IV (intrinsic viscosity) drop
Cause
Thermal/hydrolytic degradation from over-drying, high heat, or moisture lowers IV and strength.
Corrective action
Control drying temperature/time, lower melt temperature, verify resin IV on intake.
Diagnosis guide: Low intrinsic viscosity (weak preforms)
What you will see
Preform has lower IV than specified — typically caused by excessive regrind or hydrolysis. Visible as slightly hazy preforms with reduced strength. Bottles will be weak and burst-prone.
Likely causes
- Excessive regrind ratio (>30%) at Delta plant
- Hydrolysis (wet PET) reduces IV
- Wrong resin lot used
Do this first
Request IV test certificate from Delta for the lot.
How to diagnose it
- Request Certificate of Analysis (COA) from Delta for the lot
- IV should be ≥0.74 dL/g for CSD; ≥0.72 for water
- If COA unavailable, send 5 preforms for independent IV test
How to fix it
- Quarantine lot pending IV confirmation
- If IV below spec, contact Delta with COA + measurements for lot replacement under quality guarantee