Preparation Of Silica Sol Based On Water Glass And Its Applications On Functional Finishing Of Textiles

With the gradual increase of living standard, people put forward higher and higher demands for textiles. Textiles are required for not only keeping warm and beautifying body, but also having specific functions such as water and oil repellent, antistatic, wash and wear, antimicrobial and flame retardant. Functionalized fabrics have been applied to home textiles, environment and health care fabrics, decorative and industrial fabrics, fields of national defence and top science and so on. Functionalized textiles can be achieved by functionalization of common textiles. However, noneco-friendly finishing agents, such as fluorocarbons for water and oil finishing and compounds containing halogen for flame retardant finishing are challenging by rules of environment protection. Hence, environment-friendly methods to functionalization of textiles are the trends of the times.Sol-gel process starts with metal inorganic compounds or alkoxides and involves the transition of a system from a liquid sol into a solid gel phase, finally results in very fine particles of oxide. A transparent gel coating can be formed on the textile by sol-gel method. The chemical and physical modification of such coatings allows a wide range in the variation of surface properties of textile. Thus, sol-gel process with safety and versatility is a novel avenue to functional finishing of textiles.Self-assembled monolayers (SAMs) technology has been quickly developed a new method to prepare organic layers since the 1980s. SAMs are ordered molecular assemblies formed by a spontaneous chemical adsorption between head-groups of an active surfactant and substrate surfaces. Properties of SAMs can be in flexible control by changing tail groups of the constituent molecules. SAMs technology provides a new method for modification of gel coatings on the textiles.Super-hydrophobic surfaces with a water contact angle higher than 150°have attracted great attention because of their importance in industrial applications. Super-hydrophobic finishing of cotton fabrics has been investigated using water glass as starting materials and alkylalkoxysilanes as modifiers by sol-gel method and self-assembly process in this study.The preparation of nano-silica hydrosol based on water glass was studied firstly in the paper. The research results showed that stable, controllable and uniform silica hydrosols could be prepared using water glass as silicon source in the condition of hydrochloric acid catalyst. In the pH range from 10 to 11, the lower the concentration of water glass and the higher the pH of the system were, the better the stability of sols was. At the same time, particles size augmented with the decrease of pH and increase of concentration of water glass. Particles size and viscosity became big when time of storage was prolonged, resulting in a faster trend of gelation.The effect of sol treatment on the structure and surface properties of cotton fabrics was investigated by SEM, AFM, XRD, XPS, BET and FTIR-ATR. The experimental results indicated that the surface of cotton became rough after treatment with silica sol. The chemical structure and crystal structure of the cotton didn’t be changed except for a slight decrease in crystallinity when cotton was treated with sol. The research results further showed that BET surface area and wettability enhanced after treatment. The bond between silica coating and cotton fiber was not chemical bonded but mainly physical adsorption. In addition, the whiteness, strength and handing of cotton almost remained the same.Cotton showed good hydrophobicity after treatment with silica sol based on water glass and hydrolyzed alkylsilanes. The water contact angle of the treated cotton increased with the increase of concentration of alkylsilanes and alkyl length in alkylsilanes. Best hydrophobic properties could be achieved when concentration of alkylsilanes was up to 3%. Alkylsilanes with long alkyl such as hexadecyltrimethoxysilane and octadecyltriethoxysilane could endue cotton with superhydrophobic property. The treated cotton with hydrophibicity showed good environmental stability. Moreover, the treatment has no side-effects on physical and mechanical character of cotton. It could be arrived at the conclusion that low surface free energy and proper surface roughness were two key factors to prepare superhydrophobic surfaces. Rough surface with nano-micropore was formed by sol-gel process when the cotton was treated with silica sol prepared from water glass. The hydration of alkylsilane to form alkylsilanol followed by the formation of chemical bonds between the alkylsilanol and surface hydroxyl groups. Meanwhile, alkylsilanol polymerize and dehydrate each other at horizontal direction. Finally, two-dimensional and well-ordered film was formed by self-assembly process on the silica coating surface. The cooperation of self-assembling of hydrophobic groups and the rough surface with nano-micropore by sol-gel coating converted the cotton surface from hydrophilic to superhydrophobic.Good durability to laundering is a particular requirement for functionalized textiles. To improve the durability, two methods, namely, changing general process of sol-gel and adding the cross-linking agent 3-Glycidyloxypropyltrimethoxysilane (GPTMS) to water glass solution are used in the study. Compared with the technique of dip-padding silica hydrosol directly on cotton, such technique as dip-padding water glass solution on the cotton and drying, and then spraying Atkins-Pantin buffer solution with pH from 8.0 to 9.4 on the treated cotton could enhance the durability to laundering. The water repellent rating could be improved from 50 to 70 even after 30 washing cycles. On the other hand, GPTMS was added to water glass solution to modify silica sol. The results showed that the durability could be obviously enhanced when the cotton was treated with modified sol containing 2% GPTMS. The water repellency rating could remain 70 after 50 washes. In addition, the self-assembly process at different temperature and time was also investigated. The results indicated that the time has more important effect on durability more temperature in forming superhydrophobic monolayer by self-assembly. Self-assembly time of 240min was proper and the temperature could be performed at room temperature.As a whole, good hydrophobic properties could be achieved after the cotton was treated with nano-silica hydrosol based on water glass and alkylalkoxysilanes with long alkyl. Such hydrophobic properties surpassed the result that cotton was treated with hydrophobic modification sol prepared from tetraethoxysilane (TEOS) and reached the similar effect obtained by general modifiers containing fluorine. However, energy was saved and cost was reduced by cheap water glass in place of expensive TEOS and water in place of ethanol in course of preparing silica sol. Thus, it will enlarge the application of sol-gel technology in the textiles and is possible to industrialize. In addition, non-fluorinated alkylsilane as modifier is economical and safe, is also friendly to environment, which is in accord with demands of green chemistry.