Ultraviolet Rays Mechanically Strengthen Spider’s Silks

Abstract

The resistance of silks to ultraviolet (UV) rays has been one of important characteristics as materials for textiles. It has been shown that UV rays easily decompose the protein molecules of natural silks such as silkworm silks. Therefore, it has been expected that a new silk with the high resistance to UV rays except for silkworm silks should be developed as materials for textiles. And, researchers focused on the mechanical properties of spider silks because the elastic modulus of spider silks is higher than those of amorphous synthetic polymers. Since a spider captures insects in daytime by using its orb-web which is exposed to sunlight, the spider silks may be affected by the environmental factor of UV rays from sunlight. Thus, it is of great interest to study whether spider silks are mechanically resistant to UV irradiation. Many properties of spider silks have been studied including mechanical, strain energy, physico-chemical, thermal and optical properties. The chemical degradation of spider’s silks was studied by using an electron spin resonance ESR method. To my knowledge, however, no studies concerning the effects of UV rays upon the mechanical properties of spider silks have been reported. The present study focuses on the effects of UV-irradiation upon the mechanical stress of spider silks and describes findings on the mechanically strengthening of the spider silks ascribed to UV irradiation.