Overview
ISO 4504:2023 - Plastics - Polyethylene (PE) - Determination of co‑monomer content by solution state 13C‑NMR spectrometry specifies two validated solution‑state 13C‑NMR methods for measuring co‑monomer (1‑olefin) content in polyethylene copolymers. The standard covers sample preparation, instrument requirements, acquisition parameters, spectral integration, calculations and reporting. It applies to ethylene copolymers containing less than 50% (mass fraction) of a single type of 1‑olefin comonomer and excludes ethylene homopolymers and multi‑comonomer systems.
Key topics and technical requirements
- Two NMR methods:
- Method A - single pulse with inverse gated proton decoupling (direct 13C excitation).
- Method B - Refocused INEPT (INEPT: insensitive nuclei enhanced by polarization transfer) with proton decoupling (sensitivity‑enhanced 13C detection).
- Instrument minimum: PFT‑NMR spectrometer with magnetic field ≥ 7.05 T (≈300 MHz proton / 75 MHz 13C); temperature control at 120 °C ± 1 °C.
- Sample preparation: Typical sample masses - ~30 mg in 5 mm NMR tube or ~120 mg in 10 mm tube; dissolution in deuterated solvents (o‑DCB‑d4, p‑DCB‑d4 or TCE‑d2) at 120–130 °C; optional relaxation agent (Cr(acac)3).
- Acquisition parameters and quality: Relaxation delays based on 13C T1, calibrated 90° pulse, spectrum phase/baseline correction. Signal‑to‑noise ratio (SNR) targets noted (e.g., branch CH‑carbon SNR ≥ 20:1 for quantitation; isolated methylene carbon SNR targets also specified).
- Data treatment: Defined integration regions (Annex A), calculation formulae (Annex B) and conversion to mole % and branches per 1 000 carbons. Worked examples and precision data provided (Annexes C–G).
- Documentation: Requirements for test report and method validation, including precision and limits of detection/quantitation.
Applications and who will use it
- Quality control laboratories: Routine QC of polyethylene grades to verify comonomer content and branching.
- Polymer R&D: Structure–property studies, catalyst performance assessment and copolymer composition analysis.
- Process control and suppliers: Raw material certification and specification compliance for PE producers and converters.
- Analytical service labs and instrument manufacturers: Method implementation, calibration and software/protocol development.
Keywords: ISO 4504:2023, polyethylene, PE, 13C‑NMR, co‑monomer content, INEPT, inverse gated decoupling, solution state NMR, ethylene copolymer.
Related standards
- ISO 472 - Plastics - Vocabulary (terms used)
- ISO 648 - Laboratory glassware - Single‑volume pipettes (sample handling)