Glass transition temperature

Below solidifying or glass transition temperature (also referred to as “glass temperature”), the polymers not organised in the crystal lattice and polymer segments of a semi-crystalline plastic lose their ability to move. As a result, the properties of the plastic significantly change when the glass exceeds its transition temperature or falls below it.

• Hardness:
  Below the glass transition temperature, the hardness increases significantly
• Elongation:
  Below glass transition temperature, plastics loose their elastomer properties and become hard and brittle
• Volume
• Surface energy:
  And thus also the contact angle. The glass transition temperature of thermoplastics can be very easily determined by measuring the contact angle as a function of temperature.

The "solidifying" temperature has nothing to do with the melting temperature. The thermoplastic is solid below and above the solidifying temperature.