Introduction
Lubricants are essential additives in PVC processing, helping to control friction during extrusion, calendering, and injection molding. They improve processing efficiency, surface quality, and product performance.
PVC lubricants are generally classified into:
- Internal lubricants – reduce friction between PVC molecular chains and improve melt flow.
- External lubricants – reduce friction between the PVC melt and metal surfaces of processing equipment.
The following are some of the most commonly used lubricants in PVC formulations.
1. Calcium Stearate
Calcium stearate is a white powder with a melting point of approximately 148–155°C.
Characteristics
- Non-toxic and environmentally friendly
- Excellent internal lubrication performance
- Good processing stability
- Does not cause sulfide contamination
Typical Dosage
- 0.1–0.4 phr (parts per hundred resin)
Calcium stearate is widely used in PVC formulations to improve melt flow and processing efficiency.
2. Oxidized Polyethylene Wax (OPE Wax)
Oxidized polyethylene wax appears as a white or yellowish powder or granule.
Characteristics
- Functions as both internal and external lubricant at high temperatures
- Contains small amounts of polar groups
- Provides higher lubrication efficiency than conventional wax
Advantages
- Improves lubrication between polymer melt and metal surfaces
- Increases extrusion efficiency
- Enhances pigment dispersion
- Improves product transparency and surface gloss
Typical Dosage
- 0.1–0.5 phr
3. Stearic Acid
Stearic acid is a white granular material with a melting point of approximately 70–71°C.
Characteristics
- Acts as an external lubricant at high temperatures
- Functions as an internal lubricant at lower temperatures
- Helps prevent equipment scaling during processing
Typical Dosage
- 0.2–0.5 phr
However, excessive dosage may cause surface blooming or “frosting” on finished products.
4. Glycerol Stearate (GMS)
Glycerol stearate is a powder with a melting point of approximately 85–87°C.
Characteristics
- Effective internal lubricant
- Excellent heat resistance and melt flow properties
- Promotes PVC plasticization
- Allows increased filler loading in formulations
When used together with waxes, glycerol stearate can also improve the thermal stability of rigid PVC (PVC-U).
Typical Dosage
- 0.2–0.6 phr
5. Paraffin Wax
Paraffin wax has a melting point of approximately 57–63°C and contains no polar functional groups.
Characteristics
- Typical external lubricant
- Low melting point and low melt viscosity
- Narrow effective lubrication range
Applications
Paraffin wax is suitable for:
- Single-screw extruders
- Twin-screw extrusion processes
Typical Dosage
- 0.1–0.8 phr
However, paraffin wax may reduce transparency and may cause whitening or blooming if used excessively.
6. Polyethylene Wax (PE Wax)
Polyethylene wax is a white powder with a softening point of approximately 100–117°C.
Characteristics
- Higher molecular weight compared to paraffin wax
- Higher melting point and lower volatility
- Strong external lubrication performance at high temperatures and high shear conditions
Applications
PE wax is commonly used in rigid PVC extrusion processes, including:
- Single-screw extrusion
- Twin-screw extrusion
Typical Dosage
- 0.1–0.5 phr
Conclusion
Lubricants are essential for achieving stable PVC processing and high-quality finished products. Common lubricants such as calcium stearate, oxidized polyethylene wax, stearic acid, glycerol stearate, paraffin wax, and polyethylene wax each provide specific functions within PVC formulations.
By carefully selecting and balancing internal and external lubricants, manufacturers can optimize:
- Processing efficiency
- Surface finish
- Product mechanical properties
- Equipment cleanliness and stability
Proper lubricant selection is therefore critical to achieving consistent product quality and efficient PVC processing.
