What Is Polyurethane?


Since the 1930s, polyurethane has become a popular material used in a handful of applications. Polyurethane is chains of urethane linkages called monomers that make larger polymers. Polyurethane starts as two components that need to be combined to form a new solid full of polymers. The new polyurethane polymer will have properties varying in strength and elongation that come from the base monomers to provide a custom fit for an application.

Urethane linkages form with the reaction of two components: a poly (B side), an alcohol group and an isocyanate (A side), the backbone of the material. Based on the type of compound used, which will typically be polyol, you will be able to determine the properties of the final product. The polyol’s relative molecular mass, number of reactive functional groups per molecule, and molecular structure contribute to the formed material. The isocyanate is extremely reactive but becomes stable after the reaction has occurred.

Due to its flexible yet tough nature, it has been called plastic and rubber but is neither. More accurately, it is capable of having both elastic properties and high rigidity based on its formulation and final end use. It can be molded into various shapes and enhances surfaces with wear resistance, strength, and protection. Hardness, cure time, and physical properties can all vary to fit a specific need.

What Is Thermoset?

Thermoset urethanes are polymers that start as two-component liquids, and once combined, they cure into a solid. Due to cross-linking, additional heat will cause them to soften, not melt or reform, so they cannot be recycled. Thermosets are a good alternative to thermoplastics when you are unable to invest in high-end molding equipment, have an uncontrolled environment, or need alternative processing methods.

What Is Thermoplastic?

Thermoplastic urethanes are polymers that begin as a solid bead but, when heated, can be melted and molded into a specific shape. Since they have no additional cross-links, with the addition of more heat, they can be reformed into new shapes or recycled. Thermoplastics are great for repeated high-volume applications and do not require another reaction that could affect their final properties. However, they do require advanced molding processes and techniques that limit their use and in-field functionality.

Types of Polyurethane Materials

1. Elastomers

Polyurethane, when made as an elastomer, is best used in places where natural rubber would fail. It has great rebound that allows it to return to its original shape after being bent, stretched, or compressed. Compared to silicone, it is a cost-effective mold-making option for advanced part making. It captures extreme detail that will transfer to each casting for repeatable use. Other benefits the rubber can provide include resistance to impact, shock, cuts and tears, and bacteria.

2. Coatings

When formulated into a coating material, it is typically sprayed onto surfaces for protection. The coating will resist harsh chemicals, corrosion, abrasion, and impact. It can also be used for weathering protection, antibacterial properties, and many other purposes. With the ability to adhere to many surfaces, it offers flexibility and tough, long-lasting protection.

3. Foams

Thermoset polyurethanes are one of the only alternatives to expanded or extruded polystyrene foam. Using a chemical blowing agent or water, a polyurethane foam can produce a wide variety of options. Depending on the needed application, they can be rigid, semi-flexible, or flexible and have high impact strength. These two-component foams begin expanding once combined and cure to the predetermined weight and density. They are best used in void-filling applications to reduce the material costs of parts and structures. They’re also a great material for the protection of products during transit and can also be used as insulation foam.

4. Plastics

Polyurethanes, when made into a plastic, are rigid and smooth and are a good option if high strength and durability are important for the part being made. The plastic can take on extreme details of the mold it is poured into. Whether the surface is smooth, glossy, or matte, it will take on those exact qualities. As a thermoset material, it can be formulated with high heat deflection for use in high-temperature environments. It is also useful for prototyping parts and industrial part-making and can be made to be user-friendly without the need for high-end equipment.

Benefits of Polyurethane

  • It is a very versatile material since it can be manufactured as an elastomer, coating, foam, or plastic. These materials can be soft and flexible or tough and rigid. With flexibility in design, manufacturing one-off parts, prototypes, and high-volume runs is convenient. You also gain versatility that can be used in various indoor or outdoor applications and produced on job sites.
  • Unlike other rigid materials, it has high elasticity and easy moldability when needed. This molding quality allows you to create complex shapes at relatively low tooling costs.
  • It possesses high properties such as high tear resistance and high tensile strength for optimal protection. When sprayed onto surfaces, it offers protection against scratches, scrapes, and other damages that occur over time. It also resists abrasion, has substantial impact tolerance, and does not support fungal growth.
  • Compared to thermoplastic materials, it has a relatively short cure time. Most types are fast curing, which allows for increased part production and quick return to service. You’ll be able to sand, machine, and paint a lot faster than you would with other materials.

Alternative Materials

Polyurethane is commonly used for its low cost, but this low cost comes with downsides. When applying polyurethane, it is unsuitable for areas with high levels of moisture or humidity since it is sensitive to moisture. The material will bubble and leave a flawed surface. Some polyurethanes are not UV Stable, meaning UV rays can also cause degradation, so it must be protected with paint or a topcoat for indoor or outdoor use.

An alternative for coating applications would be to use polyurea. This material is much better in environments where moisture is an issue. It has improved properties that polyurethane may lack but uses high-end raw materials that make it more expensive.

An alternative to polyurea is polyurea hybrid. The hybrid material is a mix of polyurea and polyurethane. It has the benefit of being less expensive than polyurea, with better moisture resistance than urethane.

VFI High-Performance Polymers

VFI manufactures various polyurethane-based materials for various applications. Our casting rubbers and plastics are great for part-making. With different chemistries, our molding rubbers are great for making molds and forms. We’ve seen our hard coats and spray coatings used in various theming and industrial applications. Our foams can be formulated into rigid or semi-flexible structures for void-filling and high-end packaging, among other applications. Contact VFI today if you’d like to learn more about all our high-performance polymer products.