Fatigue characterization of cellulose nanofiber-reinforced - reinforced silk yarns for enhanced structural applications

With the recent increase in the adoption of silk in structural and medical applications, ensuring the long-term structural integrity of silk has become crucial. Previously, we successfully enhanced the static performance of silk by incorporating cellulose nanofibers (CNFs). This result is consistent with the common knowledge that nanofillers, such as CNFs, can alter the fatigue properties of materials. In this study, we evaluated the impact of CNFs on the fatigue performance of silk by comparing CNF-reinforced silk with regular silk. The tensile strength, Young's modulus, and toughness of the silk yarns were measured before and after cyclic loading. The evolutions of the properties between the silk types were recorded and compared. In addition, the friction coefficients of silk were measured using the Capstan method to assess the contribution of interfiber abrasion to the observed enhancement. The results showed that the CNFs significantly enhanced the fatigue performance of silk, with a notable 80.5 % increase in toughness observed after cyclic loading. Further, the friction properties of the different silk types were similar, eliminating friction as a cause of the resulting enhancement.