Elastomeric silicone processing

Spin casting can use plastic molds, such as silicone, to produce close tolerance, highly cost effective, limited production in a variety of materials. The process uses easily adjustable centrifugal force to inject liquid thermoset plastics into a circular disc-shaped elastomeric mold under pressure, completely and rapidly filling the mold cavities. 

The introduction of different types of reactive groups on the polydimethylsiloxane backbone enables crosslinking reactions to take place. The silicones can be applied as coatings on a variety of substrates, or as sealants. Elastomeric products such as seals, tubing, or other shaped products can be made by extrusion or molding processes. 

Elastomers Another major class of plastic ablators is elastomeric-base materials and particularly sihcones. During ablation, they thermally decompose by such processes as depolymerization, pyrolysis, and vaporization. The silicone elastomers provide low thermal conductivity, high thermal efficiency at low to moderate heat fluxes, low temperature properties, elongation of several hundred percent at failure, oxidative resistance, low density, and compatibility with other structural substrate materials. Elastomeric materials are generally limited by the amount or structural quality of the char formed during ablation, which restricts their use to hyperthermal environments of relatively low mechanical forces. 

Uses Pesticide intermediate mfg. of phenol, chloronitrobenzene, aniline, DDT, silicone resins, dyes, perfumes, polysulfone solvent carrier for methylene diisocyanate solvent for paints, pesticides, degreasing processes, pharmaceuticals heat transfer medium adhesive rubbers and adhesives primer or adhesive additive for adhering elastomeric coatings to syn. fiber fabrics coated with syn. rubber surf, coating dry cleaning intermediate for halogen synthesis in food-pkg. adhesives adjuvant for PC food-pkg. resins solvent in food-contact polysulfone rGsins... 

A PV process characterized by excellent separation efficiency nsing a membrane that comprised an elastomeric polymer matrix containing zeolite was patented by Hennepe et al. (1990). A preferred group of such elastomeric polymers are silicone rubbers, especially polysiloxane rubbers and in particular polydimethylsiloxane rubber the nitrilebutadiene rubbers (NBR) polyisobutylene, and the polyisoprene, and styrenebutadiene copolymer rubbers. Zeolites were incorporated into the membranes to make them as hydrophobic as possible. These membranes were particularly suitable for the separation of hydrocarbons, alcohols, esters, ethers, and amines from aqueous solutions containing these impurities by PV. PDMS is the most well-known membrane material for the extraction of VOC from aqueous waste stream by PV. Although it is quite permeable and selective to many VOCs in water, its selectivity can be improved further with appropriate zeolite fillers. Such improvement may be needed for polar solutes such as aroma and fermentation products, whose high value makes the PV process attractive. 

In the process of production of rubber articles a lot of trade products designated to spray the working surfaces of the molds is used - ranging from soap solutions to silicone oils. However, these separating substances are not suitable for the production of elastomeric pharmaceutical closures and toys from a soft thermoplastic elastomer [73],... 

Within solvent release type thermosetting sealants, there are Neoprene, hutadiene-styrene, chlorosulfonated polyethylene, EPDM, and silicones. Solvent release types constitute the largest variety of sealants and are composed of three parts (1) the liquid portion of the compound which is the basic non-volatile polymer/elastomeric vehicle, (2) the pigment component, and a (3) solvent or thinner component used to ease the process and to control the thickness. The sealant is cured and its required viscosity is controlled by the evaporation of solvent. 

Thermoplastic elastomers based on blends of a silicone rubber (cross-linked during processing) with block copolymer thermoplastic elastomers have also been prodnced (36,37). Other types that have been stndied (38) include graft copol5uners and elastomeric ionomers, but these have not become commercially important. 

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