Determine Isocyanate Content
or NCO content in aromatic isocyanates (IPDI, MDI, PMDI, TDI, HDI) by titration methods.Â
APPARATUS
a). Magnetic
Stirrer
b). Magnetic Bead
c). 500ml conical
flask.
d). 100ml measuring
cylinder (Class-A).
e). 25ml pipette
(Class-A).
f). Burette (Class-A).
REAGENTS & SOLUTIONS
a). Dry Toluene (LR
Grade)
b). 1 N HCL
reagent.
c). Rectified
Spirit (Take 95.6ml Ethanol & add 4.4ml Distilled water obtained by
distillation)
d). Bromophenol
Blue indicator.
e). Di-Butyl Amine/Toluene mixture 1.0N (Take 67.5ml of Di-Butyl Amine & add to it 250ml of dry Toluene)
The procedure of NCO content by Potentiometric Titration
a). Weigh about 2.0gm of the sample accurately in a 500ml clean dry stopper conical flask.
b). Add 100ml Dry
Toluene & 200 ml rectified spirit.
c). After complete
dissolution add 25 ml Di-butyl amine/Toulene mixture to the flask containing a
sample.
d). Now add 7-8
drops of indicator.
e). Heat the solution
while stirring to dissolve.
f). Cool the
solution to ambient temperature. Titrate the solution with standard 1N HCl
solution.
g). Prepare a blank determination of taking a 250 ml empty conical flask. Add 100 ml Toluene, 200 ml rectified spirit, and 25 ml DBA/Toluene mixture with 7-8 drops of Bromophenol blue indicator and titrate with 1N hydrochloric acid.
R-NCO
+R'-NH2Â Â =Â R-NHC=ONH-R
Calculation of Free NCO:
% Free NCOÂ =
(B-S) x N x 4.2/Wt. of the sample.
Run a blank.
% NCOÂ = 4.2 x
[(ml HCl blank) - (ml HCl sample)]/sample weight
Where:
B = Volume of HCL
used in the blank titration.
S = Volume of HCL
used with sample titration.
N = Normality of HCL
Precaution
Transfer the sample
from the pipette to avoid moisture.
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