ASTM D7389 Test Method for Determining Acid Number (Empirical) of Maleic Anhydride (MAH) Grafted Waxes.

Scope: 

The acid number of maleic anhydride (MAH) grafted waxes is determined using ASTM D7389 test procedure. The number reflects the amount of free acid present and is derived by direct titration of the substance. The data stated in SI units are to be regarded as standard. 

Test Procedure: 

In ASTM D7389, the sample is prepared and weighed to the nearest 0.001 g, and added to a 250 mL acid-value flask followed by 40 mL of xylene. The sample is heated to dissolve the sample. A few drops of phenolphthalein is added as an indicator solution and titration of the hot solution is done until the first persistent pink color. If precipitation of waxes occurs samples should be reheated. The number of mL of the standard alkali solution used is recorded. 

Sample size:  

20 g of the sample is required.

Data: 

The acid number is calculated from the test by the equation below.

Acid number = (AN × 56.1)/ B

Where,

A – milliliters of alkali solution required for titration of the sample

B – Normality of the alkali solution

N – Grams of sample used

Conclusion: 

ASTM D7389 describes test procedures for determining the acid number of maleic anhydride (MAH) grafted waxes.