Partial Acid Value of Unsaturated Polyester Resin as per DIN EN ISO 2114

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%

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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