What makes plastic strong

At first glance the problem simply appears to be one of an aesthetic nature. Because as ugly and dirty yet colorful heaps of plastic may be, plastic itself is non-toxic. The graver aspects of our plastic world only become apparent upon closer inspection — aquatic species that perish in nooses made of plastic waste or fish that ingest the tiniest plastic fragments, which could then be fed back into the human food chain. Evidence suggests, for example, that plastic softening agents could have a harmful long-term effect on fertility.

And the impact of plastic refuse on an organism when it decays into tiny particles has yet to be established. Whereas microorganisms, such as bacteria and fungi, are sometimes used to break down toxic substances in the environment, such as petroleum, plastic refuse has yet to be successfully disposed of. All decay-inducing organisms reach their limits with plastic; otherwise the material would not be so durable.

This is easily explained from a chemical perspective. All plastic materials are polymers, chemically-speaking. Polymers consist of very long chains of molecular units which in turn consist of carbon as the defining element. This is almost always combined with hydrogen.

Other elements include nitrogen and oxygen and in exceptional cases also fluorine and chlorine. The long molecular chains ensure the polymers are strong and durable and do not decompose in water. Polymers can also be extremely flexible and pliable, a valuable property not provided by mineral materials, such as clay and limestone, and only to a limited extent by metals. Polymers are not a human invention.

Wherever robustness and shape retention but also toughness and flexibility are found in living organisms, this is down to natural polymers. Cellulose, a fibrous material made of sugar components, provides plants with their stability.

Collagens and keratin are highly stable proteins — in other words, chains of amino acids — that give the skin or hair and bird feathers their stability. However, neither cellulose nor keratin last forever.

Outside of the living organism or after its death, these polymers are slowly decomposed by bacteria and fungi, i. A principle known as microbial infallibility becomes evident during this natural recycling process. For every substance formed by living organisms, there is at least one type of microorganism in nature which can break it down. However, plastics are not broken down in nature. Their chemical structure is foreign to nature and the principle of microbial infallibility does not apply here.

Several synthetic chemicals, such as detergents from washing-up liquid or insecticides, can clearly be broken down by microorganisms albeit slowly. So far there has been no indication of such degrading enzymes working on plastics. The enormous length of the chains probably presents a problem. Larry Greenemeier is the associate editor of technology for Scientific American , covering a variety of tech-related topics, including biotech, computers, military tech, nanotech and robots. Already a subscriber?

Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. M's College of Engineering who assisted with the research. Get smart. Sign up for our email newsletter. Sign Up. Support science journalism. Not much of a life, actually…. Read More: When was plastic invented? If the monomers join together lined up like a chain picture a string of pearls , the polymer is called a thermoplastic.

This plastic behaves sort of like an ice cube: it melts when heated and solidifies when cooled … like water, over and over again. Polypropylene the stuff butter tubs often are made of is an example of a thermoplastic. If the monomers connect in a three-dimensional network, the polymer is called a thermoset. An epoxy from the hardware store that hardens and cures when applied is an example of a thermoset. Because thermosets are a three dimensional network of monomers, they can be very tough.

For example, your car tires are made with thermoset plastics often called synthetic rubber. Thermoplastics are tough, too, but they often are used in less intense settings, such as lightweight bottles for soft drinks that are not subject to massive heat and friction like tires. Read More: Polyethylene density. Chemists along with other smart people over time have come up with many ways to combine ingredients to make new polymers … and even to combine polymers.