Rotational Diffusion of Cellulose Nanofibrils.

Detta är en Kandidat-uppsats från KTH/Mekanik; KTH/Mekanik

Författare: Johan Wärnegård; William Hedén; [2014]

Nyckelord: ;


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.

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