Silk is a natural protein filament consisting of two components: fibrous protein (fibroin) and glue-like protein (sericin). Fibroin is the core structure of fiber which has been covered by sericin as glue. Remarkable mechanical properties, suitable biocompatibility and biodegradable have made extremely useful in the textile industry and the fields of biological and biomedical textiles. Silk structure consist of beta-sheet, alpha-helical and random coil structures. Non-parallel beta-sheets are major secondary structure of silk fiber that is produced by spiders and silk worms and key role to stabilize proteins is obligation to physical crosslinkings. Variety of the amino acids in silk is very similar to human skin, so that it is known as the second skin. In past centuries, silk fibers were used as the sutures in medicine field. Surface and chemical modification of silk fiber are necessary to improve their properties in medical textiles such as scaffolds. One of the chemical modification methods is based on using UV irradiation. UV wavelengths are ranging from 300 and 400 nm which is invisible to human eyes. Ultra violet is only making 5% of the sun rays but they have most destructive energies on organic materials among them. In this way, the high-energy photons can break the molecular chains of silk fibroin surface, which creates free radicals on surface of the fiber. These radicals will further react with oxygen in the air and produce super active oxygen species. Super oxides then react with the surface of the fibers and cause more damages. In this study, the silk yarns and silk fabrics were treated by anthraquinone 2 - sulfonic acid and acid green 25 at concentration of 1% and 2%. Raw and dyed silk fabrics were exposed to UV-C irradiation for duration of 0, 0.5, 1, 2, 3, 12 and 48 hours. .FTIR results showed that alpha- helical and random coil structures have decreased and beta sheet structure of silk fiber has increased. Tensile strength of the treated fabric with Anthraquinone -2- sulfonic acid (AQS) increased up to 14% after 3 hours UV-C irradiation. XRD results indicated that the Crystallinity of the treated silk fabric with AQS was also increase by 3% after 48 hr irradiation. SEM images confirmed the surface degradation and Non-uniformity of silk fibres.The solubility tests of treated silk sample showed that the solubility of fibers increased by 57%. Increasing solubility which refers to the biodegradation capability of silk fabric in accordance with increasing in tensile strength and Crystallinity of treated samples is valuable achievement for modified silk fibers and indicate the possibility of their application in the field of medical textiles such as scaffolds. Key words: Silk, UV-C, irradiation, Free radicals, Crystallinity.
