Rubber silicone elastomers

Silicone elastomers, silicone elastomer rubbers and sealants... 

Yanyo, L. C. Kelley, F. N., Effect of Chain Length Distribution on the Tearing Energy of Silicone Elastomers. Rubber Chem. Technol. 1987,60, 78-88. 

Deng, Q., Hahn, J.R., Stasser, J., Preston, J.D. and Bums, G.T., Reinforcement of silicone elastomers with treated silica xerogels silica-silicone IPNs. Rubber Chem. Technol., 73(4), 647-665 (2000). 

Silicone Rubbers or Elastomers These are having high Molecular weight than the fluids. Generally they are polydimethyl siloxanes. General purpose silicone elastomers are made from polydimethyl siloxanes. 

The silicone elastomers combine the properties of rubber and silicones. They retain flexibility over 90 to 250°C temperature. 

The use of silicone elastomers for high-voltage applications (insulators and cable accessories) requires special formulations. Unusually, stringent requirements for these materials must be met.509,510 Fluorosilicone rubbers, which offer some unique combinations of properties (e.g., chemical resistance and higher temperature stability), have attracted considerable attention and have been reviewed in recent publications.511,512 It was noted that a modification of perfluoroether elastomers with silicone elastomer via hydrosilylation reaction opens the possibility of novel applications.5... 

Natural Rubber and Synthetic Polyisoprene Polybutadiene and Its Copolymers Polyisobutylene and Its Copolymers Ethylene-Propylene Copolymers and Terpolymers Polychloroprene Silicone Elastomers Fluorocarbon Elastomers Fluorosilicone Elastomers Electron Beam Processing of Liquid Systems Grafting and Other Polymer Modifications... 

Table 30 shows four typical pharmaceutical rubber formulations based on natural, halobutyl, ethylenepropylenediene (EPDM), and silicone elastomers. 

TABLE 30 Composition of Four Typical Rubbers Used as Closures for Pharmaceutical Formulations Based on Natural, Halobutyl, EPDM, and Silicone Elastomers... 

RESINS (Synthetic). A manufactured high polymer resulting from a chemical reaction between two (or more) substances, usually with heat or a catalyst. This definition includes synthetic rubbers and silicones (elastomers), but excludes modified, water soluble polymers (often called resins). Distinction should be made between a synthetic resin and a plastic the formei is the polymer itself, whereas the latter is the polymer plus such additives as niters, colorant, plasticizers etc. See also Elastomers and Plasticizers. 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

Methylphenyldimethoxysilane is used as a stabiliser (antistructuring additive) in the production of rubber compounds based on silicone elastomers and highly active fillers. Introducing up to 10% (weight) of methylphenyldimethoxysilane into a rubber mixture improves the physicochemical properties of vulcanised rubbers and helps to preserve the technological characteristics of the compounds in storage. 

All silicone elastomers have high thermal stability. When heated, they do not release toxic products and are used as main ingredients in the production of rubber compounds and heat-resistant rubbers. 

The development of silicone elastomer technology has enabled synthetic rubber plants to obtain very convenient and practical rubber compounds. 

Silicone elastomer-based rubber compounds are prepared in conventional apparatuses (closed agitators, roll mills, etc.) and consist of the following ingredients elastomer, active fillers, vulcanising agent, stabiliser, pigment additives. 

The main properties of some rubber compounds and vulcanised rubbers, as well as their applications, are given in Table 20. As seen from the table, silicone elastomer-based rubbers are designed for prolonged use in a wide range of temperatures from -50 to +250 °C, some from -70 to + 350 °C (for a short period of time). These rubbers are efficient in air, ozone and in an electric field rubbers based on IRP-1339 and IRP-1401 compounds are also efficient in case of limited air supply. They function well in high humidity and under the influence of oxidants, hot water, vapour and low pressure. They are stable in weak-acid and weak-alkali media and are nontoxic. 

Apart from high-molecular polyorganosiloxane elastomers, such rubbers are also based on low-molecular silicone elastomers with molecular weights from 25000 to 75000, especially polydimethylsiloxane elastomers SKTN. 

Low-molecular silicone elastomers can be used as a base for various rubber compositions, including sealants and compounds. 

Similarly, the coammonolysis of a mixture of dimethyldichlorosilane and vinyltrichlorosilane can yield polyvinylmethyldimethylsiloxane varnish, which has a relatively high adhesion to metals, glass and rubber based on silicone elastomers this varnish is also used in glue compositions. The coammonolysis of a mixture of dimethyldichlorosilane and phenyltrichlorosilane produces polydimethylphenylsilazane varnish. 

Rubbers based on silicone elastomers have high resistance to many solvents and oils. It is especially true for rubbers based on elastomers with up to 8% of methyl-y-trifluoropropylsiloxy-, methyl-y-cyanpropylsiloxy- or methyl-P-cyanethylsiloxy links. 

Silicone rubbers have one more very significant advantage in comparison with rubbers based on organic elastomers, and that is high dielectric characteristics. E.g., rubbers based on silicone elastomers do not conduct electric current even at 250-300 °C, whereas rubbers based on organic elastomers become conductive already at 120-150 °C. Insulating properties of silicone rubbers are preserved even at contact with water. 

Silicone elastomers do not dissolve in oils, petrol and other hydrocarbons that is why they can be successfully used in printing and as protective coatings for glass, enameled, ceramic, steel and aluminum articles. The success of silicone rubber is also due to its complete absence of corrosive effect. 

Low-molecular silicone elastomers are a basis for rubber membranes which are used in the production of containers for prolonged storage of fruit, vegetables and other kinds of food. Sealants from low-molecular silicone elastomers are more and more often used to copy articles with complex configurations. The sealant is poured to make a mold which is then filled with molding mixture. This technique is used to copy works of art, in criminalistics (to fix prints), in dentistry (to make models for dentures), etc. 

---