PE Blown Film Raw Material Drying Notes

Notes on Raw Material Drying for PE Blown Film

PE, a non-polar polyolefin with water absorption of only 0.01%–0.03%, is often thought to need no drying. Yet regrinds, modified grades or damp-stored pellets require drying to guarantee film quality. Key requirements are as follows:

1. When Drying Is Mandatory

Regrinds/scrap film: Large surface area traps moisture, causing bubbles and fish eyes.

Modified PE with slip/antistatic additives: Hygroscopic additives create surface pits and uneven smoothness.

Outdoor-stored pellets: Surface moisture absorption calls for extra drying.

2. Precise Drying Parameters

PE has moderate thermal stability; overheating triggers degradation.

Temperature: 60–90°C. 60–70°C for virgin LDPE; 70–80°C for virgin HDPE; 75–85°C for regrinds. Never exceed 100°C, which weakens tensile & impact strength and causes yellowing/odor.

Duration: 1–1.5 h for virgin pellets; 2–2.5 h for regrinds.

Material bed & airflow: Fill dryer hopper 1/3–1/2 full. Moderate airflow prevents loss of slip/anti-block additives.

3. Target Residual Moisture

Moisture content ≤0.05%.

Quick check: No popping or bubbles during extrusion.

Precision test: Karl Fischer titration to avoid unstable bubbles, film breaks and uneven gauge.

4. Special Rules for Regrinds

Sift out dirt and foreign plastic first before drying.

Stir during drying to release trapped moisture.

Dry regrinds separately before blending with virgin PE for uniform moisture removal.

5. Post-Drying Storage

Use dried pellets promptly. Seal leftover stock airtight to stop reabsorption. Insulate the extruder hopper or add a pre-dryer for steady production.

Conclusion

Drying is indispensable for PE blown film. Tuned parameters balance drying efficiency and material performance to produce defect-free film.