Overview
ISO 14900:2023 - Plastics - Polyols for use in the production of polyurethanes - Determination of hydroxyl number - specifies two laboratory methods to measure the hydroxyl number (hydroxyl value) of polyols used as polyurethane raw materials. The hydroxyl number is defined as the milligrams of potassium hydroxide equivalent to the hydroxyl content of 1 g of sample. Accurate hydroxyl-number measurement is essential to formulate polyurethane systems and for product specification, quality control and research.
Key topics and technical requirements
- Two validated methods
- Method A (Acetylation): Esterification with acetic anhydride in pyridine, catalyzed by imidazole; excess reagent hydrolyzed and resulting acetic acid titrated. Suited for readily esterified polyether polyols and sterically hindered polyols (e.g., sugar-based).
- Method B (Phthalation): Esterification with phthalic anhydride in pyridine, catalyzed by imidazole; excess anhydride hydrolyzed and resulting phthalic acid titrated. Applicable to polyether, polymer and amine‑initiated polyols but can under-report for sterically hindered polyols.
- Analytical principle: Esterify hydroxyl groups → hydrolyse excess reagent → titrate acid formed with standardized NaOH; hydroxyl number calculated from titration difference between sample and blank.
- Reagents and equipment: reagent‑grade acetic or phthalic anhydride, pyridine (specified water limits), imidazole catalyst, standardized 0.5 mol/L NaOH, phenolphthalein or potentiometric titration, hotplate/oil bath, condenser, syringes and precision balance.
- Interferences and controls
- Samples with >0.2% water must be dried before analysis.
- Primary/secondary amines and long‑chain fatty acids react with reagents and are included in results.
- Temperature and reagent concentration corrections (e.g., thermal expansion of titrant) are required for accurate calculation.
- Safety: acetic anhydride and pyridine are toxic, corrosive and flammable - use appropriate ventilation and PPE.
Applications and users
- Quality control laboratories in polyurethane manufacturers and raw‑material suppliers - to confirm polyol hydroxyl content for consistent product performance.
- Formulation chemists and polymer researchers - to determine reactive functionality and molecular characteristics for PU system design.
- Third‑party testing labs and certification bodies - for specification testing and contractual compliance.
- Uses: research, QC, specification compliance, troubleshooting formulation issues (e.g., incorrect stoichiometry, unexpected crosslinking).
Related standards
- ISO 760 (Karl Fischer water determination) - for sample water content control.
- ISO standards on hydroxyl/related values: ISO 2554, ISO 4326, ISO 4327, ISO 4629, ISO 6796.
- Comparable methods: ASTM D4274 (similar imidazole‑catalyzed procedures).
Keywords: ISO 14900:2023, hydroxyl number, polyols, polyurethanes, acetylation, phthalation, Method A, Method B, titration, quality control, laboratory procedure.
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