What occurs when a material reaches its glass transition temperature?

When a material reaches its glass transition temperature, it undergoes a significant change in its mechanical and thermal properties. At this temperature, the material transitions from a hard and relatively brittle state into a softer, more pliable state, which is often described as being more rubber-like. This characteristic allows the material to exhibit increased flexibility.

The glass transition temperature marks the point at which the molecular motion within the material increases, leading to a decrease in the material's rigidity. This means that as the temperature rises and reaches this transition point, the structure becomes less organized compared to its previous state, allowing it to absorb energy and deform slightly without breaking.

Thus, while the material indeed becomes more pliable, it doesn't necessarily lose all hardness, and immediate evaporation or crystallization does not occur at this temperature. Instead, the material’s properties are altered to be in a more malleable state, enabling it to be shaped and formed in various applications.