Highly hydrophobic textile surfaces obtained by thin-layer deposition

The potential of thin-layer deposition by physical processes for the surface modification of polymer films and synthetic fibers was investigated. A new approach to photochemical surface modification using monochromatic UV excimer lamps is described. The experiments have shown that it is possible to initiate grafting or even cross-linking of functional thin layers on the substrate surface by treatment in reactive atmospheres. The general condition to achieve such reactions is a marked difference in the absorbance of a low- or non-absorbing atmosphere and a strongly absorbing substrate, which leads to radical processes at the boundary between the atmospheric medium and the activated substrate. Using perfluoro-4-methylpent-2-ene as a medium the contact angle on poly(ethylene terephthalate) surfaces increased up to 116 degrees. In case of bi-functional substances such as 1,5-hexadiene and diallylphthalate, the increased resistance against chemical degradation as well as infrared spectroscopy provided evidence for thin layer generation. Well-known and widely applied in several industries, surface modifications by gas discharge (plasma) processes are based on activation of the substrate mainly by electrons. The surface radicals generated then react with radicals in the plasma leading to substitution, grafting or cross-linking reactions. With regard to treatment of textiles, the atmospheric pressure plasma concept allows the use of rather simple machinery and a continuous treatment. In order to deposit functional thin layers for highly hydrophobic surfaces, fluorocarbons can be used as process gases. In the work described here fluorinated thin layers with a total fluorine concentration on the surface more than 50% could be deposited. An oil repellence rating, according to AATCC, of up to 7 to 8 was achieved.