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Biodegradable (Compostable) Plastic Bags

San Francisco recently banned conventional plastic bags in grocery stores within the city limits. The city ordinance has received a lot of global press, and many states are now considering similar legislation. As a result, a lot of interest is focused on the biodegradable plastic bag. This article is designed to shed light on "biodegradable" and "compostable" bag issues.

The first key to understanding this issue is the need for a definition. The term "biodegradable" is becoming one of the most misused and misunderstood words in our vocabulary. The fact is, that given enough time and proper elements, everything on the planet biodegrades. Today the Titanic is biodegrading on the ocean floor. The fact that it hasn't completely decomposed yet over almost 100 years is the best indicator of how inadequate the term "biodegradable" is.

Second, just because something decomposes into fragments doesn't mean it will completely biodegrade. By definition, in order to be considered biodegradable the decomposed remnants must be ingested by bacteria and microorganisms to complete a process that results in CO2 and H2O. For example, when metal decomposes into rust there aren't "metal-eating bacteria" that convert the rust into CO2 and H2O.

Third, all organic products biodegrade because they are carbon based. Things that are found "naturally" on the planet are organic. To most people's surprise oil and gas are organic products and are also found naturally on earth. The point is - a plastic bag made from natural gas (U.S.) or oil, will biodegrade - given enough time and the right conditions.

The key issue in the biodegradable debate is really about time and conditions. Therefore, we know that polyethylene plastic bags will degrade over time with enough heat and light. This however will not satisfy our needs for resource management or sustainability. On the other hand, by mandating compostable bags like San Francisco, misleads the public because they are only biodegradable if sent to a proper composting facility. If discarded on the side of the road as litter or sent to a landfill, compostable bags will NOT biodegrade because these environments lack the proper conditions. Only in an organic composting facility will so-called biodegradable bags decompose.

As a further point of clarification, the yard waste that many consumers now separate curbside goes to different composting facilities than organic waste. Organic waste composting centers have much higher diversity in the waste content and require far more rigorous composting standards - i.e. the introduction of specific bacteria, temperatures of 180 degrees (F), constant turning of the materials, rodent control, etc. In the United States today there are 3000 yard waste composting facilities but only 134 organic waste centers. Permitting for organic waste composting facilities are also very difficult to obtain by municipalities.

The one positive about this type of bag is the sustainability factor. These bags are not 100% starch-based - i.e. corn, potato, and sugar cane contain polyesters which can biodegrade. If there is enough farmland to grow these vegetables to produce enough of this raw material, the argument that because it is more sustainable than products made from oil or natural gas is valid. Also, given the fact that these products are in their infancy, it is also likely that pricing will come down as these products are more mass-produced and commercially available. According to reports, it should also be noted that there is not enough farm land to convert the plastic bag industry to compostable plastic. In addition, more energy is required to produce this type of material than conventional plastic. Since we do not have a definitive science on these claims, we will report them as a footnote for sake of completeness.

In summary:

Compostable is NOT Biodegradable -
The hype about biodegradable plastic bags is just that; hype. These bags will only degrade if disposed of in an organic composting facility which is unlikely in most U.S. cities today. Bags made from these materials will not decompose if they end up in landfills. They will not degrade if they end up in trees or as litter on the side of the road. They will not break down in water and be less invasive to marine life than traditional plastic bags. The switch to compostable bags might make sense in San Francisco but it will not solve their litter or landfill problem and will have far less environmental benefit in other cities and states.

Capacity constrains exist -
The Polyethylene retail carry bag market is estimated to be between 1.5 billion and 2 billion pounds annually. The current available capacity of compostable resins is less than 300 million pounds. The majority of these resins won't work for flexible packaging (bags) as they are designed for rigid containers. Put another way, it is only possible to convert 10-15% of the bag market today to compostable bags if every pound of compostable resin was used.

End result-
Composting is not the waste policy prevalent in the United States. Without a federal mandate to build a significant number of organic composting facilities, conversion to compostable bags solves nothing. With the U.S. market for grocery sacks at 100 billion per year and paper grocery sack supply being limited to 5 billion annually, if compostable bags are mandated by municipalities, the choice by default will be no bags in stores and restaurants.

Americans want choice and mandating specific products or banning others is not the American way. Consumers should know all the facts and be allowed to make informed choices between paper, plastic, compostable, or no bag at all.

Degradable Plastic Bags

Many plastic bag companies have already begun to market products that are claiming to be biodegradable or degradable. In the last article we explained the definition of biodegradable, i.e. complete degradation to CO2 and H2O, so we won’t cover that again.

Much confusion will occur because bags that look conventional are claiming to be biodegradable. Since in most states you can call a product “biodegradable” if it simply has the ability to begin decomposition, suppliers intent on misleading the public can get away with making these claims. California has attempted to address this by passing a law that prohibits using the term biodegradable unless it meets the standard of complete assimilation back into CO2 and H2O within 180 days in a composting, but that only affects California and further confuses most consumers.

There is technology that has been available for many years that will accelerate the degradation process of polyethylene bags. These additives typically can be used with no distortion of the look, feel, or functionality of the bag. With proper use of these additives the bags will begin to become brittle and fragment in about 18 months. Within 30 – 36 months, depending on the amount of oxygen and heat, these bags can decompose into very small fragments of polyethylene powder.

While this sounds good there is no science that supports that the resulting “polymer sand” will become small enough to be ingested by micro-organisms and finish the degradation cycle making these bags truly biodegradable. Manufacturers of these additives argue that they will but to date California and others have rejected these claims. As a result we are left uncertain as to whether these bags actually biodegrade or simply fragment as in the earlier example of metal rusting.

One way to look at the argument is if you cut down a large tree and put it in a composting pile. Left as a large tree it will not biodegrade in our lifetime. If it is cut into wood chips it will decompose faster but still not completely biodegrade in any reasonable period of time. It is not until the tree is ground into small enough fragments that it is able to be biodegradable in nature.

If litter is a concern this product is actually better than conventional plastic and compostable bags because it will cause the bags in the trees or on the roadside to fragment faster. There is even some suggestion that if a bag with these additives are reused and kept out of the landfill long enough for degradation to begin, they will continue to decompose into fragments before being buried in the landfill actually taking up less space. Those claims however are difficult to verify without expensive studies.

This type of solution does not deal with the sustainability issue. If the concern is to use products that we can continue to offer from renewable sources, this product is not the answer.

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