Making strong filaments from cellulose nanofibrils (CNF) can potentially lead to new high performance bio-based composites competing with conventional glass fiber composites. Recently, Hakansson et al (Nature Communications volume 5, 4018) and Nitesh et al (ACS Nano 12, 7, 6378-6388) demonstrated a method of making such very strong cellulose filaments with excellent properties through hydrodynamic alignment by using the concept of flow-focusing. After the alignment of CNF, ions were diffused into the CNF suspension, resulting in a dispersion-gel transition, which locked the aligned structure in a gel. Furthermore, alignment in final material of cellulose fibre determines mechanical performance. Hence, an improved understanding of the alignment process is necessary to tailor material properties and for the further development and upscaling of the technology. In this work, numerical simulations, calculations and experiments are carried out to study the orientation and alignment of cellulose nanofibrils during an accelerating flow in a converging channel that is suitable for understanding the fundamentals of the alignment process. The experiments have been investigated using small angle X-ray scattering (SAXS) and alignment process is modelled using the Smoluchowski equation. As depicted in the figure on the left shows the acceleration of flow in a converging channel during which the cellulose nanofibrils were found to align. The one on right depicts the variation and a comparison of the order parameter S (S=1 is a fully aligned system and S=0 an isotropic system) between experimentally measured (SAXS diffractograms) and computed values during acceleration of flow and thereafter rotary diffusion plays a dominant role on the orientation distribution. We will also highlight the behaviour of cellulose fibril alignment in shear and extensional flow.

Orientation and alignment of cellulose nanofibrils in shear and extensional flows

2019 Spring National Meeting

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