Cellular elastomer

Foam Production This is important in froth-flotation separations in the manufac ture of cellular elastomers, plastics, and glass and in certain special apphcations (e.g., food products, fire extinguishers). Unwanted foam can occur in process columns, in agitated vessels, and in reactors in which a gaseous product is formed it must be avoided, destroyed, or controlled. Berkman and Egloff (Emulsions and Foams, Reinhold, New York, 1941, pp. 112-152) have mentioned that foam is produced only in systems possessing the proper combination of interfacial tension, viscosity, volatihty, and concentration of solute or suspended solids. From the standpoint of gas comminution, foam production requires the creation of small biibbles in a hquid capable of sustaining foam. 

The standard is primarily or entirely concerned with cellular plastics or cellular elastomers. 

For cellular elastomers and cellular plastics, rigid or flexible, the back and sides of the test specimen must be wrapped with aluminum foil and asbestos cement board used as backing. Other special requirements for cellular materials are also in effect. 

Included in the horizontal tests is the horizontal burn (HB) test. This takes place on solid polymers such as plastics. Cellular elastomers are evaluated according to the horizontal foam (HE) test. Horizontal burn foam (HBF) is the minimal rating assigned in this test, followed by horizontal foam-2 (HF-2) and horizontal foam-1 (HF-1) (the most stringent). 

ASTM Cl 166, Standard Test Method for Flame Propagation of Dense and Cellular Elastomers Gaskets and Accessories, 2011. 

A unique process for chemical stabilization of a cellular elastomer upon extrusion has been shown for ethylene-propylene rubber the expanded rubber obtained by extrusion is exposed to high energy radiation to cross-fink or vulcanize the rubber and give dimensional stability (113). EPDM is also made continuously through extrusion and a combination of hot air and microwaves or radio frequency waves, which both activate the blow and accelerate the cure. 

From Section 3.3, it was shown there are a large number of monomers and oligomers available for polyurethanes. It is often said that if cost was not of concern, then urethane-based polymers could be tailored to replace most polymers for applications that did not demand too high a service temperature [28]. Polyurethanes, besides adhesives and sealants applications, can be found as foams (rigid, flexible, micro-cellular), elastomers, and encapsulants which differ slightly in raw materials. However, processing parameters and additives make feasible a diverse synthesis of this material. 

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