Processing Special Materials like PLA, PET & WPC? Here’s the Screw Design You Need
Not all plastics are created equal — and neither are extrusion screws and barrels.
When processing biodegradable polymers like PLA, hygroscopic materials like PET, or abrasive blends like WPC (Wood-Plastic Composite), using a generic screw is a fast track to poor melt, low output, and early screw failure.
Here’s a breakdown of the challenges of these special materials and the screw design solutions you need to process them efficiently and reliably.
🌱 1. PLA (Polylactic Acid) – Biodegradable, Heat-Sensitive
Common Applications: Packaging film, disposable cups, 3D filament, agricultural mulch
Challenges:
- Low thermal stability – prone to degradation
- Narrow processing window (170–190°C)
- Sensitive to shear and residence time
- Requires precise temperature control
Recommended Screw Design:
- Gentle Compression Ratio (1:2.0 – 1:2.4)
- Extended low-shear transition zone
- No sharp shear edges
- Cooling grooves or air channels (for screw cooling)
- Optional: Barrier flight with low shear depth
🔧 Juyuan Tip: Use bimetallic barrels with enhanced corrosion resistance due to acidity of degraded PLA.
♻️ 2. PET (Polyethylene Terephthalate) – Hygroscopic, High-Speed Required
Common Applications: Sheet extrusion, strapping, thermoforming, recycled flakes (rPET)
Challenges:
- Absorbs moisture easily → hydrolysis during melting
- Requires venting or vacuum degassing
- High melting point (~260°C)
- Sensitive to thermal degradation
Recommended Screw Design:
- Two-Stage Vented Screw
- First stage for melting
- Vacuum vent zone to remove volatiles
- Second stage for pressure build-up
- Barrier section for fast melt
- Drying-free extrusion (when using crystallized rPET)
- High L/D ratio (32:1 – 36:1)
🔧 Juyuan Tip: Match screw design with vacuum port geometry and barrel venting; improper vent design = yellowed PET.
🪵 3. WPC (Wood-Plastic Composite) – Abrasive, Moisture-Sensitive
Common Applications: Decking, wall cladding, fences, door frames, pallets
Challenges:
- Contains wood fiber or powder → extremely abrasive
- High filler content → poor melt flow
- Prone to bubbles due to moisture
- Requires strong mixing and venting
Recommended Screw Design:
- Parallel twin screw (for longer wear life)
- Strong compression ratio (1:2.8+)
- Double vented zones (for degassing)
- Deep flights with reinforced flight tips
- Bimetallic barrel with tungsten carbide lining
- Spiral mixing section to prevent fiber agglomeration
🔧 Juyuan Tip: Use co-rotating twin screws for pelletizing WPC compounds and counter-rotating twin screws for profile extrusion.
📊 Comparison Table: PLA vs. PET vs. WPC Screw Design
| Feature | PLA | PET | WPC |
|---|---|---|---|
| L/D Ratio | 28:1 – 30:1 | 32:1 – 36:1 | 24:1 – 28:1 |
| Vent Zone | Optional | Required | Required |
| Screw Type | Single screw | Single screw | Twin screw |
| Shear Control | Low | Medium | Medium-High |
| Barrel Type | Nitrided / bimetallic | Bimetallic with venting | High wear bimetallic |
| Mixing Section | Optional Maddock | Spiral or Maddock | Required Spiral / Pin mixer |
🏭 Why Choose Juyuan for Special Materials?
At Zhoushan Juyuan Machinery Co., Ltd., we design application-specific screws and barrels tailored for:
- Biodegradable materials (PLA, PBAT)
- Recycled PET flakes and granules
- WPC with CaCO₃, wood powder, bamboo fiber
- Foam extrusion (PVC foam, XPS, PE)
We offer:
- Precision screw geometry simulation
- Barrel vent port integration
- Tungsten-carbide flight surfacing
- Fast delivery & global support
📞 Tell Us Your Material, We’ll Design the Right Screw
Don’t risk downtime or degradation with the wrong screw.
Let us analyze your material and extrusion goal — and recommend a proven screw-barrel combination.
Zhoushan Juyuan Machinery Co., Ltd.
🌐 Website: https://juyuan-machinery.com
📧 Email: cxj.job@gmail.com
📱 WhatsApp: +86 13905808474
Better screws. Better melt. Better products.