1.4 Oil and chemical resistance
Polyurethane elastomer, especially polyester polyurethane elastomer, is a highly polar polymer material. It has little affinity with non-polar mineral oil and is almost not corroded by fuel oil (such as kerosene, gasoline) and mechanical oil (such as hydraulic oil, engine oil, lubricating oil, etc.). It is much better than general-purpose rubber and can be used with Comparable to nitrile rubber. However, it swells greatly in alcohols, esters, ketones and aromatic hydrocarbons, and is gradually destroyed at high temperatures. It swells significantly in halogenated hydrocarbons and sometimes degrades. When polyurethane elastomer is immersed in an inorganic solution, without the action of a catalyst, it is similar to being immersed in water. It degrades faster in weak acid and weak alkali solutions than in water. Strong acid and strong alkali have a greater corrosion effect on polyurethane.
The service temperature of polyurethane elastomer in oil is below 110°C, which is higher than that in air. However, in many engineering applications, oil is always contaminated with water. Tests have shown that as long as the oil contains 0.02% water, almost all of the water can be transferred to the elastomer. At this time, the use effect will be significantly different.
1.5 Water resistance
Polyurethane elastomers have good water resistance at room temperature and will not undergo significant hydrolysis within one or two years, especially polybutadiene, polyether and polycarbonate types. Through the enhanced water resistance test and extrapolation method, it can be concluded that the time required for the tensile strength to lose half in normal temperature water of 25°C for polyester elastomer (polyethylene propylene glycol adipate-TDI-MOCA) is 10 years, polyether elastomer (PTMG-TDI-MOCA) is 50 years, that is, the polyether type is 5 times that of the polyester type.
1.6 Heat resistance and oxidation resistance
Polyurethane elastomers have good heat resistance in inert gases (such as nitrogen), and also have good oxygen and ozone resistance at room temperature, especially the polyester type. However, the simultaneous action of high temperature and oxygen will accelerate the aging process of polyurethane. The upper temperature limit of general polyurethane elastomers for long-term continuous use in the air is 80-90°C, and it can reach 120°C for short-term use. The temperature that has a significant impact on thermal oxidation realization is about 130°C. In terms of varieties, the thermal oxidation resistance of polyester type is better than that of polyether type. Among the polyester types, the polyhexylene adipate type is better than the general polyester type. Among polyether types, PTMG is better than PPG type, and both improve as the hardness of the elastomer increases. In addition, the strength of general polyurethane elastomers decreases significantly in high temperature environments.