Preparation Of Durable Superhydrophobic Surface By Sol-Gel Method With Citric Acid As Crosslinking Agent

The technology of the hydrophobic textiles has a long history and a variety of hydrophobic agents was studied and applied. However, non-eco-friendly finishing agents, such as the fluorocarbon-type hydrophobic agents, are faced with serious challenges from environmental protection. As an environment-friendly method, the hydrophobic finishing of cellulose fabrics by sol-gel method is rapidly developed and become a hot research in the recent years. Nowadays, the hydrophobicity of cellulose fabrics by sol-gel is excellent. But the washing durability of the hydrophobic cellulose fabrics is unsatisfying. So the feasibility of improving the hydrophobic durability of cellulose fabrics by sol-gel method with citric acid as the crosslinking agent was preliminarily researched in the study.Cellulose fabrics with different amounts of free carboxyl group were prepared by changing the amount of citric acid. Silica sol was prepared with hydrolysis of teraethoxyorthosilicae (TEOS) and hydrochloric acid (HCl) as the catalyst. Superhydrophobic cellulose surfaces were obtained with the hydrophobic finishing by sol-gel method. To study the influence of the amount of free carboxyl group on the durability of superhydrophobic surface, static water contact angle, spray test, hydrostatic pressure and Si concentratation were measured. All results showed that good durable hydrophobicity on cellulose fabrics was obtained by introduce of citric acid. The more the free carboxyl groups in the modified cellulose fabrics, the better the durability of hydrophobicity. Scanning electron microscopy (SEM) was used to characterize the surface morphology changes after certain washing times. It is found that no large break of silica coatings appeared after 30 times washing by SEM images, which indicated that citric acid could be used as the crosslinking agent in the hydrophobic finishing of cellulose fabric by sol-gel method.In order to simplify the technology and reduce the cost, stable, controllable and uniform silica sols were prepared using water glass as silicon source and citric acid as the catalyst. The particle size and the gelation time of sol during ageing were tested to study the influence of concentration and electrolyte on the formation and performance of sol. FTIR and CP/MAS 13C NMR were used to characterize the (citric acid-water glass) gel structure. The results showed that with the increase of citric acid in the silica sol (2