In general, the single most important variable when selecting an environmentally resistant adhesive is ambient temperature. Other important factors are humidity, and exposure to solvents and ultraviolet (UV) light. In light of this, Fabrico provides some selection guidelines for the following specific applications.
Outdoor, non-aerospace applications. The maximum temperature is not likely to exceed 140 F, while the minimum temperature probably won’t go below -25 F. Outdoor applications also involve exposure to water, UV, and perhaps salt spray, corrosive chemicals, solvents and/or fuels. Most common adhesive products are well within their performance ranges in outdoor environments.
Water applications. The adhesive selected requires special resistance to wet and humid environments. Boats and other maritime equipment, pools, spas, and water/wastewater treatment, handling and testing systems may need further resistance to the effects of solvents, fuels and other corrosive liquids that are part of the environment in which they operate.
Applications with very high temperatures or strong solvents or chemicals. Electric motors, generators, electricity transmission components and under-hood automotive components may operate at temperatures exceeding the boiling point of water and be exposed to highly corrosive chemicals. Acrylic, urethane, epoxy and silicone adhesives maintain good properties at temperatures of 300 F and above. Also, certain medical devices must be designed to withstand repeated sterilization processes that use autoclaving and cleaning solutions.
Applications that expose adhesives to the freeze-thaw cycle. Here products that undergo thermal cycling expand when heated and contract when cooled. Because dissimilar materials, such as metals and plastics, usually have very different coefficients of expansion, a rigidly fastened joint can experience stresses that cause buckling, cracking and failure.
Flexible, softer adhesives, such as urethanes, silicones, and modified silicones have an advantage in these applications because they can absorb thermal stress and have outstanding thermal and chemical resistance. But the real standouts are flexible thin bonding products that accommodate substrate expansion/contraction while maintaining outstanding durability and performance, cycle after cycle.