Determination of the acid value, hydroxyl value, and isocyanates in raw materials for the fabrication of plastics by automatic potentiometric titration

Summary

The determination of the acid value, the hydroxyl value, and the isocyanates plays an important part in the analysis of raw materials for plastics. The present bulletin describes the determination of these characteristic values by automatic potentiometric titration. The acid and hydroxyl value are measured according to ASTM, the isocyanate value is measured according to ISO.

Determination of the acid value (AV)

The acid value corresponds to the amount of carboxylic acid groups in alkyl resins, polyester acrylate resins or mixtures and is given in mg KOH per g sample. It is also used in evaluating plasticizers, in which acid values should be as low as possible.

Instruments

• Sample changer
• Titrator with DET mode
• Burette 20 mL
• Stirrer

Electrodes

Solvotrode easyClean
6.0229.020

Reagents

• Ethanol
• Diethyl ether, peroxide-free
• Phenolphthalein

Solutions

Standard

Sample preparation

No sample preparation is required.

Analysis

Titer
100 … 120 mg benzoic acid is weighed into the titration vessel and dissolved in 50 mL ethanol. The solution is then titrated using c(KOH) = 0.1 mol/L until after the first equivalence point.

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