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Rotational Diffusion of Cellulose Nanofibrils.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.
2014 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

Cellulose nanofibrils, CNF, is a technical term for the smallest crystalline constituents

of wood. Namely particles of cylindrical shape measuring 20-40 nm in

diameter and 1-2 um in length. These fibrils display high ultimate tensile strength

and a Young's modulus comparable to Kevlar. The intermutual orientation of fibrils

within a wood fibre decides the strength of the fibre; fibrils pointing in all directions

yield weak fibres and brils pointing in the direction defined by the length of the

fibre yield strong fibres.

A flow channel has been conceived and made, such that an acceleration of a CNF

dispersion align the fibrils it contains. An ensuing fixation of the fibrils, all pointing

in the same direction, allows for the making of fibres of exceptional strength. In

other words, wood is taken apart and rebuilt even stronger. The material, if large

scale production is made possible, could be used for high-performance biomaterials

such as durable textiles.

During the time between alignment and fixation in the channel, a certain increase

in disorder occurs whereby the fibrils dealign. Our thesis focuses on the study of this

process. Since the fibrils are not visible, we have resorted to studying the birefringence,

which is induced by the optical anisotropy of aligned fibrils. The birefringence

has the property of changing polarization of light having travelled through the material.

This property is used to relate a measured intensity to birefringence which in

turn is related to alignment. Using this, we examine how the dealignment is affected

by parameters such as pH of the dispersion and acceleration.

Abstract [sv]

Cellulosa nanofibriller är en teknisk term for den minsta kristallina beståndsdelen

av trä. Det ar cylinderformade partiklar som mäter 20-40 nm i diameter och 1-2

m i längd. Fibrillerna har hög brottstyrka och en elasticitetsmodul jämförbar

med Kevlar. Träfibrer består av CNF och en fibers hållfasthet bestäms av fibrillernas

inbördes orientering; ligger de härs och tvärs blir fibern svag, pekar de alla

i fiberns längdriktning blir fibern stark. En metod for att tillverka starka fibrer

genom att linjera upp fibriller for att sedan fixera dem har föreslagits. Upplinjeringen

sker i en flödeskanal, i vilken en acceleration av flodet tvingar fibrillerna att

peka i flödesriktningen.

Under tiden mellan upplinjering och fixation sker en viss ökning av oordning

varvid fibrillerna olinjeras något. Det har en negativ inverkan på fiberns hållfasthet.

Vårt arbete syftar till att studera denna process. Eftersom fibrillerna ej är synliga

med blotta ögat, har vi måst studera dubbelbrytningen som induceras av den

anisotropi upplinjerade fibriller uppvisar. Dubbelbrytande material har egenskapen

att ändra polarisationen av ljus. Det utyttjas på så sätt att en uppmätt intensitet

ger ett mått på dubbelbrytningen som i sin tur relateras till upplinjeringen.

Vi undersöker vidare hur dubbelbrytningen påverkas av parametrar såsom pH och



Place, publisher, year, edition, pages
2014. , 32 p.
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-148826OAI: diva2:737645
Available from: 2014-08-13 Created: 2014-08-13 Last updated: 2014-08-13Bibliographically approved

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