Silkworm Cocoon Waste Revitalization: Regenerated Fibers Using Higher-Molecular-Weight Fibroin Achieve High Strength and Toughness

Silkworm cocoons are removed in the industrial process when the cocoons are stained or reeled as dupion. Furthermore, a tremendous amount of used silk clothes is discarded worldwide. An artificial spinning of regenerated silk fibroin solution is a candidate to recycle silk waste. However, the mechanical strength of the regenerated silk fiber has often been lower than that of the natural counterpart, limiting the industrial use of regenerated silk fibers. Silkworm silk fibroin consists of heavy chains, light chains, and glycoproteins. The molecular weight of the heavy chain is more than 10 times higher than that of the light chain and glycoprotein. In this study, we extracted the heavy chain from the silkworm cocoon waste and applied artificial silk spinning to produce regenerated silk fibers with few structural defects with the aim of obtaining high tensile strength. The regenerated silk fibers revealed tensile strength comparable to the natural silk fibers. Furthermore, the modulus of elasticity in tension was 1.7-fold higher than that of the native counterpart. The present study will contribute not only to recycling silk waste but also to designing high-strength protein-based structural materials along with the context of sustainable development goals.