Tuning the Mechanical Properties of Silkworm Silk Fibres by Thermally Induced Modification of Crystalline Nanostructure

Antheraea pernyi and Bombyx mori silk fibres, the most important and the subjects of several studies, have attracted widespread attention due to their exceptional mechanical properties and promising applications. However, the determinants behind the variations of mechanical property between these two fibres still remains unknown. In this paper, the nanocrystalline structures of these two silk fibres were tuned by thermal treatment in order to understand how the structure affects the mechanical properties of fibres. It has been found that, along with an increase in temperature for thermal treatment, the increase in the intramolecular β-sheet leads to progressive increase in longitudinal modulus and radial hardness, whilst the reduction in crystallinity results in great reduction in breaking tensile strength. The yield strength is proportional to the average crystallite size which increases along with the annealing temperature. Compared to B. mori, A. pernyi silk fibres have more obvious temperature-dependant structural changes. These findings explain how size effects can be exploited to create bioinspired materials with tuneable mechanical properties.