Bags that break down.

11/12/2010 18:55


HERE’S one way out of the plastic bag dilemma: Simply make the bags out of biodegradable materials. In Penang, the ban is on plastic bags; so you can’t be accused of flouting it if you give out bio-degradable bags. And since many still insist on having the bags for their trash, why not make eco-friendly ones?

There are generally two groups of bio-degradable plastic. Hydro-biodegradable plastics are made from starch-based polymers (derived from tapioca, corn, potato or wheat) while oxo-biodegradable plastics are conventional petroleum-based products with some additives that hasten degradation. When exposed to the right conditions (heat, oxygen and moisture), both will undergo chemical degradation, resulting in a reduce molecular weights. The smaller molecules are then amenable to biodegradation by micro-organisms, which convert the materials to carbon dioxide and water. Some polymers require UV light in order to break (photodegradable polymer) while others need aerobic conditions (compostable polymer).

The lesser evil: Since we cannot give up the convenience of plastic bags, the next best thing is to make them biodegradable.

Hydro-biodegradable plastic, being made from starch, will biodegrade faster than oxo-biodegradable plastic. But it is expensive (eight to 12 times more) and so usually not used on its own, but mixed with conventional plastic resin. Making hydro-biodegradable bags also requires new machinery, and they must be made five times thicker to get the same strength as conventional plastic.

Oxo-biodegradable plastics are more commonplace as they are cheaper, possess better physical properties and can be manufactured using existing plastic processing equipment. Oxo-biodegradable plastic additives popularly used by local manufacturers are those made by EPI (used in Tesco bags) and Clariant.

One locally made additive is dmas, by Johor-based company Additech. The additive, introduced to the market in 2005, is supplied to plastic manufacturers who export biodegradable bags to Europe and Indonesia. The additive is also used by local company Sewanis to produce the Greenmate brand of oxo-biodegradable bags currently used by Air Asia, Mydin and municipal councils in Port Dickson, Johor Baru, Ampang Jaya and Ipoh.

“The additive has been tested and found safe and non-toxic to food and is free of heavy metals. The plastic will biodegrade within two years as compared to decades for conventional plastic,” says Additech director Alan Loh.

The use of an additive speeds up degradation of these oxo-biodegradable plastic bags,reducing them to carbon dioxide and water. They are made by the company Sewanis using dmas oxo-additive.

Ordinary plastic bags do not decompose or take a long time to do so because the plastic polymer consists of complex molecular chains. To resolve this, the oxo-additive breaks down the molecules into simpler chains, to a point where they can be ingested by micro-organisms (this part is the biodegradation process). The process is triggered by heat (such as elevated temperatures found in landfills or composting) and oxygen.

Oxo-biodegradable plastic can be used not just for bags, but also for foam packaging, stretch and shrink wraps and plastic serviceware. By varying the concentration of additive in the mix, manufacturers can customise the shelf life of the biodegradable plastic products.

Not so green?

But not everyone views these materials as the dream plastic. Many contend that the drawbacks of biodegradable plastic have not been publicised. Claims of biodegradation have been disputed, with criticisms that the material will not degrade in an oxygen-starved landfill, and the degradation itself emitting greenhouse gases such as carbon dioxide and methane. Using crops to produce bio-plastic is also said to threaten food supplies.

As for the overall ecological footprint, there are conflicting views. Some reports say the production and disposal of biodegradable plastics use less energy and water, generate less greenhouse gases, and produce less waste. But there are also studies which say otherwise.

Then there are criticisms that most so-called biodegradable plastics only degrade (changes in chemical structure and loss in mechanical properties, resulting in the plastic breaking down into small fragments) and do not biodegrade (break down and be consumed by micro-organisms).

Loh points out that anything that breaks down is better than one which does not. He says biodegradable plastic has been plagued by plenty of mis-information, and confusion still reigns over its different types. “There are agents who import additives and claim them to be biodegradable. Consumers must look out for certification which shows that the product is biodegradable. To be named oxo-biodegradable, it must meet the standard ASTM D6954-04.”

This is the American Society for Testing and Materials’ standard guide for “Exposing and Testing Plastics that Degrade in the Environment by a Combination of Oxidation and Biodegradation”.

Agreeing that greenhouse gases are released during biodegradation, Loh nevertheless, contends that biodegradable bags are still the “lesser of two evils.”

“Can we live without plastic bags? We can’t. So the next best thing is to make them biodegradable. Plastic is the cheapest and most reliable material to replace other high-energy products such as paper. It is not a magic bullet but it will solve part of the problem, especially that of uncollected plastic bags flying around. If these are made of biodegradable material, they will break down.”

Loh reckons the plastic waste menace stems from poor consumer attitude. “Japan and South Korea are high plastic bag users but they don’t have a problem as they don’t litter and they take only enough bags for use.”

The right conditions

Officials at Bgreen, a company which supplies biodegradable bags made locally using EPI’s oxo-additive, say the bags will need an initial 100 hours of exposure to sunlight and heat to trigger the degradation process. “Once that has happened, the bags will continue to biodegrade, even when buried in a landfill. In Malaysian conditions, getting 100 hours of sun and heat should not be a problem. Without sufficient heat and sun, the bags will not biodegrade,” says its business development manager Weng Chen.

In general, the more additive used, the faster the degradation. According to the EPI website, different disposal methods (landfill or composting) will require different additive formulations specific to the conditions of the disposal environment and the desired degradation performance. The website also states that independent tests confirmed that after biodegradation, all that remains are carbon dioxide and water.

The website of another oxo-additive, d2w, however, states that aside from carbon dioxide and water, inorganic materials such as harmless mineral fillers, metal salts and the like that were present in the plastic to start with, would remain even after biodegradation. It also says that biodegradation does occur in an air-tight landfill, albeit slowly. Methane is produced but it takes a long time to form and in modern sanitary landfills, is collected for energy generation.

Bgreen director Fachri Ramadhan Asmar agrees that the bags will not totally bio-degrade if environmental conditions are not right but “at least 70% of the bag would have degraded instead of 100% plastic left behind.” He, too, insists that biodegradable bags are just one of the solutions. “We must still practise the 3Rs. Now, 90% of plastic bags end up in landfills as there are no recycling facilities.”

BGreen currently supplies oxo-biodegradable bags to Le Meridien Kota Kinabalu, organic food outlets, Loh Guan Lye hospital in Penang, KPJ medical centres and Alam Flora (garbage bags).

Yes, biodegradable bags generally cost more than conventional plastic ones, but not very much more.

“The price is affordable, an additional cost of 3% to 5%,” says Chen.

Based on Loh’s estimates, 10 pieces of oxo-biodegradable T-shirt bags (40x48cm) cost 46 sen compared with 45 sen for plastic ones. And each oxo-biodegradable garbage bag costs 30 sen whereas a plastic one is 29 sen. He says based on an individual’s average usage of 150 bags annually, switching to oxo-biodegradable bags would only incur an extra 85 sen.

So it appears that biodegradable plastic bags are not beyond reach. In fact, several of the country’s biggest plastic manufacturers have been exporting them for years.

Biodegradable plastics may not be perfect, but we have to start somewhere. At the same time, we have to be mindful that these things can be red herrings – they send out the wrong message, that it is okay to discard. They can distract us from what we really need to do: curtail our use of plastic and recycle more of it.



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