Selecting the Right Coating for Your Application: Polyurea VS Polyurethane

Takeaway: Polyurethane and polyurea coatings represent an outstanding alternative for numerous applications; however, the treating time attributes and the versatility of the application procedure are important factors when considering each type.

Several methods are employed to protect metallic elements from deterioration due to serious environmental conditions, such as the effects of high humidity, seawater, heat, and chemical attacks, to name a few. Within these methods, it is extremely common to use coating systems. This article offers a basic summary of the appropriate differences between 2 protective coating products: polyurea and polyurethane.

The Chemistry of Polyurethanes and Polyureas

Polyurethanes and polyureas are polymers regularly used to produce protective coatings and linings. Both are based on a two-component system, and the treating systems are by co-reaction, where isocyanate is a typical part. The 2nd part is a polyether polyamine for polyureas, while polyether polyol is for polyurethane. It is also possible to make so-called hybrid systems, in which the isocyanate is responded with a mixture of hydroxyl and amino groups.

Polyurea and polyurethane reactions.

Polyurethanes can be manufactured throughout the polyaddition response by using ideal driver systems to increase the response time of the components. The catalysts can be defined into two broad categories: amine substances and metal complexes. The choice of catalyst controls the selectivity of the targeted isocyanate responses.

Polyurethane can be of two major types: aromatic and aliphatic, with some differences between them. The polyurethane reaction is sensitive to low-temperature levels and wetness due to the addition of drivers. The polyurethane system is susceptible to blistering when the humidity is greater than 5% due to the competition between hydroxyl-polyol and water to react with an isocyanate group.

On the other hand, polyurea can be produced in high wet conditions because they do not require drivers. For that reason, the environment can be almost filled with water without triggering blistering, which is a fantastic benefit.

However, that does not indicate they can be used over a damp substrate. The polyurea will respond over the water, but the applied system will not bond to the substrate because of the area. The ambient temperature and substrate temperature may have little effect on the reaction and remedy of a polyurea system as compared to the other. This was seen in one research study where samples of steel, concrete, and asphalt layered with a polyurea elastomer in the presence of a stream of liquid nitrogen (-196 ° C) sprayed for 30 seconds revealed no damage.

Polyurea coatings have an extremely short preliminary treatment time and, for that reason, maybe utilized in an aggressive environment, where high curing speed is required (e.g., an oil pipeline). Some polyureas are quick air-drying (less than 30 minutes, even less than 10 seconds for some cases for pure polyurea).

Polyurethanes are offered with a range of treating times, from less than one minute to several hours.

Performance Characteristics of Polyurea and Polyurethane Coatings

In general, all the polyureas (fragrant) systems are expected to have some loss of gloss, some chalking, and discoloration due to ultraviolet (UV) exposure; however, this does not affect its quality and performance. Using UV stabilizers and anti-oxidants will not prevent coating staining and fading over time when utilized in light colors for direct exterior exposure.

As for polyurethanes, the addition of pigments will enhance the resistance to UV direct exposure. Aromatic polyurethanes are resistant to UV attack and are used in exterior coating formulations. The aliphatic polyurethanes are incredibly tough with much better resistance than the aliphatic types, but they will chalk rapidly in UV light.

Polyurea and polyurethane systems show similar resistance properties to chemical products because both have the same polyether backbone in the elastomer. Innovations of polyurea systems have various polymer foundations in the chain. These can be ester, epoxy, silicone, or a combination of proprietary adjustments to the polymer chain. In general, the polyurea systems are resistant to acetone, gas, methyl tert-butyl ether (MTBE), sulfuric acid, and caustic at low concentrations (5%). See Table 1.

Chemical resistance screening for polyurea spray elastomers.

The chemical resistances for polyurethane are listed below in Table 2 and need always to be checked with manufacturing information.

Chemical resistance screening for polyurethane.

Best Practices for Applying Polyurea and Polyurethane Coatings

The Society for Protective Coatings (SSPC) supplies assistance about approaches for using polyurethane and polyurea coatings:

SSPC-Paint 39 Two-Component Aliphatic Polyurea Topcoat

SSPC-PS 28.01, Two-Zinc-Rich Polyurethane Primer/Aliphatic Polyurea Topcoat System

SSPC-Paint 43 Direct-to-Metal (DTM) Aliphatic Polyurea Coating

SSPC-PA 14 Application of Thick Film Polyurea and Polyurethane Coatings to Concrete and Steel Using Plural-Component Equipment

SSPC-Paint 45 Two-Component Thick-Film Polyurea and Polyurea/Polyurethane Hybrid Coatings

In general, polyurethanes are applied by utilizing standard spray, brush, and rollers.

Suitable Uses for Polyurea and Polyurethane Coatings

Many polyureas need an epoxy primer, as their adhesion to steel might not be enough for strong service. They are typically used with special devices, such as plural part spraying with a mixing head in the spray gun due to its very short remedy time. Nevertheless, all assistance supplied by the manufacturer relating to the mixing of multi-component products, thinning requirements, induction times, and unique application requirements should be followed.

Aromatic polyurethane coatings are suitable for a wide range of floors with various mechanical and chemical direct exposure levels. They are also suitable for concrete, plywood, metal, wood, and masonry surface areas. The application can be extended sometimes by using a waterproof membrane. This coating type can be applied in the thick movie for immersion service; some solutions enable up to 500 microns (20 mils) or more per coat for industrial and marine applications.

Aliphatic polyurethane coatings (high-performance two-component UV-stable topcoats) are generally utilized for outside coatings. Nevertheless, some solutions appropriate for exposure in environmental zones 1A (interior, normally dry), consisting of overseas structures, chemical and petrochemical plants, bridges, pulp, paper mills, and the power market omitting immersion zones.

Polyureas coatings are a high-performance item designed particularly for commercial applications where high abrasion, chemical resistance, and corrosion resistance is top priority. For waterproofing and securing functions, they can be used on a product like concrete, metal, wood, ceramic, etc. (To discover more about polyurea coatings, read The History and Industry Adoption of Polyurea Coating Systems.).

Unique raw substances in the chain reaction and using a catalyst to speed up the reaction time produce marked differences in the level of sensitivity of the reaction and the environmental conditions during application and the treatment time of the items. Other physical and chemical characteristics denote different residential or commercial properties and applications.

Conclusion.

Polyurethane and polyurea coatings represent an excellent choice for many applications. However, the curing time qualities and the versatility of the application process under severe environmental conditions make polyurea coatings the most economical system despite its basic material cost, which is higher than many other systems, including polyurethane.

Whether you go with Polyurea or Polyurethane, we recommend going with ArmorThane. As a worldwide leader in industrial coatings, ArmorThane offers a full line of top-quality polyurethane and polyurea coatings and high-tech spraying equipment and supplies. Their professionally applied pure and hybrid polyurethane and polyurea formulas are extremely durable, flexible, and safe.