ISO 5260:2023

Overview

ISO 5260:2023 specifies a quantitative 1H NMR spectrometry method for determining the epoxidation level and ring opening level of raw epoxidized natural rubber (ENR). Applicable to all commercially available ENR grades (for example ENR 25 and ENR 50), the standard describes sample preparation, NMR acquisition, spectral integration and calculation of percentage epoxidation and ring-opening from integrated proton signals. This method supports material specification and quality control requirements (it complements ISO 24483).

Key topics and technical requirements

• Scope: Quantitative determination of epoxide and ring-opening products in ENR using proton (1H) NMR.
• Sample prep: Weigh ~25–30 mg ENR, dissolve in ~2 mL deuterated chloroform (CDCl3 with 0.03% TMS), allow 16–24 h dissolution, transfer ~1 mL to NMR tube; avoid solids that broaden peaks.
• Reagent: High-purity CDCl3 (≥99.8%) containing TMS as internal reference.
• Instrument: FT‑NMR with proton probe and resonance frequency >100 MHz. Recommended acquisition parameters: 45° pulse, 5 s relaxation delay, 256 scans (document lists preferred settings).
• Integration targets (typical ppm windows):
  • NR methine proton (approx. 5.3–5.0 ppm)
  • Epoxy methine protons (approx. 2.9–2.6 ppm)
  • Furan-type protons (approx. 3.8–4.0 ppm)
  • Hydroxyl protons from ring opening (approx. 3.3–3.5 ppm)
• Calculations: Epoxidation and ring-opening percentages are calculated from the integrated areas of the above signals (epoxidation = epoxy proton area ÷ total relevant proton area ×100; ring opening = (furan + hydroxyl areas) ÷ total relevant proton area ×100).
• Precision and validation: Annex B reports precision from an interlaboratory test programme (six labs) with repeatability and reproducibility data given at a 95% confidence level.

Applications and who uses it

• Quality control laboratories in rubber manufacturing to verify ENR grade (e.g., ENR 25, ENR 50) and batch acceptance.
• Process control and production teams to monitor epoxidation reactions and minimize ring-opening by-products.
• Material suppliers and buyers to certify compliance with ENR specifications and contractual requirements.
• R&D and formulation scientists developing tyres, bearings, adhesives and other products using ENR.
• Third‑party testing labs performing standardized property measurements for regulatory or commercial purposes.

Related standards

• ISO 24483:2023 - specifications and terminology for epoxidized natural rubber (referenced in ISO 5260).
• ISO 19983 - method used to determine precision statistics reported in Annex B.

Keywords: ISO 5260:2023, epoxidized natural rubber, ENR, 1H NMR, proton NMR, epoxidation level, ring opening level, ENR 25, ENR 50, CDCl3, TMS, FT‑NMR, quality control.