How can a plastic bag be green?

To combat growing trash problems associated with plastic bags, some countries and cities have initiated bans on them.
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In 2007, the environmental movement began to question the sustainability of the polyethylene plastic bag. This is the ubiquitous bag found in grocery stores around the world; small, crinkly and actually recyclable. The big problem with polyethylene bags is that very few people go to the trouble of recycling them. In the U.S., about 1 percent of the 100 billion polyethylene bags used each year get recycled [source: CSM]. Across the globe, they land on beaches, get trapped on shrubs and provide a general hazard for wildlife. What's more, when left to degrade in the sunlight, polyethylene bags take around 1,000 years to fully break down [source: American Green Bag]. When they wind up in landfills, they may not ever break down because sunlight is usually absent in the middle of a pile filled with several tons of trash.


To curb the growing problem of polyethylene bag accumulation, some cities and countries have made it expensive to use them. In 2008, San Francisco passed a law banning plastic shopping bags at its grocery stores and pharmacies. The city followed nations like India, South Africa and Rwanda in its ban. It's not just grocery bags that pose a problem, however. Plastic bags of all stripes are environmentally unsound.

In addition to taking a millennium to degrade, plastic uses petroleum as a key ingredient. The same crude oil that eventually fuels cars as gasoline is also used to produce plastic. Since oil is a non-renewable substance, plastic bags aren't a sustainable product. As we get closer (or have already passed) peak oil -- the tipping point at which our supplies begin to decline -- petroleum is poised to become more valuable as an energy source to help get humanity past its oil addiction. In other words, we're going to need that oil to power the globe in the next few years a lot more than we'll need it to make plastic bags.

Because of the environmentally unfriendly and unsustainable nature of plastic, some manufacturers are looking to better sources of raw materials for plastic production. At least one company has figured out a way to make a plastic that's not only sustainable, it can even be tossed in a compost bin. The secret, it turns out, lies in corn. It's quite appropriate, since one of the company's biggest new clients is a corn chip maker.


Create a Green Plastic Bag, Save the Planet

Since it's an organic material, PLA can be composted.
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It seems like a pretty simple proposition: Create a biodegradable plastic bag, help save the planet. The problem is that it's trickier than it sounds. Major companies depend on plastics to keep their products from being crushed during transport, to keep food fresh and to create a generally durable product. As far as the uses for plastic goes, the petroleum-based plastic we've come to depend on since the early 20th century is tough to beat.

However, the popularity and dependability of plastic has done little to thwart the efforts of some plastic manufacturers looking for a way to make a durable product that's also sustainable. The company leading the charge is Natureworks, a Minnesota-based company that manufactures plastics made from a biopolymer called polylactic acid (PLA) that's derived from corn. This corn-based plastic -- called Ingeo -- uses starches from corn that break down much more easily than petroleum-based plastics. The degradation process is organic enough that products made from PLA can be composted with other organic materials like leaves and grass clippings.


To produce PLA, starch is extruded from corn meal, which results in a simple starch called dextrose. Dextrose is a type of glucose, which is a simple sugar that plants produce during photosynthesis. With the active ingredient in corn starch isolated, the dextrose is put through a fermentation process similar to the one used to make beer. Instead of alcohol, however, the dextrose is converted into lactic acid -- the same stuff that makes your muscles cramp when you exercise without proper hydration. Heat is applied to the lactic acid polymers, causing them to link together and form a long chain that ultimately becomes the material used to make many corn plastic products.

What sets corn plastic apart from petroleum-based plastic is that the process used to make it can also be reversed when the plastic finds its way into a compost heap. Fungi and bacteria found in soil get to work breaking down PLA into its basic parts. Under the proper aerobic (oxygen-rich) conditions, with heat and moisture, PLA will compost like any other organic material. The microorganisms found in compost consume the corn plastic and break it down into humus, a nutrient-packed, soil-like substance that acts as natural plant food. The waste products are carbon dioxide and water.

Some types of corn plastic are easier to break down than others. When corn chip maker SunChips signed on to roll out all PLA bags made with Ingeo biopolymers, the company tested the compostability of the bags it will introduce in 2010. They found that in optimal compost conditions -- like those found in a professionally-maintained commercial or municipal compost heap -- the SunChips bags made from PLA did indeed break down into humus. Even better, the bags composted in a home compost pile that was properly maintained, with moisture, air and steady heat of at least 131 degrees Fahrenheit (55 degrees Celsius). The process took between 12 to 16 weeks [source: Sun Chip].

If you're eating SunChips in 2010, think twice before tossing the empty bag in the garbage. By then, you should be able to compost it. Hopefully, other companies will soon follow.


Lots More Information

Related HowStuffWorks Articles
More Great Links

  • American Green Bag. "Is the polypropylene bag green?" January 13, 2009.
  • Arnoldy, Ben. "Seldom recycled, plastic grocery bags face bans in S.F." Christian Science
  • Learn, Brian. "Corn plastic sounds great, but it's tough to recycle and may foul systems." The Hutchison Encyclopedia. "Dextrose." Accessed April 20, 2009.
  • Oregonian. October 27, 2008.
  • Pilloton, Emily. "San Francisco bands plastic bags." Inhabitat. June 23, 2007.
  • Platt, David K. "Biodegradable polymers: market report." iSmithers Rapra. 2006.
  • NatureWorks. "NatureWorks PLA polymer 2002D." Accessed April 21, 2009.
  • SunChips. "Behind the scenes - compost conditions for SunChips PLA film." Accessed April 21, 2009.