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Biodegradable plastic bags

/ 09:27 PM June 16, 2012

Plastic bags are a wonder of modern technology. They can be made very thin, with minimal raw material, but  are still strong enough to carry a heavy load of shopping. No other carry-all container can hold 2,500 times its own weight and stay strong when wet. They are cost-effective and quite functional. No other industry has a better track record in material reduction.

Plastic bags have many advantages over alternative packaging:

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  • They are cheap.
  • They protect goods from dirt and rain.
  • They are hygienic.
  • They are reusable and recyclable many times over. Their ultimate use is being a garbage bag.
  • They use less energy to make.
  • They generate less atmospheric pollution when produced and transported.

Unfortunately, they are nonbiodegradable and are perceived to be the cause of flooding when indiscriminately thrown away, as they clog drainage and waterways.

The case against plastic bags is based on a number of fallacies. Legislation designed to reduce environmental impact and litter by banning them will not deliver the intended results. A ban would be outweighed by the disadvantages (increased solid waste and greenhouse gas emissions) that would subsequently occur using alternative types of packaging.

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The UK Environment Agency’s Report on the life cycle of supermarket carrier bags found that nondegradable HDPE (high density polyethylene) plastic bags and oxo-biodegradable HDPE plastic bags have the least environmental impact than bags made from  LDPE (low density polyethylene), nonwoven PP (polypropylene), paper, starch-polyester blend compostable plastic and cotton.

Oxo-biodegradable bags

Oxo-biodegradable plastic bags are almost the same as the nondegradable plastic bags. It is made from the same raw material using the same machine and labor. The only difference is that it contains a prodegradant additive that makes them biodegradable in soil.

What are the benefits of oxo-biodegradable plastic bags?

The use of oxo-biodegradable plastic bags complements and even adds value to solid waste management efforts of the government as well as the private sector. The benefits that oxo-biodegradable  plastic bags offer are as follows:

It gives a finite life to plastics, particularly polyethylene which is the main raw material  in making plastic bags.

They are a low-cost insurance against accidental or deliberate litter.

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Local governments with inadequate budgets for solid waste management would be less burdened with dreadful consequences of nondegradable plastic bag litters.

They are better than paper bags because:

  • The production of paper bags causes 70 percent more atmospheric pollution than plastic bags.
  • The production of paper bags use 300 percent more energy than plastic bags.
  • The production process of paper bags uses huge amounts of water and creates very unpleasant organic waste.
  • Paper bags emit methane in anaerobic conditions.
  • For the same number of paper bags and plastic bags, the delivery of paper bags uses 7 times more fuel and creates 7 times more pollution and traffic congestion.
  • Paper bags are at least 3 times more expensive.
  • Trees are the raw materials of paper.

They are also better than reusable bags because:

  • Cotton or jute bags are thicker and at least 10 times more expensive. Like paper bags, their transport causes more pollution and traffic congestion.
  • Cloth bags are a breeding ground for bacteria, yeast, mold and coliforms.
  • Reusable bags are a cost to the consumer whereas plastic bags are a cost to retailers.

Dumps would not be overloaded with nonbiodegradable plastic bag wastes.

They are reusable, recyclable and compatible with ordinary plastics.

Little dislocation to stakeholders who rely on plastic bags.

How it biodegrades

A very small amount of prodegradant additive such as BioMate® is mixed with the conventional plastic raw material during the manufacturing process. Its addition causes the plastic to degrade via a two-step process:

The plastic fragments due to oxidation (pagdudurog).

Biodegradation occurs when the plastic is consumed by microorganisms. (pagbubulok).

Do oxo-biodegradable plastic bags really biodegrade?

DTI standard

The Department of Trade and Industry has come up with the Philippine National Standard (PNS) 2092, the guide for exposing and testing plastics that degrade in the environment by a combination of oxidation and biodegradation.

The biodegradable-in-soil requirements of PNS 2092 are:

Minimum of 60 percent biodegradation rate within 24 months for a single polymer

Minimum of 90 percent biodegradation rate within 24 months for more than 1 polymer, blends and those containing high-molecular weight additives.

PNS 2092 also has heavy metal limits as well as ecotoxicity requirements.

A standard for oxo-biodegradable plastic bags is currently being crafted by a technical committee to assure the public that those plastics declared as oxo-biodegradable will indeed meet the requirement of PNS 2092.

Oxo-biodegradable plastic bags have been supplied by supermarkets abroad for more than five years, but there is no evidence that people dispose of them more carelessly and they have not been encouraged to do so.

But suppose, for the sake of argument, that 10 percent more were discarded. If 1,000 conventional plastic bags and 1,000 oxo-biodegradable plastic bags were left uncollected in the environment, 1,000 conventional bags would remain in the rivers, streets and fields for decades, but none of the oxo-biodegradable plastic  bags would be left at the end of the short life programmed into them during manufacture.

There will always be people who will deliberately or accidentally discard their plastic waste. What will happen to all the plastic waste that will not be recovered for recycling and instead litter the environment? Would it not be better if the discarded plastic bags were all oxo-biodegradable?

(Noli Jimenez is a product manager at First in Colours and a member of the Bureau of Product Standards’ technical committees 1 and 40.)

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