Overview
ISO 11357-2:2020 - Plastics - Differential scanning calorimetry (DSC) - Part 2 specifies standardized methods for measuring the glass transition temperature (Tg) and the glass transition step height of amorphous and partially crystalline plastics using differential scanning calorimetry (DSC). It defines measurement principles, required apparatus and specimen handling (referencing ISO 11357-1), detailed test procedures, and accepted methods to assign Tg and Δcp(Tg) (step height). This part of the ISO 11357 series is essential for consistent, comparable DSC results across laboratories and manufacturers.
Key Topics and Requirements
- Scope and principle: Measurement of the change in heat flow with temperature to determine Tg and the specific heat capacity change (step height) associated with the glass transition.
- Apparatus and calibration: Use equipment and calibration procedures as defined in ISO 11357-1.
- Specimen mass and preparation: Typical specimen mass between 5 mg and 20 mg (higher end for partially crystalline materials). Thermal history matters-measurements are normally taken from the second heating scan after erasing prior thermal history.
- Scan conditions: Preferred scan rate 20 K/min for heating and cooling; a 5 min pre‑purge and 5 min hold steps are specified for thermal equilibration. Cooling to about 50 °C below the anticipated Tg and reheating to about 30 K above the extrapolated end temperature are recommended.
- Tg determination methods: Three accepted methods:
- Equal‑areas method (preferred) - balances areas above/below baselines; best for samples with enthalpy relaxation.
- Half‑step‑height method - intersection at midway between extrapolated baselines.
- Inflection‑point method - assigns Tg to steepest slope point.
- Step height (Δcp(Tg)): Determined from extrapolated baselines and reported with the chosen Tg method.
- Practical constraints: Limit crucible reuse (preferably use new crucibles); inspect for mass loss or degradation; document deviations and test report details as required.
Applications and Users
ISO 11357-2:2020 is used by:
- Polymer R&D and material scientists for thermal characterization of plastics.
- Quality control laboratories verifying Tg and amorphous content proxies for production batches.
- Product designers and formulators optimizing processing and service temperatures.
- Instrument manufacturers and calibration labs implementing standardized DSC test protocols.
Practical uses include assessing processing windows, predictions of mechanical behavior near Tg, and estimating amorphous fraction in partially crystalline polymers (step height proportional to amorphous content).
Related Standards
- ISO 11357-1 - Differential scanning calorimetry (DSC): general principles (normative reference).
- ISO 472 - Plastics - Vocabulary (terms and definitions).
- Other parts of the ISO 11357 series covering additional DSC analyses and thermal transitions.
Keywords: ISO 11357-2:2020, DSC, glass transition temperature, Tg, glass transition step height, Δcp(Tg), plastics, differential scanning calorimetry, polymer thermal analysis.
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