The Rudd Government’s recent announcement that it intends to ban plastic bags in supermarkets has reignited a debate as to the best way to reduce the impact of plastic packaging on our environment.
As with most things there’s no simple answer.
Environmental sustainability has become a mainstream issue over the past two or three years and, in concert with fears of global warming, is a major issue for many people.
Nevertheless, it would be overly simplistic to argue that bioplastics - which are plastics derived from renewable biomass sources, such as vegetable oil, corn starch, pea starch or micro biota — should replace traditional petroleum-derived plastics.
Each technology has its pros and cons, arguments for and against.
The plastic packaging market has changed over the last year in particular.
Economies of scale and improved technology are steadily reducing the price of bioplastics while the price of traditional plastics has been steadily rising as oil hovers around the US$100 per barrel mark — a price unthinkable just a couple of years ago.
There still is, however, a huge differential in market share between the two types of plastic.
It’s always difficult to accurately estimate highly fragmented markets such as for bioplastics but SRI Consulting put global consumption in 2006 at around 85,000 tonnes.
By contrast, the global consumption of all flexible packaging it estimated to be around 12.3 million tonnes.
Australian Bioplastics Association president, Alan Adams, says that before considering the relative merits of bioplastics and petrochemical plastics you need to look at the three core classes of material which comprise the plastic packaging universe.
“There are bioplastics, traditional petrochemical plastics and degradable materials which are modified versions of petrochemical plastics designed to disintegrate over a period of time through the use of an additive.”
With the types of materials established, what then are some of the pros and cons of bioplastics and petrochemical plastics?
“The key thing,” PACIA chairman, Peter Bury, says, “always comes back to design, making sure that the right materials for a given application are used appropriately."
Whether it’s degradability which is one characteristic, there are a whole range of characteristics that designers need to think about such as durability, colour, safety cost and aesthetics.
“You also have to look at the issue of whole of life."
"There’s a range of things that any material needs to do. It needs to be manufactured; it needs to be turned from a polymer into a product."
"It needs to have a certain shelf or service life and it needs to deal with things at end of life."
"Different materials evolve at different times. Plastics have been around for some time and new materials evolve but the clear thing is that when designers are designing a product they need to think about the whole of life.”
CSIRO manufacturing and materials technology research head Dr. Dong Yang Wu is more forthright.
“The main advantage of bioplastics is that they are made from renewable resources and they are also biodegradable which doesn’t harm the environment," he says.
"There is the argument about whether you should use renewable resources for food or industrial purposes but we’re hoping that we’ll be able to use the waste from renewable resources such as sugar cane to make plastics."
"When it comes to cons of bioplastics one major count against is that generally speaking they cost more and the second is that most are not comparable with petrochemical plastics in terms of mechanical properties.”
When it comes to the case for petrochemical plastics, the major pros are obvious.
Conventional petrochemical polymers have been around for along time - 40, 50, 60 years some of them - and they are great at what they do.
“We come across traditional plastics every minute of every day and they are fantastic. They are lightweight, with excellent mechanical properties such as a plastic chair that can bear the weight of someone who is 100, 200 kilograms,” says Plantic chief technology officer, Dr. Kishan Khemani.
Nevertheless, there are two major counts against petrochemical plastics.
One is that they use petroleum as a raw material and oil is not only increasing in price but its reserves are finite.
“The main con,” says Dr Khemani, “is end of life. Even things like furniture don’t last forever and while some parts might get recycled the rest ends up in litter or landfill and in some countries it ends up in incinerators which contribute to CO2 in the atmosphere.”
One of the problems with both types is that there are no standards being applied to the use of the term biodegradable.
This has the effect of confusing consumers who are trying to do the right thing which has attracted the attention of the ACCC and is a very real problem.
“Getting a good handle on biodegradability versus photo-degradability [breaks down in sunlight] versus compostability is very confusing for the consumer, and for packaging technologists as well for that matter,” says consultant and AIP National Conference committee member, Robin Tuckerman.
Compostability is just one example.
Some plastics sold in Australia are marketed as compostable, which means that they should be put in the council green waste bin.
To most people, however, compostable means the substance will degrade in a backyard compost heap, says Chemiplas business unit manager of plastics, Simon Peck.
“A major bioplastics manufacturer came out with a product it claimed to be compostable but then dropped the claim because it really needed industrial composting where you have a closed vessel to get the temperature up high enough for the material to break down.”
By contrast, Adams argues that “Biodegradables are products that are tested to meet a known standard for biodegradability and the most common standard is the European Bioplastics code of EN 13432, if you meet that standard you can say your material is biodegradable and you can prove that it does biodegrade.”
What further confuses the issue is some petrochemical plastics are positioned as degradable either through the use of additives or the addition of biodegradable materials such as cornstarch.
In the first case, additives can include cobalt and magnesium and the material just breaks down to the point where the particles are so small they can no longer be seen, but can be ingested.
With petrochemical/bioplastic hybrids only the corn starch breaks down.
A further dimension to the argument is whether plastics should be being allowed to degrade, bio or otherwise.
PLA Natureworks’ Tony Seers says “composting is not necessarily the answer because you’re taking something with a high value and converting it to a low value product."
"Most bioplastics are well suited for recycling.”
This view is echoed by Peck. “I struggle with that [biodegradability and composting] as a concept. I really don’t understand why people would want to take the energy [embodied in materials] with all the environmental consequences of creating it and throw it out.”
One size rarely fits all, however and it is almost certain that a number of approaches will be required.
Thin gauge film packaging will remain difficult to recycle for the foreseeable future and the energy cost of doing so will be prohibitive so it is a prime candidate for some sort of biodegradable product.
“But some products, such as a soft drink bottle, are an easy, clearly identifiable candidate for recycling,” says Peck.
“It has stored value in the weight of the product, it’s not contaminated by its previous use and it lends itself perfectly to being recycled — it’s an absolute no brainer.”
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