ISO 2114

Testing Protocol

The analytical method of ISO 2114 involves dissolving the resin sample in a mixture of ethanol and toluene, followed by a potentiometric or visual titration against standard potassium hydroxide solution. This procedure measures both the free acid groups and any anhydride groups that may have hydrolyzed. By specifying the solvent ratios and temperature conditions, the standard ensures that measurements are highly reproducible across different laboratories.

For unsaturated polyesters used in liquid molding, this value must be kept within a narrow tolerance to prevent premature gelation or incomplete cure.

Titration Chemistry

In practice, the titration chemistry of the standard relies on the precise neutralization of acidic endgroups by the basic titrant. The endpoint is determined using a pH electrode or an indicator like phenolphthalein, depending on the transparency of the resin solution. This measurement helps compounders adjust the amount of catalyst or initiator needed to achieve a uniform cure rate.

If the acid value deviates from the baseline, it indicates incomplete reaction during polymer synthesis or subsequent thermal degradation.

Processing Correlation

For injection molders, this measurement provides a baseline to evaluate the quality of regrind polyester before it is blended with virgin resin. Elevated acid values indicate that the polymer has undergone hydrolytic or thermal degradation, which reduces its mechanical properties.