How to Optimize the Extrusion Parameters for HDPE/LDPE Film with Regranulate?

Publication date: 2025-03-20

Introduction
The extrusion of HDPE/LDPE film with regranulate requires precise control of processing parameters to ensure high quality and production stability. Since LDPE regranulate has different physicochemical properties than virgin HDPE, its proportion in the blend affects processability, melt viscosity, process stability, and final mechanical properties of the film.
Which process parameters should be optimized to obtain a uniform film with the required functional properties? This article analyzes key extrusion settings and their impact on the final product quality.

1. Extrusion Temperature – How to Adjust the Heating Profile?
Temperature is crucial for proper melting and homogeneity of the HDPE/LDPE blend. Since LDPE has lower viscosity and melting temperature than HDPE, its presence in the mixture affects melt flow and may require modifications to the extruder’s heating profile.

   Key Takeaways:

• A higher LDPE content allows lower extrusion temperatures, as LDPE requires less heat to melt.
• Excessive temperature may lead to LDPE degradation, while too low a temperature may cause insufficient HDPE melting and gel inclusions in the film.

2. Melt Flow Index (MFI) and Process Stability
Melt Flow Index (MFI) determines the fluidity and processability of the polymer melt. HDPE typically has a lower MFI (0.3–1.5 g/10 min), meaning higher viscosity, while LDPE has an MFI of 1–5 g/10 min.
How to Optimize MFI for an HDPE/LDPE Blend?

• The MFI of the regranulate should be close to the MFI of the virgin HDPE used in the formulation to avoid phase separation.
• Too low an MFI increases melt viscosity, making extrusion harder and causing pressure surges.
• Too high an MFI increases the risk of surface defects (e.g., melt fracture).

Recommendation:
With a high LDPE regranulate content, monitor the MFI of the blend and adjust temperature and extrusion speed to maintain stable melt flow.

3. Screw Speed and Die Pressure
The screw speed (RPM) and die pressure influence the degree of homogenization and film stability.

 Practical Implications:

• A higher LDPE content reduces viscosity, allowing increased screw speed.
• Die pressure should be monitored, as large viscosity differences between HDPE and LDPE may cause melt flow instability.

4. Blow-Up Ratio (BUR) and Film Orientation
In blown film extrusion, the Blow-Up Ratio (BUR) influences the directional strength of the film.
Recommended BUR Settings for HDPE/LDPE Blends:

Key Takeaways:

• HDPE requires a higher BUR to achieve high cross-directional strength.
• Higher LDPE content allows for a lower BUR, as LDPE is more stretchable and easier to form into film.

5. How to Control and Optimize the Extrusion Process?
To achieve the best results, systematic process control is essential:

• MFI Monitoring – Regular viscosity tests help avoid phase separation.
• Adjusting Temperature and Screw Speed – Dynamic adaptation of parameters ensures production stability.
• Optimizing BUR Ratio – Adjusting BUR to the blend composition enhances mechanical properties.

Conclusion
Optimizing the extrusion parameters for HDPE/LDPE films with regranulate ensures process stability and high-quality film. The key adjustments include:

• Extrusion Temperature – Lower for higher LDPE content.
• MFI Matching – Ensures homogeneity and prevents phase separation.
• Screw Speed and Die Pressure – Provides uniform melt flow.
• BUR and Film Orientation – Achieves optimal mechanical properties.

With the right settings, the proportion of regranulate in film production can be increased without compromising product performance.

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