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Glass Transition Point Important in Choosing Adhesives for High Temperature Applications

Posted on 4/20/2021 10:18:09 AM By Masterbond
  

When finding the right adhesive for high temperature applications, among the most important factors to be considered are the curing method as well as exactly how high the temperature is that the adhesive will be facing in application, and how often and for how long, it will be exposed to that high heat, in order to determine whether or not the adhesive’s operating temperature range can meet the challenge.

The glass transition temperature (Tg) of the adhesive at which it changes from a rigid and glassy state to being more pliable, flexible and rubbery,  provides a good indication of whether or not the adhesive can stand up to high temperature exposure, particularly if it has to do so for sustained periods.

As temperatures increase, the physical properties of thermosetting polymers change with them, affecting attributes such as their heat capacity, tensile strength, electrical properties and modulus. They will also significantly increase the linear coefficient of thermal expansion (CTE) as they move through the Tg range, sometimes increasing it by as much as three to five times over what it was when below the Tg range. 

This can damage the adhesive material, particularly if the temperature takes it too far over the Tg and keeps it exposed to this high heat for a long time. If the temperature drops fairly quickly to the adhesive’s ambient temperatures, its strength profile usually returns to normal.

The curing method also plays a part when choosing the right adhesive for high temperature applications. Not only does it affect the level of the Tg, but an oven cure has been shown to raise resistance to high temperatures considerably, while curing at high temperatures for a long period appears to raise glass transition temperatures, as well as high temperature resistance.