Overview
ISO 1065:1991 specifies standardized laboratory procedures to determine the cloud point of non-ionic surface-active agents obtained from ethylene oxide and mixed non-ionic agents. The cloud point is the temperature above which an aqueous solution of an ethoxylated surfactant separates into two liquid phases and becomes opaque. This property is critical because surfactant performance and formulation behavior change rapidly in the vicinity of the cloud point.
The Standard defines five measurement methods (A, B, C, D and E). Methods A–C are primarily for surfactants condensed with lipophilic bases that contain no oxypropylene groups. Methods D and E are provided for mixed or otherwise challenging materials and are intended for use after agreement between interested parties.
Key Topics
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Scope and Methods: Five methods (A–E). Selection depends on the temperature range and material type:
- Method A: use when cloudiness appears between 10 °C and 90 °C (distilled water)
- Method B: use when cloudiness appears below 10 °C, or for low solubility (use 25 % n-butyldiglycol aqueous solution)
- Method C: use when cloudiness appears above 90 °C (sealed ampoule under pressure)
- Method D: use for acidified aqueous solutions clouding between 10 °C and 90 °C (1.0 mol/l HCl)
- Method E: use for acidified solutions clouding above 90 °C (water with calcium hardness and butan-1-ol)
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Test practice: The product is dissolved at a specified concentration, heated until opaque, then cooled while stirred; the temperature where opacity disappears is recorded. Results are the arithmetic mean of at least two measurements within 0.5 °C.
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Apparatus and reagents: Ordinary laboratory glassware, thermometer (0.1 °C), sealed ampoules for high-temperature tests, n-butyldiglycol reagent, standard HCl solution and a calcium/butan-1-ol solution for specific methods.
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Precision: Repeatability (same operator, same lab) is stated as not exceeding 0.5 °C; reproducibility (different laboratories) not exceeding 1.0 °C.
Applications
- Quality control: Rapid, routine assessment of ethoxylation level and batch uniformity in manufacturing.
- Formulation development: Predicting temperature-dependent phase behavior and stability of emulsions, detergents and personal-care products.
- Raw material verification: Checking degree of ethoxylation and identifying deviations that affect performance.
- Comparative testing: Establishing baseline cloud points for product specifications and supplier acceptance.
Related Standards
The standard references other ISO documents related to sampling, apparatus and definitions that support accurate cloud point testing, including:
- ISO 607:1980 (sample division)
- ISO 1773:1976 (laboratory glassware - boiling flasks)
- ISO 2174:1990 (preparation of water with known calcium hardness)
- ISO vocabulary for surface-active agents as cited in the standard (vocabulary definition for clarification/cloud point)
Follow ISO 1065:1991 for consistent, reproducible cloud point testing of ethoxylated non-ionic surfactants and for reliable laboratory data that support product specification, formulation design and quality assurance.
Open preview (PDF)Non-ionic surface-active agents obtained from ethylene oxide and mixed non-ionic surface-active agents — Determination of cloud point
