Polyurethane rubbers

The cellular materials discussed in Section 27.5 may also be considered as polyurethane rubbers, but because of their importance are treated separately. 

Properties and Applications of Cross-linked Polyurethane Rubbers... 

Some typical properties of a Vulkollan-type polyurethane cast rubber and a black-reinforced polyurethane rubber processed by conventional techniques are compared with black-reinforced natural and nitrile rubbers in Table 27.2 ... 

Urethane rubbers have found steadily increasing use for oil seals, shoe soles and heels, fork-lift truck tyres, diaphragms, chute linings and a variety of mechanical applications. Fabric coatings resistant to dry cleaning are a recent development. In many of these applications high elasticity is not an important prerequisite so that the polyurethane rubbers must be compared not only with other rubbers but also with a variety of thermoplastics. 

It is generally more convenient to use the thermoplastic polyurethane rubbers discussed in Section 27.4.4 for those applications where a cast process is not appropriate. 

The thermoplastic rubbers have properties similar to those of the cast polyurethane rubbers but, because of the absence of covalent cross-links, have rather higher values for compression set, a common problem with thermoplastic rubbers. Their main uses are for seals, bushes, convoluted bellows and bearings. 

Whereas the solid polyurethane rubbers are speciality products, polyurethane foams are widely used and well-known materials. 

Properties and applications of cross-linked polyurethane rubbers... 

Figure 25 Variation of apparent viscosity with the percent polyurethane rubber in XNBR-AU blends.

With the shear-type coupling, the elastomeric element may be clamped or bonded in place, or fitted securely to the hubs. The compression-type couplings may be fitted with projecting pins, bolts, or lugs to connect the components. Polyurethane, rubber, neoprene, or cloth and fiber materials are used in the manufacture of these elements. 

Methylenedianiline is used to make an intermediate in the manufacture of polyurethane rubber used for making automobile parts, shoe soles, rubber wheels, and insulation foam. 

Butyl Rubber and Halo-Butyl Rubber Ethylene Propylene Rubber (q) Hard Rubber (Ebonite) (h) Soft Natural Rubber (h) Neoprene (i) Nitrile Rubber Chlorosulphonated Polyethylene Polyurethane Rubber (v) Silicone Rubbers (k)... 

The elasticity of thermoplastic polyurethane rubbers (which are also known as thermoplastic urethanes or TPUs) is a function of their morphology which comprises hard and soft phases. The hard phases consist of hydrogen bonded clusters of chain segments, which are linked by flexible chain segments that make up the soft phase. The hard blocks, which are the minor phase, exist as separate domains within a continuous matrix of the majority soft phase, as shown schematically in Fig. 25.9. 

Injection moulding of silicone and polyurethane rubbers differs, because the material mixed and injected is usually liquid. 

By combining elastomeric and brittle glassy phases it is often possible to obtain improved properties over a range of temperature and frequency. However, relatively little attention has been given to fatigue in IPNs, and to energy absorption in polyurethane rubber/poly(methyl methacrylate) (PU/PMMA) systems. 

Graft polymers were obtained by mastication of a 60/40 blend of natural rubber and chlorosulphonated polyethylene (/). From 10-55% natural rubber was obtained as side chains. Grafting presumably proceeds by transfer of chlorine atoms to the rubber radicals to give grafting sites for combination with rubber radicals. Soluble linear polymers were also obtained by mastication for 50-180 min under nitrogen for a blend 50/50 of natural rubber and a polyurethane rubber (Vulcaprene A) (/). 

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