer. CNF-kompositerna hade högre hållfasthet till följd av den låga diametern (inga problem med fiber-matris separation och sprickbildning vid låga töjningar) och kraftigt töjningshårdnande orsakad av CNF nätverket.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2016:19
Keyword
Wood, cellulose nanofibrils, hygromechanical properties, network structure, thermoset, polymer matrix composites, natural fiber composites, pulp fiber, strain hardening, humidity
National Category
Materials Engineering
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-185723 (URN)978-91-7595-924-5 (ISBN)
Public defence
2016-05-25, F3, Lindstedtsvägen 26, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

Qc 20160427

Available from: 2016-04-27 Created: 2016-04-25 Last updated: 2016-04-29Bibliographically approved

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