Durable antibacterial silk fabrics via dip-coating: Dialdehyde starch-mediated immobilization of chitosan

Developing durable and nontoxic antibacterial finishes for natural textiles remains a significant challenge. In this study, bio-derived dialdehyde starch (DAS) was used as a green crosslinker to introduce aldehyde groups onto silk fibers, enabling covalent immobilization of chitosan via Schiff-base reactions through a simple water-based dip-coating process. The grafting yield of aldehyde groups and chitosan was optimized with time and concentration, obtained after 3 h DAS treatment followed by immobilization with 2.0 wt% chitosan and 4 h batching. Aldehyde incorporation was verified by hydroxylamine titration, while chitosan grafting was confirmed by Raman spectroscopy, XPS, and SEM, and further quantified using a bicinchoninic acid (BCA) assay. The modified silk exhibited excellent antibacterial activity (99.99% reduction against Escherichia coli and Staphylococcus aureus), while untreated silk showed no antibacterial effect. The fabrics retained over 96% antibacterial efficiency after 20 laundering cycles due to stable covalent bonding of chitosan. Meanwhile, hand feel, air permeability, and moisture permeability remained largely unchanged, indicating surface-confined modification. To sum up, this water-based carbohydrate-mediated finishing strategy provides an environmentally friendly route for durable antibacterial silk textiles.