ISO 11357-8:2021

Overview

ISO 11357-8:2021 specifies a DSC‑based method to determine the thermal conductivity of solid unfilled, filled or fibre‑reinforced plastics and composites. The method uses a differential scanning calorimeter (DSC) to measure heat flow through a cylindrical specimen with a known melting substance placed on top. It is applicable to materials with thermal conductivities up to 1 W/(m·K) and enables combined characterization with specific heat capacity (so thermal diffusivity can be calculated when density and cp are known).

Key topics and technical requirements

• Measurement principle: specimen sits on the DSC sample sensor; an empty crucible is placed in the reference position and a crucible containing a certified melting substance is placed on the specimen. The melting peak slope and differential heat flow are used, together with specimen height and temperature difference, to calculate thermal conductivity.
• Instrument and calibration: DSC in accordance with ISO 11357-1; use original raw data only. Method has been verified with heat‑flux DSC and is expected to be suitable for power‑compensated DSCs. Calibration of temperature and heat follows ISO 11357-1.
• Specimen geometry and preparation:
  • Cylindrical specimens, diameter tolerance ±20 µm, height 0.5–2.0 mm (height measured to ±10 µm).
  • Plane‑parallel, smooth faces (grind with ultra‑fine abrasive P800 or better).
  • At least five specimens measured and averaged.
• Apparatus and consumables:
  • Aluminium crucibles (open or ventilated closed); crucible mass difference ≤0.1 mg.
  • Certified high‑purity melting substances (standard specifies very high purity, e.g., ~99.9999%).
  • Protective lacquer (when using reactive metals such as gallium) - continuous coating ≤30 µm thickness on crucible interior.
  • Length measuring device meeting specified accuracy.
• Conditioning and sampling: condition specimens per ISO 291 for a minimum of 2 h; drying for moisture‑sensitive materials as required. For anisotropic composites, note specimen orientation.
• Performance and reporting: procedure covers measurement steps, evaluation of melting‑peak slopes, calculation of thermal conductivity, crucible service life (e.g., when using gallium), and precision/bias guidance.

Applications and users

ISO 11357-8 is useful for:

• Materials testing laboratories and quality control teams in plastics and composite manufacturing.
• R&D and materials scientists characterizing thermal properties for component design (electronics housings, thermal management, insulation).
• Composite and filler selection studies where thermal conductivity influences performance.
• Engineers performing thermal modeling who need experimentally derived k and, combined with cp and density, thermal diffusivity.

Related standards

• ISO 11357‑1 (DSC - general principles and calibration)
• ISO 291 (conditioning and testing atmospheres)
• ISO 472 (plastics vocabulary)
• ISO 6344‑1 (abrasive grain size - referenced for surface preparation)

Keywords: ISO 11357-8, thermal conductivity, DSC, differential scanning calorimetry, plastics, composites, measurement method, thermal diffusivity, gallium, specimen preparation.