Overview
ISO 3900:2023 specifies a validated laboratory method for determining the bound acrylonitrile content of emulsion‑polymerized nitrile butadiene rubber (NBR) lattices. The method uses the Kjeldahl macro‑method adapted for nitrile latex and is applicable to NBR lattices with bound acrylonitrile in the range 18 % to 45 %. It also applies to related lattices such as carboxylic‑nitrile‑butadiene (XNBR) and nitrile‑isoprene (NIR).
The procedure requires standard sampling and sample preparation (ISO 123; ISO 24698‑2), coagulation and drying to constant mass, followed by acid digestion to convert bound nitrogen to ammonium salts and titrimetric determination of released ammonia.
Keywords: ISO 3900:2023, nitrile latex, NBR, bound acrylonitrile, Kjeldahl macro‑method, nitrogen determination, quality control.
Key Topics
- Scope: Determination of bound acrylonitrile content in emulsion‑polymerized NBR lattices (18–45 %).
- Principle: Coagulate and dry latex; digest dried polymer with sulfuric acid and catalyst; convert nitrogen to ammonium hydrogen sulfate; make alkaline and distil ammonia into boric acid; titrate with standard sulfuric acid solution.
- Reagents & Apparatus: Reagents specified follow ISO 1656 macro‑method; sulfuric acid volumetric solution (c = 0.1 mol·dm⁻³) is used. Kjeldahl apparatus with an ~800 cm³ digestion flask is recommended.
- Sample Prep & Sampling: Take ~500 g sample per ISO 123 and prepare dried test portion per ISO 24698‑2; dry at 100 °C ± 2 °C until constant mass.
- Results Expression: Bound acrylonitrile is calculated from titration volumes and sample mass and reported to the nearest 0.01 %.
- Precision: Precision data are provided in Annex A based on an interlaboratory test program (six laboratories) and include repeatability and reproducibility estimates.
Applications
- Quality control: Accurate determination of acrylonitrile content supports batch release testing and in‑process monitoring for NBR and related latex materials.
- Specification compliance: Ensures that latex raw materials meet formulation and performance requirements where acrylonitrile content affects chemical, mechanical and barrier properties.
- Traceability & reporting: Standardized test method enables consistent reporting between suppliers, manufacturers and testing laboratories.
Related Standards
- ISO 1656:2019 - Kjeldahl macro‑method for nitrogen determination in rubber (referenced for reagents and macro‑method details).
- ISO 24698‑2:2018 - Preparation of dried NBR latex test samples.
- ISO 123 - Sampling of rubber latex.
- ISO 19983:2022 - Determination of precision of test methods (precision evaluation referenced in Annex A).
For implementation, laboratories should follow the full text of ISO 3900:2023 and the referenced standards, ensure appropriate safety practices, and record all test conditions in the test report (clause 11) for traceability and reproducibility.
