How plastic bottles are made
Here at UKVending we deal with a lot of plastic bottles. We talk a great deal about how to dispose of them in an environmentally friendly way but one thing we rarely talk about is how they are made in the first place. It’s a fascinating process. The process is a complex one with many different stages.
Nearly all plastic bottles use a type of plastic called polyethylene terephthalte (PET). This is because it is strong, light and durable. The durability of this plastic is what is causing such concern about recycling the product. PET is what’s known as a thermoplastic polymer that can be made to be transparent or opaque and is made by a reaction between terephthalic acid, ethylene glycol and petroleum hydrocarbons.
The first process is to make long molecular chains. Interestingly at this stage known as polymerization there is the possibility of creating two kinds of impurities in the product: diethylene glycol and acetaldehyde. A large amount of the latter substance can affect the taste of the liquid in the finished bottle.
Once the plastic has been created it is now over to making the bottles themselves. The PET first, however, needs to be quality tested to ensure it is leak proof. This is done by checking the bottles are impermeable with carbon dioxide. Further tests are carried out to ensure the planned PET bottles are up to standard with regard to gloss, colour, shatter resistance, thickness and pressure resistance.
Bottle production can now truly start. The first stage is known as stretch blow moulding. The PET is heated and subsequently positioned within a predesigned mould. It will soon assume the shape of a long, thin tube. This process is otherwise known as injection moulding. The tube of PET is now known as a Parison, will be moved to a second, bottle shaped mould. Into the Parison is slid a thin steel rod, called a Mandrel. The Mandrel suddenly injects high pressure air and the process called stretch blow moulding begins.
The air and pressure forces the Parison to take the new bottle shape of the mould. The bottle is then cooled and removed from the mould before it is trimmed of any excess plastic. All the bottles are then collected together to be filled with whatever beverage is required.