Part 3 of Green Innovation: Recycling Plastics Series

Washing

The washing process can be completed many ways, with the main focus to remove non-plastic contaminants. For example, PRM sells many types of washers for plastic films which can be used individually or together. These include the Hot Water Washer and the Friction Washer.

The Hot Water Washer: The PRM’s Hot Water Washer works by sending plastic flakes (specifically PET) horizontally through the machine. As they travel, they are sprayed with hot water and sterilized.

The Friction Washer: Much like the hot water washer, the plastic – again PET – is sprayed with hot water as it travels throughout the machine. This time, however, the plastic is fed into the bottom of an inclined, mesh-walled cylinder. The cylinder, spinning at around 1000 rpm, flings small contaminants through the mesh and causes the plastic pieces to rub against each other, scraping of dirt and grime.

Resizing

During the resizing process, plastics are cut into much smaller pieces. This makes storage and processing both easier and more efficient. In fact, although it has been posted later in the list, it often occurs before the washing process.

In PRM’s plant recycling line, for example, they use an assortment of machinery to cut plastic films down to 10 – 20 mm in size. To learn more about the resizing equipment they use, check out the size-reduction section of their website.

Stay Tuned for Part 4 of the Green Innovation: Plastics Recycling Series!

Part 2 of Green Innovation: Recycling Plastics Series

The bulk of sorting, at least at the consumer-level, is done by the plastic collection agencies. However, in industrial-scale recycling – where businesses sometimes send their plastics without sorting them – different methods are used. Northstar’s article on the subject discusses how these plastics can be sorted with water and heat.

By placing plastics in water, their density (relative to water) can be determined. Typically, LDPE, HDPE, and PP plastics will sink while PET, PVC, and PS plastics will float.

When heating the plastics with a flame, the plastic’s identification is more precise. The plastics that float should also produce a blue flame with white smoke. Those that have a waxy smell are usually LDPE or HDPE, but the plastic with a sweet smell is typically PP.

Of the plastics that typically sink, each has their own properties when burning. If, when melting, it has a burnt-sugar smell, the plastic is likely PET. If the plastic ignites only at higher temperatures (with a blue/green flame), it is likely PVC. Finally, if the plastic does not drip and has black, sooty smoke, it is likely PS.

It’s pretty clear, however, that this process is time-consuming and inefficient for large batches of unsorted plastics. To solve this issue, a group of researchers designed a way to process almost 1.4 tonnes of plastic every hour – with computers.

They use the unique fluorescence patterns of plastics to identify and separate them. For more information on the process check out this research paper. In the future, I may create a post about the topic, so stay ready!

If you liked this post, be prepared for Part 3 of the Green Innovation: Plastics Recycling series.

Part 1 of Green Innovation: Recycling Plastics Series

In 2017, roughly 267.8 million tons of waste were generated by the American population. Of the 35.3 million tons of plastic, only 2.92 million tons were recycled or composted. For more information on these statistics, check out the EPA’s 2017 report.

While it would be nice to see the amount of recycled plastic increase, there is still a lingering question: what happens to the plastic that is recycled?

The plastic-recycling can be easily separated into a series of 6 steps:

1. Collection: This step is the most well-known, and it involves all the recycling collection processes including government services, bins in public spaces, and more.
2. Sorting: Machines sort the plastics to find which ones the plant can process and to prevent damaging the equipment or slowing the process.
3. Washing: This step is used to remove impurities, including labels, dirt, residue, and other non-plastic things.
4. Resizing: During this stage, the plastics are ground-up to make processing more efficient and remove possible impurities unaffected by the last step.
5. Identification and Separation: Here, the plastic chunks are separated by their different properties in processes that will be discussed later.
6. Compounding: During this phase, the plastic bits are combined into pellets which are then used in the manufacturing of plastic products.

In the following posts, I will discuss each in greater detail. The collection process, however, is quite straight-forward and is discussed below.

Collection

The collection process, as mentioned above, is quite simple. Plastics are collected through a variety collection methods, including trash services (retrieving designated RECYCLE-ONLY bins), non-for-profits, and recycling bins. The real “meat” of the process occurs in the following steps.

Stay posted for Part 2 of the Green Innovations: Plastics Recycling Series.

Walking down the street or within many buildings, you may see these odd-looking bins with a circle of arrows on them. Of course, these bins are not mysterious, and neither is their purpose. We use recycling bins to send our unneeded plastic, glass, and paper to the magical land of recycling factories, where they are converted into those “recycled” products we love to buy.

The recycling process, however, is not quite as simple as magic. As a matter of fact, it is a complex process that requires the use of highly-specialized machinery.

There is a recycling process for dozens of materials, but, to keep it simple, I will only begin by discussing the recycling process for a commonly used material: plastic. Furthermore, this discussion will likely miss some information on the process. For a more complete picture, let these posts serve as a gateway to research – and feel free to start with the included references throughout the entries.