Clear food tray

PET sheet is formed into a shallow tray for packaged food.

Clear food tray, illustrative image

Material

Tray body: PET

Material selection rationale

Clear walls
Allow the contents to be seen.
Thin formed structure
A rim and shaped walls stiffen a lightweight tray.
Clear wall and sealing rim
A clear shaped sheet displays the contents; the flange geometry and selected lid determine sealing rather than PET alone.

How it becomes a product

  1. Make a sheet: Suitable PET resin is extruded into sheet.
  2. Thermoform and trim: The sheet is warmed, formed against a mould and trimmed to separate the trays. Softened sheet is drawn into the mould and cooled before trimming; deep corners can thin more than the flatter areas.

Preparation routes

Terephthalic acid route

Esterification, then polycondensation. The acid and diol first form ester-linked intermediates, releasing water. Further reaction builds longer PET chains while small molecules are removed. Both feedstocks have two reacting ends, enabling repeated links rather than just one small ester. Balanced functional groups and extensive conversion are needed for long chains.

Industrial catalysts and controlled heating assist the reaction; they are not alternative monomers. Removing small-molecule products drives the reversible stages towards chain formation.

  1. Polyesters: manufacture and usesChemical Industry Education Centre, University of York

Dimethyl terephthalate route

Ester exchange, then polycondensation. The ester reacts with ethylene glycol, releasing methanol in the first stage. Further reaction builds PET chains. This complete input pair is an alternative to the acid route. Methanol identifies the initial ester-exchange route; the terephthalate and ethylene-glycol fragments retained in PET match those from the acid route.

Catalysts and heat support ester exchange and chain growth; excess glycol and other small molecules are removed as the process proceeds. Feedstock substitution changes the reaction sequence and by-products, not the required two-ended glycol.

  1. Polyesters: manufacture and usesChemical Industry Education Centre, University of York

From p-xylene to terephthalic acid

  1. p-Xylene + Oxygen from air → Terephthalic acid

    Catalytic air oxidation changes both methyl groups into carboxylic acid groups while retaining their opposite positions on the benzene ring. Acetic acid is the process solvent, not an extra carbon fragment in terephthalic acid. Recovery, purification and crystallisation produce the purified diacid used in polyester manufacture.

  1. Purified terephthalic acid: products and manufacturing, annual report 2023, page 94INEOS Quattro

From ethene through ethylene oxide to ethylene glycol

  1. Ethene + Oxygen + Water → Ethylene glycol

    First, catalytic partial oxidation converts ethene to ethylene oxide, a three-membered epoxide. In the selected thermal route, water then opens the oxide ring to form ethylene glycol. Heavier glycols also form and are separated. The two-carbon unit reaches PET through a diol, unlike the direct addition polymerisation of ethene into polyethylene.

  1. Ethylene oxide and ethylene glycol process technologyShell

Sources

  1. Thermoforming food-packaging traysFaerch
  2. PET resin: frequently asked questionsPET Resin Association