Spin Finish Oxidation Mechanics during Long Term Storage
Oxidized spin finish forms cross-linked insoluble varnishes during storage, elevating yarn friction and causing irreversible resist spots in wet processing.
Acid Value
Residual Acidity
Measurement of residual acidity provides a quantification of free carboxyl groups in polyester resins and fats. A high acid value indicates a high concentration of unreacted acids or the presence of degradation products in the material. Testing involves neutralizing a known sample mass with potassium hydroxide until a colorimetric or potentiometric endpoint is reached.
This value determines the suitability of a polymer for further processing or its shelf stability.
Polymerization Control
Monitoring the reaction progress during polycondensation is the primary use for this metric. As chains lengthen, the acid value decreases predictably, allowing the reaction to be stopped at the precise molecular weight required for specific textile applications. A value that remains too high may lead to poor hydrolytic stability in the final fibre.
Purity Indicator
Quality control labs use the titration result to detect the onset of rancidity in lubricating oils used on spinning machines. Oxidative breakdown of long-chain fatty acids increases the number of free carboxyl groups, which corresponds to a rising value.
Operational Threshold
Finished products must meet strict limits to prevent hardware corrosion or dye interference. If the acid value exceeds the specification, the material might react with alkaline dyes or metal components in the mill. Process adjustments are required when these levels drift.