Polyurea – Quick Setting Concrete Vents and Other Applications
Polyurea is an extremely hard, smooth, clear and relatively inert type of polyurethane foam. It is primarily used as a medium for filling in voids or “dormers” in polyurethane foams and also for filling in the annulus and sheath areas between layers of a rigid polymerized structure or in some cases in an air or water filled cavity. Polyurea comes in various densities, thicknesses, and chemical formulations and is frequently employed in manufacturing components for large scale products such as marine hulls, floatation tubes, pipelines, and hoses, and in components for cosmetic and dental applications as well.
Polyurea is actually a class of naturally occurring isocyanates (colored pigments) that originate from a chemical reaction between an isoconvertible polyurethane component and an aliphatic carboxylic acid component via step-growth polymerization at ambient temperature. The aliphatic isoconvertible polyurethane component is then synthesized using the appropriate catalyst in order to create the isocyanates. During the synthesis process the polyureas is mixed with various solvents in order to modify its physical properties to suit the intended reaction mixture. For example, aqueous (clear) polyurea can be combined with acetone, methylene chloride (many brands), propylene glycol, etc. Most polyureas are typically available in both single and multiple density forms (typically with a density range of about 25 to 100 kilograms/liter).
Polyurea coatings are often used for resisting abrasion, heat, and moisture. In terms of resistance to abrasion, polyurea is highly resistant to alkali attack (an increase in the level of acidity above what is found naturally in the material will result in more corrosion resistance) and to both low- and high-energy attacks by microorganisms. As such, it is used in applications where high wear resistance is important. Examples include pharmaceuticals, automotive, aerospace, cosmetics, and food processing. In terms of moisture resistance, polyurea does not perform as well (or, is unable to withstand) as other synthetic materials, but it does have its benefits.
In terms of the polyurea market itself, this coating has recently experienced significant growth. This growth has been driven by three main factors. First, polyurea coatings have reached the point where they have achieved typical performance levels for most industrial applications, including fatigue, impact, and creep; second, because production costs and service life have been reduced (a factor due to scale-up and lower capital investment); third, because of the ease of service and integration to existing manufacturing systems. Currently, there are polyurea formulations available in a variety of formulation types including: spray, liquid, bead, and granular.
There are several reasons why polyurea coatings have become so popular in recent years. One reason is that they are highly durable, and the coating itself serves to significantly reduce airborne moisture transfer. Another benefit is that they provide a solid, impervious seal against moisture intrusion, which improves plant health and increases the durability of the structure. Finally, while preventing external moisture transfer, they also help prevent external corrosion of the underlying concrete or structure, and help prevent cracking.
Polyurea coatings are on the rise in many industries, but particularly in the concrete and pore-cling industry. With these coatings, there is a greater need for quick setting concrete products. Because of this, the polyurea market has responded with a wide range of formulations, with some offering superior moisture resistance characteristics. Other quick setting products, however, have fallen victim to the lower energy densities of these polyurea formulations.