Addressing the dual challenges of plastic sustainability and antibiotic resistance, this work develops cationic cellulose nanocrystals (CNCs) with potent inherent antimicrobial activity. Functionalization of CNCs with triazole-imidazolium groups (CNC-TrMI) achieved a 56% degree of substitution, confirmed by ssNMR and elemental analysis. The resulting CNC-TrMI exhibited exceptional biocidal efficacy (>99.99% reduction) against both Gram-positive (Staphylococcus epidermidis) and Gram-negative (Pseudomonas aeruginosa) bacteria, surpassing methylimidazolium-modified CNC (CNC-MI) in efficacy against Gram-negative strains. While modifications reduced crystallinity (81% → 45%) and thermal stability (193 °C ≤ d5% ≤270 °C), CNC-TrMI’s retained thermal profile enables polymer processing.

The ultimate objective is to integrate these CNCs as sustainable antimicrobial agents into biobased poly(lactic acid) (PLA) matrices for processing via melt electrowriting (MEW). To achieve this, capillary rheology was first employed to screen and select the optimal PLA matrix among variants with differing D-isomer content. This rheological analysis directly correlates the uniaxial extensional viscoelastic response of PLA with its MEW processability, enabling reliable fabrication of biobased fibers and the subsequent incorporation of antimicrobial agents.

The synergy of CNC-TrMI’s non-leaching antimicrobial action (>4-log reduction), PLA’s biodegradability, and MEW’s precision patterning offers a sustainable platform for advanced biomedical textiles (e.g., wound dressings) and active packaging. Overall, this approach demonstrates how fundamental rheology guides the reliable integration of functional biobased additives into advanced manufacturing processes, supporting circular economy principles.