Chitosan Pad-Dry-Cure Antimicrobial Finishing

Chitosan (DD 85%, MW 200,000 Da) dissolved in 1–2% acetic acid at 1–3% concentration is applied to cotton or wool fabric via 2-roll padder at 70–80% wet pickup, dried at 80°C for 5 minutes, and cured at 120–130°C for 3–5 minutes to promote ionic bonding and partial film formation. Add-on of 0.8–2.5% owf achieves 3–4 log reduction against S. aureus (AATCC TM100). Crosslinking with citric acid (2–4%) and sodium hypophosphite catalyst (1–2%) at 170°C forms ester bonds improving durability to 25–30 wash cycles at 40°C. Yellowing (ΔE 2–4) is the primary aesthetic drawback managed by optical brightener incorporation. Treatment cost is $0.10–0.25/m² making chitosan the most affordable natural antimicrobial option.