The short answer
PP impact copolymer is polypropylene with a rubber phase that keeps parts tough below freezing. Grades run from about 1–4 g/10 min MFR (230°C / 2.16 kg) for sheet and thermoforming, through about 10–35 for general injection, to 35–100+ for thin-wall parts. Notched Izod at room temperature spans about 60–500 J/m. Specify impact at the temperature the part sees, not only at room temperature.
This page covers impact copolymer PP. To compare it with homopolymer and random copolymer, see PP homopolymer and impact copolymer.
Typical spec window
| Property | Typical range | Test method |
|---|---|---|
| Melt flow rate | About 1–4 g/10 min for sheet and thermoforming; about 10–35 for general injection; about 35–100+ for thin wall | ASTM D1238 or ISO 1133, 230°C / 2.16 kg |
| Density | 0.90–0.91 g/cm³ | ASTM D792 or ISO 1183 |
| Flexural modulus | About 0.9–1.4 GPa | ASTM D790 or ISO 178 |
| Notched Izod, 23°C / 73°F | About 60–500 J/m | ASTM D256 (ISO 180 sheets report kJ/m², which does not convert) |
| Low-temperature impact | Listed on many data sheets at −20°C / −4°F or −30°C / −22°F | Notched Izod (ASTM D256), Charpy (ISO 179) or instrumented puncture (ASTM D3763 or ISO 6603-2) |
| Heat deflection, 1.8 MPa | About 45–55°C / 113–131°F | ASTM D648 or ISO 75 |
| Mold shrinkage | About 1.2–2.0% | ASTM D955 or ISO 294-4 |
Typical ranges from published data sheets for grades in this window. Your grade’s own data sheet and the lot COA are what count.
What it’s used for
- Pails, lids, crates and totes
- Battery cases and general industrial parts
- Automotive interior trim
- Freezer and cold-storage containers
- Thin-wall tubs and lids that still need some drop resistance (high-MFR grades)
- Thermoformed and extruded sheet (low-MFR grades)
How to tell grades apart
- Impact class. Medium- and high-impact grades differ mainly in rubber content. More rubber means more cold impact and less stiffness and heat deflection. Producers rarely state the rubber percentage, so compare modulus and impact together.
- MFR. Set by the process. Within a family, impact usually drops as MFR rises.
- Nucleated or not. Nucleated grades are stiffer and cycle faster, and can shrink differently.
- How cold impact is reported. Some sheets give notched Izod or Charpy at −20°C / −4°F or −30°C / −22°F; others give instrumented puncture energy and whether the break was ductile or brittle. These numbers do not convert into each other.
- Names. Data sheets also call it block copolymer or heterophasic copolymer.
What to put on your RFQ or PO
- The type and impact class, in words. Impact copolymer, medium or high impact.
- MFR with the condition. At 230°C / 446°F and 2.16 kg, nominal value and spec range.
- Impact at the temperature that matters. Notched Izod at 23°C / 73°F, plus a low-temperature value by the same method if the part sees cold.
- Stiffness. A flexural modulus range, so a substitute does not make a crate floor or lid floppy.
- Additives. Nucleated, antistatic or UV-stabilized.
- Color. Natural, black or a color match. Some pigments nucleate PP and change shrinkage.
- Food contact. The producer’s FDA letter for the exact grade; PP letters usually cite 21 CFR 177.1520.
- COA values to check. MFR on every lot. Ask whether impact is reported per lot or only on the data sheet.
- Packaging, quantity and release size. Gaylords, 25 kg (55 lb) bags, bulk truck or railcar; the total, the amount per release and how often.
A polymer chemist reviews every request and checks the grade against your process before we quote. Every prime lot from our suppliers ships with a COA, and orders start at one gaylord.
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- Same impact class and MFR from another producer. The closest swap. Run a drop test on real parts at the use temperature.
- A higher-impact grade. More cold toughness, less stiffness. Check lids, crate floors and stacking.
- Homopolymer. Only if the part is never dropped cold. See PP homopolymer injection.
- HDPE. For service colder than even high-impact PP handles. See PP vs. HDPE.
- TPO compounds. PP blended with elastomer and often talc, for automotive parts that need stiffness and cold impact together.
Common processing problems
- Cracks, or white marks at bends: brittle or cracking parts
- Tiger stripes and dull bands: flow lines
- Bow and twist: warped parts
- Parts that do not fill: short shots
- A new lot that molds differently: new lot runs differently
Common questions
What is the difference between PP homopolymer and impact copolymer?
Homopolymer is stiffer and more heat resistant but turns brittle near 0°C / 32°F. Impact copolymer carries a rubber phase that keeps parts tough below freezing, with lower stiffness and heat deflection.
How do I compare cold impact between two PP grades?
Only at the same temperature and test method. A notched Izod at 23°C / 73°F says little about a freezer. Ask for values at −20°C / −4°F or −30°C / −22°F by the same method, or drop-test real parts at the use temperature.
Why does impact copolymer turn white when bent?
That is stress whitening. Small voids open around the rubber particles when the part is strained and scatter light. It is mostly cosmetic but marks where the part is overstressed. Larger radii and gentler ejection usually help.
Is impact copolymer the same as block copolymer?
In practice, yes. Data sheets say impact copolymer, block copolymer or heterophasic copolymer for a PP matrix with a dispersed rubber phase. Random copolymer is different: a little ethylene in the chain for clarity, with no rubber phase.
Tell us the impact copolymer you run now
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province