Overview
The two types of polyethylene (low and high) are the most commonly used types of plastic and are found in many everyday items such as containers and also construction materials. We are likely to encounter this type of plastic very frequently.
Common Uses & Applications
One interesting application of HDPE is as a liner in landfills to prevent pollutants from leaching into groundwater or soil. While products made of HDPE pile up in the landfill, HDPE in another form provides protection from the detriments of plastic pollution. Such an application highlights the benefits of plastic that have led to their proliferation and infiltration of every corner of society and the complexity when it comes to risk assessment. It also demonstrates the variability of products that can be produced from even a single type of plastic. It is also used in other construction settings or automobiles.
Chemical Structure & Properties
The production and resultant chemical structure of HDPE depends on its desired function. The monomer constituent of HDPE is ethylene which is a colorless, flammable gas and a hydrocarbon. Ethylene subunits are linked together, the process of which determines the plastic’s characteristics. Key steps in the process include temperature, pressure, and cooling time. These will affect the extent of crystallinity (this could be thought of as regularity or structure) of the plastic, which will determine the properties of the plastic such as flexibility or rigidity, strength, and chemical stability.
Environmental Impact
Like other types of plastic, the degradation timeline is long and mechanical or chemical fragmentation, when it does occur, results in production of smaller pieces of plastic known as microplastic. However, the shape generated in the fragmentation of HDPE may be less harmful to organisms than other types of plastic. There is risk of accumulation in soils, groundwater, surface water, or tissues of organisms. Another major environmental impact is the production of toxic or greenhouse gases during plastic production including methane, carbon monoxide, or nitrous oxide. Petrochemical plants where plastics are manufactured leach toxic substances in the air and water of surrounding communities, often leading to heightened incidence of cancer and other serious illness.
Recycling Process & Opportunities
Since HDPE is a thermoplastic, it is recyclable. The process generally includes collection, sorting, cleaning, shredding, heating/melting, and molding into new products. This type of plastic can be “upcycled” into plastic “lumber” that can be used to create structures and this process can be a good source of employment opportunities.