ASTM D5523-21 Acidity by Argentometric Determination of Hydrolyzable Chlorine in Aromatic Isocyanates

Scope:

The ASTM D5523-21 test method is important to determine the hydrolyzable chlorine content in aromatic Isocyanates, how it is formed and how its constituents react with alcohol and water to produce 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. This method resolved the problems with low-level acidity determination. 

Procedure:

In ASTM D5523-21 apparatus consists of a potentiometric titrator, combination silver billet electrode, oven, and magnetic stirrer. The sample is taken as per the requirements and poured into a 400mL beaker. Sample is Stirred with 100mL of 2-propanol and then  100mL of methanol is added to the beaker. Next, a concentrated nitric acid solution is added to the beaker and cooled in the ice bath.  Hydrochloric acid and urethane are produced from the carbonyl chlorides, acid chlorides, and dissolved phosgene. The chlorides are determined through potentiometric titration with methanolic silver nitrate solution. The volume of titrant added to reach the endpoint is also noted.

Specimen Size:

In ASTM D5523-21 method the sample size should be taken as per the requirements. Ten grams of sample weight can be  poured in a 400mL beaker. 

ASTM D5523-21 Method Data:

The hydrolyzable chlorine can be calculated by using the formula where: 
S = AgNO3 required for titration of the sample, mL, N = normality of AgNO3 solution, meq/mL,
W = sample weight, g, 
35.465 = equivalent weight of Cl, mg/meq, 1000 = factor for converting milligrams to grams, and 10⁶= factor for converting to parts per million.For further information on Hydrolyzable chlorine Click Here