Polyurethane materials

A full account of basic polyurethane science will be found in PST 3. The process used is reaction injection moulding, and in the next section we shall see how the chemistry given in PST 3 is adapted to the process for the manufacture of shoe soles. 

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Polyurethanes as Biomaterials. Much of the progress in cardiovascular devices can be attributed to advances in preparing biostable polyurethanes. Biostable polycarbonate-based polyurethane materials such as Corethane (9) and ChronoFlex (10) offer far-reaching capabiUties to cardiovascular products. These and other polyurethane materials offer significant advantages for important long-term products, such as implantable ports, hemodialysis, and peripheral catheters pacemaker interfaces and leads and vascular grafts. 

The advent of newer polyurethane materials is expected to lead to a new generation of cardiovascular devices. The characteristics of polyurethanes, combined with newer manufacturing techniques, should translate into direct medical benefits for the physician, the hospital, and the patient. This field offers exciting growth opportunities. 

Thermoplastic polyester elastomers such as the Du Pont product Hytrel were developed later than the polyurethane materials, being first introduced in 1972. They have similar characteristics to the polyurethanes but there is an upward shift in the hardness range (i.e. the softest grades are not so soft, but the hardest grades are harder than the corresponding extreme grades in the polyurethanes). 

Polyurethane materials are extremely versatile in that it is possible to produce a large variety of structures which range in properties from linear and flexible to crosslinked and rigid. The crosslinked PURs are thermosets, which are insoluble and infusible and therefore cannot be reprocessed by extrusion without suffering extensive thermal degradation. At present, the main sources of recyclable waste are flexible PUR foams and automobile waste. Waste and scraps of these materials may consist of 15-25% by weight of total PUR foam production. 

Report 15 Polyurethane, Materials, Processing and Applications, G. Woods, Consultant. 

How does the length of the prepolymer units affect the physical properties of a polyurethane material ... 

Macaione, D.P., "Characterization of FP100 and FP102 Polyester and Polyurethane Materials," 1984, Army Materials Technology Laboratory, Watertown, MA, Technical Report AMMRC TR 84-15. 

Uses. Cross-linking agent (hardener) in the production of polyurethane materials such as car paints, dental materials, and contact lenses... 

Hexamethylene diisocyanate is a highly reactive synthetic chemical that is widely used in the production of polyurethane materials. There is no natural somee of HDI. All of the potential exposures to this compound are associated with the production, handling, use, and disposal of HDI and HDI-containing products or materials. Exposures to HDI are often associated with exposures to its prepolymers, especially to a trimeric biinetic prepolymer of HDI (HDI-BT) (see Figure 5-Ia), whieh is widely used as a hardener in automobile and airplane paints, and whieh typieally contains 0.5-1% unreacted HDI (Alexandersson et al. 1987 Hulse 1984 Karol and Hauth 1982). There is evidence that diisocyanate prepolymers may induce asthma at the same or greater frequency as the monomers (Seguin et al. 1987) therefore, there is a need to assess the potential for human exposme to prepolymeric HDI as well as monomeric HDI. Except for limited data on occupational exposures, no information was foimd in the available literature related to the potential for human exposure to prepolymers of HDI. 

Estane". Trademark of B.F. Goodrich Chemical Co, Cleveland,Ohio for a thermoplastic, polyurethane material, suitable for wire and cable jacketing, fuel hose and tanks, belting etc... 

A promising recent approach for understanding the biologic effects of biomaterials is the use of modern proteomics approaches. Such techniques have been used for the purpose of measuring protein expression profiles of macrophages (cultured on different biomaterials) to learn more about biocompatibility. Proteomics techniques were able to demonstrate that different types of polyurethane materials led to different intracellular and structural protein expression profiles.73... 

Aniline (C6H5NH2) is made by nitration of benzene to nitrobenzene, followed by hydrogenation over a Cu/Si02 catalyst. The major use of aniline is in making diisocyanates, which are used in producing polyurethane materials (e.g., for home insulation). 

Marchsan and Morran (2002) found that flavor descriptions varied between chlorinated and nonchlorinated water in contact with PE and PP with stronger tastes frequently found in chlorinated samples. "Plas-tic/rubber" terms were used for chlorinated and nonchlorinated waters stored in PP and PE as well as in nonchlorinated waters from acryloni-trile/butadience/styrene (ABS). "Plastic/chemical" descriptors were used for chlorinated and nonchlorinated waters in PP and PE and polyurea materials, and in ABS materials for chlorinated waters only. Polyurethane materials contributed chemical tastes to chlorinated waters and medicinal flavors to nonchlorinated water. The "chemical" term also was applied to chlorinated water stored in PP, PE, and ABS and nonchlorinated water stored in ABS. "Medicinal" also was used to describe both nonchlorinated and chlorinated waters stored in PP. 

Motor Cycling. One- or two-piece protective suits normally are made from fabric-supported flexible vinyl or from polyurethane materials. A typical garment would be sewn but with welds over the seams to ensure that it is waterproof. With polyurethane, welding alone often is quite satisfactory. In some parts of the garments, patches are over-welded as re-inforcement. 

Latex-free gloves are often made of polyurethane, which cause fewer allergic reactions. These polyurethane materials can be used with oil- or water-based creams and ointments, and they deteriorate less in storage. 

NMP solvent and low acid contents. The liquid polyols thus prepared and characterized were then amenable for direct use in bulk polymerizations with MDI to form polyurethane materials. 

Polyurethane, Materials, Processing and Applications, G. Woods, Consultant. Polyetheretherketone, D.J. Kemmish, ICI, Wilton. Extrusion, G.M. Gale, Rapra Technology Ltd. 

S. S. Kelley, Incorporation of lignin copolymers into polyurethane materials, Ph.D. thesis, Virginia Polytech. Inst. State Univ., 1987, Univ. Microfilms Int., DA8814587. 

All polyurethane materials used in this study were either in the form of extruded tubes (Tygothane, Superthane, Pellethane) or as films cast on clean glass from reagent grade dimethylacetamide (DMAC). Only the luminal surfaces of the tubes and the glassfacing sides of the cast films were observed by ESCA. 

Using model compounds, the surface composition of polyurethane materials of unknown con osition can be identified. Large differences in surface structure are observed for polyurethanes. Also, the surface structure is sensitive to extraction and cleaning procedures. Some of these changes may be related to processing additives in the commercial grade polyurethanes used or to low molecular weight polyurethanes. Future experiments will look at carefully synthesized polyetherurethanes of known composition to relate bulk and surface structure. Also, extracts will be further analyzed by ESCA, GPC and IR to determine their structure. 

A polishing pad has a significant impact on the performance of the CMP process. It transports the slurry to the pad-wafer interface, impacts the polishing nonuniformity, and affects the global wafer and device planarity. Pads may consist of thin porous closed cell [28], open cell [29], or noncell [30] polyurethane material. The properties of polishing pad can be studied in detail... 

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. 

Toluene diisocyanate (TDI) is commonly used as the 2,4 and 2,6 isomers. It is used as a chemical intermediate in the production of polyurethane materials including foams, coatings and elastomers, as a cross-linking agent for nylon-6, and as a hardener in polyurethane adhesives and finishes. Polyurethane elastomers made from TDI are used in coated fabrics and clay-pipe seals. Polyurethane coatings made from TDI are used in floor finishes, wood finishes and sealers, and in coatings for aircraft, tank trucks, truck trailers, and truck fleets. 

Tables VII and VIII sumnarize present and future RIM engineering plastic developments. This is an emerging area for RIM processable materials part of which will be made possible by recent equipment developments such as hot RIM. Polyurethane materials which now exist in this hard segment range are plastics...

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