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Accueil du site > Évènements > Séminaires > Séminaires IRPHE > Archives IRPHE > 2017

Vendredi 5 Mai 2017/ IRPHE

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Séminaire exceptionnel IRPHE

Effect of length distribution on rotary diffusion of cellulose nanofibrils in a flow focusing experiment

Orateur : Christophe Brouzet
Department of Mechanics, KTH, Stockholm, Sweden

Résumé : Making high performance fibres from trees is a challenging topic of research due to the increasing demand for strong and environmentally friendly fibres used for lightweight composite materials and textiles. Recently, a process of making cellulose fibres was demonstrated using a flow focusing device : a flow with dispersed cellulose nanofibrils (CNF) is focused by through the injection of two side flows. As the core flow of CNF is accelerated, the fibrils align in the flow direction. By changing pH or salinity level of the side flows, the CNF dispersion can undergo a liquid-gel transition and thus locking the internal structure of fibrils. When the resulting gel thread is dried, a continuous cellulose fibre is obtained which can be as strong and stiff as glass fibres. The strength and stiffness of the final product have also been proven to increase with fibril alignment within the dried fibre. Understanding the alignment of the fibrils is thus crucial for optimization strategies in the process.

The major obstacle of the aligning process is found to be the rotary diffusion, which drives the fibrils towards a de-aligned state. This can be caused by e.g. Brownian motion of the CNF or the electrostatic interactions between them. It is therefore necessary to understand how the rotary diffusion varies with respect to different parameters, such as the concentration of CNF solutions, fibrils charges and lengths, in order to optimize the current fibre process.

During this presentation, I will discuss experiments which have been performed using Polarized Optical Microscopy to observe the relaxation towards isotropy of the CNF after the flow has been stopped in the channel. Using the relaxation signal at different channel locations, we establish a comprehensive scenario of the de-alignment of the CNF in the flow focusing experiment. This scenario is strongly dependent on the length distribution of the CNF.

Date et lieu : Vendredi 5 Mai à 14h, salle de séminaires IRPHE