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Organic “High-Build” Spray-in-Place Liners – An Emerging Class of Rehabilitation Methods
Polyurethane and polyurea lining materials are often placed in the same chemical category. Both polyurethane and polyurea linings are produced using an isocyanate compound, but each uses a different reacting resin producing a unique molecular chain. Polyurethane linings use a Hydroxl (OH)-ending blend called a polyol as the hardened resin, while Polyurea uses an amine (H2N)-ending blend. The polyurethane reaction utilizes a catalyst similar to that of epoxies to produce the resultant material. This reaction produces a 100 percent solids material within a matter of minutes, so additional layers for high build can be easily applied.
The polyurethane is applied centrifugally onto the pipe surface in a thickness typically between 120 and 200 mils (3 and 5 mm) using an air-driven spray head that is advanced through the pipe to form the lining. Commercially available products include the Copon Hycote 169 (the US version is named Scotchkote 169) and Spraywall. Polyurethane is also used for coating of manhole structures for the purpose of corrosion resistance (typically utilizing two layers of 75 mils each, for a total thickness of 150 mils). These coatings exhibit high chemical resistance, but are moisture sensitive and the surface of the host structure must be completely dry to ensure adhesion to the substrate.
In polyurea materials, the reaction with the amines produce very short gel times and the substance hardens very quickly (several seconds to minutes), producing a 100 percent solids material.
The installation of polyurea requires the use of a plural component, high pressure and high temperature application system (Primeaux, 2004). A catalyst is not necessary using this application technique. Polyurea is suitable for high temperature applications, as it features high heat resistance properties. Polyurethane linings can be produced with different types of polyols that can provide a rubber-like property used in pipes that may have flex potential. The urea group chain tends to produce elastomeric materials, so if a more rigid material is needed for additional structural stability and flex is not a prime concern, polyurethane linings can be used.