“Plastic perfect” – make a wish

We’re living in the Plastic Age, on our “Plastic Planet”. Plastics are crucial determinants for our era’s objects; our product world is nearly inconceivable without plastics.
It would appear that we humans love plastic, since we’re using it practically everywhere.
But there are also side-effects, and just like with medicaments we should try to minimise them.

Plastics that evade the cycle of utilisation and recovery or due and proper disposal, can be harmful in the natural environment. As is the case in other contexts as well, the adverse consequences are often not suffered by those who cause them …

Plastic waste gets caught in some corners, or ends up in our lakes and rivers. All water ultimately flows into the sea, and then plastics are concentrated in places like the Great Pacific Garbage Patch, for example (http://en.wikipedia.org/wiki/Marine_debris).

The directly visible tip of the iceberg is the disturbing images of garbage-strewn coasts and of animals entangled in sizeable plastic artefacts like lost nets or cords and as a result of this die.

Animals confuse plastic particles and fragments with food, which given the increasing quantity of these particles may endanger the population levels of the species involved. Firstly, because plastics cannot be digested, of course, and may block the ingestion of nutrients. Secondly, less visibly but no less deleteriously, pollutants are increasingly concentrated on some types of plastic:

Hydrophobic plastics (usually polyolefins), the customary material used for making screw-caps, in the water accumulate at their surface persistent (meaning almost non-degradable), fat-soluble pollutants (e.g. those of the http://en.wikipedia.org/wiki/Persistent_organic_pollutant). This means these toxins are adsorbed from the surrounding seawater and turn the plastic particle into a “toxin carrier”. In the food chain, where we humans are not infrequently at the top, these pollutants then accumulate in ever-increasing concentrations.

All these are effects that in extreme cases may upset the balance of ecosystems and even destroy them.

“Lost and littered”, this is of course also a behavioural problem.

More educative publicity and mindfulness in dealing with plastics is indubitably essential: as much material as possible has to be recovered in closed technical cycles (the PET bottle recycling rate in Europe was a not insignificant 57 % in 2014 (www.petcore-europe.org)). The PET concerned can be used to manufacture new bottles. Lids and labels are easy to detach, and the screw-caps, in particular, are a coveted secondary material. But we would be deluding ourselves if we were to believe that with good recycling systems the “loss” of plastics can be avoided entirely, meaning that no plastics would any longer escape into the natural environment. Which is why the industrial sector is also obligated to search for better solutions. Declaring the whole thing to be a behavioural problem pure and simple and shifting blame entirely to the private consumer is not contributing towards finding a solution. To make my point clear, here’s a parallel from a different field: even though road accidents are mostly attributable to driver error, it’s nonetheless the task of the development engineers and the automakers to ensure efficacious brakes and safety systems.

What can be done in order to improve the situation? Can perhaps something be changed about the material being used? Or to rephrase the question, what should the perfect plastic look like?

The “perfect plastic” should of course provide all the technical properties that it needs for its intended purpose, and its job profile – as a component in a device, for example, or as product-protective packaging.

I work in the mechanical engineering sector, and plastic bottles for beverages form part of my professional remit, which is precisely why I am here and now stating my two ideal plastics for this application: a hard, strong plastic for the bottle (at present this is usually PET) and a softer one for the screw-cap (at present this is usually HDPE). Hard on hard will not create an effective seal, which is why having just one kind of plastic is not a viable option.

  • First of all, the packaging material used must of course be safe and food-grade.
  • In the long term, humanity is going to run out of oil, so my ideal plastic should be suitable for bio-based production – there are already some good approaches here for bio-based PE (screw-caps) and partially bio-based PET (see, for example, CC “Plantbottle” http://www.coca-colacompany.com/plantbottle-technology).
  • The material must be easy to process, so that the package is affordable and can be produced with a minimised consumption of energy.
  • It should exhibit appropriate strength values, so that it can be used to manufacture a safe product package. Tearing or bursting bottles are hardly going to prove acceptable to consumers.
  • To ensure that the product – after being filled in the bottle – does not change too significantly, the “gas barrier” should also be adequately dimensioned. To ensure that the carbon dioxide (in the case of soft drinks) does not escape and the product-oxidising oxygen (in the case of juices) stays outside.
  • When it comes to beverage packages, of course, the “water barrier” is an important factor. There are plastics that are here somewhat more permeable, and it is naturally enough a problem if after a short time part of the original fill weight is missing.
  • It’s imperative that the material can be recycled, since I find it hard to believe that we shall in future still be able to afford “disposable polymers” for mass applications.
  • This entails the necessity of a certain chemical and thermal stability. “Multiple processing” has to be possible. This means that repeated melting must not destroy the plastic and that “final cleaning” for renewed contact with foods and beverages also has to be possible (recyclate is thermally decontaminated if it is to be re-used for food and beverage packaging). 

All these requirements are currently being adequately met by PET and HDPE.

Let’s now address the point where I can imagine a beneficial change for the problem I outlined at the beginning of this post: for plastics currently in use, time periods of up to 1,000 years are estimated in terms of how long these will remain in the natural environment. Couldn’t this be somewhat reduced?

One category definitely unsuitable for beverage packaging is compostable plastics – though they of course have their uses in other applications. But fast compostability mostly goes hand in hand with a poor water barrier. Life needs water, and fast biodegradability is seemingly difficult in the case of water-impermeable polymers. With a continuously wet application, it would not be helpful if bio-degradation were already to begin with the beverage still inside.

Fragmentation is another keyword in the ongoing debate. There are additives (i.e. substances admixed during processing) that in the event of light irradiation, for instance, ensure that the plastics disintegrate into very small particles (they fragment: the substances concerned are called photo-oxo-degradable-additives). Out of sight, out of mind. This, however, is problematic, primarily because we don’t know at present whether breaking them down into innumerable tiny particles will create even more problems than it solves.

At present, about 280 million tons of plastics a year are being produced and used – but these substances have only been in existence for a few decades. How much of them will we really be able to recycle in the future and how much will end up in the natural environment?

With a reduced degradation time or half-life, it would definitely be possible to reduce the amount of plastic in our environment.

If the time required for degradation were to be reduced to an average of about 500 instead of 1,000 years, for example, then the amount of waste in the natural environment would be very significantly downsized, indeed roughly halved.

Well, I’m almost finished for the time being: my wish list for material development specifies a plastic with similar properties to present-day PET, but with a somewhat shorter half-life (100 instead of 1,000 years is surely sufficient) under “normal” environmental conditions (lakes/rivers or roadside).

What’s more, for closures I want to see a material with similar properties to HDPE, but one that’s hydrophilic and not hydrophobic (because of pollutant accumulation involving fat-soluble persistent pollutants) and of course with a shorter half-life here as well.

It’s clear in this context that plastics which do not possess the requisite technical properties will not be adopted for long-term use. New materials will establish themselves only if they are not worse than their present-day counterparts.

Until this comes to pass, I comfort myself with the thought that with our present-day packaging materials, provided they are properly used and recycled, we certainly don’t have the worst solution imaginable.