| Symptom Observed in Production | Likely Technical Root Causes | Direction for Correction |
|---|---|---|
| Yellowing from the start of production | Weak initial thermal stability; early onset of degradation reactions | Review the design of the primary stabilizing system; rebalance active components |
| Color is acceptable initially but collapses suddenly | Non-linear degradation triggered by accumulation of degradation by-products | Strengthen degradation by-product control; review stabilizer balance |
| Burn marks after short stops or brief residence time increase | Insufficient stabilization under high residence time conditions | Evaluate stabilizer performance during line stops and restart conditions |
| Gels or unmelted particles in the product | the product Incomplete fusion; unsuitable processing aid | Review type and dosage of processing aid; reassess fusion control |
| Rough or non-uniform surface | Excessive slip or unstable fusion behavior | Adjust balance between internal and external lubrication |
| Deposits on die, mold, or rolls (Plate-out) | Additive incompatibility; saturation of lubrication system | Simplify formulation; review lubricant type and dosage |
| Progressive surface deterioration over time | Migration of poorly compatible formulation components | Check phase compatibility of formulation components with PVC |
| Higher-than-target density in foamed PVC | Melt weakening during the critical foaming stage | Review coordination between stabilizer system and foaming conditions |
| Collapsed foam or irregular cell structure | Insufficient melt strength during gas release | Reassess interaction between stabilizer system and foam regulator |
| Skin–core inconsistency in foam boards | Localized thermal instability in the core region | Evaluate stabilizer endurance under high residence time |
| Extruder pressure fluctuations | Unstable rheological behavior of the melt | Fine-tune lubrication system and processing aid selection |
| Line requires constant adjustment | Formulation lacks tolerance to normal process variations | Redesign additive system for stable, repeatable processing behavio |
Technical Note
In PVC processing, most defects are not caused by a single additive. When multiple symptoms appear simultaneously, the root cause is usually a lack of coordination within the additive system, rather than a deficiency of one specific component