Introduction
PVC is naturally a rigid and brittle material, especially at low temperatures. To improve its impact resistance and toughness, manufacturers add impact modifiers to PVC formulations.
Impact modifiers improve the ductility, toughness, and resistance to external mechanical stress, helping PVC products withstand impact without cracking.
Currently, the most commonly used PVC impact modifiers include:
- Chlorinated Polyethylene (CPE)
- Polyacrylate (ACR)
- Ethylene-Vinyl Acetate Copolymer (EVA)
- Methyl Methacrylate-Butadiene-Styrene (MBS)
These materials generally belong to the category of rubber-type elastomer impact modifiers.
1. Chlorinated Polyethylene (CPE)
Chlorinated polyethylene (CPE) is produced by chlorinating high-density polyethylene (HDPE).
Characteristics
CPE is widely used as an impact modifier for PVC due to its excellent performance:
- Good compatibility with PVC
- Excellent impact modification effect
- Good weather resistance because the molecule does not contain double bonds
- Improved flame resistance due to the presence of chlorine atoms
Advantages
- Cost-effective
- Stable performance
- Wide application range
Because of these advantages, CPE remains one of the most commonly used impact modifiers in PVC products.
2. Polyacrylate Impact Modifiers (ACR)
ACR impact modifiers are typically core–shell structured copolymers.
Structure
- Core: Low cross-linked acrylate rubber polymer
- Shell: Methyl methacrylate graft copolymer
Characteristics
ACR impact modifiers provide multiple benefits:
- Improve impact resistance of PVC
- Enhance processing performance
- Promote PVC gelation and plasticization
Because of this dual functionality, ACR can serve both as:
- Impact modifier
- Processing aid
ACR is widely used in PVC profiles, pipes, sheets, and foam products.
3. Ethylene-Vinyl Acetate Copolymer (EVA)
EVA is a random copolymer of ethylene (E) and vinyl acetate (VAc).
Characteristics
EVA behaves as a rubber-like elastomer and provides:
- Good flexibility
- Good impact modification
- Good weather resistance
Limitations
Despite these advantages, EVA is gradually used less frequently in PVC profiles and pipes because:
- It provides lower welding strength
- Profiles modified with EVA may have lower notch impact strength at high temperatures
As a result, EVA has largely been replaced by CPE and ACR impact modifiers in many PVC applications.
4. Methyl Methacrylate-Butadiene-Styrene (MBS)
MBS is a commonly used impact modifier for transparent PVC products.
Characteristics
- Excellent transparency
- Effective impact resistance for clear PVC materials
Applications
MBS is widely used in:
- Transparent PVC sheets
- Transparent pipes and fittings
- Clear PVC films and packaging materials
Limitations
Since MBS contains double bonds, it has poor weather resistance. Therefore, it is rarely used in outdoor PVC products such as profiles and pipes.
Typical dosage ranges from 8 to 15 phr (parts per hundred resin).
Conclusion
Impact modifiers play a critical role in improving the toughness and durability of PVC products. The most widely used modifiers include CPE, ACR, EVA, and MBS, each with different advantages depending on the application.
- CPE – cost-effective and widely used for general PVC products
- ACR – provides both impact modification and processing aid functions
- EVA – flexible but gradually being replaced in many PVC applications
- MBS – ideal for transparent PVC products
Selecting the appropriate impact modifier helps manufacturers achieve the desired balance between impact strength, weather resistance, processing performance, and cost.
