Adapting PE film blowers for degradable materials.

How to Adapt PE Film Blowing Machines for Eco-Friendly Production with Degradable Materials

The core of adapting PE film blowing machines for degradable materials lies in systematically adjusting equipment, raw material pretreatment, and process parameters based on the characteristics of degradable materials (such as low melt strength, poor thermal stability, and high moisture absorption), balancing processability with environmental performance. The specific adaptation pathways are as follows:

I. Key Differences Between Degradable Materials and PE

Degradable materials (e.g., PBAT, PLA, PBS) differ significantly from traditional PE in molecular structure and processing behavior:

Low Melt Strength: PLA and PBAT have weak melt elasticity, making them prone to sagging and film rupture during blowing;

Poor Thermal Stability: High temperatures or excessive shear can lead to degradation, causing bubbles and discoloration;

High Moisture Absorption: When PLA moisture content exceeds 0.05%, hydrolysis and chain scission occur during processing, affecting film performance;

Special Crystallization Behavior: PLA requires rapid cooling to suppress crystallization, while PBAT needs moderate insulation to enhance toughness.

These characteristics mean that PE film blowing machines cannot directly use original parameters and require targeted modifications.

II. Key Equipment Modifications

1. Screw System Optimization

PE screws (L/D ratio 25:1–30:1, compression ratio 3:1–4:1) tend to cause excessive shear with degradable materials. Adaptations include:

Adjust L/D Ratio: Increase to 30:1–35:1 to extend plasticization time and reduce shear force;

Reduce Compression Ratio: Adjust to 2.5:1–3:1 to prevent overheating and degradation in the compression zone;

Modify Screw Structure: Use barrier or separation screws to reduce material retention and improve plasticization uniformity. For blended degradable materials (e.g., PBAT+PLA), add a mixing section (e.g., pin-type screws) to enhance dispersion.

2. Die and Cooling System Adjustments

Die Gap: Due to low melt strength, reduce die gap to 0.8–1.2 mm (PE typically 1.5–2 mm) to prevent sagging. Use spiral dies instead of flat dies to improve material distribution uniformity;

Cooling Air Ring: PLA requires rapid cooling (air speed 15–20 m/s) using dual-layer air rings or low-temperature air (20–25°C) to inhibit crystallization and maintain transparency. PBAT requires lower air speed (10–15 m/s) to avoid brittleness caused by rapid cooling;

Cooling Roll: For composite degradable films, add cooling roll temperature control (set to 20–30°C for PLA, 30–40°C for PBAT) to improve film flatness.

3. Take-up and Winding System Adaptation

Take-up Speed: Degradable films have lower toughness. Match take-up speed with extrusion speed (draw ratio 1.5–2.5, compared to PE's typical 2–3) to avoid over-stretching and breakage;

Winding Tension: Use constant tension winding system, controlling tension at 5–10 N (PE typically 10–15 N) to prevent film deformation or wrinkles;

Take-up Roll Material: Replace steel rolls with silicone rolls to increase friction and prevent film scratching.

III. Raw Material Pretreatment and Process Parameter Optimization

1. Raw Material Drying

Degradable materials absorb moisture easily and require thorough drying:

PLA: Dry at 80–90°C for 4–6 hours, moisture content ≤ 0.05%;

PBAT: Dry at 60–70°C for 2–3 hours, moisture content ≤ 0.1%;

Blends: Adjust drying temperature based on blend ratio (e.g., PBAT+PLA dry at 70–80°C for 3–5 hours).

It is recommended to use a dehumidifying dryer (dew point -40°C) to avoid incomplete drying.

2. Processing Temperature Control

Degradable materials have a narrow processing temperature range and require precise zone control:

PLA: Barrel temperature 180–210°C (die head 200–210°C), avoid exceeding 220°C;

PBAT: Barrel temperature 160–190°C (die head 180–190°C), prevent high-temperature degradation;

Blends: Use mid-range values (e.g., PBAT+PLA set to 170–200°C) to ensure compatibility.

3. Blow-up Ratio and Draw Ratio Adjustment

Blow-up Ratio (BUR): Due to low melt strength, control BUR at 1.5–2.5 (PE typically 2–4) to avoid film rupture;

Draw Ratio: Coordinate with BUR to maintain uniform film thickness (e.g., BUR 2, draw ratio 2 results in film thickness half of the die gap).

4. Waste Material Recycling

Degradable material scrap can be recycled, but note:

Recycling ratio ≤ 30% to avoid performance degradation;

Recycled material must be redried and thoroughly mixed with virgin material.

IV. Additional Eco-Friendly Production Measures

Energy Optimization: Degradable materials process at lower temperatures than PE (e.g., PLA is 20–30°C lower), reducing heating power by 10%–15%;

Exhaust Gas Treatment: Install activated carbon adsorption units to treat trace VOCs generated during processing;

Quality Testing: Add film degradation performance testing (e.g., composting tests) to ensure compliance with standards such as GB/T 19277.

Conclusion

Adapting PE film blowing machines for degradable materials requires a dual approach of hardware modification + software optimization: adjust screws, dies, and cooling systems on the hardware side; enhance raw material drying and precisely control process parameters on the software side. These measures enable stable production of degradable films, retaining the efficiency of film blowing machines while meeting environmental requirements, supporting the industry's transition toward green manufacturing.