The moisture content of polyamide chips has a significant impact on the melting process, which is a reversible equilibrium reaction.
Fluoride + F′Fluoride²↔ Fluoride′ + F2Fluoride
The quality of the spinning solution is affected by the moisture content and extractable content of the polyamide chips. Too low a moisture content in the polymer can cause "repolymerization," resulting in a higher relative molecular mass and a wider distribution; too high a moisture content can generate bubbles, leading to yarn breakage, material defects, and equipment corrosion. Hydrogen bonds form between water molecules and amide groups, altering the molecular structure and properties. Therefore, the chips must be dried before spinning, generally controlled below 0.06%. Too low an extractable content will lead to polymer depolymerization and an increase in monomers and oligomers; too high an extractable content will broaden the relative molecular mass distribution and decrease the melt viscoelasticity. The levels of monomers and oligomers are also affected by equipment and processes. Generally, the extractable content is controlled at around 0.3% to 0.5%.