Will so called bio-plastics enable mankind to have all of the benefits of plastics with less of the issues for the environment?
Like it or not we live in a world in which we currently consume more than the planet can sustain. There is a mindset that encourages us to dispose of what we have and move on to the next. As such it represents a powerful challenge if global society is to move forward in a sustainable way, whilst recognising that resources are limited.
The plastics industry has for some time recognised the need to minimise its impact on the environment through its products and production processes. Such thinking lays at the root of the developments of what are often loosely termed bio-plastics. For many, developments in this area represent something akin to a universal panacea for minimising the impact of plastics on the environment and who believe the industry should focus disproportionally on their development. Unfortunately life is not quite that simple.
For example even the term bio plastics is actually not very precise. Such materials should preferably be termed bio – based and or bio – degradable depending upon a number of factors. The distinctions are subtle but significant.
Bio based plastics
Concerns about the depletion of fossil fuel resources have lead to efforts to develop new technologies in order to replace conventional oil and gas based plastics by others based on raw materials derived from renewable sources, often covered by the catch all term “biomass.”
Plastics (or more generally, polymers) are long chains of molecules. Such molecules – the basic building blocks – can be derived from natural and renewable resources such as wood (cellulose), vegetable oils, sugar and starch.
In theory many polymers can be synthesised in this way from renewable feedstock. For example corn starch can be hydrolysed and used as the fermentation feedstock for bio-conversion into lactic acid, which can in turn be used to create the recently developed plastic called poly lactic acid orPLA.
Rather than produce new plastic materials, another approach is to make well established plastics such as polyethene, whereby the basic building block- ethylene- is derived from renewable feedstock by first producing ethanol from sugar cane.
Bio-degradable and Compostable Plastics
The plastics industry is often challenged by the public to make more biodegradable products. It is argued that it would be a great help if plastics could simply disappear by natural causes after their useful life has expired. Indeed there are many good reasons for such a desire and products to match, but unfortunately it wouldn’t be right for everything for equally good reasons.
To understand this point it is necessary to recognise that every polymer will eventually degrade – the only question is when? The answer depends upon many factors including the type of polymer and the environment it is exposed to. Degradability can be measured on a sliding scale where the key criterion is the level of change in its initial properties due to chemical cleavage of the chain of macromolecules that it was built from.
Plastics designed to degrade comparatively quickly include oxo-degradable and UV degradable polymers that break down when exposed to oxygen or light respectively. .
To qualify as bio-degradable, however, this degradation has to happen, at least in part, due to cell mediated phenomena or microorganisms. As a result the polymer is eventually reduced to water, carbon dioxide, biomass and possibly methane.
There is not necessarily a direct correlation between bio – based products and biodegradability. For example some bio-based products such as polyhydroxyalkanoates are often bio-degradable where as others such as polyethene are not, even, if they have been derived from sugar cane. The key is the molecular structure of the resultant polymer.
To be considered as compostable it must meet some strict criteria as defined in national and international standards:
- Biodegrade: break down into carbon dioxide, water and bio mass.
- Disintegrate; after three months composting and subsequent sifting through a 2 mm sieve no more than 10% residue may remain.
- Eco toxicity: the bio-degradation does not produce any toxic material and the compost can sustain plant growth.
These few paragraphs are intended only to present some of the arguments around bio based and bio degradable plastics. We are interested to hear what you think. Why not enter the online debate?
Could some research be done into finding ways of breaking down these products quicker? My understanding is that currently some plastics cant be recycled, so if we had ways of decomposing these prdoucts that would surely help improve the environmental impact of these plastics.
I’d be interested to know the extent to which industry would be keen to invest and potentially adopt bio-(based or degradeable)-polymers were legislation in place to nudge them. An analogy might be drawn to the days of tetraethyl lead (TEL) in petrol as an anti-knocking agent; industry lobbied extremely hard against the prohibition of its inclusion in petrol, but after it was (near enough) banned by policy makers industry found cheaper and more efficient ways to improve octane rating.
Kosmo Vinyl
10 July 2009, 22.51
“Could some research be done into finding ways of breaking down these products quicker? My understanding is that currently some plastics cant be recycled, so if we had ways of decomposing these prdoucts that would surely help improve the environmental impact of these plastics”
All plastics will eventually biodegrade but in some cases this could take as much as 100 years. Others biodegrade very quickly. It all depends on their chemical composition and specific environment. The important factor is to meet the requirements of the specific application during its use phase, and then apply the most appropriate end-of -life treatment
This is actually two different questions.
Why can’t all plastics degrade? And will Bio-plastics replace normal Plastics from Petrochemical resources.
Normal plastics can be made to Biodegrade by the use of additives in their manufacture. An Oxo-Biodegradable additive makes the material fragment due to Oxidation under the influence of Heat, Sunlight (UV) and Mechanical Action. This additive is ideal for Polypropylene and Polyethylene products as the fragments will then harmlessly Biodegrade in soil to CO2, Water and Biomass.
The answer to part 2, will Bio-plastics replace petrochemical plastics is quite simply yes, as the Petrochemical resources will run out, therefore we must conserve them, and use each plastic etc to is best advantage. It should be noted that just because a “Plastic” come from a Bio source such as Wheat or Sugar Beet, does not mean it is Bio-degradable, some are just as inert and durable as traditional plastics. However the use of Oil to make plastics etc utilises less than 4% of the oil we extract, the rest, 96% is basically burnt to make energy, heat, and power, what a waste.
Hi James,
Thanks for your points. From the Plastics 2020 Challenge we agree with much of what you
are saying. There are a number of points though where we would like to complement what
you say.
We disagree that degrading plastics – irrespective of means – is a way to combat littering. Giving the message that an additive will turn a plastic bag into CO2, water and biomass is too simplistic and can even potentially encourage littering. The consequences on the marine environment of the gradual degradation is neither well understood.
Also from a resource efficiency perspective we think it is wrong to degrade plastics – except for a number of specific cases like e.g. a compost bag for your kitchen food waste – as it would miss the opportunity to recover it. We would like to recycle much more plastics and what cannot be recycled would be better to combust in energy efficient energy from waste plants.
Considering that plastics are currently made almost entirely from fossil feedstock – which is finite – and that the alternative, renewable feedstock use arable land with low efficiency makes the case for more efficient use of resources much stronger and that we should allow material to “disappear” much weaker.
We believe the last drop of oil will never be used. Much before this would happen transport and heating – where we use the oil for only one role for a moment – would be using other sources. We argue that society should not accept that we “waste” oil on such a simple task but should be reserved for sophisticated and essential products like chemicals, plastics and pharmaceuticals.
In your input you mention oxo degradable plastics. In the interest of completeness I would like to add that there are also other mechanisms by which plastics can degrade. These include microbes and fungi and all degradation means come with pros and cons.
Finally the example on PLA is not representative to the current feedstock mix. Producing chemicals from sugar beet in not competitive and as a consequence corn and wheat are more used. They both have a much better mass ratio than sugar beet.