What’s Polyethylene?

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Polyethylene is a type of thermoplastic polymer, which means it can be melted into a liquid and reshaped when it returns to a solid state. It is chemically synthesized from ethylene, a compound that is usually made from petroleum or natural gas. Other unofficial names for this compound include polyethylene or polyethylene; and is also abbreviated to PE. It is used in the production of other plastic compounds more often than it is used in its pure form. While it has a wide variety of uses, it can be harmful to humans and the environment.

Production and uses

Of all the plastics produced for industrial and commercial products, polyethylene is the most common. For example, 280 million tons were produced in 2011 alone. More than five times as much PE is produced each year as a closely related compound, polypropylene (PP). The broadest use of these polymers is in packaging materials, such as film and foam; and for bottles and other containers that may be used in the food, medical and other consumer industries.

The characteristics of a plastic can be adjusted by combining it with various plasticizers, which are substances added to plastics to make them stronger, pliable and transparent. The addition of chromium/silica produces high-density polyethylene (HDPE), which is used to make sturdy products such as garbage containers. Combining it with organic olefin compounds results in a type of low density PE (LDPE) which is used for plastic shopping bags or shopping bags. Other common forms of polyethylene are ultra-high molecular weight PE (UHMWPE), which is used in bulletproof vests and knee joint replacements; and medium density PE (MDPE), which is crack resistant for gas pipe pressure fitting applications.

Plastics based on the PE molecule are popular because the compound has physical characteristics considered safe and useful in a wide range of environments. These traits include the fact that it remains flexible over a long period of time while remaining inert and impervious to damage from most liquids. Because its level of softness and strength can be easily adjusted and it can be dyed in many colors, it is often used in consumer products, from food wraps to shampoo bottles, milk containers, toys and grocery bags.

Potential dangers

Depending on the compounds with which it is bound, the level of toxicity and flammability of PE varies considerably. There are concerns in particular about two versions of the compound, both of which are often used for medical and consumer purposes. Polyethylene glycol (PEG), which serves as a binding agent for many drugs and is also found in products such as shampoo and toothpaste, can cause allergic reactions in some individuals. Some people experience nausea, flatulence and diarrhea after being exposed to it, while others experience a hives-like rash. The elderly seem to be particularly prone to these side effects.

In addition, harmful chemicals, including the plasticizer phthalate, can leach from polyethylene terephthalate (PET), which has been widely used in the plastic bottling industry. Phthalates are associated with hormonal imbalances, increased allergies and reduced fertility. Some studies show that it can also contribute to the development of obesity and breast cancer.
Environmental impact
While PE can help make many useful and durable products possible, its environmental impact is of concern to many experts. It does not biodegrade easily and can sit in a landfill for hundreds of years. About 20%-24% of all landfill space in the United States alone is occupied by plastics, including polyethylene products. However, recycling can reduce this problem, as PE waste can be melted down and reused.

Additionally, an aerobic bacterium called Sphingomonas can significantly reduce the amount of time it takes to break down some forms of PE, although it’s not yet widely used. Environmental conservation efforts have also led to the development of bioplastics, with the aim of creating polyethylene from ethanol made from sugar cane.

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