Hydrophobic Modification of Cotton Fabrics with Epoxy-Functional Polysiloxanes: Comparison of Direct Deposition and Thiol-Crosslinked Coating

In this study, two epoxy-functional polysiloxanes were synthesized and applied for cotton hydrophobization using two modification routes: direct reactive deposition and thiol-crosslinking on the fiber surface. PS1 contained epoxy groups, whereas PS2 contained both epoxy groups and alkyl chains. The modified fabrics were characterized by add-on measurements, FT-IR spectroscopy, SEM-EDS, SEM imaging, washing tests, and static water contact angle measurements. Both modification strategies enabled the formation of polysiloxane-based layers on cotton, as confirmed by the presence of silicon in all modified samples and sulfur in thiol-crosslinked samples. SEM images showed continuous and relatively uniform coatings without visible fiber damage. All modified fabrics became hydrophobic and retained their properties after washing. Thiol-crosslinking was more effective than direct reactive deposition, giving WCA values up to 144°. PS1 provided stable hydrophobicity regardless of thiol type or concentration, while PS2 benefited from higher modifier concentration and the use of tetrafunctional thiol. The results show that epoxy-functional polysiloxanes, especially when crosslinked with multifunctional thiols, are effective modifiers for producing washable hydrophobic cotton fabrics.