Secondary structure transformation and mechanical properties of silk fibers by ultraviolet irradiation and water

Probing the photo-degradation of silk fibers is helpful to protect silk cultural relics. Studying the interactions between sericin and fibroin is essential for understanding the ageing degradation of silk fibers. Fourier transform infrared spectroscopy studies demonstrate that compared to the silk fibers under 38℃ water, the variety of β-sheet structure under ultraviolet (UV) irradiation with or without water increases and then decreases due to the removal of sericin and the damage to the peptide chains. Meanwhile, the mechanical properties of silk fibers are investigated by measuring the stress–strain curves and the ultimate tensile strength. The changes of E modulus on strain ε are calculated and the results are used to describe the mechanism of elastic, elasto-plastic and plastic strain in silk fibers under stretching. In addition, the stress degradation rates of silk fibers indicate that the synergetic role of water and UV irradiation can cause the breakage of crosslinks in the fibers with the increase of ageing time. The calculation of artificial degradation life estimation also shows that the existence of water affects the life of silk fibers. This study demonstrates that the appropriate condition can be employed for the protection of ancient silk fabrics.