ISO 24698-2:2018

Overview

ISO 24698-2:2018 specifies a laboratory method for determining the bound acrylonitrile content in acrylonitrile‑butadiene rubber (NBR) using the Kjeldahl method with an automatic analyser. The standard also applies to XNBR (carboxylic NBR), NBIR (acrylonitrile‑butadiene‑isoprene rubber) and NBR latex. Note that ISO 24698‑2 and ISO 24698‑1 can produce different results on the same sample.

Keywords: ISO 24698-2:2018, acrylonitrile-butadiene rubber, NBR, Kjeldahl method, bound acrylonitrile content, automatic analyser.

Key topics and technical requirements

• Principle: Convert nitrogen in the rubber sample to ammonium salt by acid digestion (K2SO4, H2SO4, CuSO4 catalyst), release ammonia with strong alkali, steam‑distill into boric acid and titrate the distillate.
• Apparatus: Use an automatic analyser with digestion, distillation and titration units plus a microprocessor to convert titration results to % nitrogen.
• Reagents: Typical reagents include sulfuric acid, hydrochloric acid (standard volumetric solutions 0.05 mol·dm−3), sodium hydroxide (10 mol·dm−3), K2SO4, CuSO4·5H2O, boric acid and ethanolic indicators.
• Sample preparation:
  • Raw NBR/XNBR/NBIR: sampling and milling per ISO 1795, solvent extraction (ethanol) per ISO 1407, drying to constant mass.
  • NBR latex: coagulation with ethanol/methanol and washing, then milling and drying per ISO 123.
• Procedure: Typical test portion 50–500 mg (preferably 5–15 mg N), controlled digestion until clear blue‑green, steam distillation, photometric or potentiometric titration, blank correction.
• Calculation: Formulas provided to convert titration volumes (using either sulfuric or hydrochloric acid) to bound acrylonitrile content (%).
• Performance: Instrument accuracy must be demonstrated with reference material (ammonium sulfate) - system calibration and precision requirements are specified; interlaboratory precision data are reported in Annex B and C.

Applications and users

Who uses ISO 24698-2:2018:

• Quality control and analytical laboratories in the rubber industry
• NBR, XNBR and NBIR manufacturers and compounders
• R&D teams developing nitrile elastomers and latex products
• Suppliers verifying raw material composition for seals, hoses, gloves and fuel-resistant components
• Regulatory and compliance testing where accurate acrylonitrile content is required

Practical uses:

• Routine QC of acrylonitrile content to ensure material performance and consistency
• Verifying latex coagulation and processing effects on bound acrylonitrile
• Comparing results across production batches or suppliers using standardized Kjeldahl analysis

Related standards

• ISO 24698‑1 (other methods for bound acrylonitrile)
• ISO 1795 (sampling and prep for raw rubber)
• ISO 123 (rubber latex sampling)
• ISO 1407 (solvent extraction for rubber)

This summary helps labs and manufacturers understand when and how to apply ISO 24698‑2:2018 for reliable measurement of bound acrylonitrile in NBR and related materials.