Impact Modifier Selection by Polymer — and the Properties You Trade Away
Direct answer
There is no universal impact modifier. The modifier has to be chosen for the matrix, because toughening works by dispersing a rubbery phase at the right particle size with the right interfacial adhesion, and each polymer accepts a different chemistry. Polyolefins take elastomeric modifiers such as POE or EPDM. Rigid PVC takes acrylic core-shell, MBS or CPE. PET and PETG take reactive or core-shell systems designed for polyester. Using a PVC modifier in PP or a polyolefin elastomer in PET does not underperform — it does nothing useful at all.
Selection by matrix
- Polypropylene. POE and EPDM raise notched Izod and low-temperature impact and improve weld-line strength. The cost is stiffness and heat deflection temperature, which is why a talc and elastomer combination is so common in automotive: the mineral gives back the modulus the rubber removed.
- Rigid PVC. Acrylic core-shell for weatherable outdoor profile; MBS where clarity is required; CPE where cost dominates and outdoor life does not. Impact modifier is one leg of the PVC formulation with the stabilizer, processing aid and lubricant — changing one leg changes fusion behaviour.
- PET and PETG. Modifiers are chosen to survive polyester processing temperature and to avoid hydrolytic degradation; clarity retention is the usual constraint.
- Engineering polymers. Reactive modifiers with anhydride functionality couple to the matrix chemically rather than relying on physical dispersion.
What you give up
Every impact modifier is a soft phase in a rigid matrix. Expect lower flexural modulus, lower HDT, reduced hardness and — with unsaturated rubbers such as EPDM — reduced UV and thermal-oxidative stability, which pushes the antioxidant and light stabilizer package up. Transparency survives only where the modifier refractive index is matched to the matrix. Loadings are typically 5 to 20 %, and the last few percent buy progressively less toughness for the same cost.
Dispersion decides the result
Impact modification is a morphology problem. A correctly chosen modifier that is poorly dispersed produces large domains that act as defects rather than as crack arrestors, and the part gets weaker. Screw configuration, melt temperature and residence time matter as much as the additive choice, which is why a modifier that worked on a twin-screw compounding line can disappoint when let down on a single-screw injection machine.
Specify it properly
State the matrix polymer and grade, the impact test and temperature that must be met — notched Izod at −20 °C is a different requirement from ambient Charpy — the minimum stiffness and HDT you cannot fall below, whether transparency is required, and the processing route. Without the test temperature, no modifier recommendation is meaningful.
What we supply
Allzone supplies impact and toughening masterbatch for PP and for PET, and acrylic impact modifier systems for rigid PVC. Dosage ranges shown on the product pages come from the supplier technical data sheets on file; validation on the target compound is recommended before series production.