Materials · polypropylene
PP cores: plain and carbonate-filled polypropylene
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What polypropylene for cores is
Polypropylene is a semi-crystalline polyolefin, like polyethylene. It comes in two main families: homopolymer, stiffer, and copolymer (with ethylene), tougher on impact and in the cold. Both are used for cores, plain or with mineral fillers. Plain PP has a density of about 0.90–0.91 g/cm³: a PP core floats in water.
Strengths
- Low weight: at the same size it weighs about 1.13 times a cardboard core, against 1.76 for PVC (Fiaptech technical documentation, a company with corporate ties to ROLL). On a 3" core with a 7.5 mm wall that is about 1.8 kg per metre.
- Temperature under light load: homopolymer HDT at 0.46 MPa is about 100–120 °C. PP copes with hot processes better than PVC, as long as the load is not high.
- Hygiene: smooth, washable surface, no fibres. There are compounds declared compliant with Regulation (EU) 10/2011.
- Chemicals: excellent resistance to many solvents, acids and alkalis.
- Recycling: mono-material, floats, goes into the polyolefin stream.
Limits
- Stiffness: the short-term modulus, 1.3–1.8 GPa for homopolymer, is about half that of PVC. Resisting wall buckling takes more thickness.
- Creep: it creeps more than PVC. EN 13476-2 allows PP pipes a two-year creep ratio of up to 4: after two years the effective stiffness can be a quarter of the initial value.
- High load and heat: at 1.8 MPa HDT drops to 50–60 °C. Under a heavy roll in summer, PP behaves worse than its light-load HDT suggests.
- Cold: homopolymer has its glass transition around 0 °C and becomes brittle in frost. For outdoor use in winter, choose copolymer.
- UV: without stabilisers it degrades in sunlight within a few months.
Calcium carbonate-filled PP
Adding calcium carbonate (CaCO₃) to polypropylene raises stiffness and lowers compound cost. According to Fiaptech documentation, at the same size a filled PP core has a 3% strength of 1.51 times cardboard against 1.15 for plain PP, and a maximum load of 3.33 against 2.54. Minimum cycles reported by customers rise from more than 10 to more than 15.
| Cardboard = 1 | Plain PP | Filled PP |
|---|---|---|
| Weight | 1.13 | 1.23 |
| Strength at 3% | 1.15 | 1.51 |
| Maximum load | 2.54 | 3.33 |
| Minimum cycles reported | more than 10 | more than 15 |
| NIAS risk indicated | none | none |
The flip side: filled PP is heavier and behaves differently in recycling. With about 15% carbonate the density exceeds 1 g/cm³ and the core no longer floats: in sink-float sorting plants it ends up with the heavy materials (ROLL Lab analysis based on the densities of PP, about 0.905, and carbonate, about 2.7 g/cm³). Fillers may also affect the PPWR recyclability grade, which will be set by delegated acts.
Food contact and clean areas
Virgin PP is the polymer most used for cores destined for food, pharmaceutical and cleanroom film. Three points to remember:
- the core usually touches the film, not the food: compliance is assessed on the real contact;
- if needed, the supplier issues a declaration of compliance with Regulation (EU) 10/2011, with the conditions of use (in Great Britain the retained version of the same regulation applies);
- post-consumer recycled PP is allowed in contact with food only from processes compliant with Regulation (EU) 2022/1616.
Washing, disinfection and sterilisation. PP copes well with hot water, alkaline detergents and the alcohols used in clean areas. Of the three main polymers it is the one that best withstands steam: suitable grades survive autoclave cycles at 121 °C, provided the core is unloaded and supported so that it does not deform. Rigid PVC deforms in an autoclave; HDPE is borderline and yields easily under load. Be careful with gamma or electron-beam sterilisation (ISO 11137): standard PP yellows and becomes brittle, and radiation-stabilised grades are needed.
Cutting: a lathe works best
PP is tough, and with a saw it tends to smear and leave strings. Fiaptech documentation gives it the top score with lathe cutting, which leaves a clean, square edge, and lower scores with saw and knife. Moderate cutting speeds stop the edge from melting. Cutting plastic cores.
End of life and PPWR
A clean PP core is plastic packaging waste (code 15 01 02) with an established recycling market. Under the PPWR the general rules apply: recyclability from 2030 and post-consumer recycled content (35% from 2030, 65% from 2040 for “other plastic packaging”; 10% and 25% if the core were considered contact-sensitive packaging). For PP cores used in food settings, finding enough suitable recyclate will be the main challenge. The same applies to the UK Plastic Packaging Tax: a virgin PP core pays the tax because it is below the 30% recycled threshold. PPWR and plastic cores.
Use the calculator below, or open the minimum wall estimate with creep full page, with method and sources.
Minimum plastic core wallPlastic doesn’t break: it gives in slowly, with heat and with time. Tell me film, roll and temperature and I’ll estimate the minimum wall with the right margin.
| Wall by material | mm |
|---|
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ROLL Lab estimate, not a test certificate. Prepare your enquiry for the manufacturer →
Frequently asked questions
Are PP cores suitable for food contact?
There are virgin PP cores declared compliant with Regulation (EU) 10/2011. Usually, though, the core touches the film and not the food, so compliance is assessed case by case with the supplier’s declaration.
Does PP take more heat than PVC?
Under light loads, yes: homopolymer PP has an HDT at 0.46 MPa of 100–120 °C. Under high loads the gap narrows: at 1.8 MPa PP sits at 50–60 °C. Under a heavy roll you still need a wall margin.
What is the difference between plain and filled PP?
Filled PP contains calcium carbonate: it is stiffer and cheaper, but heavier. According to Fiaptech technical documentation (a company with corporate ties to ROLL), the 3% strength rises from 1.15 to 1.51 times cardboard.
Do PP cores break in the cold?
Homopolymer PP becomes brittle around 0 °C and can split on impact. For outdoor use and winter transport, use copolymer PP or HDPE.
Further reading
Materials
Plastic core materials compared: virgin and recycled PVC, plain and filled PP, HDPE, PS and ABS. Density, temperature, stiffness, creep and recycling.
PVC cores
Rigid PVC cores, virgin or recycled: stiffness, weight, temperature, reuse, cutting, food contact, separate recycling and PPWR. With data, ratios and sources.
HDPE cores
Virgin and recycled HDPE cores: toughness in the cold, UV resistance with carbon black, stiffness, creep, reuse, cutting and recycling with the polyolefins.
Hygiene and food
Plastic cores for food, pharmaceutical and cleanroom film: no fibres, washing, Regs 1935/2004 and 10/2011, GMP, NIAS, recyclate, FDA and returned cores.
Cutting
How to cut plastic cores: saw, crush knife and lathe for PVC, PP and PE. Edge quality, chips, tolerances, chamfering, common defects and machine safety.
Sources
- Fiaptech technical documentation, Smart Book “Which core?” (a company with corporate ties to ROLL)
- SpecialChem, Heat Deflection Temperature of Plastics (PP homopolymer, copolymer and filled)
- EN 13476-2, creep ratio according to EN ISO 9967
- Regulation (EU) 10/2011 on plastic materials and articles intended to come into contact with food
- Regulation (EU) 2022/1616, recycled plastic in contact with food
- Regulation (EU) 2025/40 (PPWR), Arts. 6 and 7, EUR-Lex
- ROLL Lab analysis (weight per metre, density of filled PP)
- ISO 11137 (sterilisation of health care products by radiation)
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