Isocyanates (NCO) in Polyurethane Resin and Unsaturated Polyester Resin as per DIN EN ISO 14896

The isocyanate content of resins is described in terms of grams of isocyanate per 100 grams of sample. This application note explains an automated potentiometric titration method in accordance with DIN EN ISO 14896 for determining isocyanates in polyurethane resin (PUR) and unsaturated polyester resin (UPR) samples. This technique employs hydrochloric acid as the titrant.

Sample

Unsaturated polyester resin (UPR) and polyurethane resin (PUR)

Sample Preparation

Sample preparation is not required.

Analysis

Blank

The blank is determined the same way as the sample, just without sample.

Sample

Approximately 2 grams of PUR or UPR sample is taken in a beaker and weighed using the balance. 18 mL of the reaction solution and 30 mL of toluene are added to the sample beaker automatically.

The mixture is allowed to react for 10 minutes, post which 30 mL of methanol is added by the automatic program. The titration is then carried out using HCl with 1.0 mol/L concentration. The process is continued until after the equivalence point is reached.

Configuration

. .
907 Titrando 2.907.0010
800 Dosino, 4x 2.800.0010
814 USB Sample Processor (2T/0P) 2.814.0130
Dosing unit 50 mL, 2x (methanol, toluene) 6.3032.250
Dosing unit 20 mL, 2x (titrant, reaction solution) 6.3032.220
741 Magnetic stirrer, 2x 2.741.0010
843 Pump station (peristaltic) 2.843.0150
Sample rack, PP, 22 x 120 mL 6.2041.470
Titration head, 3x NS 14 6.1458.040
Sample beaker, PP, 22 x 120 mL 6.1459.300
Titration head with DIS-Cover 6.9914.158
DIS-Cover lids for 120 mL PP beakers 6.9914.164
Solvotrode easyClean, LiCl sat. in EtOH 6.0229.020
tiamo™ 2.5 6.6056.252

Solutions

. .
Titrant C(HCl) = 1.0 mol/L in ethanol, if possible this solution should be bought from a supplier.
Reaction solution c(dibutylamine) = 1.0 mol/L in toluene, if possible this solution should be bought from a supplier.

Parameters

. .
Mode DET U
Signal drift 20 mV/min
Stirrer speed 8
Max. waiting time 38 seconds
Meas. point density 4
Min. increment 10 µL
Max. increment Off
EP criterion 5
EP recognition all

Results

Sample Result / %, (n = 5) s(rel) / %
UPR 0.83 1.9
PUR 2.34 0.9

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.

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