Structure and strength of spider silk and application to environmental by use of the degradation of its orb-web

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The aim of this report is (1) to investigate structure and strength of spider silk and (2) to discuss the effect of environment of acid rain and ultraviolet ray (UV) on the deformation behavior of the orb-web of the spider Nephila clavata called Jorougumo in Japan and the applicability to an environmental assessment on its inhabitant.In order to investigate the fundamental characterristics of the spider dragline silk and capture thread, some tests of (1) surface observation, (2) amino-acid analysis, (3) FTIR analysis, (4) thermal analysis and (5) dynamic mechanical analisis were performed. Furthermore, using a home-made tensile testing machine specially devised for spider thread, stress-strain curves of draglines and capture threads were obtained to estimate the mechanical properties, and the degradation of the dragline and the orb-web due to the UV irradiation and the exposure to quasi-acid rain were investigatedIt was shown that (1) the spider dragline silk consisted mainly of neutral amino-acids of glysine and alanine, (2) the dragline with diameter of about 2-4mum was made of finer fibrils, (3) the dragline was thermaly stable up to about 250ﾟC,(4) the elastic modulus and the tensile strength of the dragline were about 5 times smaller, but the fracture strain and the energy to break were about 5 times larger than those of the best man-made fiber, (5) the UV irradiation induced the degradation of the dragline, (6) the acid rain which falled at present did not degaradate the dragline, (7) the stress-strain curve of the capture thread was J-shaped and the fracture strain was about 200%, which is 10 times larger than that of the dragline and (8) a special mecanism of the capture thread named windlass system was reconfirmed.