ASTM D4662 Determination of Acid and Alkaline Numbers of Polyols

ASTM D4662 test method evaluates the materials that can dissolve in the mixture of toluene and ethyl alcohol by measuring the acidic and basic content of the polyols. It also determines the acid and alkaline number of many other materials with the exception of polyethers. The final results of this test method can be expressed in SI units, however, there is no standard specified.

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    The ASTM D4662 test method is important to determine the acid and alkaline number of polyols with the help of titration. This test method is important to get accurate readings at different sample concentrations. It defines a standard to control the quality and measure uniformity of these polyols. It characterizes the polyols found in polyurethane products and is applicable for research purposes. It determines the hydroxyl number with the help of correction factors. It provides information about the performance of the polyols in polyurethane systems which helps specify their reliability and the extent of their reaction with acids.


    In ASTM D4662, the sample is taken as per the requirements and poured into a 250 mL flask filled with the solvent and indicator solution. It is dissolved in a toluene and ethyl alcohol mixture which is then titrated by adding KOH at room temperature. After its titration with the alcoholic potassium hydroxide solution and color change of the phenolphthalein, the sample is titrated again by adding hydrochloric acid which helps to determine the alkalinity numbers. The endpoints of the potentiometric titration are noted and the acid or alkaline numbers are determined.

    Specimen size:

    For ASTM D4662 testing, the sample size is taken as per the requirements. Six to eight grams of the sample is taken if its acid number is less than 7.


    The acid number, in milligrams of KOH/gram of sample, is calculated for ASTM D4662 testing as follows:

    Acid number ꞊ [(A – B) N × 56.1]/W
    The alkalinity number, in milligrams of KOH/gram of sample, is calculated as follows:
    Alkalinity number ꞊ [(B –A) N × 56.1]/W


    The ASTM D4662 test method is important to determine the acid and alkaline number of polyols with the help of titration.


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