Adhered single-ply membrane roof systems came into use during the latter part of the 1970s. At the time, the primary bonding adhesives in use were made from solvent-based neoprene, and the classical roof insulation boards used were wood fiberboard, perlite and rigid fiberglass with asphalt-adhered kraft paper facers. Neoprene adhesives typically were loaded with toluene and hexane; these strong solvents are needed to dissolve and carry the neoprene polymer matrix. The volatile organic compound (VOC) level in some of the original formulations was at or near 450 grams per liter.
A good bonding adhesive mates two dissimilar surfaces together; has good initial and long-term bond strength with high shear resistance; withstands large temperature swings; and resists spread of flame. The original neoprene and solvent-based adhesives were 25 percent solids (nominal); the remainder was a mixture of volatile compounds (solvents).
By the 1990s, air quality became a hot topic, and many states (and regions) set up air-quality control standards. VOC materials used in roofing came into sharp focus as the highly volatile materials can contribute to ground-level ozone as oxides of nitrogen combine with VOCs in the presence of sunlight and heat.
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