Plastics. They're durable, flexible and long-lasting. They're also everywhere.
What's not to love about these ubiquitous polymers? They're made from carbon and other materials then heated, broken down and rebuilt as plastic resin that can be molded into almost any shape desired.
That carbon, though, typically comes from oil, a fossil fuel-product that's not so good for the environment. In addition, many types of plastics aren't biodegradable. And although some plastics can be recycled, most aren't (either because they can't be or because people don't). For example, only around one-quarter of 1 percent of the more than 7 billion pounds (3.2 billion kilograms) of discarded polyvinyl chloride (PVC) is recycled each year in the U.S., and PVC is one of the world's most common plastics [source: Clean Air Council].
Yet plastics are so ingrained in our everyday lives that it's hard to imagine life without them. More eco-friendly alternatives are out there though. Ready to meet 10 of them?
Once upon a time, both moms and milkmen filled glass bottles with milk. Now look around your kitchen and you'll probably see many plastics -- water bottles, soda bottles, food storage containers. Times have changed.
Sometimes going back in time is a good thing. Unlike plastic, which often is derived from fossil fuels, glass is made from sand. This renewable resource doesn't contain chemicals that can leach into your food or body. And it's easily recycled -- whether you throw bottles in your recycling bin to be turned into new bottles or reuse glass jars for storing leftovers. Sure, glass may break if dropped, but it won't melt in your microwave.
When plastic bags first hit the scene, we had a choice: paper or plastic. Today, finding a grocery store that offers an alternative to the plastic bag is like finding a hamburger in a vegetarian's fridge. And if you're not that hypervigilant person at the checkout, you'll find yourself walking home with a bag for each item.
In fact, in countries like the United States, it's tough to make a purchase without it promptly being thrown into plastic. No wonder plastic bags seem omnipresent. About 1 billion of them pass through the U.S. every year, less than 1 percent of which are recycled [source: Clean Air Council]. What doesn't end up as 300,000 tons (272,155 metric tons) of U.S. landfill waste litters cities and towns-- and too many end up in the ocean [source: Clean Air Council]. They kill millions of sea turtles, birds and ocean mammals each year [source: Environment California]. But you have to lug those groceries home somehow. So what do you do? Reusable grocery bags, for starters.
You can get them festooned with patterns or printed with the name or your bank/gym/frozen yogurt shop. Everyone hands them out, and they come in canvas, woven plastic fiber, hemp, cotton and even leather. You'll find nylon ones that fold up into a pouch small enough to fit in your pocket. In reality, any type of bag will do, whether it's meant to carry groceries or not.
Bonus: By avoiding plastic bags, you won't have them accumulating in your cupboards, and you don't have to worry about where they go when you throw them out.
While some people are busy developing plastic substitutes, others are bent on making conventional thermoplastics biodegradable. How? By throwing in additives called prodegradant concentrates (PDCs). PDCs are usually metal compounds, such as cobalt stearate or manganese stearate. They promote oxidation processes that break the plastic down into brittle, low-molecular-weight fragments. Microorganisms gobble up the fragments as they disintegrate, turning them into carbon dioxide, water and biomass, which reportedly contains no harmful residues.
Search around for additive technologies and you'll come across the trade names TDPA (an acronym for Totally Degradable Plastic Additives) or MasterBatch Pellets (MBP). They're used to manufacture single-use plastics such as thin plastic shopping bags, disposable diapers, trash bags, landfill covers and food containers (including fast-food containers).
When added to polyethylene (the standard plastic bag material) at levels of 3 percent, PDCs can promote nearly complete degradation; 95 percent of the plastic is in bacteria-friendly fragments within four weeks [source: Nolan-ITU Pty]. While not strictly biodegradable ('bioerodable' is more like it), PDC-containing polymers are more environmentally friendly than their purer polymer cousins, which sit in landfills for hundreds of years.
All newborn mammals survive on it. Without it, there would be no ice cream. There's really no denying the value, or pleasure, of milk.
Now scientists say it could help to produce a biodegradable plastic for furniture cushions, insulation, packaging and other products. Yep, researchers are revitalizing the idea of converting casein, the principal protein found in milk, into a biodegradable material that matches the stiffness and compressibility of polystyrene.
Casein-based plastic has been around since the 1880s, when a French chemist treated casein with formaldehyde to produce a material that could substitute for ivory or tortoiseshell. But although it's ideal for jewelry that even Queen Mary admired, casein-based plastic is too brittle for much more than adornment.
Scientists have found a way make the protein less susceptible to cracking, thanks to a silicate clay called sodium montmorillonite. Freezing sodium montmorillonite into a spongelike material called an aerogel, they infused the porous network of clay with casein plastic. The result? A polystyrene-type material that, when put in a dump environment, begins to degrade completely [source: The Economist]. The modern milk-based plastic doesn't crack as easily, thanks to that silicate skeleton, and they even made the stuff less toxic by substituting glyceraldehyde for formaldehyde during the process.
The future of casein plastic isn't certain, but swapping it for petroleum-based polystyrene would certainly give us another reason to love milk.
What could be more appealing than a technology that takes waste out of landfills and transforms it into a biodegradable plastic? Disposing of chicken feathers is a problem in and of its own --more than 3 billion pounds (1.4 billion kilograms) of them have to be dealt with annually in the United States [source: ScienceDaily]. Thanks to innovation, they soon may be a resource to make a new water-resistant thermoplastic.
Chicken feathers are composed almost entirely of keratin, a protein so tough that it can give strength and durability to plastics. It's found in hair and wool, hooves and horns -- and we can all appreciate how strong a horse's hoof can be without having the pleasure of being kicked by one.
Researchers decided to tap into keratin's superstrong features by processing chicken feathers with methyl acrylate, a liquid found in nail polish. Ultimately, the keratin-based plastic proved to be substantially stronger and more resistant to tearing than other plastics made from agricultural sources, such as soy or starch, and scientists are clucking excitedly about chicken-feather plastic. After all, inexpensive, abundant chicken feathers are a renewable resource. Although not formally tested as of February 2012, chicken-feather plastic is expected to be fully biodegradable.
Next up is a promising new bioplastic, or biopolymer, called liquid wood. Biopolymers fake it; these materials look, feel and act just like plastic but, unlike petroleum-based plastic, they're biodegradable. This particular biopolymer comes from pulp-based lignin, a renewable resource.
Manufacturers mix lignin, a byproduct of paper mills, with water, and then expose the mixture to serious heat and pressure to create a moldable composite material that's strong and nontoxic. German researchers have incorporated this plastic substitute into a variety of items including toys, golf tees and even hi-fi speaker boxes.
Because it's made of wood, it can be recycled as wood, too.
The next three entries on this list are all biodegradable plastics called aliphatic polyesters. Overall, they aren't as versatile as aromatic polyesters such as polyethylene terephthalate (PET), which is commonly used to make water bottles. But since aromatic polyesters are completely resistant to microbial breakdown, a lot of time and effort is being pumped into finding viable alternatives in aliphatic polyesters.
Take polycaprolactone (PCL), a synthetic aliphatic polyester that isn't made from renewable resources but does completely degrade after six weeks of composting. It's easily processed but hasn't been used in significant quantities because of manufacturing costs. However, blending PCL with cornstarch reduces cost.
Biomedical devices and sutures are already made of the slow-degrading polymer, and tissue-engineering researchers dig it, too. It also has applications for food-contact products, such as trays.
"Naturally produced polyesters" may sound like a phrase lifted from a marketing campaign, but feed sugar to certain types of bacteria and you've got yourself a plastic production line.
That's the case with polyhydroxyalkanoate (PHA) polyesters, the two main members of which are polyhydroxybutrate (PHB) and polyhydroxyvalerate (PHV). These biodegradable plastics closely resemble man-made polypropylene. While they're still less flexible than petroleum-based plastics, you'll find them in packaging, plastic films and injection-molded bottles.
Production costs have mostly put PHA in the shadow of cheaper, petroleum-based plastics, but a little creativeness in sourcing inexpensive raw materials may make it a top choice soon. Corn-steeped liquor, molasses and even activated sludge could all supply the sugar the bacteria need to produce the plastic.
PHAs biodegrade via composting; a PHB/PHV composite (92 parts PHB/8 parts PHV, by weight) will almost completely break down within 20 days of cultivation by anaerobic digested sludge, the workhorse of biological treatment plants [source: Nolan-ITU Pty Ltd].
Producing plastic from processed corn may seem like a pipe dream, but it's happening every day. Polylactic acid, or PLA, is another aliphatic polyester and one that can be made from lactic acid, which is produced via starch fermentation during corn wet milling. Although most often generated from corn, PLA can be made from wheat or sugarcane as well.
PLA boasts the rigidity to replace polystyrene and PET, but it has an edge over the real thing: It decomposes within 47 days in an industrial composting site, won't emit toxic fumes when burned and manufacturing them uses 20 to 50 percent less fossil fuels than petroleum-based plastic [source: Nakazawa]. Often, companies blend PLA with starch to reduce cost and increase its biodegradability.
Consumers may encounter PLA in bottles, bags and film, but it's only beginning to live up to its potential. In fact, if Walmart used 114 million PLA containers a year, company executives estimate they could save 800,000 barrels of oil annually [source: Royte]. If that isn't enough, scientists are trying to make PLA stronger and more heat-resistant. This should open up new applications for the popular green plastic, from automotive parts to coffee cups.
As a totally biodegradable, low-cost, renewable and natural polymer, starch has been receiving lots of attention for developing sustainable materials lately. When it comes to replacing plastic, however, starch can't cut the mustard; its poor mechanical properties mean it has limited use for the sturdy products that plastics generate.
What one of the hottest trends in biodegradable plastic development can do is make polymer composites more biodegradable. You name it, and starch has probably been combined with it, albeit with varying degrees of success.
To make completely biodegradable starch-based plastics, the components usually blended with starch are aliphatic polyesters, such as PLA and PCL, and polyvinyl alcohol. Adding in starch also shaves plastic manufacturing costs. Starch needs to exceed 60 percent of the composite before it has a significant effect on degradation; as the starch content increases, the polymers become more biodegradable [source: Nolan-ITU Pty Ltd]. Keep in mind that adding more starch also affects the properties of the plastic. If you put wet leaves in a starch bag for a bit, you'll have a mess when you go to pick up the bag.
So, while there is no silver bullet for making plastics greener, a combination of revitalizing old ideas and revolutionizing plastic technology is a step in the right direction.
Drones and other unmanned flying machines are going green. Learn about eco-drones at HowStuffWorks.
More Great Links
- Clean Air Council. "Waste and Recycling Facts." (Feb. 17, 2012) http://www.cleanair.org/Waste/wasteFacts.html
- The Economist. "There and back again. An old idea may help solve the problem of plastic waste". Oct. 28, 2010. (Feb. 15, 2012) http://www.economist.com/node/17358583
- EMC Biofilms Web site. (Feb. 17, 2012) http://www.ecmbiofilms.com/our-product.html
- Environment California. "Keep Plastic out of the Pacific." (Feb. 17, 2012) http://www.environmentcalifornia.org/programs/keep-plastic-out-pacific
- EPI Web site. (Feb. 17, 2012) http://www.epi-global.com/en/epi-technology.php
- Nakazawa, Liz. "A new corn-based plastic disappears into the dirt." The Christian Science Monitor. 2003.(Feb. 17, 2012) http://www.csmonitor.com/2003/0904/p12s02-sten.html
- Nolan-ITU Pty Ltd. "Biodegradable Plastics- Developments and Environmental Impacts." Department of the Environment, Water, Heritage and the Arts, Australian Government. ( Feb. 17, 2012) http://www.environment.gov.au/archive/settlements/publications/waste/degradables/biodegradable/chapter3.html#3-3
- Nolan-ITU Pty Ltd. "Biodegradable Plastics- Developments and Environmental Impacts." Department of the Environment, Water, Heritage and the Arts, Australian Government. (Feb. 17, 2012) http://www.environment.gov.au/archive/settlements/publications/waste/degradables/biodegradable/chapter4.html
- Nolan-ITU Pty Ltd. "Biodegradable Plastics- Developments and Environmental Impacts." Department of the Environment, Water, Heritage and the Arts, Australian Government. (Feb. 17, 2012) http://www.environment.gov.au/archive/settlements/publications/waste/degradables/biodegradable/chapter2.html
- Packaging Knowledge. "Degradable & Biodegradable Plastic Bags." (Feb. 17, 2012) http://www.packagingknowledge.com/degradable_biodegradable_bags.asp
- Royte, Elizabeth. "Corn Plastic to the Rescue." Smithsonian Magazine. 2008. (Feb. 17, 2012) http://www.smithsonianmag.com/science-nature/plastic.html
- ScienceDaily. "Advance Toward Making Biodegradable Plastics from Waste Chicken Feathers." March 31, 2011. (Feb. 15, 2012) http://www.sciencedaily.com/releases/2011/03/110331142204.htm
- ScienceDaily. "Sweet and Biodegradable: Sugar and Cornstarch Make Environmentally Safer Plastics." Dec. 14, 2010. (Feb. 14, 2012) http://www.sciencedaily.com/releases/2010/12/101214111919.htm
- The South African Plastics Recycling Organization. "The plastics recycling industry and biodegradable films." May 2008. (Feb. 29, 2012) http://www.scribd.com/doc/62303281/SAPRO-Report-14
- Woodruff, Maria A. and Hutmacher, Dietmar W. "The return of a forgotten polymer: Polycaprolactone in the 21st century." Progress in Polymer Science. 2010. (Feb. 29, 2012) http://eprints.qut.edu.au/32270/1/c32270.pdf