ASTM D6099-18 Determination of Acidity in Moderate to High Acidity Aromatic Isocyanates

Scope:

ASTM D6099-18 test method determines the acidity of aromatic isocyanates and polyurethanes. This test method is important to get accurate readings at different sample concentrations. It defines a standard to control the quality of aromatic isocyanates.  It characterizes the aromatic isocyanates and moderate to high acidity prepolymers and is applicable for research purposes. The acidic content provides information about the performance of isocyanates in polyurethane systems which helps specify their reliability. This method resolved the problems with moderate to high-level acidity determination. 

Procedure:

The apparatus consists of beakers, pipet, automatic titration equipment, reference electrode, pH glass electrode, magnetic stirrer, watch glasses, and analytical balance in setting up. The sample is weighed and taken in a 250mL beaker. 50mL of dried toluene is poured in. 100mL of methanol is added to the solution. The solution is mixed with a stir bar and covered with a watch glass. The sample is allowed to cool at room temperature. The acidic content is determined through potentiometric titration with methanolic KOH. The difference in titer helps detect the acidity of aromatic isocyanates. The endpoints, along with the pH, are determined.

Specimen Size:

10 g of sample is poured into a 250 mL beaker.

Data:

The acidity, as ppm HCl, is calculated by applying the formula
Where: Vsam = volume of titrant needed for the sample, mL,
N = normality of the titrant solution, and
F = 36 465 (mol weight of HCl) × 1000 (factor to change mg/g to μg/g, that is, ppm).