How PET plastic is made

The plastic in a soda bottle is the same polyester as a fleece jacket, made by joining two petrochemicals.

stations: 6
things upstream: 17
raw sources: 8
steps from the ground: 5

The short version

PET is made by reacting terephthalic acid with ethylene glycol, which releases water and links the molecules into chains. The molten polymer is cooled, chopped into chips and then heated in a dryer until the chains grow longer and the chips turn from clear to semi-crystalline. Bottle makers remelt the chips.

Make the acid and the glycol

Terephthalic acid is made by oxidizing p-xylene, an aromatic compound that comes from refining naphtha. Ethylene glycol is made from ethylene.

Goes in
Para-xylene Ethylene
Combine them into short chains

The acid and glycol are heated together in a condensation reaction. Water leaves as vapor, and the product is a short-chained compound called BHET.

Goes in
Ethylene glycol
Grow the chains under vacuum

Under vacuum and heat, the short chains link up into long ones, and excess glycol is drawn off. The liquid thickens like warm honey.
Extrude and chip the strands

Molten polymer is pushed through a die into strands, cooled in water, and cut into small chips. At this point the plastic is amorphous and transparent.
Bake the chips in a dryer

Chips are heated in the solid state, which crystallizes them and lengthens the chains further. The chips go from clear to cloudy white, and the plastic becomes stronger.
Bag the resin

Chips are loaded into silos and shipped to bottle makers and fiber spinners. Because moisture degrades molten PET, the chips are dried once more before they are melted again.

End of the linePET plastic Next it goes into polyester, plastic bottle, credit card and 3 more.

Worth repeating

More than 60% of PET goes into polyester fibers rather than packaging.
PET can be either transparent and amorphous or semi-crystalline and opaque, depending on how it is processed and cooled.