You’ve probably heard that all plastic that’s ever been made still exists on earth. Why do regular plastics not biodegrade like organic materials or corrode like metals? It’s because of the properties of the polymers that make them up.
We can categorize the single-use plastics we produce. There are two main categories, thermoplastics and thermosets. The main difference is their ability to be melted and reformed. Thermoplastics can be melted and remolded repeatedly but thermosets are strengthened in their initial forming. Thermosets undergo a chemical change during the curing stage where the polymers chains are cross-linked which makes a polymer network. This is why if thermosets are heated, they don’t melt but instead burn.
Some Common Thermoplastics:
Low Density Polyethylene (LDPE)
Examples: bags, containers and food packaging
Examples: cutlery, plates and cups
High Density Polyethylene (HDPE)
Examples: shampoo bottles, freezer bags, milk bottles and ice cream containers
Polyethylene Terephthalate (PET)
Examples: water bottles, drink bottles and cleaning fluid containers
Expanded Polystyrene (EPS)
Examples: Hot drink cups, food packaging, shipping packaging
Examples: potato chip bags and bottle caps
Some Common Thermosets
Examples: mattresses, insulation panels and shoe soles
Examples: circuit boards, billiard balls, coatings and adhesives
Examples: castings, electronics encapsulation, coatings, adhesives, sealing and joining material
Examples: polymer matrix composites
Examples: plywood, particleboard and fibreboard
These are just some types of plastics and examples of items that are made of them. Let’s look at two types of plastics and how these plastics are made, polyethylene and foamed plastics. Polyethylene is made by polymerizing ethylene. They make up the majority of single-use plastic bags. Foamed plastics are more commonly known as the band name “Styrofoam” and is made by heating and expanding plastic pellets. Then they are molded and cut into various forms.
Are plastics really made from fossil fuels? The short answer is yes! The long answer is a bit more detailed. Plastics are synthesized from chemicals found in oil, natural gas or coal. Most plastics come from the chemicals found in these fossil fuels which is referred to as raw materials. Plastics are the result of these chemicals synthesized together or through another chemical reaction. These chemicals contain carbon, from once organic materials. Polymers are essentially carbon bonded together in long chains. These carbon chains can also be bonded to other molecules such as hydrogen, oxygen, nitrogen, chlorine or sulphur. One unit of the polymer is called a monomer.
For example, polyethylene, the material used to make single use plastic bags has a monomer of just one carbon atom and two hydrogen atoms. Another way to think of thermoset vs. thermoplastics is that thermosets form 3D structure, instead of just one long chain. So to sum it all up, the chemicals found in fossil fuels make up the raw materials that makes up the monomer which in turn makes up the polymer!
Single use plastics have many negative impacts environmentally, socially and economically. They’re still widely used due to the fact that they are convenient. Single use plastic bags for example are strong, cheap and hygienic for carrying food. Paper bags as an alternative is compostable but takes up more water and energy to produce. Furthermore, if they are tossed into a land fill, they take up more space.
Single use plastics are durable, but that’s also their downfall. It makes recycling them difficult and they don’t easily breakdown. We’ll be covering that and more details on their negative impacts environmentally, socially and economically in upcoming posts!