Polypropylene is the most versatile of the commodity polymers and the one where grade selection matters most. The same three letters cover a stiff, clear homopolymer drawn into raffia tape and a rubber-toughened copolymer moulded into a car bumper. Two questions separate them: which copolymer type, and what melt flow. This is a plain-English reference for buying and selling PP in any condition.
What are the three types of polypropylene?
- Homopolymer (PP-H) — propylene alone. The stiffest and highest melting of the three, with good clarity in thin sections, but brittle at low temperature. Raffia, fibre, BOPP film, general injection moulding.
- Random copolymer (PP-R) — a small amount of ethylene distributed randomly along the chain. Better clarity and impact than homopolymer, lower stiffness and melting point. Thin-wall packaging, clear containers, and PP-R pressure pipe for hot and cold water.
- Impact or block copolymer (PP-C, sometimes ICP) — a rubber phase dispersed in a homopolymer matrix. Much better impact strength, especially below zero, at the cost of clarity. Automotive parts, crates, battery cases, industrial mouldings.
Asking which of the three you are being offered is the first question, not a detail. They are priced differently and are not substitutes.
How is MFI quoted for PP, and why is it different from PE?
Polypropylene melt flow is measured at 230°C under 2.16 kg. Polyethylene is measured at 190°C. This catches people out constantly: an MFI number lifted from a PP datasheet cannot be compared with one from a PE datasheet, because the test is not the same test. Always confirm the condition alongside the figure.
Typical bands give a rough sense of the intended process:
- Raffia and tape — roughly 2 to 4, where melt strength is needed for drawing.
- Film (BOPP and cast) — commonly 2 to 8.
- General injection moulding — around 10 to 35.
- Thin-wall packaging and high-flow moulding — 35 to 100 and above, to fill long thin sections quickly.
- Fibre and non-woven — high flow, often 20 to 40 for staple and much higher for meltblown.
How is recycled and filled PP traded?
PP is heavily recycled, and two variables dominate value beyond the usual grade questions:
- Filler content — automotive and appliance compounds are frequently talc or mineral filled, often 10 to 30 per cent. Filled regrind is a different product from unfilled and must be declared; ash content is the measurement that settles it.
- Source stream — crate and case regrind, battery case material, bumper and automotive regrind, and post-consumer rigid PP all behave differently and command different prices.
- Colour — natural runs above mixed, which runs above black, on the same logic as other polymers.
- Odour — recovered PP from food or consumer streams can carry odour that rules it out of some applications entirely, and it is not visible in a photo.
Battery case material deserves a specific mention: it is usually a well-defined, consistent stream, but may carry acid residue and lead contamination depending on processing, so its handling and declaration matter.
What drives the price of PP?
- The propylene monomer and virgin resin market, which recycled and off-spec grades track at a moving discount.
- Type — homopolymer, random copolymer and impact copolymer price separately, and the buyer pool for each is different.
- MFI band and how well it fits a real process; a grade in an awkward band sells to fewer people.
- Filler and ash content, colour and odour in recycled material.
- Condition — prime, near-prime, off-spec, regrind or recycled.
- Quantity, location and incoterm, since a full load and a parcel do not price the same.
These move independently, so a fixed list goes stale quickly. PP is best priced against live offers of the same type, flow band and condition.
How does Prime Polymers handle PP?
PP listings state the type, grade, condition, quantity, location, incoterm and the seller's own asking price per tonne, so homopolymer, copolymer and filled regrind can be compared properly instead of being read as one material. Prices are shown exactly as sellers enter them — never computed, adjusted or benchmarked by us. Browsing is free and open without an account. If nothing on the board fits your flow band or filler requirement, a Wanted post puts it in front of sellers. Prime Polymers is operated by ARC Polymers Ltd, a UK polymer trading company.
Frequently asked questions
- What is the difference between PP homopolymer and copolymer?
- Homopolymer is propylene alone — stiffer, higher melting, clearer in thin sections, but brittle when cold. Copolymers add ethylene: random copolymer improves clarity and impact with lower stiffness, while impact or block copolymer disperses a rubber phase for much better low-temperature toughness at the cost of clarity.
- Why is PP melt flow measured at 230°C?
- Because polypropylene's higher melting point requires it. Polyethylene is tested at 190°C. The two figures are therefore not comparable, and an MFI quoted without its temperature and load says very little. Always confirm the condition.
- What MFI is used for PP raffia?
- Raffia and tape grades typically sit around 2 to 4 g/10min at 230°C and 2.16 kg, because the melt needs enough strength to be drawn without breaking. Thin-wall injection grades run far higher, often 35 to 100 or above.
- Does talc content change the value of recycled PP?
- Substantially. Filled compounds behave differently on the machine and suit different end products, so filled regrind is a distinct material from unfilled and prices separately. Ash content is the usual measurement, and undeclared filler is a common cause of rejected loads.
- How can I see what PP is trading at?
- Compare live offers of the same type, flow band and condition rather than a dated figure. On Prime Polymers each PP listing shows the seller's asking price per tonne next to grade, quantity, location and incoterm. If nothing matches, post a Wanted requirement and let sellers come to you.