You might find yourself questioning exactly what PET plastic must be, but we can guarantee that you have held it in your hand at least once. In this article, we are going to teach you how PET plastic bottles are created during the manufacturing process, and exactly why PET plastic is perfect for the jobs that it does.
What are PET plastic bottles?
PET is an abbreviation for polyethylene terephthalate, a substance that is used to create 70% of the soft drink bottles that are manufactured all around the world. This makes it the most popular choice on a worldwide scale, placing itself well ahead of its competitors, aluminium and glass.
Polyethylene terephthalate is a naturally transparent type of thermoplastic that has a wide applicability in the bottling and packaging industries, it can also be used as an engineering plastic when it is combined with other materials. Some people will know it better by the name that it is given due to its applicability in the textile industry, polyester.
Where did polyethylene terephthalate come from?
PET was developed more than seven decades ago, by the DuPont chemists. They set out to look for a polymer material that could be applied to the textile industry, and they produced PET during the synthesis of both ethylene glycol and terephthalic acid. They noticed that it was an incredibly strong material without the addition of additives, especially when they took into consideration how lightweight it was.
This strength meant that less material was needed for certain applications, explaining why plastic bottles are made out of material that seems to be relatively thin. Studies have also shown that PET is highly sustainable due to the way that it can be recycled and reused over and over again.
Why is polyethylene terephthalate such a useful material?
PET is a useful material due to a combination of different factors. When it comes to the bottling industry, PET is useful due to the amount of chemical resistance that it can offer to a manufacturer. It does not react with food or water, making it perfect for consumer packaging.
It is also almost completely shatterproof, making it much safer to use than a glass alternative. The PET is also much lighter than glass would be, making it easier to transport the finished products.
You also have to consider the fact that polyethylene terephthalate is a widely available substance that is also relatively affordable. After it has been used by the consumer, it can be recycled and reused. This can be done in one of two ways, the plastic will either:
a) go through a series of washing processes or
b) it will be broken down into a set of raw materials.
How are PET plastic bottles made?
There is an array of different methods that are used to make PET plastic bottles, but the most common method can be broken down into the following steps:
Step 1: The PET is initially heated up, melting it down into a molten state, before being placed into a tube shaped mould. This process is known as injection moulding. Once the PET has become the same shape as the mould, it is referred to as a parison. The parison is then cut to the correct length after it has been systematically cooled down.
Step 2: The parison is then heated back up and placed into a mould that is shaped like the bottle that is being manufactured. A steel rod is then placed inside of the parison itself, blowing highly pressurized air that stretches the parison into the shape of the mould that surrounds it. The molecules inside of the PET then polarize, and the stretching process leaves you with a plastic bottle.
Step 3: The bottle then has to be quickly cooled down and removed from the mould. There are several different methods that manufacturers frequently use to cool the bottles down quickly. Some of these methods are direct and others are indirect. For example, water can be pumped through the pipes that surround the mould, indirectly cooling the plastic bottle down. Or, carbon dioxide can be used to cool the plastic down via a direct application.
Step 4: Most of the bottles that are produced by manufacturers will then need to be trimmed down to size. If the bottles have been created during a continuous moulding process, then one bottle will need to be trimmed from the one next to it. If the bottles have been created during a non-continuous moulding process, then some excess plastic may have managed to seep through. This would need to be trimmed off.
Step 5: The bottles are now ready to be transported to their destination.
What is the role of the compressor when creating PET plastic bottles?
One common item exists no matter what method a manufacturer uses to produce PET plastic bottles, a compressor. Numerous different types of compressors are used across the industry, and the compressor is the piece of hardware that requires the most attention.
The compressor is responsible for injecting highly pressurized air into the parison, stretching the parison until it fits perfectly in the bottle-shaped mould that surrounds it. This means that a compressor has to be good enough to accurately control the overall flow of air that goes into the parison, otherwise, the shape will not form.
Traditionally, reciprocating compressors would have been used during the manufacturing process of PET plastic bottles. These compressors used pistons to create a large amount of pressure, but they were no good when it came to cost efficiency. Due to this, most new companies prefer to use centrifugal compressors. These compressors are highly cost efficient, and they utilize a lower amount of pressure.
Do quality tests take place?
Quality tests have to be done regularly during the manufacturing process of PET plastic bottles. These tests are the steps that ensure that the bottles are safe for use, while also checking for things like impact resistance and permeability to carbon dioxide.
Remember that PET has a high recycling rate, and that sustainability shows itself during the manufacturing process. A lot of PET plastic bottles are now manufactured using bottles that have previously been recycled.