TA Instruments DSC 2500

 

 

1. Overview

• DSC 2500 measures the difference in heat flow between a sample and an inert reference as both are subjected to a controlled temperature program.
• When the sample undergoes a thermal event (melting, crystallization, glass transition, curing, oxidation, etc.), it absorbs or releases heat, detected as a change in heat flow.

2. Principle

• The instrument maintains both the sample and reference at the same temperature.
• Any temperature difference due to a thermal event causes the system to adjust the heat flow to restore equilibrium.
• The heat flow difference (ΔQ/Δt) is directly proportional to the enthalpy change (ΔH) or specific heat capacity (Cp) of the sample.
• Endothermic events (melting, dehydration) require additional heat input → positive heat flow.
• Exothermic events (crystallization, oxidation) release heat → negative heat flow.

3. Data Interpretation

• DSC measures the heat flow associated with thermal transitions as a function of temperature or time.
• Typical DSC Results Include:
  • Heat Flow vs. Temperature Curve: Displays endothermic and exothermic transitions.
  • Thermal Events Identified:
    • Glass transition (Tg): Step change in baseline (no latent heat).
    • Crystallization (Tc): Exothermic peak indicating ordered structure formation.
    • Melting (Tm): Endothermic peak corresponding to phase change.
    • Thermal degradation: Exothermic or endothermic shifts at high temperatures.

4. Example Application

• Pellet Thermal Behavior (1st Heat, As Received):
  • Lower curve values attributed to water plasticizing effect.
  • ΔCP at glass transition linked to amorphous phase content.
  • Large relative standard deviation likely due to processing conditions of as-received samples.
  • Melting temperatures (TM) and heats of fusion (ΔHF) show no clear correlation with fraction of added recycle.

Reference: TA469.pdf

5. Capabilities:

• Direct heat capacity measurement
• Glass transition Tg
• Crystallization
• Melting
• Oxidation
• Decomposition

6. Features:

• Temperature range: -90 to 550°C
• Temperature accuracy: ±0.025°C
• Temperature precision: ±0.005°C
• Enthalpy precision: ±0.04%