Microcellular elastomers

Elastomers come next in order of quantity sold worldwide. Like the previous categories, elastomers cover an extremely broad range of material types and application areas. They include cast elastomers, spray and rotational casting elastomers, thermoplastic elastomers, microcellular elastomers, gels, and elastomeric fibers. Each type is covered separately.13d> 14... 

Methyl-l,10-undecadiene, ADMET polymerization of, 442 Michaelis-Menten enzymatic kinetics, 84 Microbial hydrolysis, 43 Microcellular elastomers, 204-205 Microphase-separated block copolymers, 6-7... 

The production of polyurethane involves the controlled polymerization of an isocyanate, a long-chain-backbone polyol and a shorter-chain extender or cross-linker. The reaction rates can be controlled through the use of specific catalyst compounds, well known in the industry, to provide sufficient time to pour or otherwise transfer the mix and to cure the polymer sufficiently to allow handling of the freshly demolded part. The use of blowing agents allows the formation of a definite cellular core (thus the term microcellular elastomer ) as well as a non-porous skin, producing an integral sandwich-type cross section. 

Foamed urethane elastomers are also called microcellular elastomers. The densities are in the range of about 20 to 60 pcf (320 to 960 kg/m. Integral-skin foams having a density of ca. 700 to 1,000 kg/m are sometimes referred to as microcellular elastomers. 

Preparation of Microcellular Foams. The major polyols for microcellular elastomers include aliphatic polyester diols having a molecular weight of about 1,000 to 3,000, and poly-epsilon-caprolactones. Poly(oxytetramethylene) glycols (PTMEG) can also be used. The polyisocyanates to be used for microcellular elastomers are TDI-prepolymers and liquid MDI, i.e., carbodiimide-modified MDI or urethane-modified MDI. Low-molecular-weight, active-hydrogen compounds such as chain extenders (difunctional compounds) and... 

The blowing agent for microcellular elastomers is water. The amount of water should be accurate, and its accuracy can be obtained by a water-containing solution, such as liquid sodium sulfonate of vegetable oils containing a small amount of water. The catalysts to be used are those used in urethane foams, e.g., tertiary amines, and tin catalysts. The above ingredients are mixed and poured into a hot mold and cured in a defined period of time. After demolding, a post cure is applied to complete the polymer-formation reactions. 

Applications of Microcelluiar Elastomers. Microcellular elastomers are widely used for various shock absorbing materials in automotive applications such as bumper cores, shock-absorbing elements in vehicle-suspension elements, machines, electrical equipment, cameras, precision machines, shoe soles and heels, and sports shoes. 

The footwear industry uses polyurethane as microcellular elastomer for shoe soles thermoplastic elastomers for ski boots, coatings for shoe uppers, and adhesives. The microcellular elastomer shoe soles have been used for over 10 years. The polyurethane shoe sole offers lightweight and flexibility in styling. Fine detail simulating wood, cork, leather, and handstitching can be readily reproduced. New style sport shoes have been developed to incorporate multi-colors and multi-density soles. As a result, these shoe soles are used in women s high-fashion shoes, work shoes, and a variety of leisure and sport shoes. The current demand for polyurethane shoe soles is for continued steady growth and demand. There has been a continued shift of the shoe sole market to the Middle East and Eastern European areas. 

Pure MDI, having two -NCO groups/mol, is commercialised mainly as 4,4" isomers, but it is possible to use 2,4 and 2,2 isomers. The main applications of pure MDI (especially the 4,4" isomer) are polyurethane elastomers, microcellular elastomers and some flexible foams. The structures of pure MDI isomers are presented in Figure 2.2. 

Quasiprepolymers are frequently used to transform a solid isocyanate, (e.g., pure MDI), into a liquid, and are used in flexible PU foams, in microcellular elastomers and in other PU applications. 

Applications cold moulded high resilience flexible PU foams, semiflexible and integral skin PU foams, microcellular elastomers (shoe soles) ... 

Application PU elastomers, microcellular elastomers (shoe soles) ... 

The polyether polyols based exclusively on ACN are commercialised because of their high glass transition temperature (T ) of the polyacrylonitrile solid fraction. However, they are not used for production of slabstock foams, but for PU elastomers (microcellular elastomers for shoe soles) and integral skin foams. 

AA-TMP/glycols (branched) Flexible foams, microcellular elastomers, coatings... 

Suprasec VM021 Suprasec VMOSl Suprasec VMlO 201-21 Modified, liquid pure MDI. High performance elastomers. Microcellular elastomers. Shoe-soling. Flexible coatings. RIM and RRIM. Cast elastomers. 

Solid PUR elastomers are useful engineering materials, as seals, bushes, gaiters, etc., with extraordinary abrasion resistance. Exterior car body parts such as bumper skins and wings are actually microcellular elastomers, with very high density foam. 

RIM elastomers are also termed microcellular elastomers. The molded parts produced by RIM processing consist of a microcellular core encapsulated by an integral skin of higher density elastomer of the same chemical composition (24). 

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