The quantity of potassium hydroxide needed for neutralization of half of the anhydride groups, all free acids and all carboxyl-terminated groups of an unsaturated polyester resin (UPR), is indicated by the partial acid value (also referred to as “partial acid number”).
Determination of the partial acid number using automated potentiometric titration in accordance with DIN EN ISO 2114 is explained in this application note. This technique employs KOH in ethanol as the titrant.
Samples
Unsaturated polyester resin (UPR)
Sample Preparation
Sample preparation is not required.
Analysis
Blank
A blank is determined without UPR, using the same methodology as the sample.
Sample
Approximately 3 grams of UPR sample is weighed using the balance and transferred to the titration vessel. Using automated programme, 25 mL of acetone and 50 mL of solvent mixture are added to the UPR sample in the titration vessel.
The mixture is allowed to react for 2 minutes, after which the titration is carried out using KOH in ethanol with 0.1 mol/L concentration. The process is continued until after the equivalence point is reached.
Configuration
| . |
. |
| 907 Titrando |
2.907.0010 |
| 800 Dosino, 3x |
2.800.0010 |
| 814 USB Sample Processor (2T/0P) |
2.814.0130 |
| Dosing unit 50 mL, 2x (solvent mixture, acetone) |
6.3032.250 |
| Dosing unit 20 mL, (titrant) |
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(KOH) = 0.1 mol/L in ethanol, if possible this solution should be bought from a supplier. |
| Solvent mixture |
Toluene / ethanol, Φ (toluene) = 66.6% (v/v) |
Parameters
| . |
. |
| Mode |
DET U |
| Pause |
30 seconds |
| Signal drift |
20 mV/min |
| Stirrer speed |
8 |
| Max. waiting time |
38 seconds |
| Meas. point density |
4 |
| Min. increment |
50 µL |
| Max. increment |
Off |
| EP criterion |
5 |
| EP recognition |
all |
Results
| . |
. |
| Partial acid number / (n = 5) |
s(rel) |
| 19.93 mg KOH / g |
0.1% |
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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.