Tensile properties and dimensional stability of cellulose nanofiber-reinforced silk fabrics by silkworm feeding

Cellulose nanofiber (CNF) reinforcement of silk fibroin (SF) has attracted increasing attention as a sustainable strategy for enhancing the mechanical performance of silk materials. In this study, CNF-reinforced silk was produced by directly feeding silkworms (Bombyx mori) with artificial diets containing CNF, and its mechanical properties and dimensional stability were systematically investigated across three hierarchical levels: single filaments, twisted yarns, and woven fabrics. At the single-filament level, the addition of 5 wt.% CNF resulted in significant increases in Young’s modulus and ultimate tensile strength, while the fracture elongation remained nearly unchanged. These improvements were retained at the yarn and fabric levels. The dimensional changes induced by water-absorption, swelling and subsequent drying were thereby quantitatively evaluated. While individual filaments exhibited negligible shrinkage regardless of CNF addition, twisted yarns and fabrics showed pronounced shrinkage, which was markedly suppressed by CNF reinforcement. Notably, the shrinkage rate of CNF-reinforced twisted yarns was reduced to less than one-quarter of that of unreinforced yarns. FT-IR analysis based on the amide III region revealed that CNF addition did not significantly increase the β-sheet crystallinity of single filaments, indicating that the enhanced dimensional stability does not originate from increased crystalline content. Instead, CNF is suggested to stabilize higher-order assemblies by restricting molecular mobility in amorphous regions and reinforcing inter-fiber interactions. These findings provide new insight into the multiscale design of silk-based materials with improved mechanical performance and moisture resistance.