Overview
ISO 24076:2021 - Plastics - Polypropylene (PP) - Determination of isotactic index by low‑resolution nuclear magnetic resonance spectrometry - specifies a relative, non‑destructive LR‑NMR method to determine the isotactic index (II) of polypropylene. The method is calibrated against the solvent‑extraction reference in ISO 9113 and is intended for base polymers (not mixtures). It supports identification and coding of PP‑H (types H propylene) plastics per ISO 19069‑1 and improves testing efficiency by avoiding solvent extraction during routine measurement.
Key topics and technical requirements
- Principle: Low‑resolution pulsed NMR records proton magnetization decay; faster‑decaying signal components correspond to unextractable (crystalline/isotactic) material and are related to isotactic index through a calibration curve.
- Two measurement approaches:
- Method A - Ratio method: Uses a ratio probe to compare signals of unextractable vs. whole sample.
- Method B - Absolute method: Uses an absolute probe to relate extractable‑signal to sample mass.
- Calibration: LR‑NMR results are calibrated against isotactic index values measured by the ISO 9113 n‑heptane extraction method using at least five reference samples across the relevant II range.
- Apparatus and conditions (examples from standard):
- LR‑NMR frequency: 18–25 MHz (typical 20 or 23 MHz)
- Probe diameters: ~10 mm (Method A) or ~26 mm (Method B)
- Probe temperature: 40 °C ± 0.1 °C
- Sample drying/annealing: 140 °C ± 2 °C for 2 h under ≤25 kPa
- Sample tube dimensions specified for each method; balance required for Method B (0.0001 g precision)
- Scope limits: Suitable for base polypropylene polymers only; not applicable to mixtures.
Applications and who uses it
- Quality control laboratories - faster routine monitoring of polypropylene isotactic index without repeated solvent extraction.
- Polymer manufacturers and compounders - product classification, process monitoring, and acceptance testing of PP‑H materials.
- NMR instrument vendors and method developers - implementation of validated LR‑NMR procedures and instrument calibration services.
- Standards and conformity bodies - material coding and compliance assessment when classifying PP per ISO 19069‑1.
Related standards
- ISO 9113 - Direct (absolute) n‑heptane extraction method for polypropylene isotactic index (reference calibration method).
- ISO 19069‑1 - Coding and identification of types H propylene (PP‑H) plastics.
Keywords: ISO 24076:2021, polypropylene isotactic index, LR‑NMR, low‑resolution nuclear magnetic resonance, PP‑H, plastics testing, ISO 9113, ISO 19069‑1.