Life, in short, is busy. Busy lifestyles make it difficult to consider a plan ahead for smaller things like lugging a glass water bottle to and fro as you go about your day. It takes a lot of effort (and time with the tens of thousands of designs available) to pick a bottle, fill the bottle and then lugging it, so it makes the inevitable break of the bottle much more bitter. To accommodate our in-and-out lifestyles, plastic bottles sit on shelves readily containing beverages, meals or snacks for any given time of day. It takes two seconds to find a bottle and two seconds to throw it away and the best part—it will not break on you to possibly hazardous situations.
What is PET?
Polyethylene terephthalate (PET or PETE) is a thermoplastic polymer that belongs to the polyester family of polymers. These resins are known for an excellent combination of properties, such as mechanical-, thermal-, chemical resistance, dimensional stability, resistance to moisture, alcohol and solvents. PET is highly flexible, colorless, and a semi-crystalline resin in its natural state. With different manufacturing processes, it can be semi-rigid to rigid.
Production of PET
The production of PET plastic bottles begins by mixing PET pellets and flakes of recycled PET plastic into a combined mixer. As good as it is to recycle, reprocessed plastic loses some of its physical properties, which could be undesirable for the functions of a bottle (no one likes a flimsy bottle). No more than 10% of recycled material will be used per batch of bottles to maintain the strength of the bottles manufactured. The PET mixture drops into a plastic injection machine that heats it to 315 degrees Celsius. The dry, raw mixture melts into thick and gooey plastic. The machine shoots the goo at a high pressure to cast a beginner mold called a freeform. A built-in cooling system hardens the freeform almost immediately.
The machine drops the PET freeforms down into a conveyor that feeds the freeforms into a Reheat Stretch Blow Molder—where the magic happens. In seconds, this machine heats up the freeform just enough to make the plastic malleable. A rod is inserted into the mouthpiece of the bottle to elongate the soft plastic. This rod also blows air into the warm freeform. The high pressure inside the freeform pushes the edges of the freeform against the side of the mold, forcing the freeform into the shape of the mold. Cool water circulates the mold and sets the bottle almost immediately.
For a thicker plastic or a different shape, the PET plastic has to go into a UV oven before it is shaped into a freeform. To influence the thickness and shape of the plastic, a technician has to adjust the temperature of each UV lamp inside the oven that will influence how the plastic will mold. The freeforms then go into another reheat stretch blow molder, in which the new desired shape will be reached.
Quality control tests happen at random. Technicians pull samples off the shelf to measure the thickness of the plastic and perform a compression test to gauge it’s strength. They evaluate its resistance to vacuums by sucking the air out of the bottle or blowing air into the bottle and observing the expansion capacity of the plastic. PET might be a byproduct of a much larger process, but that’s only one metaphor in reality. It takes a second to make a bottle, use a bottle and throw it away, but it took years to design it and it will take years to degrade it.