Influence of magnetic nanoparticles on the mechano-magnetic response of wet-spun sodium alginate-nanocellulose filaments

Hybrid filaments are of growing interest for a wide range of applications, including those that require stimuli-responsiveness. In this study we developed magnetic filaments by combining the properties of inorganic nanoparticles with the low density, flexibility and morphological features of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF). The hybrid filaments were synthesized by wet spinning of TOCNF using sodium alginate (SA) adjuvant in a hydrogel containing magnetite (Fe₃O₄) nanoparticles (NPs) formed in-situ by nucleation and grow. The relationship between synthesis conditions and filament mechanical and magnetic properties were investigated at NP loading as high as 25%. Saturation magnetization of 1.60, 11.31, 19.41, and 33.25 emu/g Fe₃O₄ were measured at 5, 10, 15, and 25% NPs with a penalty in filament tensile strength which nevertheless reached at least 118 GPa along with low magnetite crystal orientation. Such high strength is rarely reported and found to depend on cellulose crystal orientation. The magnetic filaments were found suitable to replace traditional magnetic systems but add to the opportunity to develop flexible microwave adsorption textiles, artificial muscles, and micro-sensors.