Polyurethanes application areas

Polyurethanes were discovered in 1937 by Otto Baryer and his co-workers at the laboratory of LG. Farbenindustrie in Leverkusen (Ulrich, 1982). Since their discovery polyurethanes have attained substantial commercial importance. The development of polyurethane technology was delayed by the Second World War. With the shortage of natural rubber during the war their wide versatility enabled them to be developed in a number of application areas. It became clear that urethanes offered greater latitude, and many new products were created. 

Table 4.1 Principal properties, products and application areas of polyurethanes...

Significantly improved UV light stability is found with polymeric substrates stabilized with bis(2,2,6,6-tetramethyl-piperidinyl-4) sebacate, an example of hindered-amine class light stabilizers, compared with those stabilized with conventional light stabilizers. Application areas covered include polyolefin fibers, films and molded sections, polyurethane, and styrenics. Synergistic performance with o-hydroxyphenyl benzotriazoles in these polymers is apparent. 

Methylene chloride is a volatile, colorless, nonflammable liquid. It is slightly soluble in water and miscible with many other solvents, such as acetone, chloroform, carbon tetrachloride, and alcohol. Under speciflc conditions it may burn. Its commercial formulations for paint stripping are particularly flammable. Methylene chloride is a widely used solvent where quick drying (i.e., high volatility) is required. Such application areas include adhesives, cellulose acetate flber production, blowing of polyurethane foams, and metal and textile treatment. It dissolves oils, fats, waxes, many plastics, bitumen, and rubber. This property is used in paint stripper formulations. It is used as an aerosol solvent, and for extraction operations in the pharmaceutical industry. It was previously used in fire-extinguishing products. ... 

Fillers are used in adhesives to improve physical properties, to control rheology, and to lower cost. The most common polyurethane fillers are calcium carbonate, talc, silica, clay, and carbon black. A more rigorous treatment of this subject can be found in Katz and Milewski [47]. Fumed silicas and carbon blacks are used primarily as thixotropes in application areas that require a nonsagging bead. Calcium carbonates, clays, and talcs are used to improve the economics of an adhesive formulation. A major concern using fillers with urethane prepolymers is the moisture content associated with the fillers. Fillers typically must be dried prior to use with urethane prepolymers or isocyanates. Hygroscopic fillers should be avoided, as moisture introduced by the filler can lead to poor shelf stability of the finished product. 

Polyurethane contributes more than 5% of the total world consumption of polymers. Although the greatest consumption of urethane products is still in the foam sector, the trend in polyurethane applications is increasing in the areas of surface coatings, adhesives, electrical insulating lacquer, packaging, footwear, furniture assembly, the automotive industry, medical products, composites and microelectronics. 

Halogenated Aliphatic Phosphates and Phosphonates. The principal use of these additives is in polyurethane foams broader reviews of this important flame retardant application area have been published (70,71). 

Polyurethane adhesives are produced in many grades such as one-component, two-component, dispersion and solvent based, and hot melted for use in different application areas. PUR adhesives have a good adhesion to wood, metal and plastics and find, therefore, end use in many industrial applications. Some applications outlined by sector are presented in this section. 

Since it possesses good properties of both PVC plastics and polyurethane elastomers, it has been used in those areas where PVC and polyurethane have traditionally played dominant roles. For example, it is a very promising replacement for flexible PVC used for medical purposes and in the food industry [I6,l7], because it essentially eliminates the concern regarding plasticizer contamination. It has been used in combination with the copolymer of butadiene and acrylonitrile (NBR) to make the abrasion-resistant aprons and rolls used on textile machines [18]. A PVC/TPU/ABS blend serves as a substitute for leather [19]. This could have a tremendous impact on the shoe industry. It has also been found to have an application as a building coating [20,21]. This trend will certainly grow and more applications will be found. This in turn should bring new developments in the material itself. 

A big increase in the number of patent applications on this topic is apparent. The area has been reviewed,177-178 and it is clear that the alkoxycyclophosphazenes find the widest range of applications, particularly in improving the flame resistance of rayon179-188 and polyurethanes.189-191 Phenoxy-substituted phosphazenes have attracted less attention.192-194 Oligomeric chlorocyclophosphazenes also have... 

In this first chapter, we seek to reinforce this perspective by including a series of case studies. We will propose problems in various areas of investigation and include specific examples of environmental remediation and advanced medical research issues addressed by polyurethanes in one form or another. While each example deals with a specific discipline, it is important to recognize that we have chosen all the examples in this chapter as surrogates with much broader applicabilities beyond the specific fields cited in the examples. 

Once a polymer is fuUy saturated, the physical tests described above can be conducted with confidence. Naturally, minimizing the evaporation of water should be considered. The one exception in this new category of testing is flow of water through the foam. This is not covered in the standard but will be very important for some applications, particularly in environmental remediation. If the intent is to build a biofilter or a continuous flow enzyme reactor, we must know the hydrodynamic properties of the materials we produce. Since polyurethanes are rarely used in these environments, the flow of water even through a reticulated foam is not described by the manufacturers. Furthermore, if we are to make composites of reticulated foams, the amount of polymer grafted to the surface will have a dominating effect on the flow of water. In a later chapter, we will describe our work in this area. 

Entrapping an enzyme within a gel is a common technique, but washout and membrane diffusion are important issues. The most effective system would be an enzyme that attaches covalently to a flow-through medium of high surface area to create a system that would represent an optimal balance of both chemical and engineering attributes. This optimal balance is the basis of several applications for polyurethane and its composites. 

The synthesis of optically active polymers is an important area in macromolecular science, as they have a wide variety of potential applications, including the preparation of CSPs [31-37]. Many of the optically active polymers with or without binding to silica gel were used as CSPs and commercialized [38]. These synthetic polymers are classified into three groups according to the methods of polymerization (1) addition polymers, including vinyl, aldehyde, isocyanide, and acetylene polymers, (2) condensation polymers consisting of polyamides and polyurethanes, and (3) cross-linked gels (template polymerization). The art of the chiral resolution on these polymer-based CSPs is described herein. 

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