PET is highly hygroscopic and absorbs moisture from the atmosphere. Tiny amounts of moisture can hydrolyse PET within the melt part, reducing molecular weight. PET should be dry just prior to processing, and amorphous PET needs crystallization prior to drying so that the particles don’t stick together as they’re going through glass transition. Hydrolysis can occur due to moisture and this often can be seen as a reduction in the IV (Intrinsic Viscosity) of the product. PET is “semi-crystalline”. When the IV is reduced, the bottles are more brittle and tend to fail at the “gate” (injection point) during blowing and filling. It is very possible that due to the initial moisture level in the resin, and the amount removed during vacuum that a significant amount of moisture still remains as it is reaching its melt phase in the extruder. In its “crystalline” state it has both crystalline and amorphous portions in its molecular structure. The crystalline portion develops where the molec