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Development of heat-insulating silicone compositions

Khn V.D. Mushenko

Among all variety of polymeric functional composite materials (PCFM) the silicone materials on the basis of low molecular weight rubbers: sealants and compounds should take a special place according to their universality and multifunctionality of application. In developing the above sealants and compounds it is necessary to take into account that the fine fillers included in their composition form interphase layers at the interface with the polymeric binders. One of the main requirements for composite silicone materials is the isotropy of their composition and structure. The required performance properties of the sealants and compounds depend on the right quantitative and qualitative combination of the polymeric binder and filler, their mutual compatibility and the basic initial properties. The performance properties of silicone PFCM should include primarily the optimum initial working viscosity of heterogeneous systems as well as the probable dynamics of initial viscosity change when the filled polymer base is combined with the liquid phase curing system (curing agent, "catalyst", various curing gas pedals). How The qualitative and quantitative initial composition of sealants and compounds determines the intensity of their curing process and the time of its completion with the formation of final solid or elastic complex polymer products. Proper selection of the initial composition and conditions of application depends on the presence of a number of determinative necessary properties of the fillers included in the system. They include stability of physical and mechanical properties (strength, hardness, resistance to abrasion, resistance to impact), ability to form conglomerates and agglomerates, resistance to external mechanical pressure, chemical inertness and fire resistance, good selective ability to be wet by liquid media, heat resistance, selective thermal conductivity. No less important are economic factors in the development of silicone PFCM, which should include along with relatively low cost and availability of components, their preferable domestic origin. In addition it is necessary to ensure minimal toxicity of both the initial components of sealants and compounds and minimal toxicity of their combustion products. The essential thing is the domestic origin of the fillers used as well as chemical components for their technological preparation. The most important factors in selection of fillers is their good wettability by liquid or viscous components of polymer base, physical and chemical compatibility with polymers required for complete dispersion and formation of isotropic compositions. Of no less importance is the stability of the properties in storage conditions, which can be due to both the particles' own properties and the properties of their labile agglomerates, as well as the results of chemical pretreatment of the particles, such as directional hydrophobation and mechanochemical processing. Considerable experience of our works on creation of sealants and compounds based on silicone, epoxy, polyurethane and polyester composite materials allows to realize development of materials with required technical and some selective properties. First of all it is necessary to point out development of materials with increased heat conductivity, heat insulating, heat absorbing, antistatic, electrically conductive properties. There appeared additional technical possibilities for directed modification of some properties of serially developed materials in order to change quantitative limits of some or other technological and operational characteristics. Modern and perspective methods of fillers pretreatment by means of mechanochemical activation, hydrofobization, combined milling and temperature treatment of solid mixtures of fillers with different qualitative and quantitative composition have been mastered on the production base of "Functional Materials" Ltd. In this respect, there are broader prospects for the use of such traditional fillers as silicon, titanium, zinc and iron oxides. They can be used in combination with oxides, hydroxides and oxide-hydroxides of aluminum developed and produced by LLC "Functional Materials". These are compounds of aluminum with varying degrees of dispersion, passed various stages of mechanical, thermal and mechanochemical treatment. To the mentioned classes of materials it is necessary to add also a number of the fillers, bearing such specific properties, as selective radio absorption, high and low thermal conductivity, properties of antistatic, heat conducting properties and a number of others. At development of PCFM it is necessary to carry out systematic complex selection of polymeric binder bases in their combination with plasticizers, curing systems, solvents, solvents-diluents

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