Development and characterisation of magnetic alginate-nanocellulose composite filaments

Abstract

Hierarchical polysaccharide composite filaments were fabricated by wet spinning and characterised systematically to study the interdependence between their structures and properties, with the objective to developing a family of sustainable composite filaments with significant magnetic responsiveness whilst maintaining mechanical performance at high nanoparticle loadings. Two naturally derived polysaccharides, alginate (AG) and rod-like cellulose nanocrystals (CNCs) prepared by acid hydrolysis of cotton pulp, were used to make continuous filaments and their influence on several filament properties was determined. Independent of CNC loading and draw ratio, all AG/CNC filaments exhibited a grooved surface in their axial direction and had irregular cross-section. High CNC loading significantly increased the orientation of CNCs within filaments such that the Herman's orientation factor increased to a maximum of 0.81 at a CNC content of 70 wt%, whereas elevating draw ratio in the investigated range did not significantly affect the CNC alignment. Compared to pure AG, the increase in CNC content resulted in an over 60% increase in filament specific modulus. The increase in draw ratio enhanced both specific strength and specific modulus of filaments, with this effect being more pronounced at higher CNC loadings. Two kinds of magnetic nanofillers were subsequently synthesised to endow AG/CNC filaments with magnetic responsiveness: superparamagnetic iron oxide nanoparticles (SPIONs) obtained by co-precipitation (diameter less than 20 nm and saturation magnetisation (Ms) of 75.6 emu/g) and ferromagnetic spindle-like magnetic nanorods (MNRs) prepared by calcination of an iron oxide hydroxide precursor (length ~170 nm and width ~50 nm and Ms of 52.9 emu/g). AG/CSM filaments spun from AG and CNC-SPION mixtures (CSMs) demonstrated magnetic properties with the highest Ms value of 20.7 emu/g and excellent mechanical properties with strain at break of 16.8% and specific elastic modulus of 4.1 MN m/kg at high SPION content up to 35 wt%. High CNC content was instrumental in promoting alignment of CNCs along axis of magnetic filaments, whereas high contents of cubic-shaped SPIONs disrupted CNC orientation. Wet-spun AG/CRM filaments based on AG and CNC-MNR mixtures (CRMs) exhibited irregular porous cross-sections and grooves on the surface with roughness associated with MNR content; these also demonstrated ferromagnetism with the highest Ms value of 4.8 emu/g. Both anisotropic CNCs and MNRs showed alignment along filament axis, and their orientation increased as the MNR content decreased. AG/CRM filaments with the lowest MNR loading exhibited the best mechanical performance with tenacity of 77.4 kN m/kg and specific modulus of 6.5 MN m/kg.

Date of Award	4 Sept 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Bill Sampson (Main Supervisor) & Jonny Blaker (Co Supervisor)