Where does my recycled trash go? Plastic’s journey toward mechanical recycling
2024. 12. 13
Every day, we remove and collect plastic bottle labels and wash and recycle milk cartons. All the beverage cans and bottles are sorted just as meticulously. As I watch the wave of people joining in, each in their own way and know how, I wonder if there’s ever been a people more serious about recycling. But when I look at the heaps of plastic that pile up on trash days, I can’t help but wonder:
As for the plastic waste that we work so hard to separate, the majority of recyclable waste plastics go through a process called mechanical recycling (MR). It’s as intuitive as the word “mechanical” suggests.
The big process may seem simple, but when you dig deeper, it must meet multiple conditions. The most important step is at the beginning: collecting waste plastics. As with anything in life, the end result is only as good as raw materials. The same goes for plastics. To produce high-quality recycled plastics, the raw feedstock must be uncontaminated, single-source plastics.
While it would be best if everyone disposed of their waste plastics in a suitable state for recycling in the first place, there are realistic limits to individual efforts. The bottom part of one of the most common items, plastic water bottles, is made of PET (polyethylene terephthalate). The label is PP (polypropylene), and the cap is usually made of HDPE (high-density polyethylene). Since plastic bottles, as well as most plastic products, are made up of a combination of different materials, it’s practically impossible for an individual to distinguish between them. This is especially complicated because plastics are often used in combination with ferrous and non-ferrous metals, rubber, wood, and more.
As mentioned earlier, the key to producing high-quality recycled plastic is to select and collect the right materials. If you mix different materials, the quality of the recycled plastic will suffer. This is why our recycled plastic waste is taken to a recycling center, where each item is sorted and categorized by humans. That’s a lot of work and effort that goes into it. Unfortunately, perfect sorting is impossible to achieve through human effort alone.
To ensure that the quality of the recycled plastic is close to perfect, the initially sorted plastic must be crushed. From PET bottles to electronic plastics made from composites, mechanical recycling of all plastics starts with the details of crushing. This is because it is easier to clean the foreign substances after crushing and allows for more detailed sorting. The most basic step in plastic recycling is called pulverizing. The pulverizing stage utilizes hammers and rollers to shred the plastic product into small pieces. The shredded plastic pieces are called flakes, and recyclers then perform a series of operations to clean the flakes and sort out debris. There are many ways to filter out foreign substances, most of which we learned in science experiments at elementary school. The appropriate methods for sorting are applied in several stages, from magnetism and static electricity to using differences in specific gravity and distance blown by strong winds. Only after all this complexity is the material ready for extrusion, the final stage of mechanical recycling.
The final outcome of recycled plastic should be of uniform size, weight, and quality. This makes it easy to mold it into various injection-molded parts. The waste plastic that has just been pulverized, washed, and separated comes in all different sizes and shapes, and it needs to be extruded to make it uniform. This is where a machine called an extruder comes into play, which transforms the unevenly shaped pieces of waste plastic into a consistent shape and quality. It’s easy to understand how an extruder works when you think of the noodle maker. Using high temperature and pressure, the plastic pieces are pushed through an extruder, which ejects long strands of noodle-like plastic. When the strips are sliced evenly, the result is uniform recycled plastic granules shaped like rice grains. The recycled plastic is then extruded one more time using a recipe developed by LG Chem, resulting in a much higher quality recycled plastic that is closer to new plastic.
We reviewed a very short version of the process of mechanically recycling plastics. The bottom line is that all of these laborious and complex processes are necessary to produce high-quality recycled plastic. Why are we putting all this effort into recycling plastic when it would be cleaner and easier to just make new plastic? The reason is simple. While there are differences between each plastic material, the carbon footprint of producing recycled plastic is only 40% of producing new plastic. This is all the more reason for us to recycle plastic in an era where reducing carbon emissions is a top priority. Plus, reducing the amount of waste plastic that ends up in landfills or in the ocean is a big reason we’re committed to recycling. The global regulatory trend is also in line with this. Since 2021, the EU has been imposing a tax of 0.8 euros per kilogram on non-recyclable plastic packaging. Furthermore, they passed a law requiring all plastic beverage packaging to contain at least 30% renewable content by 2030. In other words, if a company wants to sell plastic products to European countries, it will soon have to use a certain percentage of recycled or easily recycled plastic.
In fact, plastic was born to be green. More than 150 years ago, plastic was created to replace elephant ivory in billiard balls and piano keys. While it was created to preserve elephant populations, because it was burned and dumped into the ocean, plastic suddenly became associated with harming nature. There’s no such thing as an eco-friendly disposable. Reusability and longevity are what make a product truly environment-friendly. The same goes for plastics. There really isn’t a bad plastic in the world. There are only bad uses for them. The only true eco-friendly thing is to use and reuse them for our planet and future generations to come.
The following post is based on the content from ZEROBOOK published by LG Chem, ‘The Journey of Plastic Towards Mechanical Recycling’ (Writer & Photographer: LG Chem Brand Team Heo Woong).
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