CoatingsPro Magazine

MAR 2015

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Page 53 of 90

COATINGSPRO MARCH 2015 53 Science Behind It Polyurethane and Polyurea Technologies: Working Together? By Rodney D. Jarboe, President for Creative Polymers T here has been an industry competition between polyurea and solventless/fast-set polyurethanes for the past two decades, and it is probably a little confusing to the average contractor. In reality, some of the application and performance diferences between a polyurea and a polyurethane may be occasion- ally overhyped. In fact, the physical properties between the polyurea and polyurethane systems are really relatively close when compared to other coatings and elastomers. But despite the way these diferent systems are touted, the chemistry of each of these systems can infuence what appli- cations suit their attributes. System Similarities Tere are both diferences and similarities between these two coatings systems, and each system has some advantages depending on the end-use application. One of the similar- ities is that the "A Component" used in both systems is an isocyanate polymer; the same product could be used as the A Component for both the polyurea and polyurethane systems. Another similarity is that both systems typically use a 1:1 ratio between the A and B sides. Tey can also both be sprayed with the same plural component spray proportioner and plural spray gun. Te key diference between the two systems is the B side, or resin. Te polyurethane system is based on a blend of resins (a polyol) that require a catalyst system in order to cure quickly with the A side. Te polyurea system, on the other hand, is based on a resin-blend system (polyetheramines) that is "auto‚Äźcatalytic," meaning that it will cure quickly and automatically with the A side without a catalyst. Chemistry in Action Now let's look at how these chemistries infuence application and physical properties. Both systems can be formulated to cure in less than 30 seconds, so a major advantage is their fast-cure properties. Tis property can allow a contractor to fnish his or her projects in a portion of the time that tradi- tional coating systems may ofer. On top of that, polyurea systems can cure at a colder temperature than polyure- thane systems, thus providing a longer application season; however, there are times when fast-cure is not an advantage. For instance, there are some applications where a geotextile is required to be embedded into a membrane system, which means the system might cure too fast to allow the proper "wetting out" of the geotextile. In this type of application, which is what happened at the St. Louis bridge deck project, the polyurea systems are not a good candidate; however, a polyurethane system (with a 5- to 10-minute cure time) might be ideal for this type of application, since it allows the geotextile to be embedded into the polyurethane coating system prior to it curing. Additionally, solventless polyurethane systems typically have slightly more abrasion resistance, chemical resistance, and elongation than polyurea. But polyurea systems typically have higher tensile and tear resistance than polyurethanes. Working Together In the case of the concrete land bridge deck project that required waterproofng in front of the St. Louis Arch grounds, the contractor used the advantages of both the polyurea and polyurethane waterproofng systems to accomplish the required end result. Te specifcation for this project required 100 mils (2,540 microns) of a polyurea system followed by 50 mils (1,270 microns) of a polyurethane system with a geotextile embedded into the topcoat. Te polyurea system provided the productivity of curing fast, the tolerance for cooler temperatures, and the tolerance for potential moisture in the concrete deck. Te polyurethane system ofered abrasion resistance and a slower cure time, so that it could be sprayed over the polyurea and have enough open time so that the geotextile could be rolled into the membrane prior to it curing. (Te polyurethane system was slowed down by adjusting the catalyst type and amount to have an eight-minute cure time.) Using both systems enabled the contractor to get the most of each of the two types of systems. Both polyurea and polyurethane systems have their pluses and minuses, but this project goes to show that using diferent systems together can sometimes have the best result. CP Polyurethane Isocyanate Polyol + = Polyurea Isocyanate Amine + = CHEMISTRY CHEMISTRY Polyurethane Part A Isocyanate Polyol Part B + = Polyurea Part A Isocyanate Amine Part B + =

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