Hydrophobic behaviour of non-fluorinated sol-gel based cotton and polyester fabric coatings

Water repellency was conferred to cotton and polyester fabrics by an hybrid organic-inorganic finishing obtained by hydrolysis and subsequent condensation of octyltriethoxysilane (OTES) under acidic conditions, in combination with melamine based crosslinking agent N,N,N,N,N,N-hexakis(methoxymethyl)-1,3,5-triazine-2,4,6-triamine (MF). The application on textile samples was carried out by padding followed by drying and thermal treatment. Water-resistance properties were determined in terms of the contact angle, water uptake and drop adsorption times, whereas the surface composition of treated fabrics was characterized by attenuated total reflectance Fourier transform infrared analyses. Textile fabrics treated with the hybrid OTES-MF sol exhibited the best water-repellent properties, when compared to those treated with OTES or MF finishing alone. In particular, cotton and polyester samples, treated with a 60 g/L MF solution in a 1:4 MF:OTES molar ratio, showed a water contact angle of 130 degrees and 150 degrees, respectively. The high hydrophobicity of the treated fabrics is supposed to be due to the structural and stereochemical properties of the finishing. The presence of the MF triazine ring seems to favour both the improvement of the outward orientation of the OTES alkyl chains, and the crosslinking of N-methylol groups to form a three-dimensional film around the fibres which increases the surface roughness. The contact angle values and the characteristic IR peaks confirmed the presence of the hybrid coating on cotton fabrics even after multiple washing cycles.