| Superhydrophobic fabric has been widely used in practical applications such as anti-rain and snow clothing, tents, military combat uniforms thanks to its advantages of being self-cleaning, anti-rain and snow, antipollution, and antioxidant. There are various techniques can be used to make a common fabric superhydrophobic, but most of them are time-consuming and inconvenient which either involve multistep processes, expensive raw materials and special equipments or can’t achieve large-scale surfaces. So, it is necessary to explore a simple and effective superhydrophobic textile finishing method. Phase separation method has been reported to be a facile technique to fabricate superhydrophobic surface, which are usually applied on a smooth surface by forming a hydrophobic microporous films. However, this effective method are seldom used on a textured surface. In the present work, phase separation method was introduced into the fabric finishing process to achieve superhydrophobic, and a simple and effective approach with solution immersion process to transform normal hydrophilic cotton fabrics into superhydrophobic ones were presented.In the first part, polypropylene (PP) superhydrophobic films were prepared by thermally-non-solvent induced phase separation method using p-xylene as solvent and2-butanone (MEK) as non-solvent. Contact angle (CA) results showed that the surface hydrophobicity varied with the processing conditions including the initial concentration of PP, drying temperature and the volume fraction (vol%) of2-butanone (MEK). The optimum value of the water contact angle of the obtained films reached159.1°. SEM results showed that the film was composed of many microspheres and voids in submicron scale and the detailed morphology of the film surface had a close relation with their hydrophobicity. The smaller the diameter of microspheres was, the higher the film CA value would be.Two kinds of finishing routes were then explored based on the processing conditions of preparing PP superhydrophobic films. For route A, the fabric was directly immersed into the mixed solution of PP/p-xylene (solvent)/2-butanone (non-solvent), and was then kept in a certain temperature to make the PP on fabric surface get phase separated. For route B, the fabric was immersed into PP/p-xylene solution first to get enough PP coating and then into the2-butanone solution. After the two step of immersion, the fabric was then kept on a certain condition to fulfill phase separation. Results showed that the finishing effects of route B is better that Route A, and the CA of fabric obtained by the former one displayed higher value which were all beyond150℃. The influence of processing conditions on the water repellency effects of treated fabrics by route B was then systematically evaluated by contact angle and sliding angle measurements. It showed that the hydrophobicity of the fabric could be enhanced by increasing the PP concentration. The processing temperature also had an influence on the finishing effects, higher non-solvent temperature and lower phase separation temperature were helpful for obtaining better hydrophobicity.In order to explore the optimum processing condition, orthogonal experiment design was also conducted in this work. Results showed that the optimum condition were as follows:the initial PP concentration was30mg/ml, the temperature of2-butanone solution was130℃, and the phase separation temperature was20℃. Primary and secondary sequence of parameter was the2-butanone temperature, phase separation temperature and the initial PP concentration. The optimum treated fabric had a water contact angle of156.4°and a sliding angle of8.6°The influence of different fabric conditions on the finishing effects was also investigated. Cotton fabrics with different thread counts were treated under the above optimum processing condition and were then evaluated through CA and SA measurement. It showed that the hydrophobicity performance for loosely woven fabric were better than the closely woven ones. In addition, fabric of the same structure with cotton yarns or polyester yarns were also treated respectively under the same condition. Results showed that cotton fabrics obtained better finishing effects than polyester ones. It may be attributed to the relatively rougher surface topography for cotton fibers than the polyester ones, which may provide more locating and nucleating points for the re-aggregation of PP macromolecules during the phase separation process.Besides the wettability, other properties of the treated cotton fabrics were also tested in this work. Results showed that the wear behavior of fabrics were well kept after the superhydrophobic treatment, it was evidenced that the breaking strength of fabrics got increased, the moisture permeability, bending properties and wrinkle resistance properties kept almost unchanged, the whiteness raised slightly. The durability of the finishing effects were also observed by immersing the treated fabrics in solution of different PH for one month. It was obvious that the fabric could still display an outstanding water repellent property.In summary, the finishing method based on PP phase separation mechanism is of a promising approach to obtain superhydrophobic cotton fabrics. |
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