ISO 22821:2021

Overview

ISO 22821:2021 specifies a thermogravimetric (TG/TGA) method for determining fibre weight content (weight %) in carbon‑fibre‑reinforced composites (CFRP). The method applies to prepregs, parts and finished products and uses a thermogravimetric analyser to remove the polymer matrix by controlled heating in inert and oxidizing atmospheres. Compared with older combustion/acid techniques, TG offers improved safety and reduced reagent waste.

Key topics and technical requirements

• Principle: measure mass loss as a function of temperature (thermogram) and its derivative (dm/dT) to distinguish resin pyrolysis from carbon fibre combustion.
• Sample preparation: test specimens of about 10 mg ± 2 mg, thickness < 1 mm, lateral dimensions 3–5 mm; condition samples per ISO 291.
• Apparatus: thermogravimetric analyser with a microbalance (up to 50 mg capacity, readable to 1 µg), controlled furnace, gas selector and data acquisition. Recommended pans/crucibles: platinum or alumina.
• Gases: high‑purity nitrogen (≥ 99.995 % mass fraction) for pyrolysis and dry air (or reconstituted N2/O2) for combustion.
• Operating program (typical):
  • Initial temp ~35 ± 10 °C
  • Heat under N2 at 10 or 20 °C/min to 650 °C, dwell 5–10 min
  • Cool to 400 °C, switch atmosphere to air
  • Heat under air at 10 or 20 °C/min to 800–850 °C, hold until mass is constant
  • Gas flow typically 20–250 cm3/min (100 cm3/min if no manufacturer guidance)
• Data analysis: use the thermogram and derivative plot to identify mass points before and after pyrolysis and after fibre combustion. Fibre weight percent is calculated from the initial mass and the residual masses recorded at defined stages.
• Precision and reporting: precision data (reproducibility) is provided in Annex B; test reports must include sample description, test conditions, equipment, heating/flow rates, individual results and other test details.

Practical applications

• Quality control and acceptance testing of CFRP materials and parts
• Materials development and R&D for composite formulations
• Process control for prepreg and part manufacture
• Failure analysis, certification, and regulatory compliance where accurate fibre content is required

Who should use this standard

• Composite manufacturers and suppliers (prepreg, laminate, component producers)
• Materials testing laboratories and third‑party certification bodies
• R&D teams and material scientists working on CFRP characterization
• Quality engineers responsible for incoming inspection and production control

Related standards

• ISO 14127 - methods for fibre content (combustion/acid approaches)
• ISO 291 - conditioning atmospheres for testing
• ISO 9924‑3 - TG method references for related materials

Keywords: ISO 22821:2021, carbon-fibre-reinforced composites, thermogravimetry, TG, thermogravimetric analyser, fibre weight content, CFRP, thermogram.