Glass Transition Temperature (Tg)
What is Glass Transition Temperature
The Glass Transition Temperature (glass transition temperature) is, in short, a term used to describe when polymeric materials such as silicone or epoxy transition from a glassy structure to a soft and elastic state. It is often abbreviated as Tg.
At this temperature, the molecules of the material become more mobile, making the material more flexible. Tg is therefore more precisely the determination of when this process occurs. Knowing this phenomenon is useful when working with adhesives because it indicates how the adhesive behaves at different temperatures once it has cured.
When an adhesive reaches its Tg, it affects flexibility, chemical resistance, volume, strength, and hardness.
Tg is not a single specific temperature but rather a temperature range within which the material drastically changes its properties. It is important to emphasize that Tg is not a melting point. It is the temperature at which the properties mentioned above change.
This means that an adhesive can still be used after it has transitioned from a glassy to a more elastic state. In some cases, it can even be advantageous to use an adhesive above its Tg.
For example, Tg for many silicone adhesives (which are flexible products) is below -100°C, while for epoxy adhesives (which are brittle products) it is above +60°C. When the adhesive goes above its Tg, it becomes more flexible and more resistant to impact, vibrations, and material expansions. If the adhesive is later cooled below its Tg, it will revert to the brittle glassy state.
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