The short answer
Injection-molding PP homopolymer typically runs about 8–35 g/10 min melt flow rate at 230°C / 2.16 kg, with density about 0.90–0.91 g/cm³. It is the stiffest and most heat-resistant unfilled PP, which suits caps, closures, living hinges and housewares. It turns brittle near 0°C / 32°F, so parts that get dropped cold need impact copolymer. Specify MFR with the test condition, and say whether you need a nucleated, clarified or antistatic grade.
This page covers homopolymer PP for injection molding. To choose between homopolymer, random and impact copolymer, see PP homopolymer and impact copolymer. For the full family, see polypropylene.
Typical spec window
| Property | Typical range | Test method |
|---|---|---|
| Melt flow rate | About 8–35 g/10 min; most general injection grades about 10–35 | ASTM D1238 or ISO 1133, 230°C / 2.16 kg |
| Density | 0.90–0.91 g/cm³ | ASTM D792 or ISO 1183 |
| Flexural modulus | 1.2–1.8 GPa; nucleated grades toward the top | ASTM D790 or ISO 178 |
| Tensile strength | 31–37 MPa | ASTM D638 or ISO 527 |
| Notched Izod, 23°C / 73°F | 20–50 J/m | ASTM D256 |
| Heat deflection | About 80–105°C / 176–221°F at 0.45 MPa; about 50–60°C / 122–140°F at 1.8 MPa | ASTM D648 or ISO 75 |
| Melting point | About 160–165°C / 320–329°F | DSC, ASTM D3418 or ISO 11357-3 |
| Mold shrinkage | 0.8–2.5% | 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
- Caps and closures, including flip-top living hinges
- Housewares, storage containers and kitchenware
- Food containers and lids
- Appliance parts and small housings
- Thin-wall packaging at the top of the window and above it
How to tell grades apart
- MFR. Higher MFR fills thinner walls and longer flow paths and cycles faster; lower MFR is a little tougher. When matching, staying within about 10–20% of the current MFR is a common starting point.
- Nucleated or not. Nucleating agents raise stiffness and the crystallization temperature, which shortens the cycle. They also change shrinkage, so a nucleated swap can move dimensions.
- Clarified homopolymer. More see-through than standard homopolymer, but random copolymer is clearer. See clear PP random copolymer.
- Controlled-rheology grades. Some grades are made by breaking down a lower-MFR resin with peroxide. They fill evenly and tend to warp less, at a little less stiffness.
- Antistatic. Keeps displayed housewares and packaging from collecting dust.
What to put on your RFQ or PO
- The type, in words. Homopolymer.
- MFR with the condition. At 230°C / 446°F and 2.16 kg (ASTM D1238 or ISO 1133), nominal value and spec range. A PE melt index at 190°C / 374°F is not comparable.
- Density and stiffness. Density, plus a flexural modulus range so a substitute does not make a lid floppy.
- Additives. Nucleated, clarified, antistatic or UV-stabilized. For closures, say if a slip agent is present, since it changes removal torque.
- Color. Natural, black or a color match, and whether you add masterbatch.
- 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.
- Packaging. Gaylords (a standard gaylord holds roughly 1,200–1,400 lb of PP), 25 kg (55 lb) bags, bulk truck or railcar.
- Quantity and release size. Total quantity, how much 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.
Get an email when resin prices move
A short note when PP, PE, nylon or other prices shift. No spam; unsubscribe anytime.
By signing up you agree to receive emails from ResinBridge. Unsubscribe anytime by replying or using the link in any email. PrivacyEquivalents and substitutes
- Another homopolymer at the same MFR and additives. The closest swap. Check first-article dimensions if nucleation differs.
- Impact copolymer. If parts are dropped or used cold. See PP impact copolymer.
- Random copolymer. If the part must be see-through.
- Talc-filled PP. For more stiffness and flatter parts. See glass-filled vs. mineral-filled.
- HDPE. Tougher in the cold, softer and lower in heat resistance. See PP vs. HDPE.
Common processing problems
- Bow and twist: warped parts
- Dimples over ribs and bosses: sink marks
- Parts that do not fill: short shots
- Cracking, especially in the cold: brittle or cracking parts
- Strings at the sprue: stringing and drool
Common questions
What MFR PP homopolymer do I need for injection molding?
Most general injection runs on about 10–35 g/10 min at 230°C / 2.16 kg. Use higher MFR for thin walls and long flow paths and lower MFR for thicker parts that need a bit more toughness. Thin-wall packaging grades go well above 35.
Is PP homopolymer good for living hinges?
Yes. Most hinge grades are homopolymer or random copolymer at a mid melt flow, gated so the melt flows across the hinge. Flex the hinge a few times right after molding, while it is still warm, to orient it.
Why do my PP homopolymer parts crack in winter?
Homopolymer turns brittle near 0°C / 32°F. Its notched Izod is typically only 20–50 J/m at room temperature and drops further in the cold. If parts are dropped or shipped cold, switch to an impact copolymer.
Can I swap a nucleated PP for a standard grade?
Often, but check dimensions. Nucleation changes stiffness, cycle time and shrinkage, so first articles can measure differently in the same mold.
Tell us the PP grade 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