Rigid PVC is strong and stiff, but brittle on impact, especially at low temperatures. An impact modifier forms small rubbery domains inside the PVC that absorb impact energy. The two types used most often are CPE and ACR.
CPE: cost-effective for pipe, conduit and gutters
CPE (chlorinated polyethylene) raises the toughness of rigid PVC, including at low temperatures, and takes filler well. It also helps processing, which suits pipe, conduit and gutter formulations that use filler. Endura CP-110 is an example, dosed at 2.0–5.0 phr for pipe and fittings and 4.0–8.0 phr for gutters and profiles.
ACR: weather resistance for roofing and ceiling panels
ACR (acrylic core-shell) delivers impact strength with excellent weather resistance and color retention. That is why ACR is widely used for sun-exposed products such as roofing, ceiling panels and outdoor profiles. Endura AC-210 is an example, dosed at 6.0–10.0 phr for outdoor roofing and 4.0–8.0 phr for ceiling panels.
MBS: for clear products
MBS has a refractive index close to PVC, so impact rises without clouding the product. It is used for rigid film, clear sheet and thermoformed packaging, but it is not recommended for outdoor products.
What often gets missed
- Impact strength rises along an S-curve. Past the ductile point, more modifier adds little except cost.
- CPE domain size depends on shear and process conditions, so results on one machine can differ from another.
- When switching impact modifier type, the lubricant package needs adjusting.
The safest way to choose is a measured trial: compare impact results at several dosage levels, then pick the point with the best balance of performance and cost for your product.