Microcellular polyurethane

ElastocelL [BASF] Microcellular polyurethane suspension components. 

Microcellular polyurethanes for shoe soling are of both the polyester and polyether types. Polyester types were developed first and owing to their generally superior mechanical properties they tend to be used in the thinner sole, high quality section of the market. Such polyester systems are usually based on quasi-prepolymers (made from part of the polyester and the MDI) and a resin blend made up of the rest of the polyester, the chain extender (usually butane diol), catalysts, surfactants and water to produce carbon dioxide to blow the foams. The use of a quasi-prepolymer enables the two... 

Parks, K.L., Beckman, E.J., 1996. Generation of microcellular polyurethane foams via polymerization in carbon dioxide. II foam formation and characterization. Polymer Engineering and Science 36, 2417-2431. 

Thermoplastic polyurethanes are designed to be processable by standard plastic machinery such as extruders and injection molding machines. Thermoplastic polyurethanes have been used in biomedical applications. They also can be used in the microcellular form where the apparent density can be reduced. Some applications include tubing, handles, automotive parts, and shoe soles and heels. 

Polyurethane rubber (PUR). Not only in the thermosets (and the thermoplastics), but also in the field of synthetic elastomers polyurethanes have found a position, namely as a softer type. It is, again, formed from two components and is, with a blowing agent, processed into a foam. Polyether mattresses belong to this category, but also microcellular structural foams, used in bumpers, head- and arm-rests in motorcars, etc. 

Low clamping pressures only are needed, and this in turn means that quite large products can be made on inexpensive plant. By varying the raw materials it is possible to produce either rigid or flexible articles, microcellular or otherwise, and (if required) to include fillers or reinforcing sections. Thermosets other than polyurethane can be used—like epoxides and polyesters (with the latter, the process is known also as resin transfer moulding ). 

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. 

Nelson (16, 39) reported a method of making polyurethane-foam composites by means of the SRIM process. Two different types of polyurethane materials were used an amine-modified polyurethane suitable for static elastomer uses and a polyurethane material with high crosslink density designed for use as a microcellular structural material. 

This book describes the chemistry, manufacture and use of the wide range of flexible polyurethane foams, from low-density open-cell upholstery foams to microcellular and reaction- injection-molded and reinforeed-reaction-injection-molded materials. The related effects of varying the raw-material chemistry and the production process and machinery on the properties and service performance of the final product are indicated. 

Polyurethane elastomer shoe soles have received wide acceptance for women s fashion shoes as well as a variety of sports footwear. The lightweight microcellular shoe soles have permitted wide styling flexibility in women s shoes. Fine details simulating wood, cork, leather, and hand-stitching can be readily reproduced. New style sports shoes incorporate multi-color and multi-density soles. Other polyurethane elastomers will find ready use in high performance applications utilizing their superior wear, corrosion and abrasion resistance properties. 

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. 

Formrez , [Witco] Adipate polyesters or polyether triok used for coatings, chain extenders, cast polyurethane elastomers, microcellular urethanes, potting compds., enctqrsulating agents, print-iiig tolls, coatings, adhesives. 

The major applications for polyurethane catalysts are in flexible and rigid foam, which account for over 80% of the catalyst consumption. Other applications are in microcellular reaction injection-molded (RIM) urethanes for automobile bumpers and a variety of noncellular end uses such as solid elastomers, coatings, and adhesives. 

Many aspects of manufacturing have been covered in Chapter 6 on RIM. However, there are some additional factors which apply to the fully solid polyurethane elastomers (the RIM materials are microcellular). 

The modern polyurethane (PU) foam sole may be regarded as evolving from these processes. Both direct and indirect processes are used. The moulding process is an application of reaction injection moulding (RIM), in which the appropriate chemical reagents are metered via a mixing chamber into the mould, where the polyurethane forms. Clarks process produces microcellular foams but, for some products, separate injections of skin and foam (two-shot process) has been adopted more recently. 

Mi, H.-Y, Sahck, M.R., Jing, X., Jacques, B.R., Crone, W.C., Peng, X.-E, Tumg, L.-S., 2013. Characterization of thermoplastic polyurethane/polylactic acid (TPU/PLA) tissue engineering scaffolds fabricated by microcellular injection molding. Materials Science and Engineering C 33 (8), 4767-4776. 

The principal advantages of RIM processing of polyurethanes and polyureas are the ability to mold large parts such as automobile fascias and body panels, motor housings, and bodies of recreational vehicles, and that the molded parts made can be lightweight. The microcellular structure of RIM parts permits densities to be quite low, while the stiffness modulus can be... 

Control of the reaction sequence in making flexible, open-cell, polyurethane foam using the one-shot process is accomplished by choosing the polyol, the surfactant, and the combination of tertiary-amine and organometallic, usually tin, catalysts. As in the previously described procedures for making urethane elastomers and microcellular products, for foams, polyols— poly(propylene oxide) polyols often containing minor amounts of ethylene oxide—are used. These polyols are selected by functionality, molecular weight, and reactivity (see Table 3). 

Chenglong, D., Cailiang, Z., Wenyi, H., Kung-Chin, C., Ly, J. L. (2013). Thermoplastic polyurethane microcellular fibers via supercritical carbon dioxide based extrusion foaming, Polym. Eng. ScL, 53(11), 2360-2369. 

Skochdopole demonstrated that the effect of free convection within cells was negligible for cells below 4 mm in diameter [1]. Consequently, thermal conductivity of a microcellular polymeric foam board consists mainly of conduction through the polymer matrix, conduction through the gas inside cells, as well as thermal radiation. To date, thermal transport in polyurethane and polystyrene foams has been researched by Biedermann [2] and Vo [3]. Thermal radiation in polymeric foams was studied by Glickman [4] and Kuhn [5]. Effusion of blowing agents... 

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