Oil Encapsulation in Core-Shell Filaments from Cellulose Nanocrystals and Methylcellulose via Dry-Jet Wet Spinning

The incorporation of oils into structured and water-compatible materials remains a key challenge for cellulose-based materials. Here, we demonstrate the production of core-shell filaments from cellulose nanocrystals (CNCs) and methylcellulose (MC) via a dry-jet wet spinning process, enabling the encapsulation of either plant-based oils or CNC-stabilized Pickering emulsions. The use of a physically entangled MC-CNC hydrogel as the shell allows continuous filament formation from an aqueous formulation without chemical cross-linking. By varying the core composition, distinct structural regimes were obtained: oils alone led to bead-on-string morphologies, while emulsions yielded beadless filaments, consistent with the replacement of a continuous oil core by prestabilized micron-sized oil droplets. Estimated oil contents up to 47 wt % were achieved for corn oil alone and 24 wt % for corn oil emulsions. Turmeric and tea tree oils could also be encapsulated within the MC-CNC shell, although the retained oil content varied with oil type. The modular coaxial spinning setup developed here provides a versatile platform for the fabrication of biobased filaments containing oil. These findings establish a simple strategy to integrate hydrophobic components into continuous cellulose-based materials for future exploration in applications requiring oil-containing structured materials.