ISO 4629-1:2016

Overview

ISO 4629-1:2016 specifies a titrimetric method without a catalyst for determining the hydroxyl value of binders and binder solutions used in paints and varnishes. The method quantifies free hydroxyl groups (e.g., polyhydric alcohols, polyester end groups, hydroxylated fatty acids) by acetylation with acetic anhydride, hydrolysis of the excess reagent, and back-titration of the resulting acetic acid with potassium hydroxide. This Part 1 method is designed for routine laboratory quality control and formulation work where catalytic activation is not used.

Key topics and requirements

• Scope and limitations
  • Applicable to binders and binder solutions for paints and varnishes.
  • Not applicable to resins that contain both hydroxyl and epoxy groups (epoxy groups would bias results), cellulose nitrate, or phenolic resins.
  • When testing binder solutions, consider other constituents that may contain hydroxyl groups.
• Analytical principle
  • Acetylation of hydroxyl groups → hydrolysis of excess acetic anhydride → titration of acetic acid with KOH (potentiometric or indicator-based end point).
• Reagents and apparatus
  • Uses analytical-grade reagents and laboratory glassware as referenced (e.g., burettes, pipettes).
  • Typical reagents: acetic anhydride-based acetylating reagent, potassium hydroxide in methanol (~0.5 mol/L), phenolphthalein or mixed indicators; potentiometric titration is an optional alternative.
• Procedure essentials
  • Duplicate determinations; use prescribed test portion masses (table provided in the standard) and 5.00 ± 0.02 ml acetylating reagent.
  • Perform blank test and determine acid value (ISO 2114) for correction.
  • Report mean of two valid replicates to nearest 1 mg KOH/g. If duplicates differ by >5% (relative), repeat.
• Performance
  • Precision varies with hydroxyl value (examples from interlaboratory study provided: repeatability and reproducibility figures).

Applications

• Quality control testing in paint, varnish and binder production.
• Raw material evaluation for formulation and specification compliance.
• Formulation development and stability studies where hydroxyl number / hydroxyl value is critical (e.g., crosslinking stoichiometry, polyester and alkyd binder characterization).
• Laboratories performing routine titrimetric and potentiometric analyses.

Related standards

• ISO 4629-2 - Part 2: titrimetric method using a catalyst (complementary method).
• ISO 7142 - Determination of hydroxyl value for epoxy resins (when epoxy groups are present).
• ISO 2114 - Determination of acid value (used for correction in results).
• Laboratory glassware and sampling references: ISO 385, ISO 648, ISO 3696, ISO 15528.

Keywords: ISO 4629-1:2016, hydroxyl value, binders for paints and varnishes, titrimetric method, acetylation, potassium hydroxide titration, potentiometric titration, paint binder testing.