Polyethylene (PE) — types, properties, applications and transport

Definition

Polyethylene (PE) is the most common thermoplastic, obtained by polymerisation of ethylene, supplied to processors as a granulate with a density of 0.91–0.96 g/cm³, used for the production of films, packaging, pipes and moulded products.

It is by far the most frequent — though not the only — cargo passing through our terminal; alongside PE and PP we also handle ABS, PS, PA and other plastics, and in general anything that pours well and is not a dangerous good. Polyethylene is a commodity plastic — produced on a scale of tens of millions of tonnes a year, more than any other plastic — and its logistics are the foundation of the entire bulk materials industry in which we have worked for over three decades. The seemingly uniform “plastic” is in fact a whole family of materials with very different properties and transport requirements, and distinguishing them correctly is the first step towards flawless logistics.

Types of polyethylene

Polyethylene is classified primarily by density, which results from the structure of the polymer chain — its degree of branching. The fewer branches, the more tightly the chains pack, the higher the density and the greater the rigidity.

Beyond these basic groups there are special variants: UHMWPE (ultra-high-molecular-weight polyethylene) for sliding elements and technical parts, as well as metallocene polyethylenes (mPE) with a narrow mass distribution, producing films of above-average strength. From a logistics standpoint these differences are secondary — all these materials are transported similarly, as bulk granulate — but for the processor they determine the end use and are strictly controlled.

The second classifying parameter, alongside density, is the melt flow rate (MFR/MFI) — a measure of melt fluidity that determines the processing method. Granulate with a low MFR is suitable for pipe extrusion, with a high one — for injection moulding of thin-walled products. For logistics, MFR has no transport significance, but it is one of the parameters that must remain unchanged: mixing two grades of different MFR renders the material useless to the processor. This is one of the reasons why batch traceability and the absence of contamination are so jealously guarded in this industry.

Properties and granulate form

Polyethylene is a light material, flexible (LDPE) or rigid (HDPE), chemically resistant, with good insulating properties and a melting temperature in the range of around 105–135 °C. It reaches processors almost exclusively in the form of granulate (pellet) sized 2–5 mm — lenticular or cylindrical, usually natural (milky-white, translucent) or coloured.

One parameter is key from the transport perspective: low bulk density, around 0.50–0.60 kg/l for loosely poured granulate. This means PE is a “volume” cargo — a silo tanker fills up by volume before it reaches the permissible gross combination weight. That is why high-capacity trailers (the 55–65 m³ class) with the lowest possible tare weight are selected for granulate transport.

PE granulate has one more important characteristic: it is prone to electrostatic charging. During pouring and pneumatic conveying the grains accumulate electrostatic charge, which promotes caking, sticking to walls and — in extreme cases — the risk of discharges. This is another argument for gentle transloading methods and the proper choice of antistatic packaging for sensitive materials.

Applications

The versatility of polyethylene stems precisely from the diversity of its variants:

• LDPE and LLDPE — packaging films, stretch and shrink film, sacks, agricultural and construction films, coatings, wire insulation. This is the domain of “soft” PE.
• HDPE — bottles and canisters for household chemicals, milk and detergents, water and gas pipes, crates, pallets, caps, HDPE films (light carrier bags), injection- and blow-moulded products.
• MDPE — primarily gas pipes and some technical films.
• UHMWPE — guides, sliding linings, parts with high abrasion resistance.

This diversity translates into scale: polyethylene is present in almost every packaging, construction and household appliance supply chain, and demand for granulate — including recycled — rises along with regulations on recycled content. It is worth emphasising that the same plastic, depending on the grade, ends up in products with extremely different requirements: from single-use food film to a gas pipe with a 50-year service guarantee. For logistics this means one thing — although we transport “polyethylene”, we in fact handle dozens of specific grades, each with its own recipient and specification, and an error in batch identification is costly.

Transport and logistics of PE granulate

PE granulate is transported by two routes that usually complement each other. The big bag (1000 kg) dominates at the production and import stage — in it the material arrives in containers from Asia and the Middle East, and in it it also rests in the warehouse. The silo tanker handles bulk delivery on the last leg, directly to the processor’s silo.

At our terminal in Chorula these two worlds meet: we receive big bags from containers, store them in a 2000-unit buffer and transfer the granulate into silo tankers in step with the customer’s collections. The terminal’s throughput is 200 tonnes per day. Among our regular customers in granulate logistics are, among others, LG Chem, Borealis, Synthos and Orlen.

A typical import chain for PE granulate from Asia looks like this: the material leaves the production plant (e.g. in Korea or on the Persian Gulf) in big bags packed into sea containers, sails to a European port, and from there travels by road to an inland transloading terminal in Poland. Here comes the key moment: repacking or transfer into a silo tanker for the last, shortest leg to the recipient’s plant in Central and Western Europe. Locating the terminal close to the motorway network shortens this leg and lowers the delivery cost — for the importer, what matters is not only the price of the granulate itself but the total cost of getting it to the silo ready for processing.

The big bag and the silo tanker are therefore not competitors but successive stages of the same journey: the sack works where the material has to wait or cross an ocean, and the silo tanker where fast, maintenance-free bulk delivery straight to the recipient’s installation matters.

Quality requirements — why the transloading method matters

Polyethylene is a chemically “simple” material, but demanding in terms of cleanliness. Three risks recur most often:

• Contamination — foreign granules of another plastic or colour, dust, black specks. For a film processor a single contaminated sack can mean rejection of a batch of product.
• Angel hair and fines — thin filaments and particles that form when a grain rubs against pipe walls during high-pressure pneumatic conveying. They clog the processor’s filters and installations and degrade product quality.
• Moisture — although PE is barely hygroscopic, water on the granulate surface or in the packaging causes defects during processing. Hence the requirement for dry air and a dry warehouse.

This is precisely why for the most demanding granulates we use pneumatics-free transloading — a gentle, gravity-fed flow through a sieve, without compressed air and without mechanical impacts. The grain is not accelerated in pipes, so no angel hair forms and the risk of contamination drops to a minimum. For plastics producers, for whom granulate parameters are sacred, this is an argument more important than the speed of the operation itself.

The plastics industry has, moreover, developed its own standards in this respect. The international Operation Clean Sweep programme commits producers, processors and logistics operators to preventing uncontrolled escape of granulate into the environment — because lost pellets are not only material loss but also microplastic entering water and soil. Clean, tight transloading therefore serves two goals at once: it protects batch quality for the recipient and limits the environmental footprint of the whole operation. In a terminal working with granulates these two things go hand in hand — good quality practice is at the same time good environmental practice.

Major producers

The polyethylene market is consolidated around a few global corporations. The largest producers include LG Chem, Borealis, Dow, ExxonMobil, INEOS, LyondellBasell and SABIC. In Poland, polyolefins (PE and PP) are made by the Orlen group through the Basell Orlen Polyolefins plant in Płock. Producers of recyclates (R-HDPE, R-LDPE) are also playing an increasing role, driven by regulations on recycled content in packaging.

For Central Europe, the supply direction is also important. Some granulate comes from local production, but a significant part arrives from Asia and the Middle East, where a cheap feedstock base allows polyolefins to be produced at competitive cost. This import is precisely the stream that transloading terminals handle — the link connecting the sea container with the processor’s silo. The more efficient and cleaner the transloading at this interface, the lower the total cost and the smaller the quality risk for the end recipient.

Regardless of the source — local production or import from across the ocean — granulate on the last leg of the chain needs the same thing: clean transloading and efficient bulk delivery to the silo.

Polyethylene recyclates (R-PE)

An ever-larger part of the granulate stream is recycled polyethylene — R-HDPE and R-LDPE. It is driven by regulation: the EU Packaging Regulation (PPWR) introduces mandatory recycled-content levels in plastic packaging, which raises demand for high-quality regranulate. From a logistics standpoint, recyclate is transported the same way as virgin material, but it sets even higher cleanliness and traceability requirements — it is a material more expensive to source, with greater batch variability, in which contamination is especially costly.

In practice this means that a terminal handling recyclates must guarantee separation of streams, thorough cleaning between batches and full documentation of origin. The growing importance of R-PE is one of the reasons why we invest in transloading methods that minimise the risk of material contamination.

Related topics

It is worth comparing polyethylene with polypropylene, the second pillar of the polyolefin market, with which it shares many transport properties but differs in end use and processing parameters. Equally important is the transloading method, which determines granulate quality at the interface of container and silo. The full offering of bulk material transport can be found on the PHS Magnum portal.

Sources

• ISO 1872 / ISO 1183 standards — designation and classification of polyethylene and the density of plastics.
• PE producers’ technical materials (granulate data sheets).
• Industry guidelines on granulate cleanliness (Operation Clean Sweep).
• Operational practice of the SMIALA terminal, Chorula — Aleksy Pasternak.