Selecting the Right Polyurethane for Various Applications
Lecture By
Dr. Ronald W. Fuest
Uniroyal Chemical Company
The ultimate key to functional design success is, of course, the selection of the right material to meet the demands of the application. In some instances steel, aluminum or other metals are the materials of choice; in other cases plastics— ABS, polystyrene, PVC or phenol formaldehyde resins are best, and in a growing number of needs, polyurethanes offer superior design and performance characteristics.
You will note that I cited “polyurethanes” in the plural. The variety of these elastomers is substantial. Each composition has its attributes and shortcomings. So what is essential, in terms of applications engineering, is to appraise each and then to select the particular polyurethane that meets the criteria of both economics and performance.
The following, it is hoped, will serve as a useful, macro guideline to the types of PU elastomers that are available, the kinds of physical and environmental resistance properties they have, and the typical applications that each will fulfill.
First, let’s define just what polyurethane is. The chemical term polyurethane can apply to many different kinds of materials.
WHAT IS POLYURETHANE ?
Castable Elastomers
Foams—Rigid and Flexible
Adhesives
Sealants
Thermoplastics
Millable Gums
Coatings
There are the castables elastomers, which are the materials of primary importance in this discussion. There are foams, both rigid and flexible types. Rigid foams are used for applications such as insulation while flexible foams are used in upholstery and cushioning. These are each very large markets.
Many types of adhesives are also formulated from urethanes.
Sealants based on urethane chemistry are widely used for applications such as sealing automobile windows.
Thermoplastic urethanes are materials which are fully reacted and processed by a melting and extrusion or injection molding procedure.
Millable gums are handled in very much the same way as conventional rubber, that is, they are compounded with fillers and other ingredients, are processed on rubber machinery and are cured by vulcanization processes with peroxides or, in some cases, with sulfur. In this way the unique properties of urethanes can be achieved by the same methods used to process conventional rubbers.
Coatings, also widely based on urethane materials, cover a broad range from the types of varnishes and paints that are often used on furniture, to the sprayable coatings for high abrasion or corrosion resistance. The latter are not just for protection of the surface from weather, but to provide a tough, durable lining for industrial pipe, or added service life for
costly mining machinery.