How Can Different Degumming Treatments Help the Valorization of Waste Silk for Epoxy Composite Applications?

Valorizing silk textile waste as composite reinforcement requires removing the sericin coating (degumming) without damaging the load-bearing fibroin or the fiber/matrix interface. Using floss Bombyx mori silk waste, the effect of five degumming protocols, alkaline NaOH and Na2CO3 baths and a mild hot water treatment, on the silk/epoxy interface was investigated. The interfacial shear strength (IFSS) was measured by microdebonding, the single-fiber tensile strength and apparent modulus by single-fiber testing with Weibull statistics, and the fiber chemistry and morphology by FT-IR and SEM. Conventionally computed from a circular cross-section, these properties were re-evaluated from the measured, non-circular geometry of the same fibers, which raised the raw stress about 1.65 times. The three properties give a single ranking: the mild hot water treatment, which removes only about 21% of the mass and leaves residual sericin, simultaneously yields the highest IFSS (9.0 MPa), tensile strength (σ0 = 454 MPa) and apparent modulus (E0 = 11.3 GPa). It performs best despite, not because of, its residual sericin: gentle degumming preserves the fibroin surface and core, whereas aggressive alkaline routes fully strip sericin but expose and damage the fibroin. Mild hydrothermal degumming thus emerges as a favorable compromise for silk waste epoxy composites.