Determination of Hydrolyzable Chlorine of Isocyanates ASTM D4663-20

Scope:

The ASTM D4663-20 test method is important to determine the hydrolyzable chlorine content in Isocyanates, how it is formed, and how its constituents react with alcohol and water to produce urea, carbonates, carbon dioxide, and hydrochloric acid. This test method is important to get accurate readings at different sample concentrations. It defines a standard to control the quality of Isocyanates.  It characterizes the toluene diisocyanates found in polyurethane products and is applicable for research purposes. Hydrolyzable chlorine content provides information about the performance of Isocyanates in polyurethane systems which helps specify their reliability.

Procedure:

The sample is taken as per the requirements and poured into a 400 mL beaker. 50 mL of methanol is stirred with the sample until the beaker becomes hot, and crystals show up. Hydrochloric acid is produced by reacting hydrolyzable chlorine with methanol. Then water is added and the reaction mixture is boiled for 30 minutes. The beaker is cooled, and nitric acid is added. Then the chlorides are determined through potentiometric titration with silver nitrate solution.

Specimen size:

The sample size is taken as per the requirement. Nine to 11 grams of sample is weighed and poured in a 400 mL beaker. 18 to 22 g of sample is used if hydrolyzable chlorine content is lower than 0.01%.

Data:

The hydrolyzable chlorine as weight percent can be calculated as follows:
Hydrolyzable chlorine, % ꞊ 35. 45 ×A × N × 100/(1000 × W )
꞊ 3.545 × A × N/W
Where: A = silver nitrate solution required for titration of the sample, mL.
N = normality of the AgNO3 solution, meq/mL.
W = sample used, g, and 3.545 = constant combining the atomic weight of chlorine.