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 |
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This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.
For more information on this source, please visit Metrohm AG.