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Treesearch Insight 2023

20. Optimisation of Spinnability and Mechanical Properties of Bio-based Filaments by Dispersion Characterisation and Processing Conditions

A double flow-focusing channel technique has been developed as a proficient device for aligning cellulose nanofibrils (CNFs) and producing bio-based filaments. Utilising the outstanding mechanical properties of CNF fibrils themselves, these filaments are recognised as one of the strongest natural-based filaments. However, the coupling between the performance of the macro-scale fibres and properties of CNF dispersions remains incomplete. This study aims to identify the spinnability conditions for CNFs and identify the coupling between processes pre- and post-spinning to enhance the filaments’ mechanical properties.

CNF dispersions must be characterised before spinning using well-established techniques. To address the effects of remaining agglomerates and aggregates after storage, ultrasonication and centrifugation are employed to purify CNF dispersions and achieve more homogenous distributions. AFM analysis reveals that the cleaning process shortens CNFs, requiring higher concentrations to maintain suitable crowding factor that allows robust spinning. Rheological data corroborate this finding, indicating a favourable viscosity range for optimal dispersion consistency. A flow-stop technique utilising polarised optical microscopy (POM) allows for tracing the CNF network during flow. Fast and slow rotary diffusion coefficients, Dr,fast and Dr,slow, can be obtained through this method, reflecting CNF entanglement and the effects of Brownian motion. Spun filaments were dried at varying temperatures below the thermal degradation temperature. Results indicate that water molecules act as plasticisers, with increased drying temperature leading to faster removal and lower strain at break, but higher modulus due to the reduction of variability and less of weak filaments by high capillary forces.

1Mu-Rong Wang, 1Korneliya T. Gordeyeva, 1Tomas Rosén, 1L. Daniel SöderbergKTH, Royal Institute of Technology, Sweden