DSC · Thermal Analysis · ISO 11357

DSC Analysis of Plastics — Glass Transition, Melting & Crystallinity

Updated: 2026-07-02 Category: Thermal Analysis Standard Typical use: Material ID · QC · Failure Analysis Editorial: KunststoffWissen

DSC is the most informative single thermal test for plastics. A small sample is heated (and cooled) at a controlled rate while the instrument records heat flow. Peaks and steps in the curve pinpoint melting, crystallisation and the glass transition — fingerprints that identify a polymer, check a batch, or explain a failure. The method is standardised in ISO 11357.

What DSC measures

DSC records heat flow versus temperature. Different transitions appear as characteristic features:

Transition	Curve feature	Tells you
Glass transition (Tg)	Step in baseline	Amorphous softening temperature
Melting (Tm)	Endothermic peak	Crystalline melt (semi-crystalline polymers)
Crystallisation (Tc)	Exothermic peak (on cooling)	How/when the polymer crystallises
Crystallinity	Melt enthalpy ΔH	Degree of crystallinity (vs 100 % reference)
OIT	Onset of oxidation (isothermal)	Stabiliser/antioxidant level

Standardisation: ISO 11357

The ISO 11357 series standardises DSC for plastics: general principles (11357-1), Tg (11357-2), Tm and Tc (11357-3), specific heat capacity (11357-4), crystallisation/melting behaviour and OIT in later parts. Standardised heating rates and specimen handling make results comparable between labs. ASTM D3418 is the corresponding US method.

Typical uses

DSC is used to identify a polymer (melting point fingerprint distinguishes PE, PP, PA6, PA66, POM, PET), verify incoming material (batch consistency, contamination, regrind content via shifted Tm/crystallinity), and investigate failures (degradation, insufficient stabilisation via low OIT, incorrect processing via altered crystallinity). It complements mechanical standards such as ISO 527 and thermal-mechanical tests like ISO 75 (HDT).

FAQ — Frequently Asked Questions

What can DSC tell me about a plastic?

DSC reveals the glass transition (Tg), melting temperature (Tm), crystallisation temperature (Tc), degree of crystallinity (from melt enthalpy) and oxidation induction time (OIT). From these you can identify the polymer, check batch consistency and detect degradation or insufficient stabilisation.

Which standard governs DSC of plastics?

The ISO 11357 series: ISO 11357-1 (general principles), -2 (glass transition), -3 (melting and crystallisation), -4 (specific heat capacity) and further parts for crystallisation behaviour and OIT. The equivalent US method is ASTM D3418.

How does DSC identify an unknown polymer?

Semi-crystalline polymers have characteristic melting points (e.g. PE ~130 °C, PP ~165 °C, PA6 ~220 °C, PA66 ~260 °C, POM ~165–175 °C, PET ~250 °C). The melting peak, combined with Tg and crystallisation behaviour, acts as a thermal fingerprint. Amorphous polymers show a Tg step but no melting peak.