Polyolefin (PO): What It Is and What Types Exist
A polyolefin is a thermoplastic polymer obtained through the polymerisation of simple olefins, such as ethylene or propylene, both derived from petroleum or natural gas. It is the most widely used family of plastics at industrial level and includes materials as common in everyday life as polyethylene and polypropylene.
Polyethylene and polypropylene, the most common polyolefins
Within the polyolefin family, two materials account for virtually all production: polyethylene (PE), obtained through the polymerisation of ethylene, and polypropylene (PP), obtained through the polymerisation of propylene. Both share the chemical origin characteristic of polyolefins, although they have different properties: PE stands out for its flexibility, while PP offers greater rigidity and thermal resistance.
Other less common polyolefins
Beyond PE and PP, there are other types of polyolefins used for more specific applications. Polybutylene (PB) stands out for its resistance to creep under sustained temperatures, a property that makes it suitable for underfloor heating pipes, where it must withstand constant pressure for decades without deforming. Polymethylpentene (PMP), on the other hand, is one of the least dense polyolefins in existence and, unlike the others, is practically transparent and performs well under high-temperature sterilisation, which is why it is used in laboratory equipment and medical devices. There are also ethylene-propylene copolymers such as EPR and EPDM, which incorporate both monomers into the same chain to obtain elastomeric properties. They are used in seals, electrical insulation and sealing profiles, applications where the flexibility of rubber combined with the chemical resistance characteristic of polyolefins is desirable.
Why polyolefins dominate the plastics market
Polyolefins are not just another segment within the plastics sector: according to Plastics Europe’s Circular Economy for Plastics report (2024), European plastic production is dominated by polyolefins (PP and PE), ahead of PVC and PET. This leading position is driven by four specific technical factors:
- Raw material cost: ethylene and propylene are among the cheapest and most abundant petrochemicals, as they are obtained directly from the cracking of petroleum or natural gas.
- Control of properties through catalysis: catalysts such as Ziegler-Natta or metallocene catalysts make it possible to adjust density, crystallinity and the arrangement of molecular chains during polymerisation, resulting in very different materials without changing the chemical family. This is the same principle that explains, for example, why polypropylene can be manufactured in its isotactic form (rigid, the most common in industrial applications) or atactic form (soft, used in adhesives), starting from the same monomer.
- Chemical inertness: because they consist solely of carbon and hydrogen atoms, without oxygen or nitrogen in the main chain, polyolefins are highly resistant to corrosion and most chemical agents.
- Thermoplastic reprocessability: they can be melted and moulded repeatedly without significant degradation, reducing industrial processing costs and also supporting the entire mechanical recycling industry.
Comparison of the main types of polyolefins
| Type | Approximate density | Key property | Main use |
|---|---|---|---|
| Polyethylene (PE) | 0.91–0.97 g/cm³ | Flexibility, varying according to density | Packaging, film, pipes |
| Polypropylene (PP) | 0.895–0.92 g/cm³ | Rigidity and thermal resistance | Automotive, packaging, technical textiles |
| Polybutylene (PB) | 0.91–0.925 g/cm³ | Resistance to creep under sustained pressure | Heating pipes |
| Polymethylpentene (PMP) | ~0.83 g/cm³ | Transparency and resistance to sterilisation | Laboratory and medical equipment |
Reference values according to ASTM D792 and manufacturers’ technical data sheets.
Common properties of polyolefins
All polyolefins share a basic set of properties derived from their chemical structure, although each one expresses them differently:
- Low density, all below 1 g/cm³, making it possible to manufacture lightweight products without compromising their strength.
- Chemical inertness, thanks to a chain formed solely by carbon and hydrogen, without reactive functional groups.
- Low moisture absorption, preventing deformation or deterioration in humid environments.
- Low production cost, directly inherited from the low cost of their raw materials.
- Thermoplastic behaviour, the ability to melt and be remoulded repeatedly without losing their essential properties.
Uses and applications of polyolefins
Thanks to this combination of properties, polyolefins are present across a wide range of sectors. In packaging, they dominate the market for films, bags, jerry cans and rigid and flexible packaging for food, detergents and cosmetics. In construction, they are used in pipes and water, gas and heating systems, as well as in waterproofing sheets and insulation. In automotive, they are used in bumpers, interior panels, fuel tanks and under-the-bonnet components, while in technical textiles, they form part of non-woven fabrics, geotextiles and synthetic fibres for raffia and ropes.
A significant part of this growth can be explained by a specific phenomenon: in recent decades, polyolefins have progressively replaced glass and metal in multiple packaging applications, offering significantly lower weight without compromising the required strength. This lower weight translates into less fuel per transported unit and, therefore, a direct reduction in emissions associated with logistics, an argument that is increasingly important in packaging decisions made by industrial and food companies.
Polyolefin recycling
As thermoplastic materials, polyolefins are particularly well suited to mechanical recycling: they can be melted, filtered and pelletised to re-enter a production process without the need for additional chemical processes. This technical suitability is also reflected in industry figures: according to Plastics Recyclers Europe, flexible polyolefins, rigid polyolefins and PET account for more than 80% of total installed recycling capacity in Europe.
In the industrial sector, the circular recycling of polyolefin packaging makes it possible to significantly reduce dependence on virgin raw materials, while at the same time minimising the volume of waste that ends up in landfill.
Frequently asked questions
What is the difference between a polyolefin and a polymer?
A polymer is any material made up of repeating molecular chains; a polyolefin is a specific type of polymer obtained through the polymerisation of olefins such as ethylene or propylene.
Are polybutylene and PMP also polyolefins?
Yes, although their use is much more specific and limited than that of polyethylene and polypropylene, which account for most production and industrial consumption.
Are all polyolefins recyclable?
Yes, as thermoplastic materials, all polyolefins can be mechanically recycled through melting and remoulding, although each follows its own processing route depending on its density and composition.
What is the difference between polyethylene and polypropylene?
Polyethylene offers greater flexibility, while polypropylene provides greater rigidity and thermal resistance. This comparison of when to choose polyethylene or polypropylene details the technical criteria for deciding between the two according to the application.
Two materials, one chemical family with a future in recycling
Understanding polyolefins as a family helps reveal something that often goes unnoticed: polyethylene and polypropylene are not isolated plastics, but two branches of the same chemical base, sharing advantages in terms of cost, processing and recyclability. This common foundation also enables both materials, together with lesser-known variants such as PB or PMP, to continue gaining ground in applications previously occupied by glass, metal or paper.
At SINTAC Recycling, we recover the two main polyolefins: polyethylene (PE) and polypropylene (PP), offering a wide range of recycled materials for industrial applications. Our portfolio includes different grades, colours, densities and melt flow indices (MFI), developed to meet the specific requirements of each process and application. We offer recycled polyethylene and polypropylene in different formats, including pellets, regrind and flakes, adapted to the processing needs of each customer. This diversity makes it possible to incorporate recycled materials into applications such as injection moulding, extrusion, blow moulding, thermoforming and compounding, providing versatile solutions for different industrial sectors. With extensive experience in the recycled polymer market, at SINTAC Recycling® we work to offer consistent materials and solutions that combine technical performance, versatility and circularity, facilitating the incorporation of recycled polyolefins into new manufacturing processes.
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