How Biodegradation Additives Work

Plastics make up so many of our most common products, which are incredibly durable. Biodegradable plastics could help ensure that your great-great grandkids don’t stumble onto that fork you lost at a picnic in 1998. See more green science pictures.
Courtesy Bio-Tech

Thousands of years from now, it's quite possible that future civilizations will be digging through the remnants of ours. Maybe they'll unearth crumbled skyscrapers. They'll discover our crumbling bones. And almost certainly, they will bring to light endless amounts of buried plastics, from tools to toys. "Oh look, it appears to be the crimson light saber once carried by the great Lord Vader!"

We are living in the plastics age, in which many of us can't go more than a minute or two without touching a product that's made at least partly of this malleable, strong and durable material. And it's that last trait that has so many resource- and environment-minded people concerned.


Plastics have staying power -- they don't degrade much in natural environments or landfills. Recycling is one great option to reuse some types of plastics, and more people are becoming recycling savvy. Still, in the United States alone, only about 7 percent of all the plastic products used are recycled; and 28 million tons (yes, tons) gets chucked into landfills every year [source: EcoLogic].

To make sure plastics don't become permanent pollutants, some newer plastics technologies incorporate biodegradable additives into their chemistry. These additives are designed to allow plastics to break down naturally, whether they're in a landfill or planted roadside by a litterbug.

As they degrade, such plastics break down into carbon dioxide, humus or biomass (a basic organic matter similar to soil) and methane gas. That's a big improvement over nearly indestructible detergent and soda bottles that might announce their presence to future archaeologists.

But before biodegradable additives can expand into most products, there's a whole lot of work to be done in terms of government regulations, recycling standards and consumer public relations.

On the next page, we get our hands dirty with delicious decay -- and delve into what makes biodegradation so cool.


Tiny Appetites for Destruction

The world all around us is teeming with microorganisms, which are also called microbes. Microbes may be invisible to the naked eye, but their appetites are evident, as they initiate and accelerate the decomposition of all sorts of organic matter, from newspaper, to animal droppings, to pizza crusts and much, much more.

There are many types of microbes working the magic of decomposition. They include bacteria, fungi, protozoa, algae, actinomycetes and others. Different types of microbes work their magic in different ways and they digest different materials, but they all contribute to the breakdown of organic matter, which can also be called biodegradation.


Environmental factors play a vital role in any decomposition process. The presence of water, light, heat, oxygen and other variables all affect the way microbes and their energy sources (see: food) interact.

Oxygen levels in particular greatly impact degradation. Your backyard compost pile is an example of aerobic environment, meaning that oxygen is present. A monstrous landfill, on the other hand, is an anaerobic environment, or one that largely lacks oxygen exposure.

In an aerobic setting, microbes use acids and enzymes to convert the large molecules of a material and into smaller and smaller compounds. After the molecules reach smaller size, microbes can absorb the material and use it for energy.

The same process occurs in anaerobic conditions, but with notably different byproducts – the microbes produce a lot of methane and carbon dioxide. Landfills with methane recovery equipment can capture the gas and sell it to local energy companies; others simply burn off the gas so that it doesn't contribute to greenhouse gas emissions.

Water is even more important than air. Without water, life on Earth wouldn't exist as we know it. The same concept applies in landfills. Landfills with higher moisture levels exhibit much faster biodegradation, while those in drier regions aren't nearly as biologically active.

Yet even when water is plentiful, impermeable conventional plastics are like kryptonite to microbial ka-pow. Plastics tend to resist and deflect just about all of nature's attempts to deconstruct them. Keep reading and you'll see why plastics are so stubborn and tough to break apart.


Otherworldly Plastics

Plastics are ultimately based on petroleum, which is itself the result of decayed organic matter. So microbes should have a veritable feast in the form of plastics, right?

Nope. Microbes generally turn their noses up at plastics.


That's because during the manufacturing process, the petroleum undergoes changes at a molecular level, shifting from simple monomers (single chemical units) to polymers, which are much larger, more complex units connected by strong chemical bonds. They're waterproof and airtight, and as such, they're splendid for making, protecting, shipping and preserving untold human products.

These kinds of gigantic polymers aren't created by Mother Nature. They're the result of humankind's chemical achievements. Polymers come in many varieties denoted by esoteric acronyms that echo their unnaturalness: PE (polyethylene), PP (polypropylene) and PS (polystyrene) are just a few.

To the natural world, plastics are a chemical freak show. Microbes aren't equipped biologically to attack and break them down the way they do organic material.

As a result, it could take hundreds of years or more for microbes to make any headway on that plastic spork you dropped during your picnic at the park. We don't actually know how long that utensil could wind up lasting – maybe forever.

Still, you've probably seen plastic out on a beach or field that looks brittle or dilapidated. It's not because of biodegradation. Instead, ultraviolet light and oxygen are what causes this exceedingly slow destruction, which often results in chunks of plastic that still do plenty of polluting.

For plastics to really biodegrade, we need to use additives that help microbes begin to do their jobs. Whet the appetites of these little guys and they can do some seriously helpful destruction.

We'll get up close and personal with additives shortly, but before we do, keep reading for more about what makes plastics degrade, and how their demise isn't always natural or clean.


Biodegradation versus Disintegration

Mix pellets of treated plastic resin in with its own polymers, and a manufacturer can create products that degrade on a specified timeline.
Courtesy EcoLogic

Plastics are a diverse technological wonder. And as with all technological advances, polymers need some sort of regulation to guide their usage and disposal. The ISO (International Organization for Standardization) started by defining six types of degradable plastics.

The first four types are degradable, photodegradable, oxidatively degradable and hydrolytically degradable. Degradable plastics are simply plastics that degrade in some measurable way. Photodegradable plastics are broken down by light. Oxidatively degradables are degraded by oxidation; rust is a type of oxidation, and the same kind of process can happen to polymers. Oxo-degradable plastics have an additive that speeds this "rusting" process. And hydrolytically degradable plastics are broken down by the interaction of the polymer and water.


For example, a plastic bag that degrades due to sunlight or oxygen exposure might fall apart into tiny, microscopic pieces, which aren't necessarily benign. That leftover particulate matter could be absorbed by small creatures and work its way up through the food chain, affecting the body chemistry of each organism along the way – with unknown consequences.

The final two types of ISO-defined degradable plastics are biodegradable and compostable. A biodegradable plastic is simply one that our aforementioned microbe friends can dismantle to water and carbon dioxide, but on a timeline that's not necessarily well-defined. Compostable plastics degrade at a rate that's similar to other types of compostable materials, and they result, again, in water, carbon dioxide, humus, and inorganic compounds.

One big difference between compostable and biodegradable plastics is that the former require the high heat of a professionally-managed compost pile or landfill in order to rot. This distinction is vital, because 10 to 15 billion pounds, or 75 percent, of all plastics wind up in landfills [Source: PEC]. Truly biodegradable plastics will break down best in a landfill, but they'll also degrade in a roadside ditch.

It's not such a bad thing if biodegradables wind up in a landfill instead of a recycling center. In a landfill, the methane they release can be captured and combusted for our energy needs. Of the 1,200 operating landfills in the United States, about half capture methane. In 2008, those landfill gas energy (LFG) projects generated around 12 billion kilowatt hours of electricity in just one year.

Now, let's get the down-low on the dirty work of plastics additives.


Biodegradation Additives for Plastics

These plastic pellets contain biodegradable additives. The pellets can be melted and used to make all sorts of plastic products.
Courtesy Bio-Tech

Biodegradable additives give microbes the chemical leverage they need to body slam plastics into oblivion. Additives, which are also called degradation initiators, involve seriously complex chemical engineering that must balance the usefulness of the product, consumer safety and the ultimate end us of the plastic, be it recycling or decomposition.

These additives are proprietary (i.e. top-secret) blends of organic compounds. Specific recipes of additives manipulate microbes in different ways, and companies tout their formulas as superior to others.


When blended into regular plastics, they make up only about 0.5 to 2 percent of the product's total composition, and crucially, they don't change the polymer's performance. That is, you won't go on vacation and come home two weeks later to an orange juice jug that's crumbled to messy pieces. They also don't affect a container's content in any way, and they don't have adverse effects on traditional plastics recycling.

In fact, you'd never know anything was different about the plastic until it hits the landfill, which is really the only place that has the right combination of moisture and various microbes that can exploit the additive in the plastic. The additives will do their job outside of a landfill, too, but the process will take significantly longer.

The process doesn't happen right away. At first, just a few microbes are attracted to the additive; those first microbes create a small chink the plastic armor. More species of microbes arrive, their combinations of acids and enzymes, along with water, eventually allows them to break down huge polymers into smaller and smaller bits.

But what about compostable plastics? Well, there are no additives used with these so-called bioplastics (often made of polylactic acid or PLA). They're made from natural materials such as corn or pea starch or types of vegetable fats and oils. What's more, not all bioplastics are intended to decompose. Rather, they are made from renewable substances (like corn) for sustainability purposes. Some kinds won't degrade much at all in a landfill setting.

Bioplastics and plastics with additives often compete with each other for a share of the polymer market. Sometimes that competition erupts into an extremely public slugfest. Keep reading and you'll see how the waters of the biodegradable plastics conversation are anything but placid.


The Biodegradation Additives Debate

You’ll see more and more degradable products appearing on the market, often with markings that indicate biodegradable properties.
Courtesy Bio-Tech

Plastics are everywhere. Plastics are big, big business. So, many organizations have a lot at stake when it comes to the regulation and politics of biodegradability. A lot of people argue the details about whether various plastics really rot. And if they do, how long it takes and what sort of byproducts they leave behind.

To define biodegradability, governments and companies turn to the American Society for Testing and Materials (ASTM). ASTM develops voluntary consensus standards for all sorts of products and services, both in the United States and internationally.


The ASTM standards for biodegradability are still evolving, and although it's not yet a standard, many organizations adhere to the ASTM D-5511-11 testing method. This test helps companies determine the biodegradability of plastics in an anaerobic environment like a landfill.

Because decomposition tests take time and trial-and-error, there's plenty of room for disagreement as to what the test results mean. Companies that make various types of biodegradable plastics, oxo-degradable plastics, and compostable bioplastics push each other for proof that their approach is superior.

Charles Lancelot, executive director of the Plastics Environmental Council, has been working with plastics for 40 years. He says that politics and PR games, especially in California, have misled the public about the differences between these plastics.

He points to PLA-based bioplastics, which are made from corn starch, as one example. Corn and agriculture lobby groups want PLA in more products because doing so will increase the demand -- and eventually the price -- for corn.

But Lancelot says that PLA products just don't degrade unless they're composted professionally. And from an environmental point of view, that makes them less desirable than plastics that truly biodegrade in landfills and ditches. He also highlights a drawback of oxobiodegradable plastics; they need UV light and oxygen in order to degrade, and those variables are in short supply in a landfill.

In order to calm controversy and build exacting standards for biodegradation, Georgia Tech and North Carolina State Universities are performing landfill simulations and will submit their findings and recommendations to the U.S. government. New standards will be publicized by the media and likely will affect public opinion on various types of degradable plastics for years to come.

Public pressure, as well as more efficient means of making biodegradable plastics, could well accelerate the acceptance and use of these additives in many products. In the end, that could mean more environmentally friendly plastics, ones that disappear completely -- instead of lasting for millennia as a hallmark of a civilization that knew how to make wonderfully durable products yet couldn't find a way to properly dispose of them.


Author's Note

I spend a lot of time running and walking the gravel and dirt roads near my Nebraska home. It never ceases to infuriate me when I see the results of intentional and accidental littering; fast-food debris, beer cans and bottles and plastics galore. Yet I know the visible garbage strewn across the landscape is just a small fraction of the waste we all produce. The biggest percentage of trash winds up in landfills, including the stuff that really should be recycled.

The experts I interviewed for this story hastened to say that biodegradable plastics are not a panacea for pollution. They insist that the old rule of reusing what you can and recycling the rest is still applicable to our current state of environmental affairs. But with biodegradable plastics, perhaps our trashy lifestyles will have just a little less impact on generations to come.


Related Articles


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