Aragon Elastomers, LLC - Polyurethane - Technical Expertise (II of IV)

What is polyurethane?

Polyurethane is a polymer (a material composed of many repeating chemical subunits) which has urethane as a repeating unit. Precisely, a urethane chemical group is a collection of 5 specific atoms (two oxygen, one nitrogen, one carbon, and one hydrogen) arranged in certain way. The urethane chemical group (chopped out of the middle of the polymer) looks like this:

What is the difference between polyurethane and urethane?

As shown above, polyurethane is just "many urethanes", so, technically, urethane is just the chemical group shown above and polyurethane is a material than incorporates many urethane groups.

What are the service temperature limitations of polyurethane?

Most polyurethanes are limited to continuous service temperatures to about 225F; however, special formulations can extend that to about 300F in some cases.

What is durometer or shore hardness and how is it measured?

There is an instrument called a durometer which has a spring-loaded indenter that pushes into the surface of a flexible material like polyurethane. It measures the amount that it penetrates, and this is called the durometer hardness of the material. There are two durometer scales, the A-scale and the D-scale that are most commonly used in measuring the hardness of polyurethanes. The "A" scale durometer reads from zero to 100. A measurement of 100 means that the indenter did not penetrate the material at all (i.e., infinitely hard) whereas a measurement of zero implies nearly no resistance of the material. As examples, a rubber band is about 20A, car tires and running shoe soles tend to be about 75A, hard skateboard wheels about 95A. The D-scale is for harder materials; the 95A skateboard wheels would be about 40D. "Shore" is a company name for a durometer instrument, so "Shore" and "durometer" mean the same thing.

Is polyurethane toxic?

Some of the liquid raw materials that go into making polyurethane are toxic and must be handled with caution. However, once the urethane reaction is completed, the solid material is safe to use as intended.

Caution: NEVER burn polyurethane (the fumes are toxic), and the dust created when urethane is sanded can be toxic.

What are the environmental concerns with polyurethane?

Polyurethanes do not break down easily, and their lifetime of service is often quite long. When disposed of they will biodegrade extremely slowly (like polyethylene), but it is unlikely that they pose a toxic risk in a normal disposal manner. Some of the raw materials that go into polyurethanes are toxic, and manufacturers (e.g. Aragon Elastomers) need to be careful in the management of these raw materials. At Aragon we have zero disposal of toxic liquid waste, because our chemical background permits us to only have to dispose of solid, non-toxic polyurethane materials.

Will polyurethane crack or harden with age?

Polyurethanes which are properly formulated for outdoor exposure should last many years. For example, a 14"x14"x1" firewood splitting backstop made of black 80A polyurethane has been used for over 20 years with no loss of serviceability.