| With the development of society and human progress, there're more and more demands in multi-functional textiles. Water-repellent textiles, because of their properties such as anti-contamination, antisticking and self-cleaning, are widely used in medical workers'clothes, outdoor sports fields and decoration, etc. Various studies have been reported for preparing water-repellent textiles by sol-gel process. However, the application of traditional silica alcosols process is under restrictions due to the safety issue of alcohol. Therefore, water-repellent cotton fabrics were prepared via silica hydrosol process using surfactant for emulsification in this study.In this experiment, water-repellent cotton fabrics were successfully obtained by two different finishing processes. Firstly, silica hydrosols were prepared via the hydrolysis and condensation of methyltrimethoxysilane (MTMOS) with the solvent of distilled water and the anionic surfactant sodium dodecyl benzenesulfonate (SDBS) in the presence of the base catalyst. Non-fluorinated hydrophobic cotton fabrics with silica particles could be obtained firstly by dip-coating the silica hydrosols to obtain rough surface, and then immersing the hydrolyzed alkyltrialkoxysilanes with different structures and concentrations for surface modification. Silica hydrosols with different sizes and polydispersity indexes (PDI) were prepared by controlling the experiment conditions. The effects of the amount of ammonia, precursor and water, surfactant concentration, experiment temperature and different structures and concentrations of the alkyltrialkoxysilanes on the water-repellent property were discussed in this paper. The results showed that when the concentration of hexadecyltrimethoxysilane (HDTMS) was 3wt.%, the water contact angle (WCA) and water sliding angle (WSA) of the treated plain weave cotton fabrics were 145.9°and 14°, and the WCA and WSA of the treated twill cotton fabrics were 151.9°and 13°, achieving superhydrophobicity. However, the treated cotton fabrics were deficient in resistance to surface wetting and durability.Secondly, a one-step coating to obtain water-repellent cotton fabrics was presented in order to simplify the finishing technology. Based on the two-step process, silica hydrosols were modified by adding alkyltrialkoxysilanes and then dip-coated onto cotton fabrics. The influence of ammonia amount, surfactant concentration, reaction time, fabric structure and the alkyltrialkoxysilanes with different structures and concentrations on the water-repellent property were discussed. After being treated by the modified silica hydrosol adding 2wt.%HDTMS, the plain weave cotton fabrics exhibited good hydrophobicity. The water contact angle and water sliding angle were 146.3°and 11°, and the spray rating was 90. Meanwhile, superhydrophobic twill cotton fabrics with a water contact angle of 151.9°and a water shedding angle of 13°were successfully obtained. Moreover, the spray rating of twill fabrics achieved 100, showing excellent superhydrophobicity.The surface morphology of treated cotton fabrics were characterized by scanning electron microscopy (SEM), field-emission scanning electron microscopy (FESEM) and atomic force microscope (AFM). The results showed that the modified silica nanoparticles had been coated onto the cotton fiber surface, resulting in a certain surface roughness. The Si element was detected on the treated cotton fabrics by X-ray photoelectron spectroscopy (XPS). In addtion, physical properties of the treated fabrics showed slight change except the permeability, which could meet the application requirements. By comparing the two different processes, it was found that the washing resistance of the cotton fabrics treated by one-step process was improved but still insufficient.Finally, in order to improve practical performance of treated cotton fabrics, especially their washability, the modified silica hydrosols were optimized by adding tetraethyl orthosilicate (TEOS). The effects of the type of silane coupling agent and the adding dosage on durable washing properties were investigated. Testing result showed that when 2g TEOS was added to the modified silica hydrosol, the corresponding treated twill fabrics had a much better durability with a spray rating of 75 after 20 washing cycles. |
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