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Online determination of anisotropy during cellulose nanofibril assembly in a flow focusing device
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
2015 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, no 24, 18601-18608 p.Article in journal (Refereed) Published
Abstract [en]

In order to utilize the high strength (ultimate tensile strength = 3 GPa) [Saito et al., Biomacromolecules, 2012, 14, 248] and stiffness (Young's modulus = 130 GPa) [Sakurada et al., J. Polym. Sci., 1962, 57, 651] of cellulose nanofibrils in a macroscopic material or composite, the structure of the elongated fibrils in the material must be controlled. Here, cellulose nanofibrils in a dispersed state are partly aligned in a flow focusing device, whereafter the anisotropic nano-structure is locked by a dispersion-gel transition. The alignment process has been studied by Hakansson et al., [Nat. Commun., 2014, 5, 4018], however, the location of the phase transition as well as at which alignment (anisotropy) the fibrils were locked was not investigated. In this study, the degree of alignment is determined with small angle X-ray scattering experiments and the location of the phase change is measured with polarized light experiments. Furthermore, the anisotropy of the hydrogel thread is determined and the thread is seen to still be anisotropic after six months in a water bath.

Place, publisher, year, edition, pages
2015. Vol. 5, no 24, 18601-18608 p.
Keyword [en]
Alignment, Aluminum, Cellulose, Dispersions, Elastic moduli, Locks (fasteners), Nanofibers, Nanostructures, Tensile strength, X ray scattering, Biomacromolecules, Cellulose nanofibrils, Degree of alignments, Flow focusing devices, Gel transitions, Macroscopic materials, On-line determination, Ultimate tensile strength
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-150582DOI: 10.1039/c4ra12285bISI: 000349999200053Scopus ID: 2-s2.0-84923239980OAI: oai:DiVA.org:kth-150582DiVA: diva2:744271
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20150407. Updated from manuscript to article in journal.

Available from: 2014-09-08 Created: 2014-09-08 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Orientation of elongated, macro and nano-sized particles in macroscopic flows
Open this publication in new window or tab >>Orientation of elongated, macro and nano-sized particles in macroscopic flows
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Non-spherical particles are present all around us, in biological, industrial and environmental processes. Making predictions of their impact on us and systems in our vicinity can make life better for everyone here on earth. For example, the ash particles from a volcano eruption are non-spherical and their spreading in the atmosphere can hugely impact the air traffic, as was also proven in 2010. Furthermore, the orientation of the wood fibres in a paper sheet influences the final properties of the paper, and the cause of a specific fibre orientation can be traced back to the fluid flows during the manufacturing process of the paper.

In this thesis, experimental and numerical work is presented with the goal to understand and utilize the behavior of elongated particles in fluid flows. Two different experimental setups are used. The first one, a turbulent half channel flow, aims at increasing the understanding of how particles with non-zero inertia behave in turbulence. The second setup is an attempt to design a flow field with the purpose to align nanofibrils and create high performance cellulose filaments.

Experiments were performed in a turbulent half channel flow at different flow set- tings with dilute suspensions of cellulose acetate fibres having three different aspect ratios (length to width ratio). The two main results were firstly that the fibres agglom- erated in streamwise streaks, believed to be due to the turbulent velocity structures in the flow. Secondly, the orientation of the fibres was observed to be determined by the aspect ratio and the mean shear, not the turbulence. Short fibres were oriented in the spanwise direction while long fibres were oriented in the streamwise direction.

In order to utilize the impressive properties (stiffness comparable to Kevlar) of the cellulose nanofibril in a macroscopic material, the alignment of the fibrils must be controlled. Here, a flow focusing device (resulting in an extensional flow), designed to align the fibrils, is used to create a cellulose filament with aligned fibrils. The principle is based on a separation of the alignment and the assembly of the fibrils, i.e. first align the fibrils and then lock the aligned structure. With this process, continuous filaments were created, with properties similar to that of the wood fibre at the same fibril alignment. However, the highest alignment (lowest angle) of the fibrils in a filament created was only 31o from the filament axis, and the next step is to increase the alignment. This thesis includes modeling of the alignment process with the Smoluchowski equation and a rotary diffusion. Finding a model that correctly describes the alignment process should in the end make it possible to create a filament with fully aligned fibrils.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xiii, 81 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2014.19
Keyword
Orientation, fibre, fibril, turbulent channel flow, particle streaks, flow focusing, cellulose nanofibrils, extensional flow, Smoluchowski, rotary diffusion
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-150493 (URN)978-91-7595-254-3 (ISBN)
Public defence
2014-09-25, Kollegiesalen, Brinellvägen 8, KTKH, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20140908

Available from: 2014-09-08 Created: 2014-09-04 Last updated: 2014-09-08Bibliographically approved

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