Making packaging greener – biodegradable plasticsBiodegradable plastics made with plant-based materials have been available for many years. Their high cost, however, has meant they have never replaced traditional non-degradable plastics in the mass market. A new Australian venture is producing affordable biodegradable plastics that might change all that.
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Key textOur whole world seems to be wrapped in plastic. Almost every product we buy, most of the food we eat and the many of the liquids we drink come encased in plastic. In Australia around 1 million tonnes of plastic materials are produced each year and a further 587,000 tonnes are imported. Packaging is the largest market for plastics, accounting for over a third of the consumption of raw plastic materials – Australians use 6 billion plastic bags every year!Plastic packaging provides excellent protection for the product, it is cheap to manufacture and seems to last forever. Lasting forever, however, is proving to be a major environmental problem. Another problem is that traditional plastics are manufactured from non-renewable resources – oil, coal and natural gas. Plastics that break down In an effort to overcome these shortcomings, biochemical researchers and engineers have long been seeking to develop biodegradable plastics that are made from renewable resources, such as plants. The term biodegradable means that a substance is able to be broken down into simpler substances by the activities of living organisms, and therefore is unlikely to persist in the environment. There are many different standards used to measure biodegradability, with each country having its own. The requirements range from 90 per cent to 60 per cent decomposition of the product within 60 to 180 days of being placed in a standard composting environment. The reason traditional plastics are not biodegradable is because their long polymer molecules are too large and too tightly bonded together to be broken apart and assimilated by decomposer organisms. However, plastics based on natural plant polymers derived from wheat or corn starch have molecules that are readily attacked and broken down by microbes. Plastics can be produced from starch Starch is a natural polymer. It is a white, granular carbohydrate produced by plants during photosynthesis and it serves as the plant's energy store. Cereal plants and tubers normally contain starch in large proportions. Starch can be processed directly into a bioplastic but, because it is soluble in water, articles made from starch will swell and deform when exposed to moisture, limiting its use. This problem can be overcome by modifying the starch into a different polymer. First, starch is harvested from corn, wheat or potatoes, then microorganisms transform it into lactic acid, a monomer. Finally, the lactic acid is chemically treated to cause the molecules of lactic acid to link up into long chains or polymers, which bond together to form a plastic called polylactide (PLA). PLA can be used for products such as plant pots and disposable nappies. It has been commercially available since 1990, and certain blends have proved successful in medical implants, sutures and drug delivery systems because of their capacity to dissolve away over time. However, because PLA is significantly more expensive than conventional plastics it has failed to win widespread consumer acceptance. Plastics can also be produced by bacteria Another way of making biodegradable polymers involves getting bacteria to produce granules of a plastic called polyhydroxyalkanoate (PHA) inside their cells. Bacteria are simply grown in culture, and the plastic is then harvested. Going one step further, scientists have taken genes from this kind of bacteria and stitched them into corn plants, which then manufacture the plastic in their own cells. What’s the cost? Unfortunately, as with PLA, PHA is significantly more expensive to produce and, as yet, it is not having any success in replacing the widespread use of traditional petrochemical plastics. Indeed, biodegradable plastic products currently on the market are from 2 to 10 times more expensive than traditional plastics. But environmentalists argue that the cheaper price of traditional plastics does not reflect their true cost when their full impact is considered. For example, when we buy a plastic bag we don’t pay for its collection and waste disposal after we use it. If we added up these sorts of associated costs, traditional plastics would cost more and biodegradable plastics might be more competitive (Box 1: Life cycle analysis). Biodegradable and affordable If cost is a major barrier to the uptake of biodegradable plastics, then the solution lies in investigating low-cost options to produce them. In Australia, the Cooperative Research Centre (CRC) for International Food Manufacture and Packaging Science is looking at ways of using basic starch, which is cheap to produce, in a variety of blends with other more expensive biodegradable polymers to produce a variety of flexible and rigid plastics. These are being made into ‘film’ and ‘injection moulded’ products such as plastic wrapping, shopping bags, bread bags, mulch films and plant pots. Mulch film from biodegradable plastics The CRC has developed a mulch film for farmers. Mulch films are laid over the ground around crops, to control weed growth and retain moisture. Normally, farmers use polyethylene black plastic that is pulled up after harvest and trucked away to a landfill (taking with it topsoil humus that sticks to it). However, field trials using the biodegradable mulch film on tomato and capsicum crops have shown it performs just as well as polyethylene film but can simply be ploughed into the ground after harvest. It’s easier, cheaper and it enriches the soil with carbon. Pots you can plant Another biodegradable plastic product is a plant pot produced by injection moulding. Gardeners and farmers can place potted plants directly into the ground, and forget them. The pots will break down to carbon dioxide and water, eliminating double handling and recycling of conventional plastic containers. Different polymer blends for different products Depending on the application, scientists can alter polymer mixtures to enhance the properties of the final product. For example, an almost pure starch product will dissolve upon contact with water and then biodegrade rapidly. By blending quantities of other biodegradable plastics into the starch, scientists can make a waterproof product that degrades within 4 weeks after it has been buried in the soil or composted. Landfill sites aren't compost heaps To maximise the benefit of the new bioplastics we’ll have to modify the way we throw away our garbage – to simply substitute new plastics for old won’t be saving space in our landfills. Although there is a popular misconception that biodegradable materials break down in landfill sites, they don't. Rubbish deposited in landfill is compressed and sealed under tonnes of soil. This minimises oxygen and moisture, which are essential requirements for microbial decomposition. For biodegradable plastics to effectively decompose they need to be treated like compost. Composting the packaging with its contents Compost may be the key to maximising the real environmental benefit of biodegradable plastics. One of the big impediments to composting our organic waste is that it is so mixed up with non-degradable plastic packaging that it is uneconomic to separate them. Consequently, the entire mixed waste-stream ends up in landfill. Organic waste makes up almost half the components of landfill in Australia. By ensuring that biodegradable plastics are used to package all our organic produce, it may well be possible in the near future to set up large-scale composting lines in which packaging and the material it contains can be composted as one. The resulting compost could be channelled into plant production, which in turn might be redirected into growing the starch to produce more biodegradable plastics. An Olympic effort – recycling 76 per cent of waste For anyone who thinks such schemes aren’t feasible, you only have to look at the recycling success of the Sydney Olympics to see that where there’s a will, there’s a way. More than 660 tonnes of waste was generated each day at its many venues. Of this, an impressive 76 per cent was collected and recycled. Part of this success was due to the use of biodegradable plastics used in the packaging of fast food, making the composting of food scraps an economic proposition as it eliminated the need for expensive separation of packaging waste prior to processing. With intelligent use, these new plastics have the potential to reduce plastic litter, decrease the quantities of plastic waste going into landfills and increase the recycling of other organic components that would normally end up in landfills.
Environmental costs Many environmentalists believe the price we pay for a product should reflect its 'life cycle' cost. Traditional plastic packaging is an example where the environmental cost is not reflected in the price we pay for the product. It is relatively cheap to manufacture and this is reflected in its inexpensive price. But this doesn’t factor in the costs of disposing of the plastic, its impact on wildlife or the large volume of landfill it takes up. Recycling Recycling schemes sound good are they economic when you take into account the resources consumed in transporting, processing and reworking the material to be recycled? At this stage there are no rigorous environmental studies on plastic that take into account greenhouse gas emissions, air pollution or energy consumption. Quantitative or qualitative analysis Life cycle analysis, often referred to as ‘cradle to grave’ analysis, is great in concept, and central to any sound approach in ecodesign. In practise, however, it’s difficult to apply quantitatively because there are no universal standards of comparison and many of the costs are impossible to define precisely. For example, what is the long-term impact of generating more carbon dioxide when we still don’t know the basic mechanics of global climate change. However, even when applied qualitatively, and acknowledging our imperfect knowledge, life cycle analysis quickly demonstrates that the price we pay for a product often bears no relation to the environmental cost of creating it. Sustainability is all about taking this into consideration. Related sites
Ecos Issue 134, 2007 page 7 Fast-degrading nappies lighten the load on landfill Reports on the development of a fully biodegradable disposable nappy.
No. 130, 2006, page 5 Ozmotech's plastic-to-fuel solution in demand Describes the development of Australian technology to recycle plastic waste into commercial grade diesel fuel.
No. 128, 2005/2006, page 6 A sweet European deal for Plantic’s bioplastic An update on the commercialisation of biodegradable plastic.
No. 108, 2001, pages 4-5 Green plastic (by Wendy Pyper) Describes biodegradable plastic products being developed in Australia.
New Scientist 9 May 2007, pages 28-29 Recycled plastic to get clean bill of health (by Michael Reilly) Looks at the benefits of the generation of recycling plants.
7 April 2007, pages 37-41 Packaging - unwrapped (by Jessica Marshall) Discusses what can be done about the tide of apparently pointless packaging.
8 October 2005, page 6 Cigarette butts go green Describes compostable cigarette filters.
8 January 2005, page 11 Seabirds ingest bellyfuls of plastic pollution (by Rob Edwards Texel) Reports on a study looking at plastics found in the stomachs of seabirds.
11 September 2004, page 30 Battle of the bag (by Caroline Williams) Looks at consumer attitudes to plastic bags.
6 May 2004 Rising tide of micro-plastics plaguing the seas (by Maggie McKee) Reports on a study looking at the amount of microscopic plastic fragments in the ocean.
23 November 2002 Food scraps make perfect plastic (by Ian Sample) Discusses a biological reactor that converts food waste into a biodegradable plastic.
Inside Science (No. 50), 19 October 1991 Degradable plastics (by John Emsley) Covers biodegradation and photodegradation of plastics.
Newsline Issue 37, Autumn 2006, pages 8-9 Plastics, naturally (by David Bradley) Reports on research to develop environmentally friendly ways to produce and dispose of plastics.
Scientific American 27 February 2006 Bacteria turn styrofoam into biodegradable plastic (by David Biello) Reports on the use of bacteria to turn styrofoam into PHA, a biodegradable plastic.
August 2000, pages 24-29 How green are green plastics? (by Tillman U. Gerngross and Steven C. Slater) Covers the environmental pluses and minuses of making plastics using green plants.
Solve Issue 10, February 2007 Eco-packaging challenge (by Gio Braidotti) Looks at efforts to assist the packaging industry to assess the biodegradability of products.
Velocity March 2007 “Green” nappy is biodegradable Reports on the invention of the world’s first completely biodegradable nappy by a west Australian researcher.
Packaging materials (Key Centre for Polymer Colloids, Australia)
A case study that covers the use of plastic as a packaging material and the search for replacements (eg, starch).
Australian Government Department of the Environment and Water Resources
Plantic Technologies receives award for biodegradable plastic (A to Z of Materials, Australia) Reports that the Australian Museum Eureka Prize for Industry 2004 was awarded to an Australian company for its biodegradable plastic.
Biopolymers from crops: their potential to improve the environment (Proceedings of the 11th Australian Agronomy Conference, 2003)
Discusses the possibilities of developing a biopolymer industry in Australia.
Non-food crops: turning the corner? (e-zine, Royal Society of Chemistry, UK)
Discusses the potential of plant-derived chemical products and why so many basic chemicals are still primarily derived from fossil fuels.
Bacterial plastics (Department of Bacteriology, University of Wisconsin, USA)
A more technical look at the biodegradable plastics that are synthesised by bacteria.
How green are green plastics? (Scientific American, August 2000)
Looks at how plastics manufacturing affects the environment.
biodegradable. Able to be broken down into simpler substances by the activities of living organisms and therefore unlikely to persist in the environment. composting. Breaking down aerobically plant and animal material using microorganisms. For successful composting there must be sufficient water and air to allow the microoganisms to break down the material. Material derived from the aerobic breakdown of plant or animal material by microorganisms. culture. To grow microorganisms such as bacteria and fungi in a laboratory under controlled conditions. decomposer organism. An organism, usually a bacterium or a fungus, that breaks down organic material into simple chemical components, thereby returning nutrients to the physical environment. gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule. (Nova) greenhouse gas. A gas that is transparent to incoming solar radiation and absorbs some of the longer wavelength infrared radiation (heat) that the Earth radiates back. The result is that some of the heat given off by the planet accumulates, making the surface and the lower atmosphere warmer. For more information see The greenhouse effect (CSIRO Atmospheric Research, Australia). monomer. A molecule that can join with other molecules to form a large molecule called a polymer. A monomer is the smallest repeating unit in a polymer chain. photosynthesis. The biochemical process in which green plants (and some microorganisms) use energy from light to synthesise carbohydrates from carbon dioxide and water. Photosynthesis can be shown as: CO2 + H2O + energy® [CH2O] + O2 polyhydroxyalkanoate (PHA). A biodegradable polymer produced by bacteria that has the qualities of plastic. At one extreme, PHAs share properties with polypropylene, and at the other end of the range, they are similar to natural rubber. For more information see Material: PHAs – polyhydroxyalkanoates (Design inSite, Denmark). polylactide (PLA). A biodegradable polymer derived from lactic acid. Because this polymer is broken down in our bodies, it has biomedical applications (eg, sutures). For more information see Material: PLA – polyactide (Design inSite, Denmark). polymer. Polymers are large molecules that are made up of many units (monomers) linked together in a chain. There are naturally occurring polymers (eg, starch and DNA) and synthetic polymers (eg, nylon and silicone). More information can be found at The basics – polymer definition and properties (Plastic Resource, USA), Introduction to polymers (Case Western Reserve University, USA) and History of polymers and plastics for teachers (Hands On Plastics, American Plastics Council). tuber. A thickened short underground stem or branch formed by some plants (eg, potatoes) as a food storage organ. Each of the 'eyes' on a potato are buds that can grow into new roots and shoots.
External sites are not endorsed by the Australian Academy of Science. Posted February 2002. The Australian Foundation for Science is also a supporter of Nova.
This topic is sponsored by the Australian Government's National Innovation Awareness Strategy.
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