PET Hydrolytic Degradation Nomograph
How to use this Nomograph:
The Nomograph is interactive; simply drag the left end of the line to the starting IV of your PET resin, and set the right end of the line to your resin moisture content. Where the line crosses the middle scale represents the predicted IV of the preform.
IV Drop due to Moisture:
This Nomograph will determine the IV Drop expected from the moisture level in the starting resin. It concentrates exclusively on the hyrdolytic degradation of PET and does not take into account other sources like :
1. Oxidative Degradation
2. Thermal Degradation
3. Mechanical Degradation
As a rule, Hydrolytic Degradation accounts for the majority of IV loss in PET, and therefore knowing the loss due to moisture will be a fairly accurate measure of IV loss in extrusion. The standard specification for moisture content in PET prior to melt processing is 50 ppm (0.005%). Moisture content in the resin which is much higher than this level results in unacceptable IV loss in the finished product (preforms). PET resin which is dried to a level much lower than 50 ppm has diminished returns with respect to IV loss.