Definition
PET (polyethylene terephthalate) is a thermoplastic polyester from the terephthalate group, obtained by polycondensation of terephthalic acid (or dimethyl terephthalate) with ethylene glycol, supplied to processors as bottle-grade granulate or recyclate with a density of about 1.38 g/cm³, hard, transparent and strongly hygroscopic, used for bottles, polyester fibres and films.
Within the family of commodity plastics, PET stands somewhat apart from the polyolefins. Polyethylene and polypropylene are light, chemically inert hydrocarbons that float on water and absorb little moisture. PET is heavier, polar, sinks and — most importantly from a logistics standpoint — greedily absorbs water from the air. These two characteristics, density and hygroscopicity, determine how PET granulate must be transported and transloaded.
Granulate form and variants
PET reaches processors in several forms that are worth distinguishing:
| Form | Characteristics | Typical purpose |
|---|---|---|
| Bottle-grade granulate | virgin, high intrinsic viscosity (IV), usually crystallised | bottles, preforms, food packaging |
| Amorphous PET | transparent, lower softening temp., prone to caking | films, straps, some products |
| Crystallised PET | matt, heat-treated, resistant to sticking in the dryer | granulate for bottles, feedstock for further crystallisation |
| Flakes | shredded, washed recycled bottles | fibres, straps, feedstock for regranulation |
| Regranulate (rPET) | melted and homogenised flakes, repeatable parameters | bottle-to-bottle recycling, packaging |
A key quality parameter of PET is the intrinsic viscosity (IV), a measure of the length of the polyester chain. Higher IV means a longer chain and better mechanical properties — which is why bottle granulate has a higher IV than fibre granulate. IV drops with every hydrolysis (decomposition under the influence of water at high temperature), hence the overriding role of drying and protection against moisture. For the logistics operator this is important context: although in transport PET is simply a dry, free-flowing substance, every water contamination triggers degradation whose effects will only show up at the processor’s.
The division into amorphous and crystallised has direct operational significance. Amorphous PET softens and sticks in the dryer before it even has a chance to dry — which is why bottle-grade granulate is supplied in crystallised, matt form, which withstands drying at 160–180 °C without caking. This is a good example of how granulate form is not a cosmetic matter but follows directly from process requirements.
Properties
The most important properties of PET from the material and logistics perspective:
- Density of about 1.38 g/cm³ — PET is denser than water and sinks. This distinguishes it from the polyolefins and makes it the heaviest of the common granulates handled at a bulk materials terminal. In transport practice this means a silo tanker fills up by weight before it reaches its volume limit — the opposite of the situation with light PE or PP.
- Strong hygroscopicity — this is the defining characteristic of handling PET. The granulate absorbs moisture from the air, and water present at processing temperature hydrolyses the polyester chain, lowering IV and degrading the product. That is why PET must always be dried before processing (usually below 50 ppm moisture), and protected from dampness in transport and storage.
- Hardness and transparency — amorphous PET is clear and rigid, which makes it ideal for bottles and packaging where appearance and a gas barrier matter.
- Good barrier to CO₂ and oxygen — hence the dominance of PET in carbonated-drink packaging.
- Thermal resistance — glass transition temperature about 70–80 °C, melting about 250–260 °C; PET withstands more than the polyolefins, but a standard bottle is not suitable for hot filling without additional treatment.
From the terminal’s perspective all these properties come down to two practical conclusions. First: PET is a heavy cargo, so the payload limit is set by weight, not volume — unlike with the polyolefins. Second: PET is a water-sensitive cargo, so packaging tightness and a dry transloading installation are not an option but a condition for delivering the material in a state fit for processing.
Applications
PET is one of the most widespread plastics in the world, and its applications concentrate in a few large groups:
- Bottles and beverage packaging — the most recognisable application. Transparency, a CO₂ barrier and light weight make PET the standard for waters, carbonated drinks and oils. The bottle is formed from a preform in a stretch blow-moulding process.
- Polyester fibres — historically the first and still the largest application by volume of polyester: woven and knitted fabrics, fillings, nonwovens. A significant part of recovered PET returns precisely as fibre.
- Films — BOPET films (biaxially oriented) for packaging, laminates, technical and electrical-insulation applications.
- Strapping — strong packaging straps, often produced from recyclate and flakes.
- Thermoformed packaging — trays, blisters, food packaging from PET and APET film.
For the logistics operator it is important that under the single name “PET” hide materials with very different requirements: a food bottle requires food-contact approvals and high IV, fibre — a different profile, strapping tolerates a larger share of recyclate. These are further streams that must not be mixed, and batch traceability remains just as important as with the polyolefins.
rPET and recyclates
PET is the plastic with the best-developed recycling system of all commodity plastics — and this area is growing fastest. The recyclate stream begins with the collection and sorting of bottles, their shredding and washing, the result of which is flakes. Flakes can be used directly (e.g. for fibres and straps) or melted and homogenised into regranulate (rPET) with repeatable parameters.
The most demanding direction is bottle-to-bottle recycling: food-grade rPET, approved for repeated food contact, returns to the production of new bottles. This requires decontamination at elevated temperature and often an increase in IV in a viscosity-improving process, because recyclate usually has shorter chains than virgin material.
The driver of this growth is regulation. The EU Packaging and Packaging Waste Regulation (PPWR) introduces mandatory minimum recycled-content levels in plastic packaging, including PET bottles. For the market this means rising, guaranteed demand for high-quality rPET and a shift of a significant part of the PET stream towards recovered material.
From the terminal’s perspective, rPET and flakes are transported the same way as virgin material, but they set even higher cleanliness and traceability requirements. Recyclate is more variable batch to batch, more expensive to source and especially sensitive to contamination — contamination wastes all the effort put into recovery. Flakes, because of their irregular shape and greater tendency to accumulate moisture, require special care for dryness. This is another argument for gentle, well-documented transloading, which gains in importance with the development of the circular economy.
It is also worth adding that the density difference between PET and the polyolefins is a practical recycling tool. In float separation, PET bottles (which sink) are separated from PE and PP caps and labels (which float) in a water bath — which explains why beverage producers increasingly select closure materials so as to ease this separation.
Transport and transloading of PET granulate
PET is transported in the same scheme as other granulates: in big bags (FIBC) at the production, import and storage stage, and in bulk by silo tanker on the last leg to the processor’s silo. The terminal in Chorula, with a buffer of 2000 big bags and a throughput of 200 tonnes per day, handles this material in its standard collection rhythm — with one caveat that is decisive for PET: the transfer station must be dry and the material’s path tight.
Two characteristics of PET nevertheless require separate attention. First — moisture. Protecting the granulate against dampness is critical here, far more important than with the polyolefins. The granulate must stay dry along the entire path, the packaging tight, and the compressed air used for discharge dried. Damp PET cannot be distinguished visually from dry, and the effects — a drop in IV and product defects — only show up in processing, so discipline in maintaining dryness is a matter of trust and documentation, not just technique.
Second — weight. With a density of about 1.38 g/cm³, PET is the heaviest granulate in circulation. In a silo tanker with a capacity of ~60 m³ the permissible combination weight becomes the limit, not the tank volume — the trailer “fills up by weight” before it uses its whole cubic capacity. This is the reverse of the situation with light PE and PP, where volume is the limit. So in planning PET loads, payload matters above all, not capacity.
For PET granulate we use pneumatics-free transloading — a gravity flow through a sieve instead of pneumatic acceleration of the grain. With PET this method has a double advantage: it limits not only dust and contamination but also the air blast, which for such a hygroscopic material is an additional carrier of moisture. With rPET flakes, which are more prone to dusting and sensitive to moisture, a gentle transloading method is especially beneficial — and a dry, verified silo tanker is a condition here, not a convenience. PET, as a polyester, belongs to a different family of plastics than the polyolefins that make up most of the stream handled at the terminal, which, combined with the requirement to maintain low moisture, makes handling it more demanding than light PE or PP.
Some PET granulate comes from European production, some arrives by import from Asia and the Middle East, and a growing share of rPET is produced locally, close to the sales market — and it is precisely this last stream that increasingly reaches the inland terminal as the first link, rather than after a sea crossing. The full big-bag-to-silo-tanker transloading offering can be found on the service page big bag to silo tanker transloading, and comprehensive bulk material transport — on the PHS Magnum portal.
Producers
The PET market is divided into producers of virgin resin (bottle-grade) and a growing sector of recyclers supplying rPET. Large PET resin producers include, among others, Indorama Ventures (one of the largest in the world), Equipolymers and Neo Group on the European market. Alongside them operate numerous regional manufacturers and recycling plants whose share of supply is rising quickly under the influence of regulation.
For a bulk materials terminal the origin of the resin matters mainly for logistics: virgin material often arrives by import and requires transloading from big bags or containers on the last leg to the processor, while rPET is increasingly produced locally, closer to the sales market. Regardless of the source, the requirement is the same — to deliver granulate dry, clean and with batch traceability preserved.
Related topics
PET is best understood in comparison with the polyolefins — the light, non-hygroscopic PE and PP, from which it differs in higher density and sensitivity to moisture — as well as with PVC as another commodity plastic with its own transloading specifics. Granulate quality at the interface of container and silo is determined by pneumatics-free transloading, and the material itself is transported in big bags (FIBC) and in bulk by silo tanker. The full range of terminal services is described on the SMIALA services page.
Sources
- ISO 1183 (density of plastics) standards and the determination of intrinsic viscosity (IV) of polyesters.
- PET resin producers’ technical materials (data sheets and granulate drying guidelines).
- Provisions of the EU Packaging and Packaging Waste Regulation (PPWR) regarding recyclate content.
- Industry guidelines on granulate cleanliness (Operation Clean Sweep).
- Operational practice of the SMIALA terminal, Chorula — Aleksy Pasternak.
