Meaning
Quantitative measurements provide a calculation of the mass of potassium hydroxide required to neutralize the free acids present in one gram of a chemical substance. This acid value determines the concentration of unreacted carboxylic groups in polyester or polyamide resins. High values indicate a low degree of polymerization or the presence of residual catalyst residues that can promote degradation.
It provides a baseline for evaluating the quality of raw materials before they enter the manufacturing stream.
Titration Chemistry
A neutralized solvent system dissolves the resin sample before a standardized alkaline solution is added to reach a specific endpoint. The acid value indicates the number of milligrams of reagent needed for the reaction. It provides a benchmark for batch consistency during polycondensation.
Processing Influence
Excessive acidity in the melt leads to moisture sensitivity and potentially impacts the mechanical properties of a finished part. When the acid value exceeds the specification on a material datasheet, the risk of hydrolysis during injection molding increases significantly. This drift often forces a reduction in regrind ratios to maintain structural integrity.
Degradation Measurement
Thermal stability depends on the chemical environment within the extruder barrel. A rising acid value suggests that the polymer chains are breaking down into smaller acidic fragments. This process eventually damages the mold surfaces through chemical attack.
