%NCO Percentage Determination

Principle

Reactive isocyanate is reacted with excess n-dibutyl amine to form substituted ureas.

The excess dibutyl amine is then back-titrated with aqueous hydrochloric acid.

Procedure

Accurately weigh, in duplicate, 2.0 – 5.0g of sample.
Pipette exactly 50 ml of 0.2 N n-dibutyl amine into the solution.
Add a 1” teflon coated stirring bar and cap jar tightly.
Add a magnetic stirrer, agitate sample gently until completely dissolved.
Add 6 drops of bromphenol blue indicator and titrate till yellow-green endpoint with 0.5 N HCl to get A.
Run a blank at the same time as the sample, following the same procedure to get B.

%NCO calculation

=  [4.202 (NHCL) (B-A)] / Sample Wt

B : Blank titer
A: Sample titer
N: Normality of HCL


Recommended sample weight (g) used:

= 25.1 / Expected %NCO