How is Plastic Made?

Plastics are made from crude oil found deep in the Earth, which must be extracted by machines. The extracted crude oil is sent to a factory called a refinery, where it is heated up to 400°C (752°F). The hot oil enters a fractional distillation column, in which it is separated into its various components, including the petrol to run your car, the Vaseline® you might rub onto your chapped hands, and asphalt to build roads.

One component of crude oil is a liquid called naphtha, which is used to make plastics. Single units of naptha, called monomers, are joined together to form long chains called polymers. The polymers are mixed with other things to make different types of plastic with different properties.

The process of making plastic requires a lot of energy. Energy is needed for extracting the crude oil, heating it, and more. Fossil fuels are burned to make all this energy, which releases greenhouse gases into the air. Therefore, even the first step in plastic’s life—manufacturing it—is bad for the environment.

What Happens to Plastics After we Use Them?

After you finish eating your ice cream on a hot summer day, do you know where the wrapping goes? How about the clothes you outgrew, which were made of plastic-based fibers like polyester? If 300 million tons of plastic are produced each year [1], where does it all go?

Half of the world’s plastic is buried underground in landfills, while 19% is incinerated (burned) for energy. Worldwide, only 9% of plastic gets recycled. The remaining plastic, around 22%, escapes into the environment, often ending up in the ocean. Figure 1 shows various options for what can happen to plastics at the end of their life.

Incineration

During incineration, plastic waste is burned and energy is produced. Plastic comes from crude oil, which might make you think it can safely be used as fuel, right? So why is burning plastic a bad idea, and why are many incinerators around the world shutting down?

The main reason is that burning just one ton of plastic releases more than two tons of carbon dioxide into the atmosphere! This means that the energy produced from burning plastic is even worse for the environment than the energy produced by burning coal, which is considered to be one of the worst fuel sources. Burning plastic also creates harmful gases, like dioxin, which can cause cancer.

Plastic Waste Leakage

About 22% of the world’s plastic waste is not managed properly and ends up as litter. This plastic ends up in the oceans or coastal cities, a problem known as plastic waste leakage. Plastics often break into smaller pieces, called microplastics. Microplastics are harmful because they carry dangerous chemicals and spread them everywhere, even into our food! Microplastics are found everywhere on Earth, and it is almost impossible to remove them from the ocean and environment.

Landfills

Landfills are holes in the ground where garbage is thrown and then buried. Landfills are the cheapest and most common way of dealing with waste. However, they are unfortunately one of the worst. It can take plastics decades or even centuries to break down in landfills, due to the lack of water and air deep underground. Once they do break down, they form microplastics and chemicals, which harm the nearby environment. Landfills also require large plots of land and must be built far away from cities because of how much pollution they produce.

Recycling

Only 9% of plastic is recycled. Sadly, we can only recycle plastics a few times before they become less usable. Recycling is expensive and difficult. It is also harmful to the environment because it uses a lot of energy and creates harmful waste. But, if we use clean energy and better technologies, we can lessen the environmental damage caused by recycling plastics. This will hopefully make recycling a good option for removing plastics in the future.

Life Cycle Assessment to Measure Plastics’ Impact

How can we measure plastic’s total effect on the environment, from the time it is “born” (refined from crude oil), up to when it is thrown away? We can do this using a method called a life cycle assessment (LCA), which consists of computer software designed to measure the total environmental impact of a product. An LCA looks at all the emissions, waste, and energy made and used throughout a product’s life. We just need to tell the software about the steps in making the product, the machines used, the type of fuel (like fossil fuels or solar energy), and other details to make the results accurate. For example, let us do a simple LCA for a plastic water bottle (Figure 2A).

The first step in making plastic is to extract the raw materials using big machines. These machines burn fuel and emit carbon dioxide, and the software counts these emissions. Then, crude oil is heated and separated into different components, and carbon dioxide is produced when making the electricity that heats the oil. When electricity travels through power lines, a little of it is lost as heat, so power stations must burn extra fuel to replace that lost energy, this creates additional carbon dioxide that is also counted. This process is repeated for each step in manufacturing the plastic water bottle. Other emissions apart from carbon dioxide are also counted when they are produced in manufacturing. These include nitrogen dioxide, which forms smog, or sulfur dioxide, which leads to acid rain. Finally, the software adds up all the emissions and shows the total impact on the environment from producing the plastic bottle.

There are several types of LCAs, as shown in Figure 2B. One is called cradle-to-gate, and it measures the impact from when raw materials are extracted to when the product is made and ready to leave the factory. Another is cradle-to-grave, which measures the impact from extraction through when the product is made, used, and then thrown away—either burned or recycled. A third type is cradle-to-cradle, and it measures everything, including recycling. A cradle-to-cradle LCA is useful for making products more eco-friendly.

In one example of a cradle-to-gate LCA, we used software to measure the impact of making a plastic called polypropylene. The software calculated the total emissions by looking at how polypropylene was manufactured, and the machines used. The software then found the quantity and types of different emissions produced by making polypropylene (Figure 3) [2]. The types of emissions can tell us about the impact manufacturing has on the environment or humans. For example, we know that carbon dioxide is bad because it increases global warming by trapping heat inside Earth.

The results of the LCA for making polypropylene show how polluting plastic is for the environment. Sadly, we cannot easily stop using plastics because we need them in daily lives. But we can reduce plastic’s impact by recycling and using renewable energy. One LCA found that, just by recycling plastic and using renewable energy, carbon emissions could be cut by 42% [3]!

What this Means for Our Planet

LCAs measure the impact a product has on the environment across its whole life. By conducting an LCA, we found that making polypropylene creates a lot of emissions. However, another LCA found that recycling plastic with renewable energy could almost cut carbon emissions in half! These studies show how LCAs can help us measure the environmental impact of plastic products. It also allows us to find ways to reduce emissions. In the future, fun apps or games could even help kids learn how to recycle better by scanning plastics and showing the best recycling options—an idea suggested by one of our young reviewers! Using LCAs to reduce environmental impacts help us move toward a cleaner, greener future!

Glossary

Crude Oil: ↑ Thick, dark liquid from underground that we turn into fuels and materials, including plastics.

Fractional Distillation: ↑ Separating a liquid into its various components based on their boiling points.

Naphtha: ↑ A light liquid made from crude oil that is used to make plastic.

Plastic Waste Leakage: ↑ Plastic trash that escapes bins or landfills and ends up in nature, like rivers, oceans, or soil.

Microplastics: ↑ Tiny pieces of plastic, often smaller than a grain of sand, that can spread through water, air, and food.

Life Cycle Assessment: ↑ An analysis of the environmental impact of a product throughout its life.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

AI Tool Statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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