Instrumental characterization and functional assessment of the two-color silk fabric coated by the extract from Dioscorea cirrhosa tuber and mordanted by iron salt-containing mud

The extract from Dioscorea cirrhosa tuber is rich in condensed tannins, and in China it is used to produce a traditional two-color silk fabric (Gambiered Guangdong silk) characterized by shiny black on the face side and reddish brown on the back side. The process of Gambiered Guangdong silk identified as a National Intangible Cultural Heritage includes repeated coating with the condensed tannin solution from Dioscorea cirrhosa tuber followed by mordanting with iron salt-containing mud. In this work, the color characteristics, structures, chemical compositions, thermal behaviors, and functional properties of two-color silk fabric were studied. Condensed tannin coating and iron salt mordanting significantly changed the morphological structure and thermal behavior of silk fabric, and imparted a series of functionalities including flame retardant, waterproof, antioxidant and antibacterial properties to silk fabric. In particular, tannin coating as a char forming agent during combustion improved the flame retardancy of silk fabric, and the blocking of the spaces between silk fibers by an amount of coated tannins and tannin-iron complexes made silk fabric possess good waterproof function.