This area provides the history and background of plastics – when and why they were invented and the types of applications that they are used in today. It also contains information about resin identification codes.
When Alexander Parkes developed the first man-made plastic in the 1860s, he had no idea of the role that it would come to play in our everyday lives. Over the years, plastics have led to many advances in cutting-edge technologies. Just think about how plastics have contributed to the international space program, to consumer electronics and to medical applications like heart valves, incubators and even IV tubes. Plastics have also had a role to play in the more everyday applications, like consumer packaging, transportation and sports equipment.
All of these great materials, collectively known as plastic, owe their start to Alexander Parkes. He was the individual who introduced “plastic” at the 1862 Great International Exhibition in London. This material, which was dubbed “Parksine” was an organic material derived from cellulose that could be moulded when heated and then made to retain its shape when cooled. Parkes claimed that the new material could do anything that rubber was capable of, but at a lower price. Parksine soon lost its luster, however, when investors pulled the plug on the product due to the high cost of the raw materials needed for its production.
Now skip forward to the latter part of the 19th century. The game of billiards was on the rise and elephants everywhere were being killed for their ivory tusks. In 1866, American John Wesley Hyatt came up with a solution when he accidentally spilt a bottle of collodion in his workshop and discovered that the material congealed into a tough, flexible film. Unfortunately, when the billiard balls were made from this material, they shattered upon impact. But a solution was soon found via the addition of camphor. This made celluloid the very first thermoplastic: a substance that could be moulded under heat and made to retain that shape even after the heat and pressure of the mould have been removed. Celluloid went on to be used in the first flexible photographic film and for still and motion pictures.
Rayon – another modified cellulose – was first developed in 1891 in Paris by Louis Marie Hilaire Bernigaut, the Count of Chardonnet. He was searching for a way to produce man-made silk. After studying silkworms, Chardonnet noticed that the worm used a narrow orifice to secrete a liquid that would harden upon exposure to air and turn into silk. He deduced that if he could find a liquid that would have similar characteristics to silk before being secreted, he could then pass it through a man-made apparatus to form fibres that could be spun and feel like silk. The only problem with his new invention was that it was highly flammable. This problem was later solved by Charles Topham.
Cellophane was discovered by Dr. Jacques Edwin Brandenberger, a Swiss textile engineer, who came upon the idea for a clear, protective, packaging layer in 1900. Brandenberger was seated at a restaurant when he noticed a customer spill a bottle of wine onto the tablecloth. The waiter removed the cloth replacing it with another and disposed of the soiled one. Brandenberger swore that he would discover some way to apply a clear flexible film to cloth, which would keep it safe from such accidents and allow it to be easily cleaned with the swipe of a clean towel. He worked on resolving this problem by using different materials until he hit pay dirt in 1913 by adding Viscose (now known as Rayon).
Brandenberger added viscose to cloth but the end result was a brittle material that was too stiff to be of any use. But he saw another potential for the viscose material. Brandenberger developed a new machine that could produce viscose sheets, which he marketed as Cellophane. With a few more improvements, Cellophane allowed for a clear layer of packaging for any product – the first fully flexible, water-proof wrap.
The first completely synthetic man-made substance was discovered in 1907, when a New York chemist – Leo Baekeland – created a liquid resin which he named Bakelite. Baekeland had developed an apparatus – that he called a Bakelizer – which enabled him to vary heat and pressure precisely so as to control the reaction of volatile chemicals. Using this pot-like apparatus, Baekeland developed a new liquid (bakelite resin), which rapidly hardened and took the shape of its container. Once hardened, the resin would form an exact replica of any vessel that contained it. This new material would not burn, boil, melt, or dissolve in any commonly available acid or solvent. This meant that once it was firmly set, it would never change. This one benefit made it stand out from all previous "plastics" produced. Previously, celluloid-based substances could be melted down innumerable times and reformed. Bakelite was the first thermoset plastic which would retain its shape and form under any circumstances.
Bakelite could be added to almost any material – such as softwood – and instantly make it more durable and effective. Numerous products began to be manufactured based on this new material. One of the sectors of society most interested in its development was the military.
Bakelite was also used for domestic purposes such as an electrical insulator, and it proved to be more effective than any other material available. In fact, it proved so effective that it is still used as such today. Bakelite was electrically resistant, chemically stable, heat-resistant, shatter-proof and, would neither crack, fade, crease, nor discolour from exposure to sunlight, dampness or sea salt.
The 1920s witnessed a "plastics craze", as the use of cellophane spread throughout the world. One of the industry leaders – DuPont – became a hotbed for plastics innovation. Wallace Hume Carothers, a young Harvard chemist, became the head of the DuPont lab. The company was responsible for the moisture-proofing of Cellophane and was well on its way to developing Nylon, which at the time they named Fiber 66. Carothers saw the possible value that a new tough plastic, such as Fiber 66, could possess. The fibre replaced animal hair in toothbrushes and silk stockings. The stockings were unveiled in 1939, to great public acceptance. H. Staudinger, in Germany, was the first to recognize the structural nature of plastics, but Carothers built upon this theory. As demonstrated by Carothers, by substituting and inserting elements into the chemical chain, new materials and uses could be developed. During the 1940s, the world saw the use of such materials as nylon, acrylic, neoprene, SBR, polyethylene, and many more polymers take the place of natural material supplies.
Another important plastic innovation of the time was the development of polyvinyl chloride (PVC), or vinyl. Waldo Semon, a B.F. Goodrich organic chemist, was attempting to bind rubber to metal when he stumbled across PVC. Semon later discovered that this material was inexpensive, durable, fire-resistant, and easily moulded. Vinyl found a special place in the hearts of consumers as an upholstery material that would last for years in the average family's living room.
In 1933, Ralph Wiley, a Dow Chemical lab worker, accidentally discovered yet another plastic – polyvinylidene chloride (better known as Saran). Saran was first used to protect military equipment, but it was later discovered that it was perfect for food packaging. Saran would cling to almost any material – bowls, dishes, pots and even itself; thus, it became the perfect tool for maintaining the freshness of food at home.
A DuPont chemist named Roy Plunkett discovered Teflon, in 1938. Teflon today is widely used in kitchenware. Plunkett discovered the material accidentally by pumping freon gas into a cylinder left in cold storage overnight. The gas dissipated into a solid white powder. Teflon is unique because it is impervious to all acids in addition to both cold and heat. Teflon is now best-known for its slipperiness – which makes it highly effective in pots and pans for easy cooking and cleaning.
In 1933, two organic chemists working for the Imperial Chemical Industries Research Laboratory were testing various chemicals under highly pressurized conditions. In their wildest imaginations, the two researchers E.W. Fawcett and R.O. Gibson had no idea that the revolutionary substance they would come across – polyethylene – would have an enormous impact on the world.
The researchers set off a reaction between ethylene and benzaldehyde, using two thousand atmospheres of internal pressure. The experiment went askew when their testing container sprung a leak and all of the pressure escaped. Upon opening the tube they were surprised to find a white waxy substance that greatly resembled plastic. When the experiment was carefully repeated and analyzed, the scientists discovered that the loss of pressure was only partly due to a leak; the greater reason was the polymerization process that had occurred leaving behind polyethylene. In 1936, Imperial Chemical Industries developed a large-volume compressor that made the production of vast quantities of polyethylene possible. This high-volume production of polyethylene actually led to some history-making events.
For instance, polyethylene played a key supporting role during World War II – first as an underwater cable coating and then as a critical insulating material for such vital military applications as radar insulation. This is because it was so light and thin that it made placing radar onto airplanes possible; something that could not be done using traditional insulating materials because they weighed too much. In fact, the use of polyethylene as an insulating material reduced the weight of radars to little more than 270 kilograms in 1940 and even less as the war progressed. It was these lightweight radar systems, capable of being carried onboard planes, that allowed the out-numbered Allied aircraft to detect German bombers under such difficult conditions as nightfall and thunderstorms.
It was not until after the war, though, that the material became a tremendous hit with consumers and from that point on, its rise in popularity has been almost unprecedented. It became the first plastic in the United States to sell more than a billion pounds a year and it is currently the largest volume plastic in the world. Today, polyethylene is used to make such common items as soda bottles, milk jugs and grocery and dry-cleaning bags in addition to plastic food storage containers.
A plastic that has struck the fancy of many youngsters over the years is plastic putty – better known as silly putty. James Wright, a GE engineer, came upon the material by mixing silicone oil with boric acid. The compound possessed some rather unique qualities. It acted very much like rubber in its ability to rebound almost 25 per cent higher than a normal rubber ball. This "Nutty Putty" was also impervious to rot and unable to maintain a shape for more than a short period of time. It could be stretched many times its length without tearing. This material also would copy the image of any printed material that it was pressed upon. In 1949, the material was sold under the name of Silly Putty, selling faster – at that time – than any other toy in history with over $6 million in sales for the year.
The birth of Velcro, yet another unique plastic product that has impacted nearly all of our lives, occurred in 1957. A Swiss engineer named George de Maestral was impressed with the way that cockleburs – a type of vegetation – would use thousands of tiny hooks to cling to anything with which they came into contact. He devised a product, using nylon, that replicated this natural phenomenon. The result, Velcro, could be spun in any required thickness, would not rot, mould or naturally degrade – and it was relatively inexpensive.
Since the 1950s, plastics have grown into a major industry that affects all of our lives – from providing improved packaging to giving us new textiles, to permitting the production of wondrous new products and cutting-edge technologies in such things as televisions, cars and computers. Plastics even allow doctors to replace worn-out body parts, enabling people to live more productive and longer lives. In fact, since 1976, plastic has been the most used material in the world and was recently voted one of the top 100 news events of the century (listed 46th). None of the applications and innovations we take for granted would have been possible if it weren't for the early scientists who developed and refined the material. Those pioneers made it possible for us to enjoy the quality of life we do today.
Plastics are polymers. What is a polymer? The most simple definition of a polymer is something made of many units. Think of a polymer as a chain. Each link of the chain is the "-mer" or basic unit that is usually made of carbon, hydrogen, oxygen, and/or silicon. To make the chain, many links or "-mers" are hooked or polymerized together. Polymerization can be demonstrated by linking countless strips of construction paper together to make paper garlands or hooking together hundreds of paper clips to form chains, or by a string of beads.
Polymers have been with us since the beginning of time. Natural polymers include such things as tar and shellac, tortoise shell and horns, as well as tree saps that produce amber and latex. These polymers were processed with heat and pressure into useful articles like hair ornaments and jewelry. Natural polymers began to be chemically modified during the 1800s to produce many materials. The most famous of these were vulcanized rubber, gun cotton and celluloid. The first truly synthetic polymer produced was Bakelite in 1909 and was soon followed by the first synthetic fibre, rayon, which was developed in 1911.
Many common classes of polymers are composed of hydrocarbons. These polymers are specifically made of small units bonded into long chains. Carbon makes up the backbone of the molecule and hydrogen atoms are bonded along the backbone. Below is a diagram of polyethylene, the simplest polymer structure.
There are polymers that contain only carbon and hydrogen. Polypropylene, polybutylene, polystyrene, and polymethylpentene are examples of these.
Even though the basic makeup of many polymers is carbon and hydrogen, other elements can also be involved. Oxygen, chorine, fluorine, nitrogen, silicon, phosphorous, and sulfur are other elements that are found in the molecular makeup of polymers. Polyvinyl chloride (PVC) contains chlorine. Nylon contains nitrogen. Teflon contains fluorine. Polyester and polycarbonates contain oxygen. There are also some polymers that, instead of having a carbon backbone, have a silicon or phosphorous backbone. These are considered inorganic polymers. One of the most famous silicon-based polymers is Silly Putty.
Think of how spaghetti noodles look on a plate. This is similar to how polymers can be arranged if they lack a specific form or are amorphous. Controlling and quenching the polymerization process can result in amorphous organization. An amorphous arrangement of molecules has no long-range order or form in which the polymer chains arrange themselves. Amorphous polymers are generally transparent. This is an important characteristic for many applications such as food wrap, plastic windows, headlights, and contact lenses.
Obviously not all polymers are transparent. The polymer chains in objects that are translucent and opaque are in a crystalline arrangement. By definition, a crystalline arrangement has atoms, ions, or in this case, molecules in a distinct pattern. You generally think of crystalline structures in salt and gemstones, but not in plastics. Just as quenching can produce amorphous arrangements, processing can control the degree of crystallinity. The higher the degree of crystallinity, the less light can pass through the polymer. Therefore, the degree of translucence or opaqueness of the polymer is directly affected by its crystallinity.
Scientists and engineers are always producing better materials by manipulating the molecular structure that affects the final polymer produced. Manufacturers and processors introduce various fillers, reinforcements, and additives into the base polymers, expanding product possibilities.
Polymers are divided into two distinct groups: thermoplastics and thermosets. The majority of polymers are thermoplastic, meaning that once the polymer is formed, it can be heated and reformed over and over again. This property allows for easy processing and facilitates recycling. The other group, the thermosets, can not be remelted. Once these polymers are formed, reheating will cause the material to scorch.
Every polymer has very distinct characteristics, but most polymers have the following general attributes.
- Polymers can be very resistant to chemicals. Consider all the cleaning fluids in your home that are packaged in plastic. Reading the warning labels that describe what happens when the chemical comes in contact with skin or eyes or is ingested will emphasize the chemical resistance of these materials.
- Polymers can be both thermal and electrical insulators. A walk through your house will reinforce this concept, as you consider all the appliances, cords, electrical outlets and wiring that are made or covered with polymeric materials. Thermal resistance is evident in the kitchen with pot and pan handles made of polymers, the coffee pot handles, the foam core of refrigerators and freezers, insulated cups, coolers and microwave cookware. The thermal underwear that many skiers wear is made of polypropylene and the fibrefill in winter jackets is acrylic.
- Generally, polymers are very light in weight with varying degrees of strength. Consider the range of applications, from toys to the frame structure of space stations, or from delicate nylon fibre in pantyhose.
- Polymers can be processed in various ways to produce thin fibres or very intricate parts. Plastics can be moulded into bottles or the bodies of cars or can be mixed with solvents to become an adhesive or a paint. Elastomers and some plastics stretch and are very flexible. Other polymers can be foamed, like polystyrene and urethane, to name just two examples. Polymers are materials with a seemingly limitless range of characteristics and colours. Polymers have many inherent properties that can be further enhanced by a wide range of additives to broaden their uses and applications.
In addressing all the beneficial attributes of polymers, it is equally important to discuss some of the environmental aspects of the material. Plastics deteriorate but never decompose completely, but neither does glass, paper or aluminum. Plastics make up 9.5 percent of our trash by weight compared to paper, which constitutes 38.9 percent. Glass and metals make up 13.9 percent by weight.
Applications for recycled plastics are growing every day. Recycled plastics can be blended with virgin plastic (plastic that has not been processed before) to reduce cost without sacrificing properties.
Recycled plastics are used to make polymeric timbers for use in picnic tables, fences, and outdoor toys, thus saving natural lumber. Plastic from 2-litre bottles is even being spun into fibre for the production of carpet and fleece.
An option for plastics that are not recycled, especially those that are soiled, such as used microwave food wrap or diapers, can be an energy recovery system.
The controlled combustion of polymers produces heat energy. The heat energy produced by the combustion of plastics not only can be converted to electrical energy but can help burn the wet trash that is present. Paper also produces heat when combusted, but not as much as plastics. On the other hand, glass, aluminum and other metals do not release any energy when combusted.
To better understand the energy recovery process, consider the smoke coming off a burning object and then ignite the smoke with a Bunsen burner. Observe that the smoke disappears. This is not an illusion, but illustrates that the by-products of incomplete burning are still flammable. Energy recovery technologies can burn the material and the by-products of the initial burning.
The Society of the Plastics Industry, Inc. (SPI) introduced its voluntary resin identification coding system in 1988 at the urging of recyclers around the country. A growing number of communities were implementing recycling programs in an effort to decrease the volume of waste subject to rising tipping fees at landfills. In some cases, test programs were driven by government recycling mandates. The SPI code was developed to meet recyclers' needs while providing manufacturers with a consistent, uniform system that could apply nationwide. Because municipal recycling programs traditionally have targeted packaging - primarily containers - the SPI coding system offered a means of identifying the resin content of bottles and containers commonly found in the residential waste stream. Recycling firms have varying standards for the plastics they accept. Some firms may require that the plastics be sorted by type and separated from other recyclables; some may specify that mixed plastics are acceptable if they are separated from other recyclables; while others may accept all material mixed together. Not all types of plastics are generally recycled, and recycling facilities may not be available in some areas.
Click here for a pdf copy of the seven most popular types of plastics used in household packaging applications.
Uses of Plastics
Whether you are aware of it or not, plastics play an important part in your life. Plastics' versatility allow them to be used in everything from car parts to doll parts, from soft drink bottles to the refrigerators in which they get stored. From the car you drive to work to the television you watch when you get home, plastics help make your life easier and better. So how is it that plastics have become so widely used? How did plastics become the material of choice for so many varied applications?
The simple answer is that plastics are the material capable of providing the things consumers want and need. Plastics have the unique capability to be manufactured to meet very specific functional needs for consumers. So maybe there’s another question that’s relevant: What do I want? Regardless of how you answer this question, plastics can probably satisfy your needs.
If a product is made of plastic, there’s a reason. And chances are the reason has everything to do with helping you, the consumer, get what you want: Health; Safety; Performance; Value. Plastics help make these things possible.
Just consider the changes we’ve seen in the grocery store in recent years: Plastic wrap helps keep meat fresh while protecting it from the poking and prodding fingers of your fellow shoppers. Plastic bottles mean you can actually lift an economy-size bottle of juice. And should you drop that bottle accidentally, it is shatter-resistant. In each case, plastics help make your life easier, healthier and safer.
Plastics also help you get maximum value from some of the big-ticket items you buy. Plastics help make portable phones and computers that really are portable. They help major appliances – like refrigerators and dishwashers – resist corrosion, last longer and operate more efficiently. Plastic car fenders and body panels resist dings, so you can cruise the grocery store parking lot with confidence.
Modern packaging – such as heat-sealed plastic pouches and wraps – helps keep food fresh and free of contamination. That means the resources that went into producing that food aren't wasted. It’s the same thing once you get the food home: Plastic wraps and resealable containers keep your leftovers protected – much to the chagrin of kids everywhere. In fact, packaging experts have estimated that each pound of plastic packaging can reduce up to .77 kilograms (1.7 pounds) of food waste.
Plastics can also help you bring home more product with less packaging. For example, less than 1 kilogram of plastic can deliver more than 28,000 grams – roughly 30 litres – of a beverage such as juice, soda or water. You'd need almost twice as much aluminum to bring home the same amount, four times as much steel or more than 12 kilograms of glass. Plastics make packaging more efficient, which ultimately conserves resources.
Plastics engineers are always working to do even more with less. Since 1977, the 2-litre plastic soft drink bottle has gone from weighing 68 grams to just 51 grams today, representing a 25 per cent reduction per bottle. That saves more than 93 million kilograms of packaging each year. The 1-gallon plastic milk jug has undergone an even greater reduction, weighing 30 per cent less than what it did 20 years ago. How many of us can say that?
Plastics also help to conserve energy in your home. Vinyl siding and windows help cut energy consumption and lower your heating and cooling bills. For example, the U.S. Department of Energy estimates that use of plastic foam insulation in homes and buildings each year will ultimately save nearly 60 million barrels of oil over other kinds of insulation.
The same principles apply in appliances, such as refrigerators and air conditioners. Plastic parts and insulation have helped to improve their energy efficiency by 30 to 50 per cent since the early 1970s. Again, this energy savings helps reduce your electric and cooling bills. And appliances run more quietly than earlier designs that used other materials.