Applications polyurethane rubbers

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

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. 

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

MAJOR POLYMER APPLICATIONS PA, PVC, PP, PE, ABS, HIPS, polyester, polyurethanes, rubber, epoxy... 

In order that the polyurethanes shall be elastomeric in nature it is necessary to choose basic materials to ensure that a high proportion of the resultant polymer structure has highly flexible segments, so that any crystallinity that may be present is confined to discrete domains, and so that there is a generally low level of inter-chain attraction and a low level of cross-linking. Such a specification is, of course applicable to rubbers in general and not restricted to polyurethanes. 

Acetylene is reacted with formaldehyde and then hydrogenated to make 1,4-butan-ediol for polyurethane rubber applications. 

The low hardness has led to uses in printers rollers and stereos. It is, however, to be noted that when the material has been used to replace cellular rubbers or flexible polyurethane foams in sealing applications, problems have arisen where it has not been appreciated that although the rubber is very soft it is for practical purposes incompressible. 

A wide range of polyurethane-type products has become available in recent years for coating applications. These include simple solutions of linear polyurethanes, two-pot alkyd-isocyanate and polyether-isocyanate systems and a variety of prepolymer and adduct systems. The coatings can vary considerably in hardness and flexibility and find use mainly because of their toughness, abrasion resistance and flexibility. Uses include metal finishes in chemical plant, wood finishes for boats and sports equipment, finishes for rubber goods and rain-erosion-resistant coatings for aircraft. One type of coating is potentially competitive with PVC leathercloth. Both alkyd-di-isocyanate and adduct-diisocyanate compositions may be coated on to fabrics from solutions of controlled viscosity and solids content. Such coated fabrics are soft, flexible and, unlike PVC leathercloth, free from plasticisers. 

Many isocyanates have good adhesive properties and one of them, triphenyl-methane-pp /7"-triyl tri-isocyanate, has been successfully used for bonding of rubber. Isocyanates are, however, rather brittle and somewhat limited in application. Somewhat tougher products are obtained from adhesives involving both polyols and isocyanates, i.e. polyurethane-type materials. The major application of these materials to date is in the boot and shoe industry. 

Block copolymers can contain crystalline or amorphous hard blocks. Examples of crystalline block copolymers are polyurethanes (e.g. B.F. Goodrich s Estane line), polyether esters (e.g. Dupont s Hytrel polymers), polyether amides (e.g. Atofina s Pebax grades). Polyurethanes have enjoyed limited utility due to their relatively low thermal stability use temperatures must be kept below 275°F, due to the reversibility of the urethane linkage. Recently, polyurethanes with stability at 350°F for nearly 100 h have been claimed [2]. Polyether esters and polyether amides have been explored for PSA applications where their heat and plasticizer resistance is a benefit [3]. However, the high price of these materials and their multiblock architecture have limited their use. All of these crystalline block copolymers consist of multiblocks with relatively short, amorphous, polyether or polyester mid-blocks. Consequently they can not be diluted as extensively with tackifiers and diluents as styrenic triblock copolymers. Thereby it is more difficult to obtain strong, yet soft adhesives — the primary goals of adding rubber to hot melts. 

Paints are complex formulations of polymeric binders with additives including anti-corrosion pigments, colors, plasticizers, ultraviolet absorbers, flame-retardant chemicals, etc. Almost all binders are organic materials such as resins based on epoxy, polyurethanes, alkyds, esters, chlorinated rubber and acrylics. The common inorganic binder is the silicate used in inorganic zinc silicate primer for steel. Specific formulations are available for application to aluminum and for galvanized steel substrates. 

Recent trends in protective coatings used on buried pipelines have been away from reinforced hot applied coal tar and asphalt enamels and butyl rubber laminate tapes, particularly where applied over-the-ditch . The more recently developed coatings based on fusion bonded epoxies, extruded poly-ethylenes, liquid-applied epoxies and polyurethanes, require factory application where superior levels of pipe preparation and quality control of the application process can be achieved. 

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