Meaning
Analytical procedures quantify the mass of potassium hydroxide required to neutralize free fatty acids in one gram of substance. Reliable acid number determination identifies the level of oxidation in polyester resins or recycled feedstocks. Chemical reactions between the reagent and the sample terminate when the acidic groups are fully neutralized.
Titration Variable
Standard laboratory practice involves dissolving the resin sample in a solvent mixture of toluene and isopropyl alcohol. Manual acid number determination uses phenolphthalein to indicate the endpoint through a color shift. Potentiometric methods provide higher precision for dark or opaque recycled materials.
Degradation Indicator
High acidity levels in virgin resin often indicate incomplete reaction during synthesis or subsequent hydrolytic degradation. Since acid number determination measures the concentration of carboxyl end groups, it predicts the risk of gas formation during injection moulding. Moisture during processing reacts with these groups to cause splay or brittle failure in the final part.
Mechanical strength drops as the average molecular weight decreases during these chain scission events. The resulting part fails to meet the impact requirements specified by the customer. Monitoring these values ensures that the material remains within the processing window defined by the manufacturer.
Sourcing Specification
Batches exceeding specified acidity limits typically require discount pricing. Strict acid number determination prevents the use of unstable material.
