From trees to tires, from lunch to grocery bags, from breakfast cereal to school clothes: Polymers play an essential role in the human and natural world. As people become more environmentally aware, many are looking for ways to replace artificially created items with more sustainable substitutes. Polymers are no exception.
TL;DR (Too Long; Didn't Read)
TL;DR (Too Long; Didn't Read)
Examples of natural polymers include cellulose, chiton, carbohydrates like starches and sugars, proteins ranging from skin and muscle to spider silk and wool, DNA, RNA and natural rubber.
What are Polymers?
Polymers are long molecules made from monomers. "Poly" means many, and "mono" means one or single. "Mers" means parts. Polymers therefore means many parts, and polymers are made of many monomers or single parts. Different polymers form from different monomers. Also, when the arrangement of monomers changes, a different polymer may form.
Connecting the Monomers
Monomers connect in two different ways. In the first, the monomers connect directly, like building blocks linked together. These are called addition polymers. Many synthetic monomers form addition polymers. In the second kind of connection, the monomers release a water molecule when they link together. These are called condensation polymers. Most natural polymers are condensation polymers, so water is a natural byproduct of the linking monomers.
Natural polymers abound. Proteins, starches, carbohydrates, even DNA are natural polymers. A hamburger consists mostly of polymers. The cardboard container the hamburger came in and the napkin used to wipe up any ketchup spills are also made of polymers. Understanding natural polymers' structure, characteristics and uses can help people make environmentally conscious and informed choices. Some important natural polymers include the following examples.
The most common natural polymer is cellulose. Cellulose comes from trees and plants. Cellulose consists of long, stretched out strands of glucose, the sugar that plants make during photosynthesis. These stretched out cellulose polymers form very strong supports for the plant, which is why trees can stand as tall as they do. These stretched out cellulose polymers also form the fibers in cotton and hemp, which can be used to make clothes. Cellulose fibers also make paper products. Because of how the monomers fit together, cellulose doesn't dissolve in water, making cellulose a very useful natural polymer.
Chiton is the second most common natural polymer on Earth. Chiton is found in the cell walls of fungi, including mushrooms, and the exoskeletons of insects, spiders and crustaceans like crabs and lobsters. Chiton's chemical structure only differs from cellulose by a single molecule in the glucose monomer. When refined, chiton is used to make edible plastic food wrap, as a thickener for foods and to help clean up industrial waste water.
Carbohydrates, another group of polymers, form from glucose, just like cellulose. Sugar and starches, both forms of carbohydrates, serve as food for plants and animals. The glucose monomers connect differently in carbohydrates than in cellulose, though, bunching up instead of stretching out. This bunching up of the polymer chain means that the carbohydrates take up less room, letting plants store their food in fruits and vegetables like potatoes and carrots. One result of how these monomers connect is that carbohydrates dissolve in water. People can digest carbohydrates but not cellulose because carbohydrates dissolve in water but cellulose doesn't. Also, people lack the enzyme that will break the cellulose polymer.
The millions of different kinds of protein polymers are all made from amino acid monomers. Although there are only 20 different kinds of amino acids, the many different combinations and arrangements result in a great variety of proteins. Some different types of protein polymers include skin, body organs, muscles, hair, fingernails, feathers, hooves and fur. A wide range of animal fibers, from wool to silk, come from protein polymers. Spider silk, one of the strongest fibers known, is a protein polymer. Leather, made from animal skin, results from protein polymers.
DNA and RNA
Two nucleic acid polymers, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), form from monomer nucleotides. DNA contains the genetic code for an organism and RNA carries the genetic information from the DNA to the cytoplasm where proteins are then made. Like most natural polymers, nucleic acid polymers are condensation polymers.
Natural rubber comes from the latex (a special type of sap) of rubber trees. While most natural polymers are condensation polymers, natural rubber is an addition polymer formed from isoprene monomers. Natural rubber bounces and stretches because of the monomer connections. The monomers of a similar natural polymer called gutta-percha connect differently, resulting in a brittle rather than flexible material.
Synthetic or Artificial Polymers
Advantages of synthetic or artificial polymers include stability and consistency of the product. Synthetic rubber, for example, doesn't rot like natural rubber will. Synthetic rubber can also be customized for different purposes. Synthetic polymer examples include nylon, epoxies, polyethylene, Plexiglas, Styrofoam, Kevlar® and Teflon®. From plastic containers to furniture to clothes to spray foam polymers, synthetic polymers permeate modern life.
Unfortunately, however, the stability of synthetic polymers means that these polymers don't break down naturally, creating disposal problems and adding to worldwide pollution. Burning at high temperature does destroy synthetic polymers, but also releases carbon dioxide and other (often toxic) chemicals into the atmosphere. In addition, most artificial polymers are made from petroleum, a non-renewable fossil fuel.
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