Industrial Resins and the Environment

To understand what resins (or plastics, take your pick for a term) are, it's helpful to be clear that they're not just one thing.

"One way to think about resins is to think about metals," says Kingsbury. "They are lead and gold and aluminum and iron. They all fall under the category of metals, but they have different properties. They're mined differently and have different cost structures. Plastic is the same." Translated into the world of resins, that means that there are many different types under the umbrella term of plastics, including polyethylene terephthalate (PET) -- one of the most common kinds, often used in water bottles -- and high density polyethylene (HDPE), which comprises milk bottles.

Of course, the question really isn't "What products are resins in?" It's "What are they not in?" As mentioned, resins are found in all sorts of packaging, as well as in airplanes. But that's just the beginning. There are lots of resins used in plenty of different products, and here are a few examples: Polyurethane resins are used to make furniture foam and footwear; alkyd resins are used in paint; and formaldehyde resins are used in wood glues [source: O'Lochlainn].

Although it's important to know there are a variety of resins, there are some broad generalizations that can be made about how they're all produced. For the most part, resins are derived from natural gas and oil -- think of gas and oil as the feedstock or building blocks of most plastic (though there are some exceptions, which you'll learn about on the last page of this article). To take that a step further, on a basic molecular level, resins are simply links of monomers derived from oil and natural gas. So, when you hear the term polymer used interchangeably with resins or plastics, that's because it's perhaps a more precise description of the end product of the process used to produce resins: Polymers are made of many monomers.

An example will probably help. Polyethylene, the most common plastic in the world, is made up of many monomers called ethylene. In order to get polyethylene, a process takes place that breaks a double carbon bond in ethylene gas and joins it to another ethylene [source: Kingsbury]. And when you string together enough ethylene monomers, you not only have polyethylene, you actually have a solid, which can be shaped to form a container like a milk bottle.

Even better, though, is to think of it the way Bill Carroll describes it. Carroll, who is chairman of the board of the American Chemistry Council, says it's best to think of monomers as small, one-inch pieces of yarn. If a few of them are piled in front of you, it's easy to pick them apart strand by strand. But if you have a pile of much longer pieces of yarn all entangled and intermingled, it's going to be much more difficult to pull them apart. In other words, the tangled mess of yarn is equivalent to resins, plastics or polymers. "This is how you should understand where the strength of polymers and plastics comes from," Carroll says.

Obviously, monomers don't think. Which means that they don't wake up one day and decide they want to join up with a bunch of other monomers and create a polymer. Rather, monomers link up with their own kind with the help of a chemical reactor, a device that facilitates controlled chemical reactions. UC Berkeley's Kingsbury explains a bit about how the monomer-to-polymer reaction takes place.

"Typically, you would have to keep them at high temperatures or high pressures or with some solvent to keep them flowing. Otherwise, reactors get gummed up with a giant chunk of plastic," Kingsbury says. Once out of a reactor, resins come out of the factory door as pellets that look like grains of rice, which are shipped to companies that make them into a wide variety of products.

The impacts resins have on the environment are varied. First of all, the very fact that they are derived from oil and natural gas means the use of a substantial amount of fossil fuels, albeit far less than what's used for, say, transportation. But the environmental effects of resin wastes go even further.

"[Resins] are known for being flammable and toxic, and the fumes produced after they catch fire are quite dangerous," says Ross O'Lochlainn, who works with ERA Environmental Management Solutions, an environmental consultancy.

O'Lochlainn says that the use of resins as surface coatings and applications requires them to be sprayed as part of a volatile mixture of chemicals, known as volatile organic compounds (VOCs). "These chemicals are required as the delivery medium, and because of their volatility, they evaporate quickly, leaving behind the resin coating. These VOCs are harmful to the environment and are closely monitored by environmental protections agencies," he says.

O'Lochlainn adds that resin mixtures can lead to the contamination of waterways if, for example, they're poured down the drain. Most wastewater treatment plants aren't designed to break down the chemicals and simply discharge them.

The simple truth is that plastic bags -- along with most yogurt and milk containers and a wide variety of other packaging -- can be recycled. That's the good news. Unfortunately, at least according to the U.S. Environmental Protection Agency, only 8 percent of all plastics were recycled in 2010, meaning that billions of bags and bottles ended up in landfills or, worse, in oceans, streams and trees [source: EPA].

Nevertheless, the fact remains that, for many resins, recycling is possible, and there are a number of companies across the U.S. -- including Industrial Resin Recycling Inc. in Michigan -- that handle that.

"Basically, these companies gather all the different post-industrial resin products, whether it be plastic seat covers, plastic wire casings or any plastic defective parts," says Andrew Schrage, co-owner of Money Crashers, a Web site that provides personal finance as well as sustainability coverage and advice. "These products are then melted into large chunks of plastic. In turn, those are ground or shredded and reduced for reuse."

Although still a niche market compared to traditionally produced resins, bio-based plastics are becoming more common. One indication of their growth is the variety of products that now use resins made of such material as corn and sugarcane. For example, recyclable Dasani water bottles are made with up to 30 percent plant material. But plant-based resins are in all sorts of other packaging materials besides bottles, including bags and other containers, as well as less obvious items such as car parts and components. Learn more about these sustainable resin options on the next page.

Resins can be made from source material besides oil and natural gas. There are a number of different ways this is done. The most common alternate source material is polylactic acid, which is derived from corn.

"[Companies that produce bio-based resins] take corn sugar and feed it to microorganisms that produce a waste product called lactic acid, which is the monomer," says UC Berkeley's Kingsbury. "You separate out the lactic acid and make it into a plastic."

The environmental benefit of using a plant-based source material, obviously, is that it avoids the consumption of more fossil fuels, and the products made can be composted as well.

But there are some downsides, especially with the use of corn. After all, corn requires the use of a lot of petroleum-based fertilizer to grow, and the runoff enters waterways, leading to the creation of so-called "dead zones" -- spots where oxygen is cut off -- in places like the Gulf of Mexico, imperiling marine life.

Kingsbury says a better alternative to corn is sugarcane, which uses the same basic procedure to produce resins but doesn't need as much land and produces fewer emissions during processing. But whether you're dealing with a corn or sugarcane-based resin, it's still important that the products they're used to create be disposed of properly.

Indeed, Kingsbury says that all too often, people see that a bottle or container is compostable and think it's just fine to toss it onto the side of the road. "A problem we run into is that people litter more when they believe it magically disappears, and that's the last thing we want," he says. "We want it in compost or recycling, not along the side of the road."