Question

Arrange the following transition temperatures given by Differential Scanning Calorimetry (DSC) in ascending order.
A. Melting temperature
B. Crystallization temperature
C. Degradation temperature
D. Glass transition temperature

• A. D, B, A, C
• B. A, C, B, D
• C. B, A, D, C
• D. C, B, D, A"

Hint:

Think of the states of a semi-crystalline polymer as you heat it: 1. Glassy Solid (Amorphous part is frozen). 2. Heat past Tg \(\rightarrow\) Rubbery Solid (Amorphous part is mobile). 3. (Sometimes) Heat further \(\rightarrow\) Crystallization (Tc) (Mobile chains organize). 4. Heat past Tm \(\rightarrow\) Liquid Melt. 5. Heat much further \(\rightarrow\) Degradation (Td) (Burning/Decomposition). So, Tg < (Tc) < Tm < Td.

Answer 1

The Correct Option is A

Step 1: Define the thermal transitions for a semi-crystalline polymer as temperature increases.
- D. Glass transition temperature (Tg): This is the temperature at which the amorphous (non-crystalline) regions of the polymer change from a rigid, glassy state to a more flexible, rubbery state. This is the first major transition that occurs upon heating.
- B. Crystallization temperature (Tc): When an amorphous polymer is heated above its Tg, the polymer chains gain mobility. If held at a certain temperature, they can arrange themselves into ordered, crystalline structures. This process is called crystallization. On a DSC scan of a polymer being cooled from a melt, Tc is the peak where heat is released as crystals form. When heating an amorphous sample, it can also appear as an exothermic peak after Tg. It logically occurs after Tg but before melting.
- A. Melting temperature (Tm): This is the temperature at which the crystalline regions of the polymer melt and the material becomes a viscous liquid. This requires more energy than the glass transition, so Tm is always higher than Tg.
- C. Degradation temperature (Td): This is the temperature at which the polymer's chemical bonds begin to break, and the material starts to decompose. This is a chemical change, not a physical transition, and it occurs at a much higher temperature than melting.

Step 2: Arrange these temperatures in ascending (increasing) order. The sequence is: Glass Transition \(\rightarrow\) Crystallization \(\rightarrow\) Melting \(\rightarrow\) Degradation.
This corresponds to the order D, B, A, C.