Bioplastics could put some shrimp in your Barbie
PITTSBURGH, Pa. — Chemists have been working on ways to “green” our environment by creating materials that will break down, not persist as long-lived trash. Two teens have now unveiled their own innovative contributions. They made plastics from ingredients that are themselves wastes (not the fossil-fuel-based hydrocarbons used for most plastics).
Plastics have long been considered wonder materials. They weigh little, are relatively cost and have a broad range of potential uses. Many also last almost forever. That last trait is both a blessing and a curse.
In many places, plastics litter the environment. Many roadways and city streets are strewn with bags and other types of plastic debris. Large zones of the open seas are aswirl with tiny bits of plastic. Landfills are growing fat with discarded plastics. Bits of plastic even show up in the deepest, most remote spots in the ocean — and in the guts of fish.
To help limit this waste buildup, researchers have been exploring ways to make plastics biodegrade. These strategies rely on microbes in the environment to help digest wastes — break them down — into simpler materials. One key to succeeding, researchers suggest, might be to make the plastics from something other than petroleum products.
Angelina Arora, 15, is an 11th grader at Sydney Girls High School in Sydney, Australia. Mohammad Arafa and Jassin Zaki, both 18, are 12th graders at 6 of October STEM Egypt School in Giza, Egypt. All three rose to the challenge of designing green plastics that will naturally break down in the environment.
The three also described their new bioplastics here, three weeks ago, at the Intel International Science and Engineering Fair (ISEF). They were among almost 1,800 finalists from 81 nations, regions and territories. The winners collectively took home about $5 million is prizes and scholarships.
About one in every three finalists took home some sort of award. Angelina was part of that group. For her project, she earned a fourth-place award in environmental engineering. It came from the Intel Foundation and was valued at $500. Angelina also snagged a scholarship from Arizona State University.
Society for Science & the Public created ISEF in 1950 and has been running the event since then. (The Society also runs Science News for Students and this blog.) Intel sponsored this year’s competition.
Plastics from the sea
Shrimp are tasty, which is why people eat millions of tons of them each year. What people can’t eat, however, are the animals’ tough shells. They are chock full of a material called chitin (KY-tin). It develops when chemical reactions inside certain cells take molecules of glucose, a simple sugar, and attach other molecules to them — then string the resulting units into a long molecule. It’s known as a polymer. The flexible but resilient polymer forms the shrimp’s external support system (similar to those on insects). It’s known as an exoskeleton.
Usually, shrimp shells go to waste, Angelina notes. But she’s come up with a way to use them in a plastic. First, she grinds the shells into a powder. Then she soaks the powder in acid. This removes some of the minerals that were in the shells. Now she soaks what’s left in an alkaline bath to remove other minerals. The only thing left after that step is pretty much pure chitin, she says.
Angelina’s plastic also contains a substance called fibroin. It’s a protein in the silk created by spiders. It’s also a big fraction of the silk in the cocoons spun by the larvae of certain insects. For her project, the teen got her fibroin from low-quality silkworm cocoons. Typically, only the best cocoons are used for the silk used to make fabric, she says. The rest, like shrimp shells, often are trashed as a waste.
For her plastic, Angelina simply blended the chitin and fibroin. Then, she pressed the mix into thin sheets and let them dry.
The results were impressive. Sheets of her bioplastic were more than 90 percent as strong as low-density polyethylene (LDPE). That’s the plastic used to make many grocery-store shopping bags, among other things. Slightly increasing the thickness of her polymer should yield bags just as strong as those used now, she says.
But unlike those made from LDPE, bags made from Angelina’s plastic should not generate large amounts of long-lived trash. In fact, her tests show that her bioplastic dissolves in sea water more than a million times faster than LDPE does. So, any bags that ended up in the ocean shouldn’t stick around forever to be eaten by marine creatures. Instead, they’d dissolve in about five weeks.
Plastics from a tree
Most plastics are made from chemicals derived from petroleum. Few microbes eat such plastics, notes Mohammad. So, these plastics don’t tend to break down in the environment. What’s more, he notes, there is very little recycling of plastics in Egypt, where he lives. To keep plastics from taking up precious space in landfills, he and Jassin, a classmate, came up with the idea for a biodegradable material made from plants.
The teens started with banana peels. They’re full of starch, a natural polymer, Mohammad notes. They added in a slick, sweet liquid called glycerol (GLIH-sur-awl). It’s a plasticizer, a chemical that makes materials soft and pliable. Their goal was to make a plastic that would last at least two months. So the students also mixed in a preservative to keep the plastic from decomposing too quickly. (This chemical is called sodium metabisulfite.)
Mohammad and Jassin tested several recipes. Then they compared their strength and flexibility to that of containers made with a type of plastic commonly used for bottled water or milk. Their best results came when their plastic included less than 8 percent glycerol.
Unfortunately, their best-performing plastic was still only three-quarters as strong as the plastic used by businesses today. For a container to be just as strong as those used now, it might need to be up to twice as thick. Adding a little clay might also strengthen their plastic, Mohammad and Jassin say.
Overall, the teens believe their new bioplastic shows promise. When buried in soil, the bottles they made broke down in less than 5 months. But sitting on a shelf, the bottles were able to hold their shape and strength for at least two months before they started to break down. And even if there’s a bit of clay in the recipe, it wouldn’t harm the environment when the plastic eventually decomposes.
Overall, bioplastics offer hope for greening the environment, these young scientists report.
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alkaline An adjective that describes a chemical that produces hydroxide ions (OH-) in a solution. These solutions are also referred to as basic — as in the opposite of acidic — and have a pH above 7.
biodegrade To break down, based on the activity of microbes, into simpler materials. This usually occurs in the presence of water, sunlight or other conditions that help nurture those organisms.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemical reaction A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).
chitin A tough, semi-transparent substance that is the main component of the exoskeletons of arthropods (such as insects). A carbohydrate, chitin also is found in the cell walls of some fungi and algae.
clay Fine-grained particles of soil that stick together and can be molded when wet. When fired under intense heat, clay can become hard and brittle. That’s why it’s used to fashion pottery and bricks.
debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
density The measure of how condensed some object is, found by dividing its mass by its volume.
develop To emerge or come into being, either naturally or through human intervention, such as by manufacturing. (in biology) To grow as an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.
digest (noun: digestion) To break down food into simple compounds that the body can absorb and use for growth. Some sewage-treatment plants harness microbes to digest — or degrade — wastes so that the breakdown products can be recycled for use elsewhere in the environment.
dissolve To turn a solid into a liquid and disperse it into that starting liquid. (For instance, sugar or salt crystals, which are solids, will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.)
engineering The field of research that uses math and science to solve practical problems.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
exoskeleton A hard, protective outer body covering of many animals that lack a true skeleton, such as an insect, crustacean or mollusk. The exoskeletons of insects and crustaceans are largely made of chitin.
fibroin A natural, insoluble protein. It is present in spider silk and the silky cocoons of silkworms.
glucose A simple sugar that is an important energy source in living organisms. As an energy source moving through the bloodstream, it is known as “blood sugar.” It is half of the molecule that makes up table sugar (also known as sucrose).
glycerol A colorless, odorless, sticky syrup that can be used as an antifreezing agent.
green (in chemistry and environmental science) An adjective to describe products and processes that will pose little or no harm to living things or the environment.
high school A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.
hydrocarbon Any of a range of large molecules containing chemically bound carbon and hydrogen atoms. Crude oil, for example, is a naturally occurring mix of many hydrocarbons.
Intel International Science and Engineering Fair (Intel ISEF) Initially launched in 1950, this competition is one of three created (and still run) by the Society for Science & the Public. Each year now, approximately 1,800 high school students from more than 80 countries, regions, and territories are awarded the opportunity to showcase their independent research at Intel ISEF and compete for an average of almost $5 million in prizes.
landfill A site where trash is dumped and then covered with dirt to reduce smells. If they are not lined with impermeable materials, rains washing through these waste sites can leach out toxic materials and carry them downstream or into groundwater. Because trash in these facilities is covered by dirt, the wastes do not get ready access to sunlight and microbes to aid in their breakdown. As a result, even newspaper sent to a landfill may resist breakdown for many decades.
larva (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)
marine Having to do with the ocean world or environment.
microbe Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
mineral Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns). (in physiology) The same chemicals that are needed by the body to make and feed tissues to maintain health.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
petroleum A thick flammable liquid mixture of hydrocarbons. Petroleum is a fossil fuel mainly found beneath the Earth’s surface. It is the source of the chemicals used to make gasoline, lubricating oils, plastics and many other products.
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
plasticizer Any of several chemicals added to certain synthetic materials to make them soft and/or pliable.
polyethylene A plastic made from chemicals that have been refined (produced from) crude oil and/or natural gas. The most common plastic in the world, it is flexible and tough. It also can resist radiation.
polymer A substance made from long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).
protein A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.
range The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
silk A fine, strong, soft fiber spun by a range of animals, such as silkworms and many other caterpillars, weaver ants, caddis flies and spiders.
society An integrated group of people or animals that generally cooperate and support one another for the greater good of them all.
starch A soft white chemical made by all green plants. It’s a relatively long molecule made from linking together a lot of smaller, identical building blocks — all of them glucose, a simple sugar. Plants and animals use glucose as an energy source. Plants store that glucose, in the form of starch, as a reserve supply of energy. Animals that consume starch can break down the starch into glucose molecules to extract the useful energy.
trait A characteristic feature of something.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.