Basic characteristics of polyurethane elastomers

- Nov 15, 2017 -

Although polyurethane elastomers have different properties due to their different raw materials and preparation methods, they have a series of common properties because of the same structure. The elastic modulus of polyurethane elastomer is between rubber and plastic. The biggest characteristic is that it has high hardness and high elasticity, and this property is not available for other rubber and plastics. In addition, the excellent wear resistance is one of its advantages. Therefore, the use of polyurethane elastomers is not limited to rubber, but can be made into a variety of polymer materials products.

Polyurethane elastomer polyester and polyether two categories, compared with physical properties, it can be seen that the general low hardness elastomer with polyester type performance is better, while polyether type is poor. The polyether elastomer is the best for the elastomer with high hardness.

In addition, the polyester has good oil resistance, heat resistance and good adhesion to metal, while the properties such as hydrolysis resistance, cold resistance and bacteria resistance are better.

The two stage crosslink bond formed by intermolecular hydrogen bonds has a considerable effect on the mechanical strength of polyether polyurethane elastomers cured with two amines. With the increase of temperature, the hydrogen bonding force gradually decreases and the physical properties decrease, but at this time it can also be comparable to the strength of ordinary rubber. The temperature of the polyurethane elastomer used for a long time is 80 ~ 90 degrees, and it can reach about 120 degrees in a short time.  The low temperature resistance is good, the brittleness temperature of polyester polyurethane elastomer is -40, and the polyether rubber is -80 ~ -70 centigrade, but it is hard to harden at low temperature.

Polyurethane elastomers are generally good in oil resistance and solvent resistance, especially for lubricating oils and fuel oils. The resistance of most solvents at room temperature is better than that of NBR, but with the increase of temperature, the performance of the rubber decreases rapidly even without swelling..

Because of the poor hydrolysis resistance of polyurethane elastomer, the application of polyurethane elastomer has some limitations. The polyester polyurethane elastomer has worse hydrolysis resistance than polyether polyurethane elastomer, and the latter has 5~10 times as much water resistance as the former. Because the most easily hydrolyzed urethane chain in the polyether polyurethane bond is urethane, it is much stronger than the urethane bond easily hydrolyzed by polyester type polyurethane, and the ether bond is very resistant to hydrolysis.

Water has two kinds of effects on polyurethane elastomer: one is plasticizing from the water absorbed by it. That is to say, the water absorbed by the polar group of the polyurethane polymer formed hydrogen bonds, which weakened the hydrogen bond between the polymer itself and reduced the physical properties. However, the water absorption process was reversible, and the physical properties returned to the original after drying. The water absorption rate of polyester type is lower than that of polyether type. Under the condition of saturated water absorption, the reduction rate of polyester strength is 10%, and the polyether type is 20%.

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