Plastic bottles are most commonly produced from polyethylene terephthalate (PET), a thermoplastic polymer. The advantages of using PET for bottling are its strength, light weight, and recyclability. In order to manufacture plastic bottles, the PET must first go through polymerization to create long molecular chains. This process can be complicated and can result in inconsistencies between batches of PET. The two most common impurities that polymerization can create are diethylene glycol and acetaldehyde.Diethylene glycol levels are kept to a minimum so that it does not affect the final product. To make sure that the beverages are not affected by acetaldehyde, manufacturers use optimum injection-molding techniques which keep acetaldehyde concentration levels very low. Once the PET is polymerized, the bottle manufacturing process begins.
Step 1:PET is first heated up and placed in a tube shaped mold called a parison, which is cut into the correct length after it’s cooled.
Step 2:The parison gets heated up and placed into a bottle shaped mold, with a screwtop included. A mandrel (steel rod) is inserted into the parison to allow highly pressurized air to enter and stretch the plastic. The molecules then polarize, due to the combination of stretching and high temperature, and produce a bottle.
Step 3:The bottle is cooled quickly to avoid creep and then removed.
There are a number of tests done after manufacturing to guarantee that the bottles are safe for use. Manufacturers will test for the following:
- Resistance to creep
- Impact resistance
- Permeability to carbon dioxide
- Transparency
- Gloss
Compared to other plastics, PET has a high recycling rate. However, state and federal governments have plans to increase the recycling rate even more. Here are their recycling goals that they hope to reach in the near future:
- Recycle 25 to 50 percent of PET
- Recycling of PET be made available to one-half of the U.S. population
- 4000 curbside recycling programs be implemented
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