Biodegradable Plastics

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.

Biodegradable plastics made with plant-based materials have been available for many years. Because of their higher cost they have never replaced traditional non-degradable plastics in the mass market.

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 add up these associated costs, traditional plastics would cost more and biodegradable plastics might be more competitive.

If cost is a major barrier to the uptake of biodegradable plastics, then the solution lies in investigating low-cost options to produce them.The Cooperative Research Centre (CRC) for Food Manufacture and Packaging Science is looking at ways of using basic starch, which is economical 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.

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 that 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.

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.

Depending on the application, scientists can alter polymer mixes 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.

Compost may be the key to maximizing 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.
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 channeled into plant production, which in turn might be redirected into growing the starch to produce more biodegradable plastics.

For anyone who thinks such schemes aren’t feasible, you only have to look at the recycling success of the 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.

The new generation plastics fully degradable from symphony environmentals offers considerable advantages such as increased landfill capacities by 20-30% and can be engineered to degrade in as little as 60 days or over 5 years to suit end required application.

The process of degradation is through the breakdown of carbon-carbon bonds in the polyethylene reducing the molecular weight down to the level of 4000 from a quarter million, at which point the material can be digested by microorganisms in the soil and water. The DCP additive is neither water soluble nor toxic and hence safe for disposal in landfill sites.

The materials is also degradable under other conditions viz. photo and thermal degradation. The bags degrades to mulch in just 55 days.

The new polyethylene promises extensive applications that include small produce bags, carrier bags, industrial products packaging and even degradable plastic aprons. Refuse sacks are already in the market.

BAK, a semi-crystalline largely transparent thermoplastic developed by Bayers is a new biodegradable polyester amide plastic claimed to be 100 percent biodegradable and recyclable with excellent properties including high tensile produced without solvents, chlorine or any aromatic ingredients, adds to its green credentials. The biodegradability is achieved as it breaks down into carbondioxide, water, biomass under composting conditions. The rate of degradation is similar to other organic materials and properties similar to typical polyolefins. The new developed material also seem to be amenable to various process conversions that include extrusion, blow, thermoforming, colouring, printing etc., Applications are extensive including agrihorticulture and food etc.,

Recycling regulations have spurned ecologically safe consumer friendly bioplastics. The leading chemical industry in Germany, BASF is testing food bags and packaging from its ecoflex bioplastic which contains a biodegradable petrochemical polymer.

The latest development of bioplastic in Australia lends itself to biodegrade at temperatures as low as 0.5 degrees Celsius or mere exposure to moisture and micro organism in the soil. The technology appears to be unique as ascertained by Biodegradable Institute in New York.

Plastics has patented its development of the polymeric looking material – that looks, feels and is flexible like any conventional plastic. The process uses standard industrial extruders to produce cornstarch based pallets and can be converted by blowing and moulding. The prices are comparable to petroleum based plastics. However, the drawback of inadequate product preservation under adverse conditions need to be overcome. This could add to the cost and thus the costs should come down for plastic to expand and reach out wider markets. The market trials by leading multinational food companies should provide the lead for further developments.