You know that plastic doesn’t break down into other compounds, so it basically lasts forever. Did you ever wonder why? After all, it’s made from petroleum, an organic substance.

And did you ever wonder if it’s possible to make a biodegradable plastic?

The answer to the latter question is, yes. Unfortunately, the current generation of bioplastics doesn’t solve plastic’s environmental problems.

Not yet, anyway. Scientists are working on it.

Why microbes don’t eat plastic

The process of making plastic creates gigantic molecules. They have an exceptionally strong carbon-carbon bond that does not occur in nature.

How gigantic? The atomic weight of a single water molecule is 18; that of a single plastic molecule is typically more than 10,000. Microorganisms cannot eat plastic, or if they can, it takes too much effort.

Look at it this way: According to Guinness World Records, the world’s largest pizza, created in 2010, has a surface area of 13,580 square feet. Who would order one that size when it’s so easy to get something more manageable?

A small amount of plastic gets recycled. And even smaller amount is burned for fuel. All the rest either winds up in a landfill or becomes litter. So much plastic litter makes its way to the ocean that the plastic debris in the Great Pacific Garbage Patch outweighs plankton by a ratio of 36:1.

Plankton is a major food source for marine life. Plastic is a poison that sea creatures eat, thinking it’s plankton. It has reached our plates in the seafood we eat.

As waste plastic breaks into smaller and smaller pieces, much remains chemically unchanged. Sunlight and heat can degrade plastic and change its chemistry somewhat, but it still has those huge molecules.

[Update: Some microbes have been discovered that digest PET. So far, the discovery isn’t much more than a scientific curiosity. It’s  not like they’ll provide a method of plastic recycling anytime soon.]

Bioplastics

Biodegradable plastics are made in such a way that microorganisms can degrade them the same way they degrade fallen leaves.

Except the leaves enrich the soil. Biodegradable plastic does not necessarily make good compost. In fact. it may even leave a toxic residue.

The definition of compostable plastic requires that they yield biomass and other components at a rate comparable to the rate of any other compost.

What’s more, they must leave no other visible or distinguishable residue, toxic or otherwise.

The Society of the Plastics Industry, the industry’s trade association, has recently released a definition of “bioplastics” as “partially or fully biobased and/or biodegradable.”

It intends to simplify the term so that the public can more easily understand the industry’s commitment to waste reduction and sustainability.  

Biobased means that the feedstock to make bioplastic comes from plants (or less commonly, animals), and not fossil fuels.

Biodegradable means that biological action will completely degrade material into carbon dioxide, methane, and water. It will do so in both a defined timescale and a defined environment.

Biobased materials may or may not be biodegradable. Biodegradable materials may or may not be biobased.

If you are thinking that the SPI’s new definition doesn’t seem very simple, you are not alone. Terms used to define “biobased” and “biodegradable” have a very technical meaning. The general public uses some of the same terms differently.

Are bioplastics compostable?

Defined environments for biodegradability include anaerobic digestion, composting, soil, and marine environments.

Compostable, in this context, means specifically industrial composting, not a homeowner’s own backyard compost pile. Unfortunately, for homeowners to compost bioplastic would require a third waste process in addition to landfills and municipal recycling programs.

The United States currently has only about 200 such composting facilities. And some of them refuse to accept biodegradable plastics, considering them contamination risks.

Therefore, marketing bioplastics as biodegradable and compostable amounts to greenwashing.

What ought to work in principle does not work in practice given today’s infrastructure. Biodegradable plastic may never make sense financially. Why create an energy-intensive synthetic material and intend for it to rot?

Durable (non-biodegradable) bioplastics can serve as alternatives to PET bottles used for soft drinks or water. They are manufactured with up to 30% ethanol. They can be tossed in recycling containers with ordinary bottles.

Durable bioplastics, therefore, fit existing infrastructure better than biodegradable bioplastics. Unfortunately, not all of them can be recycled.

They can be sustainable under two specific conditions.

• Our society needs to curb its appetite for plastic in the first place. Especially for single-use disposable products
• The process of making bioplastics to meet this reduced demand must use non-edible feedstock, such as organic wastes.

Much of the biobased polymers, fillers, and additives used to make bioplastic now come from sugar cane or other food plants. As long as that is the case, bioplastics will have the same drawback as ethanol. That is, they will be competing with edible food for agricultural land to grow them.

Fortunately, suitable feedstock can come from inedible plants, like switchgrass, that grow well on land that can’t support food crops. It can also come from waste byproducts of agriculture or food production and microbial activity.

A hopeful development in bioplastics

Despite these misgivings, a sustainable future includes bioplastics.

Scientists in Zaragoza, Spain, have recently concluded the Dibbiopack Project. They studied development of biobased, biodegradable, compostable plastic packaging.

The project results include a biodegradable bioplastic film made from agricultural waste. It uses nanotechnology to make it stronger.

As much as I have heard about nanotechnology, I hadn’t read anything about its possible environmental effects. I have wondered about the prospect for nasty unintended consequences. A brief Internet search tells me that science is indeed looking into it.

Perhaps armed with foresight, nanotechnology will not reach back and bite us in a few decades like so many other transformative technologies have.

The film is intended to protect food, medicine, and cosmetics. The nanotechnology gives it adequate strength even though it is only a nanometer thick. It doesn’t come in direct contact with the products.

It also contains sensors that change color according to the amount of oxygen in the packaging. In other words, it gives visual evidence of whether the product is still good or has spoiled.

Films such as those that cover packages of raw meat appear to be an exception to the general rule that biodegradable plastics aren’t worth manufacturing. The world would be much better off without the plethora of single-use products, but it’s hard to imagine a reusable plastic film for covering a package of hamburger.