life cycle assessment of plastic and glass

Plasttic

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.

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.

Water bottles produced from bioplastics are made from plant materials which are processed to form polymers. Bioplastics are believed to be better for the environment, since they do not require the extraction and handling of crude oil, a non-renewable resource, and companies which manufacture them often try to use the best possible environmental practices. Furthermore, bioplastics decompose rapidly; the life cycle of a plastic bottle made from bioplastic is extremely short. In fact, some bottles made from bioplastics will even start to deform and leak if they are kept on the shelf too long.

However, bioplastics are not without environmental issues. The production of such plastics requires dedicating large areas of farmland to the production of crops for plastics, rather than food, and these crops eat up a great deal of water, fuel, and other resources. Bioplastics must also be manufactured with the assistance of a variety of chemicals, and, like regular plastics, they require shipping to an end destination, consuming more fuel along the way. Because they are designed to be disposable while still being relatively environmentally friendly, some activists fear that they may also distract consumers from more environmentally friendly choices, like reusable glass and metal containers.

Depending on the size of a bottling plant, a company will either order preforms and use them as needed, or it will order plastic bottles which are ready for use. The plastic bottles must be sterilized so that they are safe for beverages, and then they are filled, capped, labeled, packed into cases, and prepared for shipping. At this stage in the life cycle of a plastic bottle, the bottle could end up in any number of places, from a relief camp for refugees to the shelf at a high-end supermarket.

When a plastic bottle enters a landfill, it can take hundreds of years to decay, and it can have a profound environmental impact. The route to the landfill is often quite long, as plastic bottles are a very common form of litter around the world, requiring volunteers or government agencies to collect such bottles and bring them to a facility for recycling or other forms of disposal. As plastic bottles decay, they take up precious landfill space, and some leach harmful chemicals into the ground, potentially polluting the soil and water.

Glass

From the 19th century, various types of fancy glass started to become significant branches of the decorative arts. Objects made out of glass include not only traditional objects such as vessels (bowls, vases, bottles, and other containers), paperweights, marbles, beads, but also an endless range of sculpture and installation art as well. Colored glass is often used, though sometimes the glass is painted, innumerable examples exist of the use of stained glass.

Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted ingas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.

After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by thefloat glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish Container glass for common bottles and jars is formed by blowing and pressing methods. Further glass forming techniques are summarized in the table Glass forming techniques.

Once the desired form is obtained, glass is usually annealed for the removal of stresses. Surface treatments, coatings or lamination may follow to improve the chemical durability (glass container coatings, glass container internal treatment), strength (toughened glass, bulletproof glass, windshields), or optical properties (insulated glazing, anti-reflective coating).