Use of Polyurethane Adhesives and Insulation in the Roofing Industry Riku Ylipelkonen, Technical Service Manager, Polyset Roofing Adhesives, ICP Building Solutions Group
Otto Bayer is credited with developing polyurethane in 1937. Original development applications were related to aircraft coatings for World War II and flexible foams. Commercial applications began later in 1952 and grew steadily as polyurethane foams became a viable choice for rigid foam buns and molding parts where the reaction occurred in the mold for the finished part. The advantages of polyurethane foam (PUF) helped grow many applications and uses. High heat resistance and long-term stability due to the polymer being a thermoset plastic led to the development of PUF adhesives in roofing applications. Polyurethane is a reaction polymer, where isocyanates react with polyols and result in a thermosetting polymer. The main feature of thermosetting polymers is that they do not melt or breakdown with the application of heat. For example, when eggs and flour are combined and cooked, a pancake is made. The pancake cannot be returned to eggs and flour by heating it up. The opposite of thermoset polymers is thermoplastic polymers. Thermoplastic polymers will return to their original state if heated. As an example of this, an ice cube will become water if it is heated. However, if the water is returned to a freezer, it will become an ice cube again. The other benefit of thermosetting polymers is the long-term stability of the polymer. However, the stability of polyurethane polymers is mainly susceptible to exposure of ultraviolet (UV) light. When PUF is exposed to sunlight, which contains UV light, there is a yellowing discoloration that occurs over time. The higher energy of UV light can also cause reactions that break-up the PUF and flake the exposed foam off as exposure time is prolonged. Prevalent uses of PUF in the roofing industry have slowly grown over the years. The applications that 14
FLORIDA ROOFING | April 2021
are specified have used different polyurethane formulations which vary based on the raw materials used. Sprayed polyurethane foam (SPF) roofs are popular and substantial low slope roof applications that use the physical properties of polyurethane more as an insulation than an adhesive. Raw materials are varied to result in a high closed-cell content that create excellent insulation properties. The use of spray equipment, where the reaction is controlled on the rooftop, helps to minimize preparation process to the job site. The top coating is used to minimize sunlight and UV light exposure, to maintain the physical properties and waterproofing qualities of the finished roof. A growing application for SPF is as an adhesive for roofing materials. On low slope roofing, these adhesives are used to adhere common building materials to make the final roof assembly. On steep slope roofing, SPF adhesives are used for adhering clay and concrete roof tiles. SPF can be advantageous for several reasons. There is no need for high temperature materials like hot asphalt that cost money to heat and transport to the installation site safely (crew safety, property destruction and insurance considerations). SPFs are usually low in volatile organic compounds (VOC), reducing site complaints of fumes during application, environmental considerations for the project and simpler, less costly personal protective equipment (PPE) for installers. SPF adhesives can also minimize
