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Stiffness contribution of cellulose nanofibrils to composite materials
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
2014 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, no 5, 945-953 p.Article in journal (Refereed) Published
Abstract [en]

Nanocomposites, reinforced by different types of cellulose fibrils, have gained increased interest the last years due to the promising mechanical properties. There is a lack of knowledge about the mechanical properties of the cellulose fibrils, and their contribution to the often claimed potential of the impressive mechanical performance of the nanocomposites. This paper investigates the contribution from different types of cellulose nanofibril to the overall elastic properties of composites. A multiscale model is proposed, that allows back-calculation of the elastic properties of the fibril from the macroscopic elastic properties of the composites. The different types of fibrils used were nanofibrillated cellulose from wood, bacterial cellulose nano-whiskers and microcrystalline cellulose. Based on the overall properties of the composite with an unaged polylactide matrix, the effective longitudinal Young's modulus of the fibrils was estimated to 65 GPa for the nanofibrillated cellulose, 61 GPa for the nano whiskers and only 38 GPa for the microcrystalline cellulose. The ranking and absolute values are in accordance with other studies on nanoscale morphology and stiffness estimates. Electron microscopy revealed that in the melt-processed cellulose nanofibril reinforced thermoplastics, the fibrils tended to agglomerate and form micrometer scale platelets, effectively forming a microcomposite and not a nanocomposite. This dispersion effect has to be addressed when developing models describing the structure-property relations for cellulose nanofibril composites.

Place, publisher, year, edition, pages
2014. Vol. 51, no 5, 945-953 p.
Keyword [en]
Nanocomposite, Cellulose nanofibrils, Elastic properties, Multiscale modeling, Inverse modeling
National Category
Engineering and Technology
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
URN: urn:nbn:se:uu:diva-220777DOI: 10.1016/j.ijsolstr.2013.11.018ISI: 000331158400004OAI: oai:DiVA.org:uu-220777DiVA: diva2:707339
Available from: 2014-03-24 Created: 2014-03-20 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Elasticity of Cellulose Nanofibril Materials
Open this publication in new window or tab >>Elasticity of Cellulose Nanofibril Materials
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The demand for renewable load-carrying materials is increasing with increasing environmental awareness. Alternative sources for materials manufacturing and design have to be investigated in order to replace the non-biodegradable materials. The work presented in this thesis investigates structure-property relations of such renewable materials based on cellulose nanofibrils. Cellulose is the most abundant polymer on earth and exists in both ordered and disordered phases, where the ordered crystalline cellulose shows excellent mechanical properties. The celluloses nanofibril is composed of partly crystalline cellulose where the stiff crystal regions, or crystallites, are orientated in the axial direction of the fibrils. The cellulose nanofibrils have a high aspect ratio, i.e. length to diameter ratio, with a diameter of less than 100 nm and a length of some micrometres. In the presented work, different properties of the cellulose nanofibril were studied, e.g. elastic properties, structure, and its potential as a reinforcement constituent. The properties and behaviour of the fibrils were studied with respect to different length scales, from the internal structure of the cellulose nanofibril, based on molecular dynamic simulations, to the macroscopic properties of cellulose nanofibril based materials. Films and composite materials with in-plane randomly oriented fibrils were produced. Properties of the cellulose nanofibril based materials, such as stiffness, thickness variation, and fibril orientation distribution, were investigated, from which the effective elastic properties of the fibrils were determined. The studies showed that a typical softwood based cellulose nanofibril has an axial stiffness of around 65 GPa. The properties of the cellulose nanofibril based materials are highly affected by the dispersion and orientation of the fibrils. To use the full potential of the stiff fibrils, well dispersed and oriented fibrils are essential. The orientation distribution of fibrils in hydrogels subjected to a strain was therefore investigated. The study showed that the cellulose nanofibrils have high ability to align, where the alignment increased with increased applied strain.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 60 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1215
Keyword
Cellulose nanofibrils, Elastic properties, Micromechanics, Composites
National Category
Engineering and Technology
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-240250 (URN)978-91-554-9135-2 (ISBN)
Public defence
2015-02-13, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2015-01-22 Created: 2015-01-06 Last updated: 2015-03-09

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Josefsson, GabriellaGamstedt, Kristofer

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