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Specialized Adhesives Withstand Thermal Cycling

  

Thermal cycling has traditionally presented challenges for creating a durable adhesive bond. During thermal cycling, components alternate between two temperatures which can vary from extreme heat to cryogenic conditions. High temperatures can stress and break adhesive bonds and very low temperatures often cause brittleness. Engineers have compensated for stress by trying to select adhesives and substrates with comparable coefficients of thermal expansion (CTE). Unfortunately, matching CTEs is challenging and limits construction options. Contemporary adhesive formulas offer more user-friendly alternatives.

Today epoxies, silicones, and ultraviolet (UV) cure adhesives are all available for thermal cycling. For any of these, a high glass transition temperature (Tg) will indicate that the adhesive performs well at high temperature. Flexibility will indicate the adhesives ability to withstand stress and cold temperatures. Epoxies are traditionally brittle adhesives, but modern epoxies can be formulated for flexibility and toughened with rubber or elastomer modifiers. The addition of rubber once required a trade-off of lower Tg, but this too has been overcome in recent formulas. Silicones have the natural high-temperature resistance and flexibility that epoxies are modified to achieve. This makes silicones a natural choice and one of the best options for thermal cycling. However, silicones form weaker bonds with more limited substrate options than epoxies. Finally, UV cured adhesives require toughening to be suitable for thermal cycling, and have a more limited temperature range than epoxies. But within the appropriate temperature range, UV cure adhesives have the advantage of being single-component, fast-curing products.