(Not to be confused with short story of the same name published in the Feb 2019 edition of antisf magazine)

Sliced bread dries out quicker and needs packaging to keep it fresh. The answer, that allowed sliced bread to take over the world  in the 1950s was plastic.

Sixty years later, it is out of favour again, but what exactly is it and what can we do to fix the problems it has given us? Back in Blog 5 (Energy, hydrocarbons) I pointed out that ethane was used to make ethylene as part one of the process to make plastics.  This simply requires heat and distillation.

Methane is a gas with the formula CH4 (often called C1) while ethane is a slightly more complex gas with the chemical formula C2H6 (or C2). If you replace one of the hydrogen atoms with an OH radical it becomes ethanol.  If you convert one of the carbon single bonds to a double bond you get ethylene (C2H4)

Ethylene is found naturally in fruits, where it is necessary to complete the ripening process. It is a flammable gas with a sweet odour in its monomer form, that is where individual molecules occur.  It can also be polymerised to make polyethylene (also known as polythene), the most common of all plastics.  It has the formula (C2H4)n where n is some large number which defines the specific PE product.  This simply involves heating the gas in the presence of a catalyst (eg titanium chloride).

Polythene or PE is a simple plastic that biodegrades in UV light and so generally has a stabiliser added (eg carbon powder). It is used to make plastic bottles, cling wrap and plastic bags.  Many versions of PE are now made with a variety of uses.  A common one is HDPE or High Density Poly Ethylene, the hard plastic used to make kids toys, thick plastic bottles, polypipe etc.

After that it gets more complicated as extra elements are brought in. If we replace one of the hydrogen atoms of ethylene with chlorine and polymerise it we get PVC or poly vinyl chloride (vinyl) with formula (C2H3Cl)n.  This is used in similar ways to HDPE but PVC is considered a carcinogen by WHO.

There are so many different plastic compounds these days that it is difficult to know which ones are suitable for any particular use and it is even more difficult to know how to effectively recycle each one.

They have now been categorised with six identification codes plus a seventh which is a mixed bag of all the others. These codes are the triangles that you see on a plastic product with a number from 1 to 7 inside it.

Category 1 is PET (Poly Ethylene Terephthalates) also known as polyester. It is used in clothing and drink bottles as it is impervious to oxygen and carbon dioxide.  It may be toxic and it is one of the plastics most likely to end up in our oceans.  Anytime you wash polyester clothing, fibres break off and flow out to sea.  It is estimated that this accounts for about 85% of the plastics in the ocean.

Cat 2 HDPE

Cat 3 PVC

Cat 4 LDPE is Low Density PE or simply polythene

Cat 5 PP or Poly Propylene, used in food containers

Cat 6 PS or Poly Styrene.

Category 7 is anything else including Poly Carbonates (PC) and Poly Amides (PA) like nylon.  Nylon fishing nets are the bulk of the macro plastics in the ocean and the commercial industry needs to clean up its act.

Each of these plastics needs to be separated for recycling, and each has a different level of biodegradability and toxicity. Some can be heated and some give off toxins if heated.  Some go in our yellow bins and some don’t and each jurisdiction has different policies.

We also have bio plastics that are made from carbohydrates rather than fossil hydrocarbons. It is worth noting that it does not matter what source a plastic is made from, it is still exactly the same plastic.  HDPE made from sugar or ethane is still exactly the same HDPE.  It only has an environmental benefit because it does not release additional CO2 into the atmosphere.

PLA or Poly Lactic Acid is a bio plastic made from corn biomass, which is described as biodegradable and compostable, but may not be either. PLA needs high temperature to decompose and these are not available in regular compost bins, nor in a cold oceans.  There is also the question of whether food crops should be used to make plastics?

So what can we do? Modern life relies on them too much to simply ban them, and long life plastics are probably not a large environmental menace if handled well. Throw away plastic is a different story and it is largely up to us to pressure governments into effective product licencing and recycling schemes and it is up to us to ensure that we follow through with that recycling.  We each need to be aware of what we can recycle and how to go about it.  The best bet is to not use throw away plastics wherever we can.

Throw away plastics should be used sparingly and either be recycled or be made of bioplastic and treated appropriately. Deposits on drink containers and banning single use bags are a must, but we still need suitable treatment for all classes of plastic.  Toxic plastics need to be replaced.

We need to filter microfibers from washing water and dispose of those micro plastic fibres appropriately. Better still, we should replace synthetics with natural fibres (although cotton production is problematic).  Hemp is a good solution.

What about these new fangled, home plastic munchers that seem to be advertised everywhere recently? They crunch plastic into small pieces, heat these up to extrude a plastic filament and then reheat this to make various plastic products.

While they sound like a good idea, I am not sure of their usefulness. First, anyone using one would need to understand the ins and outs of every plastic that they are munching, its toxicity and biodegradability and keep each type separate.  No recycler would take the stuff due to its unknown origins.  Heating unknown plastics may release toxic chemicals.  Products made of unknown plastics would have a limited life and very limited use as they could not be used for food or drink.

Whatever you do, don’t cook up PVC and don’t mix your BPA free with general plastics.

One Comment

  1. Andy McGee

    Short Story with same name in February 2019 edition of antisf magazine

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