Modified silica sol coatings for water-repellent textiles

The preparation of water repellent textiles by coating with different modified silica sols has been investigated. For this, pure and with 3-glycidoxypropyl triethoxysilane co-condensed silica sols were modified by three types of additives: alkyltrialkoxysilanes, polysiloxane derivatives and a fluorine containing silane. Hydrophobic properties of the coated fabrics of polyamide and of polyester mixed with cotton were determined using contact angle measurements. The hydrophobicity increases with increasing concentration of the alkylsilane additive in the silica sol and the length of the alkyl chain but with high additive concentrations plateau values in hydrophobicity were reached. Analogously textile coatings with high hydrophobicity were gained using hydrophobic polysiloxane or fluorine containing silicon compounds. The comparison of the different variants reveals that high wash-out stabilities were reached only by silica sols containing fluorine compounds and hexadecylsilane additives. Therefore long-chain alkyltrialkoxysilane compounds could be used as substitutes for fluorine compounds for the surface modification of textiles in some practical applications.