Overview
ISO 247-2:2018 - "Rubber - Determination of ash - Part 2: Thermogravimetric analysis (TGA)" specifies two TGA-based methods for measuring ash content in raw rubbers, compounded rubbers and vulcanizates. The standard applies to rubbers of the M, O, R and U families (ISO 1629 nomenclature). It describes sample preparation, instrument settings, calibration, test procedures (Method A for raw rubber; Method B for compounded/vulcanized rubber) and expression of results. Note: the methods are not applicable to rubbers containing chlorine, bromine or iodine, and the standard does not interpret ash in terms of inorganic chemistry.
Key topics and technical requirements
- Test principle: Thermogravimetric analysis - the sample is heated under nitrogen to decompose polymeric material, then switched to oxygen/air to burn carbonaceous residue; the remaining mass is reported as ash.
- Methods:
- Method A - for raw rubbers. Typical TGA program: heat to 500 °C in N2, then to 550 °C in O2/air until constant mass.
- Method B - for compounded or vulcanized rubbers. Typical program: heat to 550 °C in N2, then to 650 °C (or up to 850 °C for inorganic fillers like CaCO3) in O2/air until constant mass.
- Sample size & prep: Test portions typically 10–20 mg taken from homogenized or milled material per ISO 1795 and ISO 248-1 guidance.
- Apparatus & gases:
- Thermogravimetric analyser with thermo-balance, furnace, temperature programmer and gas flow control.
- Sample pans (platinum or alumina); analytical balance capable of 0.1 mg.
- Dry nitrogen and oxygen (or dry air) with ≥ 99.99% purity.
- Calibration & precision: Temperature and mass calibration per manufacturer; recommended periodic mass calibration (e.g., monthly). The standard includes precision data from an interlaboratory study.
- Reporting: Include reference to ISO 247-2:2018, method used, heating rates, final temperatures, apparatus type, results and any deviations.
Applications and who uses it
- Quality control laboratories performing routine rubber testing and incoming inspection.
- Rubber manufacturers and compounders verifying ash (inorganic residue) levels in raw materials, compounds and finished vulcanizates.
- R&D and formulation teams assessing filler and inorganic content effects on performance (note: ISO 247-2 does not provide chemical interpretation of ash).
- Third‑party testing and certification bodies requiring standardized, reproducible ash determinations using TGA.
Related standards
- ISO 1629 - Rubber nomenclature (M, O, R, U families)
- ISO 248-1 - Determination of volatile-matter content (hot‑mill/oven)
- ISO 1795 - Sampling and preparative procedures
- ISO 19983 - Precision of rubber test methods
Keywords: ISO 247-2:2018, thermogravimetric analysis, TGA, ash determination, rubber testing, compounded rubbers, vulcanizates, rubber quality control, TGA calibration.
