Glass Transition Temperature Explained
Last updated : 2025/9/12
What is Glass Transition Temperature?
When resins are heated past a certain temperature, they become soft and rubber-like as their molecules gain mobility. When cooled, molecular movement slows, resulting in a hard, glass-like state. The temperature at which this transition occurs is called the glass transition temperature, or T₉.
How It Differs from the Melting Point
The melting point refers to the temperature at which a solid becomes a liquid; for example, ice melting into water. However, water is a low-molecular substance, so there only three states: solid, liquid, and gas.
In contrast, thermoplastic resins have high molecular weight and exhibit up to four distinct states:
Liquid
Rubber (soft)
Glass (hard)
Crystalline solid
The Glass Transition Temperature occurs at that critical transition between the soft rubbery and hard glassy states. While the glass state appears solid, it lacks crystalline structure and isn’t technically considered a true solid.
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