Overview
ISO 16564:2004 - "Rubber, raw natural - Determination of average molecular mass and molecular‑mass distribution by size exclusion chromatography (SEC)" - specifies a relative SEC method for measuring the molecular‑mass characteristics of raw natural rubber dissolved in tetrahydrofuran (THF). Calibration is performed with a set of polystyrene standards; an informative annex describes an alternative procedure using cyclohexane and polyisoprene standards. The standard defines sample preparation, chromatography conditions, calibration, data processing and reporting (including gel content).
Key topics and technical requirements
- Sample dissolution and filtration: Dried natural rubber is dissolved in HPLC‑grade THF (BHT antioxidant added if needed), kept warm (example: 37 °C for 24 h) and filtered through PTFE membranes (0.45–1 μm) to remove gel and insolubles. Gel content is quantified by filter mass change.
- Chromatograph setup: Uses SEC columns (typically styrene‑divinylbenzene packings) connected largest‑to‑smallest pore size, a degassed solvent reservoir, temperature control (columns commonly 30–45 °C), pump (example flow 1.0 mL/min at 35 °C) and an RI or other suitable detector.
- Calibration: A traceable set of polystyrene standards is used for retention‑time vs log(M) calibration. Standards are prepared by swelling (not shaking) and injected in triplicate to obtain average retention times for the calibration curve.
- Data and outputs: Instrument/software calculates mass‑average (Mw), number‑average (Mn), z‑average (Mz), polydispersity (Mw/Mn) and peak molecular mass (Mp) and provides graphical molecular‑mass distribution.
- Alternative (Annex A): Cyclohexane solvent with polyisoprene standards - requires higher column oven temperatures (e.g., 65 °C), BHT stabilization, centrifugation for gel determination and may need universal calibration or Mark–Houwink conversions when comparing to polystyrene‑calibrated results.
Practical applications
- Characterizing raw natural rubber batches for research, quality control and process monitoring.
- Determining molecular‑weight distribution parameters that correlate with mechanical properties, processing behavior and product performance.
- Comparing production lots, optimizing polymerization/harvesting conditions and validating supplier materials.
Who should use this standard
- Rubber testing laboratories, quality assurance teams in rubber manufacturing, R&D scientists in polymer science, and third‑party testing bodies requiring reproducible molecular‑mass data for natural rubber using SEC.
Related guidance
- Annex A (informative) provides the cyclohexane/polyisoprene alternative and practical notes (centrifugation, UV detection, column oven) for labs facing THF‑related issues.
- When interpreting results across solvents/standards, consider calibration differences and apply universal calibration or Mark–Houwink corrections where needed.
Keywords: ISO 16564:2004, size exclusion chromatography, SEC, natural rubber, molecular mass, molecular‑mass distribution, tetrahydrofuran, polystyrene standards, cyclohexane, polyisoprene, gel content.
Open preview (PDF)Rubber, raw natural — Determination of average molecular mass and molecular-mass distribution by size exclusion chromatography (SEC)
