Polyurethane rubbers properties

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 ... 

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. 

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

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. 

By careful formulations it is possible to produce polyurethane rubbers with a number of desirable properties [50]. The rubbers can be thermoplastic (linear) or thermoset (slightly cross-Knked) products. 

Polyurethane rubbers, in general, and the Vulkollan-type rubbers, in particular, possess certain outstanding properties. They usually have higher tensile strengths than other rubbers and possess excellent tear and abrasion resistance. The urethane rubbers show excellent resistance to ozone and oxygen (in contrast to diene rubbers) and to aliphatic hydrocarbons. However, they swell in aromatic hydrocarbons and undergo hydrolytic decomposition with acids, alkalis, and prolonged action of water and steam. 

Varghese, S., Gatos, K.G., Apostolov, A.A., KargCT-Kocsis, J. Morphology and mechanical properties of layered silicate reinforced natural and polyurethane rubber blends produced by latex compounding. J. Appl. Polym. ScL 92, 543-551 (2004)... 

Polyurethane rubbers have now been used as seal materials for some time on account of their unique ability to combine resistance to swelling in oil with high strengths and high stiffnesses. Their ability, in some classes, to be processed as thermoplastics, is also considered useful as manufacture of the seal can then be automated and hence quality is more reproducible. A limitation in their use has been that they depend upon physical types of crosslinking for their elastic and strength properties and when certain specific temperatures are reached these crosslinks rapidly weaken and the polyurethane elastomer melts and fails. At present most rubber seals are made from vulcanized covalently crosslinked rubbers where crosslinks are based on sulphur or carbon, and these do not melt at elevated temperatures, but instead decompose. 

POLYURETHANE ELASTOMER PROPERTIES COMPARED WITH THE PROPERTIES OF VULCANIZED RUBBER AND RUBBER-LIKE POLYMERS... 

Table 13.4 gives some comparative abrasion-resistance properties for polyurethane, rubbers, plastics and some common metals. 

Good anti-mildew and algicide properties are claimed for a non-arsenic-based anti-microbial agent, Amical from Argus Chemical, which is also non-irritating. It is approved by the US EPA for plastics use. Low levels of dosage in plasticized PVC, polyurethane, rubber, and other products prevent embrittlement and premature decay. 

This has an important bearing on the properties of polyurethane rubbers, particularly the thermoplastic polyurethane elastomers discussed in the next chapter. 

Whilst the inter-relation of cross-link density and physical properties is far from simple with hydrocarbon rubbers, with polyurethane rubbers it is even more complex. 

---