Overview
ISO 22768:2020 - "Raw rubber and rubber latex - Determination of the glass transition temperature by differential scanning calorimetry (DSC)" specifies a standardized DSC method to measure the glass transition temperature (Tg) of raw rubber and rubber latex. The document defines the test principle, sample preparation, instrument calibration, thermal cycle, result expression (inflection point at a 20 °C/min heating rate) and reporting requirements. It also includes precision data (Annex A for raw rubber and Annex B for rubber latex).
Key topics and technical requirements
- Test principle: Measure the change in specific heat capacity vs temperature using a differential scanning calorimeter (DSC) and determine Tg as the inflection point of the transition curve.
- Sample preparation:
- Raw rubber: representative specimen; ISO cites specimen mass around 0.01–0.02 g.
- Rubber latex: dry films (105 °C ±5 °C) and cut into ~2 mm × 2 mm pieces (see ISO 124:2014).
- Specimen mass and loading: DSC determinations typically use 5–20 mg; ensure good thermal contact and sealed pans; avoid handling with bare hands.
- Thermal cycle:
- Cooling to a stable baseline (e.g., ~−140 °C for very low-Tg rubbers) at 10 or 20 °C/min.
- Heating at 20 °C/min until ~30 °C above the upper limit of the glass transition range.
- Tg is defined as the midpoint/inflection point of the DSC curve (software or first-derivative DDSC may be used).
- Instrumentation & calibration:
- Use a DSC compliant with ISO 11357-1.
- Inert gas (nitrogen or helium) with flow rates typically 10–100 ml/min (±10%).
- Calibrants recommended: n‑octane, n‑heptane, cyclohexane, and indium for higher temperatures.
- Reporting: Must reference ISO 22768:2020 and include sample ID, specimen mass, instrument type, gas and flow rate, calibrants, thermal cycle, Tg (°C) with DSC curve, and test date.
- Precision: Interlaboratory precision data are provided; consult Annexes A and B before applying precision limits to acceptance criteria.
Applications and users
ISO 22768:2020 is intended for:
- Quality control and acceptance testing in rubber manufacturing
- R&D and formulation development to characterize polymer behavior and Tg
- Material selection, processing temperature selection and performance assessment for elastomers
- Independent test laboratories performing standardized DSC rubber testing
Typical uses include monitoring batch-to-batch consistency, evaluating the effect of additives or extraction residuals, and comparing natural vs synthetic rubbers or latex-derived materials.
Related standards
- ISO 11357-1:2016 - Plastics - Differential scanning calorimetry (DSC) - General principles
- ISO 124:2014 - Latex, rubber - Determination of total solids content
- ISO 1407 - Rubber - Determination of solvent extract
- ISO 23529 - Conditioning procedures for rubber test pieces
Keywords: ISO 22768:2020, glass transition temperature, Tg, differential scanning calorimetry, DSC, raw rubber, rubber latex, rubber testing, ISO standard.