Foundation, Concrete and Earthquake Engineering

How is Plastic Recycled?

You took the first step by placing your plastic products into the recycling bin. Have you ever wondered what happens to all your recycling efforts? Will the coke bottle you recycled yesterday get turned into a t-shirt?

The recycling process is actually pretty long winded and complicated! It involves a lot of sorting, cleaning, and melting before it can be reused. Let's get started, shall we?

Most recycling centers use what is known as a single stream recycling system. That is, all recyclable goods including plastic, metal, glass, paper are collected all at once. These different types of recyclable goods must first get sorted.

Unlike recycling glass, metal, and paper which is pretty straight forward, plastics must be further sorted by plastic types (that is PP, PE, ABS, PET, etc…). This is because some plastic types cannot be melted with each other due to differing melting points and properties. If two plastic types are melted together, the resulting mixture is usually weak in structure and will solidify in layers (like oil and water). Therefore, mixed plastic types cannot be efficiently used for product manufacturing.

In fact, most recycling centers only take two types of plastic products, commonly type 1 PET plastic and type 2 HDPE plastic. The plastic numbers are usually found imprinted at the bottom of plastic products. This is the number inside the recycle symbol (three circulating arrows). Before sending any plastic to the recycling center, make sure you do a little research. If you send a recycling facility something they do not handle, it may end up in landfills.

Now that we have the plastic sorted by type, depending on the recycling facility, it may end up being further sorted by colors. Clear, natural, and white colored plastic is always the most desirable because it can be dyed to produce other colored plastics. For example, if you have a load of green plastics, it cannot be changed to blue. If you have a mixed colored lot, it usually gets dyed to produce black plastic products.

As the sorting process is very labor intensive, after the plastic is sorted by type, it is usually packaged and shipped to Asian countries for processing.

The plastic must now be washed to remove any residual sodas or juice. Let's follow how the common coke bottle is cleaned. While the coke bottle itself is made from PET (or PETE), the bottle cap and label is made from a different plastic type, PP or PE. Luckily, both PP and PE has densities less than 1 and will float in water. PET, when placed in water, will sink. When the bottle shreds are placed in a tank of water and mixed around, the plastic floating at the top is PP or PE and is manually removed. The bottom layer is PET and will move onto the next step.

While water takes care of partially cleaning the plastic, it must now be cleaned using a corrosive solution to remove any glues or chemicals. We now have a sorted and cleaned batch of plastic shreds which are placed in large dryers to remove moisture. At this time, the flakes are either sold or transported to another location for production into plastic pellets or nurdles (as pictured above).

Plastic pellets are the raw materials required for product manufacturing. One thing to note is that recycled plastics are never as versatile or "good" once it is reused. Recycled plastics are therefore usually "downcycled" into other products. That is, old milk bottles never get to make new ones, instead they are made into a different product all together such as toys.

Often times, recycled plastic is sold to manufacturers that mix recycled materials with virgin material to produce products. This way, they can ensure the finished product to be high in quality while saving (money) the environment.

1 comment:

  1. It is really a must thing to do. We should know how to conserve properly our environment.