Tuning Alignment, Strength, and Toughness in Functional Cellulose:Helux Filaments: A Molecular Trade-Off.

The complex architecture of wood motivates studies of bioinspired materials that combine strength, toughness, and mechanical integrity. We explore the interplay between nanofiber alignment and molecular interactions in composite filaments formed from cellulose nanofibers (CNFs) and a dendritic polyampholyte, Helux. Helux enhances strength by 60% and increases toughness 5-fold through ionic bonding and thermal covalent cross-linking. However, wide-angle X-ray scattering (WAXS) reveals reduced nanofiber alignment in Helux-containing samples, resulting in a 25% decrease in stiffness─highlighting a trade-off between structural order and cohesion. Polarized optical microscopy (POM) and in situ small-angle X-ray scattering (SAXS) attribute this reduced alignment to enhanced rotary diffusion, driven by carboxylate groups of the Helux. With Helux, multivalent links across the nanofibers give a denser and tougher network with fewer voids. This behavior resembles lignin and hemicellulose interactions in wood, where flexibility and cohesion govern the performance.