Azoic Deep Dyeing of Silk and UV Protection Using Plant Polyphenols and Diazonium Coupling

This study investigated azoic dyeing as an approach to improving the natural dyeability of silk fabric while avoiding the use of metallic mordants, which are toxic to health and the environment. An aryl diazonium salt was prepared from p-nitroaniline and used to couple with silk fabric pretreated with plant polyphenols. The interaction triggered in situ production of azo dye within the silk fibers. This dyeing approach was demonstrated to overcome the poor tinctorial strength and fastness of natural dyes. Plant polyphenols were extracted from oolong tea and mangrove bark. The CIE L*a*b* and K/S values were measured, and compared with the results of post-mordant dyeing using aluminum potassium sulfate. Even at low concentrations, aryl diazonium salt was shown to achieve deep dyeing, producing an intense brown/orange shade. The effect of azoic dyeing on color strength was strongly dependent on the primary aromatic amine concentration. At 7 % owf, the oolong tea extract produced a K/S value approximately six times that of the comparable post-mordant sample, and the mangrove bark extract approximately three times. The grater color strength achieved by the tea extract was due to the higher TPC concentration. The natural extracts conferred UV protection greater than 50 in all dyeing processes.