from an article on WiseGeek
Plastic bottles are used to package a wide variety of things, from juice to soft drinks, and they play a ubiquitous role in the lives of many consumers, along with other plastic products. With a growing awareness of the environmental issues which surround plastics, many people have become interested in the life cycles of plastic products, from manufacturing to eventual disposition in a landfill or recycling facility. Being aware of the process behind the production of plastics can encourage consumers to think more carefully about how they use and dispose of such plastics. Because plastic bottles are a very visible form of plastic use, plastic bottles make an easy target for activism and education.
The life cycle of a plastic bottle starts, obviously, with the creation of the plastic used to make it. The vast majority of plastic bottles are manufactured from petroleum, some of which comes from deposits as much as three billion years old. Some manufacturers use bioplastics made from plant materials to create their plastic bottles, out of concern for the environment.
In the case of a plastic bottle made from petroleum, the oil must be extracted before being shipped to a processing facility and then distilled to separate out the various hydrocarbons it contains. Oil extraction is performed all over the world in a variety of locations, and it has a number of environmental impacts. In areas where oil is drilled from the seafloor, for example, oil spills are common, and regions like the Middle East are famous for their heavily polluting oil fires, caused by intentional or accidental combustion of oil fields. In some nations, oil extraction is also bound up with a number of social issues. Nigeria, for instance, has an oil industry notoriously plagued with problems; oil workers are often poorly paid and exposed to very hazardous conditions, and periodic devastating fires along oil pipelines are not uncommon.
Once oil has been extracted, it is typically moved into container tankers for shipping to refinery facilities. At a refinery, the oil can be submitted to a variety of distillation processes, such as fractional distillation, where the crude oil is heated, causing its various components to separate so that the refinery can make gas, fuel oil, plastics, and a variety of other products. Crude oil can also be “cracked” with chemical catalysts to generate hydrocarbon chains of a desired length; this practice is common, because demand for various petroleum products constantly fluctuates, and cracking ensures that oil is used extremely efficiently and generates the maximum possible profit.
Most plastic bottles are made from polyethylene terephtalate (PET) plastic, and almost all water bottles come from virgin plastic; an estimated 30% of the world's PET goes into plastic bottles. The plastic used in plastic bottles is made by mixing hydrocarbons extracted from crude oil with chemical catalysts, triggering polymerization. Next, manufacturers produce plastic pellets, which are melted down into “preforms,” which look like small test tubes; the preforms, in turn, can be heated, causing them to expand and turn into conventional water bottles. Typically bottling companies order preforms, expanding the water bottles at their own facilities as needed.