Optimizing Dual-Surfactant System for Nylon Textiles: Toward a Fluorine-Free Water-Repellent Coating

Per- and polyfluoroalkyl substances (PFAS) coatings are widely used to impart water repellency to textiles, but their drawbacks, including the lack of biodegradability and potential effects on human health, underscore the need for fluorine-free alternatives. Current replacement products, such as PTFE (polytetrafluoroethylene) layers and wax applications, experience durability issues and require reapplication. In this study, a dual-surfactant coating comprising pentanoic acid (C5) and octadecylamine (C18) was developed to impart hydrophobicity to woven nylon 6,6 fabrics. The proposed mechanism involves thermal treatment after exposure to pentanoic acid to create carboxylate-rich surface sites, followed by electrostatic association of octadecylamine to form a non-polar monolayer. Process conditions were optimized by varying heating time, temperature, and pentanoic acid soaking time. Pristine nylon showed a water contact angle of 60.6°, whereas the fully coated fabric had a water contact angle of 118.8°. ATR-FTIR (Attenuated Total Reflectance Fourier Transform Infrared), FESEM (Field Emission Scanning Electron Microscope), and XPS (X-ray Photoelectron Spectroscopy) demonstrated successful coating on the nylon surface. Weight and color analysis indicated near-surface alkyl enrichment with minimal visible change to the fabric. The short-term durability has been confirmed by measuring water contact angle after aging and laundry cycles. These results present a simple fluorine-free strategy for producing hydrophobic nylon 6,6 textiles.