PU elastomers are made in a wide variety of hardnesses: from around 10 Shore A to over 60 Shore D.
PU elastomers are generally tough abrasion-resistant materials with good chemical and solvent resistance.
High quality elastomers are based on isocyanate-terminated polyester or polyether prepolymers. The prepolymer is mixed with a chain extender at elevated temperatures ( 50 – 130 C) and poured into heated moulds. Alternatively it can be sprayed or rotational cast (as in the spinning of pipe linings). The most common polyether polyol used is PTMEG (polytetramethylene ether glycol)
The isocyanate used in the prepolymer can be TDI, MDI or in limited cases NDI. The chain extenders used include 1,4-butanediol (14BD), Trimethylolpropane (TMP) and in particular ‘MOCA’ (methylene bischloraniline)which is a known animal carcinogen and should be treated with extreme caution.
These high grade elastomers find particular application in the mining industry where they are used in mineral processing as separating screens, pipe linings, conveyor scrapers, idler rolls and various components in flotation processes. Outside the mining industry there are many applications in wheels, tyres and rollers.
These elastomeric materials based on MDI are designed to be mixed and poured (or sprayed) at temperatures below 50 C. They are easy to handle but they do not achieve the high level of properties accorded to hot cast elastomers. They are often used in potting and encapsulation applications, whereas the spray application is used for coating metal to prevent wear or corrosion for instance.