ISO 6721-11:2019

Overview

ISO 6721-11:2019 specifies standardized methods to determine the glass transition temperature (Tg) of plastics using dynamic mechanical analysis (DMA) in a linear heating scan. The standard defines how to extract Tg from temperature-dependent dynamic mechanical properties - storage modulus, loss modulus and loss factor (tan δ) - for amorphous polymers and amorphous regions of partially crystalline polymers. It covers unreinforced and filled polymers, rubbers, foams, adhesives and fibre‑reinforced composites, and includes procedures to account for thermal lag and heating‑rate effects.

Keywords: ISO 6721-11:2019, glass transition temperature, Tg, dynamic mechanical analysis, DMA, plastics testing, thermal lag

Key topics and technical requirements

• Measurement principle: Oscillate a specimen at fixed frequency while performing a controlled linear temperature scan; record load, displacement and phase to calculate storage modulus, loss modulus and tan δ.
• Characteristic Tg definitions: Tg can be determined from:
  • Peak of the loss modulus curve (T_M'')
  • Inflection point of the storage modulus curve (T_M')
  • Peak of the loss factor (tan δ) curve (T_tanδ)
• Heating rates and frequencies: Instruments must support heating rates typically between 1 K/min and 10 K/min and operation at reference frequencies (e.g., 1 Hz or 10 Hz); heating-rate accuracy ±5% is required.
• Thermal lag correction: The temperature sensor measures the chamber environment, not the specimen; the standard provides procedures to assess and correct heating‑rate dependent thermal lag and to extrapolate a zero‑heating‑rate Tg.
• Specimen and apparatus: Test specimen geometry follows ISO 6721-1; DMA modes (flexure, torsion, shear, compression, tension) are allowed as appropriate to sample form. Equipment calibration and identical test atmospheres for calibration and measurement are required.
• Reporting: Results include storage modulus, loss modulus and tan δ curves, the Tg value(s) derived, test conditions and calibration details.

Applications and users

ISO 6721-11:2019 is used in:

• Materials R&D for polymer characterization, formulation optimization and identifying transition behavior.
• Quality control and acceptance testing in plastics manufacturing, composites, adhesives and rubber industries.
• Design and engineering, to select materials with suitable service temperature ranges and predict mechanical performance near Tg.
• Certification and failure analysis, where accurate Tg values inform performance limits and thermal stability assessments.

Typical users: polymer testing laboratories, QA/QC engineers, materials scientists, composite manufacturers, test instrument suppliers and certification bodies.

Related standards

• ISO 6721-1 - Plastics: General principles for dynamic mechanical properties (test modes, specimen requirements).
• ISO 11357-2 - Differential scanning calorimetry (DSC) methods for Tg (alternative technique).
• ISO 472 - Plastics vocabulary (terms and definitions).

This standard helps ensure reproducible, comparable Tg measurements using DMA, offering practical guidance for testing setup, thermal correction and interpretation of dynamic mechanical data.