| Microwave method in the functional finishing of cellulose fabrics is rapidly developed and becomes a research point in recent years. As a novel heating method, microwave radiation could heat the reaction system rapidly, accelerate the reaction, improve the reaction selectivity. Microwave method is widely used in many aspects of material processing and synthesis, etc. In this paper, superhydrophobic cotton fabric was prepared by using Al2O3nanoparticles and microwave in situ finishing methods, which was different from traditional aluminum-soap method. Under microwave heating, aluminum oxide sol was prepared using inexpensive aluminum salts (NaAlO2and Al(NO3)3) instead of expensive aluminium isopropoxide as raw materials, and water instead of ethanol as solvent. The nano-alumina coating was formed in situ on the surface of fabric. After that, the nano Al-treated fabric was treated under microwave using stearic acid as hydrophobe. It is the synergistic effect of the Al2O3rough surface and hydrophobe stearic acid that induced the superhydrophobicity of fabic.In this study, Al sol was prepared using NaAlO2and Al(NO3)3·9H2O as raw materials through adjusting their molar ration or introducing nitric acid as peptizor to make the pH of mixed solution3.5-4.5. It was observed that the size of nanoparticles in the aluminum sol prepared without peptizor was relatively large with large polydispersity index (PDI). It was shown that the aluminum sol with nitric acid as peptizor was very stable. The size of nanoparticle is uniform and regular at room temperature, and did not show remarkable change (40nm～75nm) under the change of concentration of the precursor (molar ratio of NaAlO2to Al(NO3)3·9H2O was3:1). Moreover, Al content on the surface of fabric increased with the increase of Al content of sol detennined by ICP.Superhydrophobic surface has been successfully prepared first by in situ microwave-assisted nano-Al sol treatment, then the nano Al coated-fabric was modified with stearic acid in the same way. The wettability of treated fabrics was characterized by water contact angle, spray test and hydrostatic pressure test. The effect on hydrophobicity of hydrophobic agents, Al content of the nano-Al sol, stearic acid (SA) concentration, microwave reaction temperature and time was also investigated. The best processing condition was investigated.The results showed that the cotton fabric samples treated only with the nano Al sol (the molar ratio of NaAlO2to Al(NO3)·9H2O was3:1, with nitric acid as peptizor) showed a good water repellency with contact angle138.31°even in the absence of stearic acid (SA) under microwave. Furthermore, the nano Al-treated fabric samples with the treatment of stearic acid showed superhydrophobicity with contact angle145.61°. The water contact angle, hydrostatic pressure and water spray grade all increased with the increase of the Al content and stearic acid (SA) concentration. However, the water contact angle values and water spray grade decreased certainly under high stearic acid (SA) concentration. The hydrophobicity of samples also increased with the increase of the microwave reaction temperature and time. The results showed that the best processing condition was the concentration of0.50%Al sol,15mmol/L stearic acid and microwave reaction at85℃for60min for excellent hydrophobicity.In order to study the changes of fabric surface morphology before and after hydrophobic finishing under microwave, the surfaces of native cotton and hydrophobic-treated samples were investigated by field emission scanning electron microscopy (FESEM). It was showed that the surface of treated samples after nano-Al sol treated was no longer smooth as raw cotton. The granular and sheet nano-Al could be observed on the surface of fabric. The increased roughness of fabric surface has great effect to the hydrophobicity. The amorphous nano-alumina on the fabric was also confirmed by FTIR and XRD. The results also showed that no obvious strength loss of cotton fabric was observed after the in situ microwave-assisted Al/SA hydrophobic processing. The experimental results also showed that the treated cotton fabric maintained good physical and mechanical properties.In conclusion, energy was saved by fast, easy microwave-assisted processing instead of traditional processing. In addition, the combination of nano Al coating and stearic acid not only functionalized cotton fabrics with superhydrophobicity, but also is cheap and environmentally compatible. It would outlook that the proposed in situ microwave-assisted Al/SA hydrophobic processing would enlarge the application of microwave technology in the textiles and is possible to industrialize in the future. |
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