METHOD OF REDUCING THE YELLOWNESS INDEX OF POST-CONDENSED POLYESTER GRANULES

摘要

The invention concerns a method of reducing the yellowness index of post-condensed polyester granules (intended for drink bottles, for instance). The invention calls for the crystallization of the polyester material (copolyester or homo-PET) to be carried out at temperatures of less than 145 C. The subsequent thermal treatment at much higher temperatures (solid-phase post-condensation) is carried out using the usual equipment. Compared to crystallization at higher temperatures, there is a drastic reduction in the yellowness index of the end product of the solid-phase process.