Overview
ISO 14322:2018 - Plastics - Epoxy resins - Determination of degree of crosslinking of crosslinked epoxy resins by differential scanning calorimetry (DSC) specifies a DSC-based method to quantify the degree of crosslinking in epoxy resin systems. The method measures the heat of reaction remaining in a partly crosslinked sample and compares it to the total heat of reaction of the uncured system to calculate crosslink percentage. It is intended for epoxy systems with moderate or slow crosslinking speeds and may not be suitable for systems that cure very rapidly at ambient temperature.
Key Topics and Requirements
- Principle: Determine total reaction heat (uncrosslinked) and residual reaction heat (partly crosslinked) by DSC; degree of crosslinking C = (1 − Hs / Hr) × 100, where Hr = total heat of reaction and Hs = heat remaining in the sample.
- Sample and measurement:
- Typical sample mass: 10–20 mg, weighed to 0.01 mg precision.
- DSC apparatus requirements: heating rate up to 10 °C/min, temperature measurement within ±0.1 °C, heat-flux precision ±1%, operating range at least 20 °C–300 °C.
- Gas flow around sample with flow meter able to measure 10–50 ml/min.
- Pans must be thermally conductive and chemically compatible.
- Calibration and controls: Calibrate per ISO 11357‑1; indium is commonly used.
- Preliminary test: Verify applicability by measuring total heat of reaction on two uncured samples taken consecutively - agreement must be within ±10% relative to the average.
- Procedure: Conduct DSC for uncured and partly cured samples under identical time‑temperature programs; average duplicates for final values.
- Precision & reporting: Clause on interlaboratory precision and required test-report contents (sample ID, DSC program, measured heats, calculated degree of crosslinking).
Applications
- R&D and formulation development: Optimize curing schedules and catalyst or hardener selection.
- Production and quality control: Verify batch-to-batch cure state and ensure target crosslink levels in adhesives, coatings, composites and encapsulants.
- Failure analysis and process validation: Confirm incomplete cures or overcure in thermoset systems used in electronics, automotive and aerospace components.
- Users: Polymer scientists, materials engineers, QC laboratories, DSC analysts and thermoset manufacturers.
Related Standards
- ISO 11357‑1 - Differential scanning calorimetry (DSC) - General principles (calibration and measurement basics).
- ISO 11409 - Heats and temperatures of reaction by DSC (methods for calculating reaction heats).
Keywords: ISO 14322:2018, epoxy resins, DSC, differential scanning calorimetry, degree of crosslinking, heat of reaction, epoxy cure testing.
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