November 28, 2019|
3 min read
We are constantly warned of the damaging effects of the plastics which are filling up our oceans and landfills across the world. Our awareness of the permanence of single-use plastics after we have thrown them away has led many of us to reach for reusables: keep-cups, Tupperware and refillable bottles. But what are the processes which make plastic in the first place? What makes it so hard to break down? And, in those moments where we really just do need to use single-use plastic, how can we do our best to recycle the stuff? The following blog piece is going to answer these questions and more as best it can and let you know the basics to plastic recycling, so just scroll on down to find out.
What is plastic?
Plastic is a substance made up of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and can be molded into solid objects.
What is plastic made of?
These materials include cellulose, coal, natural gas, salt and crude oil.
How do we turn the raw materials into plastics?
Intense processes that break down these materials and combine them with other materials lead to the formation of monomers. These monomers are then joined together by chemical polymerization mechanisms to form polymers. Different combinations of monomers can yield plastic resins with different properties and characteristics. For example:
- Poly(ethene) ‘polythene’
- Properties: Flexible, cheap, can be made into thin films
- Uses: Carrier bags, shampoo bottles, food wrap
- Poly(propene) ‘polypropylene’
- Properties: Flexible, strong, resists shattering
- Uses: Buckets, bowls, crates, ropes, carpets
- Poly(chloroethene) ‘PVC’
- Properties: Tough, electrical insulator, can be made hard or flexible
- Uses: Insulation for electrical wires, windows, gutters, pipes
- Poly(tetrafluoroethene) ‘PFTE’
- Properties: Slippery, chemically unreactive
- Uses: Non-stick coatings for pans, containers for laboratory substances
How can plastic be broken down to be recycled and used as a different product?
n general, there are two key methods by which plastics can be recycled: the first is mechanical recycling, commonly known as “chop and wash, where the plastic is washed, ground into powders and melted. The second is chemical recycling, where the plastic is broken down into basic components.
For both of these processes plastic needs to be separated into its different resin type (this is which different monomers make it up).
Mechanical recycling – After sorting, the plastic recyclables are then shredded. These shredded fragments then undergo processes to eliminate impurities like paper labels. This material is melted and reshaped into the form of pellets which are then used to manufacture other products.
Chemical recycling – For some polymers, it is possible to convert them back into monomers, for example, PET can be treated with an alcohol and a catalyst to form a dialkyl terephthalate. The terephthalate diester can be used with ethylene glycol to form a new polyester polymer, thus making it possible to use the pure polymer again.
What do we need to do to make it work?
So we can see from the above that the following things are very important for plastic recycling:
- Sorting is incredibly important to make the processes of breaking down the plastics much smoother. Check your recycling bins to make sure you are putting the right recycling in the right places. Don’t assume that just because it is plastic it can all be recycled or can all be put in the same bin. (For instance, soft plastics like shopping bags and cellophane don’t go in most ordinary recycle bins in the UK)
- Wash your plastics, this is so important as the plastic has to be clean for the above processes to work.
- Opt for things packaged in the following plastics which are easier and cheaper to recycle: for instance, the most widely recycled plastics are the two used to make soft drinks bottles and milk bottles: PET and HDPE.
What about biodegradable plastic?
Biodegradable plastic is something you will have heard a lot about in recent years. In fact, our own recent post on Biodegradable Phone Cases touched on the benefits and uses of such plastics and how they can be made. Another common place you will see biodegradable plastics is in glitter and cutlery and food implements.
These plastics are made from all-natural plant materials. These can include corn oil, orange peels, starch, and plants. The phone cases from Wild for example are made from Bamboo fiber. The process is similar to normal plastics in as much as elements are broken down and then rejoined in specific polymers that make the appropriate shape or material for different uses.
Instead of breaking these products down through intense chemical or mechanical processes the plastics will slowly biodegrade in the right conditions. This then turns into soil or earth or another natural product that can be used for other purposes, like any other compostable object.
There are some problems though. The conditions required can be more demanding for certain forms of bio-plastics and also bio-plastics of a certain size and thickness. Most biodegradable plastic, for example, food packaging, needs to be in heat above 50C – hence, if they go into the ocean they will behave like any other plastic and continue to clog up the ocean or break down into micro-plastics. It is very important that if you get a bio-degradable plastic, you look up the brand or type of plastic in order to identify how to best biodegrade it.
It is also worth pointing out that the biodegrading process of bio-plastics does let off CO2 which is of course on the face of it not positive for the environment. Some do, however, point out that this is merely the CO2 that would have been created if the plant had decomposed in the first place. But the very creation of the plant in the first place may not have happened if it wasn’t for the demand for the plastic.
So in all, bio-plastic can be better if you can identify the appropriate way to let it decompose. The decomposing is less intensive and uses less machinery and also gives back to the earth. But opting for reusable plastic and cutting down your use of most plastics is always best.