Waterproofing silicones

Solid, rubbery silicones likewise retain their plasticity at low temperatures and are resistant to many forms of chemical attack they are now incorporated in paints for resisting damp and for waterproofing. Silicones are also used in moulds to avoid sticking of the casting to the mould. 

Table 19. Properties of waterproofing silicone oligomers and conditions for their application...

An introduction of small amounts of ethers of orthotitanium acid into solutions or emulsions of waterproofing silicone liquids increases water-repellent properties of these liquids. 

WATER - WATERPROOFING AND WATER/OIL REPELLENCY] (Vol 25) -ethoxysilanes for [SILICON COMPOUNDS - SILICON ESTERS] (Vol 22)... 

Early waterproofing treatments consisted of coatings of a continuous layer impenetrable by water. Later water-repellent fabrics permitted air and moisture passage to improve the comfort of the wearer. Aluminum and zirconium salts of fatty acids, silicone polymers, and perfluoro compounds are applied to synthetic as well as natural fibers. An increase in the contact angle of water on the surface of the fiber results in an increase in water repellency. Hydrophobic fibers exhibit higher contact angles than cellulosics but may still require a finish (142). 

Exemplary water-repellent treatments for masonry surfaces include metal stearates, oils, waxes, acrylates (both polymers and monomers), silicones (solvent-based and emulsion), siliconates, silanes and, fluorochemicals. In contrast, to waterproofing coatings, water-repellent coatings, because they are permeable to water vapor, do not trap moisture and, therefore they can reduce spalling. In addition most water-repellent coatings do not alter the appearance of a porous masonry. 

The patent of Fujiwara et al (Ref 32) suggests that a silicone oil mixt be used as a waterproof barrier for underwater blasting using a liq expl. 

Capillary rise is responsible for water being drawn into a sponge or a cloth. When the cloth is coated with a waterproofing material, such as silicone, the adhesive forces are reduced, the contact angle is greater than 90°, and there is no longer a tendency for water to be drawn into the cloth. 

Similarly to triacetoxymethylsilane, acetylation of chlorosilanes with metal acetates can also yield tetraacetoxysilane and other al-kyl(aryl)acetoxysilanes. The physicochemical properties of important acy-loxyorganosilanes are given in Table 13. The practical value of acetoxysi-lanes is that their hydrolysis, unlike the hydrolysis of organochlorosilanes, forms weak acetic acid, rather than hydrogen chloride. That is why acetox-ysilanes can be used to waterproof various materials (textiles, paper, etc.). Alkyl(aryl)acetoxysilanes are also used to obtain some silicone varnishes and as hardeners for low-molecular silicone elastomers. 

Many silicone compounds have water-repellent (waterproofing) properties. Usually materials are waterproofed with silicone oligomers with various reactive groups, which interact with the treated surface chemically or physically. Effective waterproofers are silicone oligomers with =Si-I I, =Si-OH or =Si-Ona groups. They differ in their chemical composition and application. 

In order to describe the reactions of waterproofing materials with alkyl-hydridesiloxanes, let us consider the interaction of the =Si-H bond with different functional groups. If a negative ligand is introduced, the silicon atom with its larger volume receives a positive charge due to polarisation,... 

Considering the physical aspect of waterproofing, we should note that all particles of the waterproofed material that have been in touch with the waterproofing agent are coated with a very thin film of silicon oligomer. This is what makes a product waterproof. The size of pores and particles, the appearance and texture of the surfaces of the material remain virtually the same. 

Waterproofing liquids Protecting various materials and articles from the destructive influence of water seems one of the most important uses for silicone liquids however, waterproofing should be achieved with liquids which do not impair other characteristics of the material. 

E.g., inorganic materials (ceramics, glass, porcelain) can be waterproofed with easily hydrolysed alkylchlorosilanes (methyltrichlorosilane, dimethyldichlorosilane, ethyltrichlorosilane, diethyldichlorosilane). Metals and porous materials (paper, leather, textile, plaster, cement, gypsum, etc.) should not be waterproofed with alkylchlorosilanes, because they release hydrogen chloride, which destroys these materials. Alkylchlorosilanes can be successfully replaced with silicone oligomers with aminogroups or hydrogen atoms in the molecule. 

The addition of 0.02% of an aqueous emulsion of silicone liquid into sand fibre slate reduces its water absorption by two and noticeably increases its cold resistance. Silicone liquids can be also put on finished constructions in the form of a 5% aqueous solution, which penetrates to the depth of 3-6 mm and after drying forms a durable waterproof surface for 5-10 years. This treatment can be used on various works of art, famous architectural buildings, etc. Plastered facades can also be waterproofed with good results. Treated plaster does not absorb rain drops on the other hand, common plaster completely absorbs all rain drops after 30 seconds. 

Water sharply decreases the durability of paper and can destroy it altogether. This is how valuable manuscripts, books, papers, drawings are sometimes lost. If manuscript pages or a drawing are impregnated with silicone liquids, the image will not be erasable either with an eraser or with water. After waterproofing, even filter paper does not absorb water or aqueous solutions. 

Leather can also be waterproofed. Treated with silicone compounds, leather is very resistant to water and is not subject to rot, mildew, etc. Waterproof leather is used to manufacture waterproof shoes, clothes, sports goods. 

Waterproofing is also used for sports equipment and fishing gear. Glass fibre waterproofed with silicone liquids is used to manufacture floats, buoys, etc. 

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