Functionalization of silk with chitosan and Rubia cordifolia L. dye extract for enhanced antimicrobial and ultraviolet protective properties

Natural dyes have attained the interest of scientists over the last decade due to their functional activities in addition to their primary role of color impartation on textile materials. This study is the first report on the functionalization of silk with antimicrobial and ultraviolet protective properties using a dye extract from the roots of Rubia cordifolia L. in conjunction with chitosan as a bio-mordant. Alum mordant was also used in the dyeing process alongside chitosan for comparison purposes. Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy were utilized to determine the anthraquinone-based components of the dye extract. Furthermore, the structure and surface morphology of silk fibers before and after dyeing were investigated. The dyed silk samples exhibited good fastness against washing, rubbing, and lighting. The chitosan mordanted-dyed silk presented remarkable antimicrobial properties with maximum inhibitions of 96.71% and 99.08% against Escherichia coli and Staphylococcus aureus, respectively, and only 2.3% spore germination of white mold (Aspergillus spp.). Likewise, an excellent ultraviolet protection factor was achieved in the chitosan modified-dyed silk. The findings of this study demonstrated the potential of the Rubia cordifolia L. extract as a functional dye, as well as the advanced properties of chitosan in increasing the fastness and functional performance for the dyed silk compared to alum mordant.