Meaning
Standardized alkaline solutions prepared in organic solvents are used to quantify acidic functional groups in polymer resins. Using potassium hydroxide titrant allows the precise neutralization of carboxyl end groups in dissolved polyester specimens. This measurement is critical for evaluating the hydrolytic degradation of raw materials.
Titration Chemistry
The titration is performed by slowly adding the alkaline solution to the dissolved polymer until a colorimetric or potentiometric endpoint is reached. Using potassium hydroxide titrant in a non-aqueous solvent like benzyl alcohol prevents the precipitation of the polyester during the assay. The volume of titrant consumed corresponds directly to the concentration of acid ends in the sample.
This chemical value represents the susceptibility of the polymer to subsequent thermal degradation.
Process Control
Moulders use end-group data to determine the suitability of recycled PET for high-stress applications. If the titration reveals a high acid content, the material will degrade rapidly during subsequent melting. This information allows production managers to adjust drying times or modify the blending ratio of recycled flakes.
Standardization Requirement
Alkaline titrants absorb atmospheric carbon dioxide, which reduces their effective concentration over time. Daily standardization against a primary standard like potassium hydrogen phthalate is necessary to ensure accuracy. This calibration prevents measurement drift and guarantees that the acid values obtained remain consistent across different production shifts.
