Acid value (mgKOH/g) is the mass of potassium hydroxide needed to neutralize one gram of sample. Here it reflects the number of free P–OH groups: more monoester means a higher acid value.
A high acid value means more anchoring groups and greater adhesion potential, but also higher hydrophilicity, poorer compatibility with alkaline components and more interference with cure.
The right choice is a match, not a maximum: high acid value for metal and glass, medium for light and water-resistant systems, low for electronics and batteries.
Method matters. Phosphate esters are not water soluble, so titrate in ethanol or isopropanol with a blank correction; use potentiometric titration for dark samples. Results from different methods are not comparable.
Free acid and acid value are different things. High free acid corrodes equipment and destabilizes storage even when the acid value looks normal.
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