Morphology and structure of silkworm cocoons

Silkworm cocoons are natural polymer fibre composites made from silk fibres and sericin binder. While silk is an interesting natural material per se, an understanding of the role of silk within one of its main functional applications in silkworm cocoons will provide inspiration and tools for the design of new artificial silk composites. Here, we describe in some detail the structure and morphology of the cocoons of 27 different species of silkworm. While cocoon morphology can be described very broadly as a nonwoven fibre composite, we demonstrate a diversity of structural features such as: the number and connectivity of layers through the cocoon wall thickness, the amount and distribution of sericin binder, the diameter and packing density of the silk fibres, the degree of orientation of the nonwoven structure, the distribution of larger holes within that structure, and the presence of calcium oxalate crystals.