image: Plastic transitioning from solid to amorphous

One of the most common terms that you hear when discussing polymers used as adhesives and coatings is the “glass transition temperature” (often abbreviated T_g). This property is in fact one of the most critical to consider when choosing the correct material for your application. Since many of us never got further than high school physics and chemistry, this term can be a little confusing and deserves explanation.

A layman’s definition of the glass transition temperature of a polymer is the temperature at which an amorphous polymer moves from a hard or glassy state to a softer, often rubbery or viscous state.

Unlike thermoplastic alternatives such as hot melt adhesives, cured thermosetting epoxies will not re-flow or melt when heated. Instead, epoxies will undergo a transition from a hard-rigid state to a more pliable, rubbery state. The temperature range during which this transition takes place is known as the glass transition temperature, T_g.