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D4662-20 – Standard Test Method Technical Guide
📐 Scope and Terminology
These test methods, designated D4662-20, are used to measure the acidic and basic constituents in polyols and other materials of high acidity or alkalinity that are soluble in mixtures of toluene and ethyl alcohol. They are applicable for quality control and specification testing in polyurethane raw materials. Note that these test methods do not apply to polyethers.
Key terms are defined per Terminology D883 and E456. The specific definitions for this standard are:
| 🟦 Term | 📐 Definition | 🎯 Unit |
|---|---|---|
| Acid Number | The quantity of base, expressed in milligrams of potassium hydroxide, required to titrate acidic constituents present in 1 g of sample. | mg KOH/g |
| Alkalinity Number | The quantity of base, expressed as milligrams of potassium hydroxide, present in 1 g of sample. | mg KOH/g |
⚠️ Safety Notice: The standard does not address all safety concerns. Users are responsible for establishing appropriate safety, health, and environmental practices.
⚙️ Test Procedure and Reagents
The sample is dissolved in a mixture of toluene and ethyl alcohol to form a single-phase solution. This solution is titrated at room temperature with alcoholic potassium hydroxide solution. The endpoint is detected by the color change of phenolphthalein indicator. For alkalinity numbers, a back-titration is performed after adding excess hydrochloric acid. Potentiometric determination can also be used.
Reagents must be of analytical grade, conforming to the specifications of the Committee on Analytical Reagents of the American Chemical Society. Use of other grades is permitted if they do not lessen the accuracy of the determination.
| 📐 Parameter | ⚡ Specification |
|---|---|
| Solvent | Toluene and ethyl alcohol mixture |
| Temperature | Room temperature |
| Indicator | Phenolphthalein (color change endpoint) |
| Titrant | Alcoholic potassium hydroxide solution |
| Back-titration | Excess hydrochloric acid for alkalinity number |
💡 Technical Note: Ensuring a single-phase solution is critical. Use sufficient solvent to avoid precipitate or turbidity before titration.
📊 Significance and Use
The acid and alkalinity numbers are important indicators of batch-to-batch uniformity in polyols. They are used as correction factors in calculating hydroxyl number. These test methods are suitable for quality control, specification tests, and research. The results reflect the extent of reaction with acids and help monitor product consistency.
These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and Subcommittee D20.22 on Cellular Materials – Plastics and Elastomers.
❓ Frequently Asked Questions
🔍 What is the scope of ASTM D4662-20?
These test methods measure acid and alkalinity numbers in polyols and other materials soluble in toluene and ethyl alcohol, but do not apply to polyethers.
💡 How are acid and alkalinity numbers determined?
The acid number is found by titration with alcoholic KOH using phenolphthalein. The alkalinity number is determined by back-titration after adding excess HCl.
⚡ What safety considerations are highlighted?
The standard does not address all safety concerns; users must establish appropriate safety, health, and environmental practices.
📌 Why are polyethers excluded from these test methods?
Polyethers are excluded due to potential solubility issues or inaccuracy when using this method.