There are many methods used to classify plastics. The most common method is to classify them according to their polymer backbone. Plastics can, however, also be classified according to the glass transition temperature or thermoplastic versus thermoset.
No matter the classification, all plastics are polymers, which is a long chain of atoms that are bonded to one another. These chains are comprised of monomers, which are repeating molecular units. Most plastics are made of carbon polymers or carbon polymers combined with nitrogen, oxygen, sulfur, or chlorine in the backbone, which is the main path linking the units together. Plastic is then customized by “hanging” different molecular groups to the backbone.
One of the positive characteristics of plastic is the fact that it is durable. Unfortunately, this is not a positive characteristic when it comes to the environment. The fact that plastic is durable means it degrades slowly. In addition, burning plastic can sometimes result in toxic fumes.
Minimizing this, thermoplastics can be recycled, reground and used again in production and thermoset plastics can be ground up and used for filler. Unfortunately, the purity of these plastics was compromised each time it was reused. To assist in the plastic recycling program, the Plastic Bottle Institute of the Society of Plastics Industry created a method for marking plastic bottles in order to determine what type of plastic it is made of.
You can find here a graphic of all 7 above types with it's characteristics and common uses.
- PET - Polyethylene Terephthalate - PET is most often used for cooking oil bottles, soft drink bottles, butter jars.
- HDPE - High Density Polyethylene - HDPE is commonly used for milk jugs, detergent bottles and crates.
- PVC - Polyvinyl Chloride - PVC is used for plastic pipes, water bottles, outdoor furniture, shrink-wrap, liquid containers.
- LDPE - Low Density Polyethylene - LDPE is often used for trash can liners, produce bags, and food storage containers.
- PP - Polypropylene - PP is used for drinking straws and bottle caps.
- PS - Polystyrene - PS is used to make packaging pellets, commonly referred to as 'Styrofoam peanuts'.
- OTHER - Plastics listed in the OTHER category are any not listed in the first six categories.
Plastic has benefited our society in a number of ways. In fact, plastic has helped aeronautics technology take giant steps forward over the past 50 years, including advancements in satellites, shuttles, aircraft, ... In fact, in any field we can come up plastics has it's larger or smaller use nowadays.
Plastic in Aeronautics - Plastics were first introduced to the world of aerospace during World War II, mostly because other materials were limited. During the war, plastic slowly started to be used as a substitute for rubber in items such as fliers' boots and fuel-tank linings. The fact that plastic was able to withstand heat also lead to its being recognized as an important material in aerospace technology. Today, plastics are used in the solid fuel boosters form rockets and in the ablative shields for reentry of space shuttles.
Plastic materials are also used in the making of helicopters because they are rigid and durable, yet flexible enough to withstand the vibrations made by helicopters. The fact that plastic is both lightweight and strong also has its advantages in the field of aerospace because the weight of the aircraft can be reduced by using plastic. This results in improved aerodynamics, which leads to improved fuel efficiency and performance.
Plastics in the Building and Construction - Plastics play a significant role in the building and construction industry as well. In fact, the industry is the second largest consumer of plastic, followed only by the packaging industry. In the construction industry, plastics are used for items such as pipes and valves. They are also used for decorative elements and heavy-duty uses because they are so easy to handle, are durable, and are attractive.
Plastics are highly used in piping and valves because of their superior resistance to corrosion. In fact, they can be used for everything from freshwater to saltwater, from crude oil to laboratory waste. They are much lighter than other materials and easier to instal and are also less expensive.
Plastics in Electronics - Due to the thermal and insulating properties of plastic, it is ideal for use in house wiring. In fact, nearly all modern homes use plastic electrical connectors, switches, and receptacles. It is great for making small appliances such as can openers, food processors, microwave ovens, mixers, coffee makers, shavers, irons, and hair dryers. Even refrigerators use a special plastic foam for insulation purposes, while the interior is made from plastic that is durable and easy to clean. Without plastic, these products would last about half as long and would use 25% more energy.
Computers as we know them today would probably not exist without plastic. Plastic made smaller computers possible by being able to house all of the electronics necessary within a dust free and well-insulated environment. Components such as circuit boards and computer chips are able to be miniaturized without losing their abilities - or while also improving their performance - thanks to the use of plastic.
Plastics and Packaging - Plastic is extensely used for a variety of packaging purposes. If the product needs to be well protected, the plastic can be rigid and tough. If the packaging needs to be convenient to carry, the plastic can be flexible. Or, a combination of the two can be achieved. Furthermore, the packaging can be designed into any shape or size desired and it can be clear or any color imaginable.
Plastic is also used to store a variety of goods commonly found in the home. Creating shatterproof bottles with plastic to protected people from harm, leak proof and child-resistant packaging, and a miriad of other applications that we now take for granted.
Plastic in Transportation - Because plastic is tough, resistant to corrosion, durable, lightweight, and easy to color, it is a popular choice when making modes of transportation. For that reason, it can be found in the fenders, bumpers, trunk lids, housings for headlights and sideveiw mirrors, grilles, hoods, doors, and wheel covers. Through the use of plastic, the average passenger car has lost 145 pounds since 1988. The lighter weight translates to better fuel efficiency and has saved approximately 21 million barrels of oil.
Of course, other means of transportation, such as bicycles, roller skates, kayaks, canoes, skateboards, snowboards, surfboards, motorcycles, and even some athletic shoes take full advantage of plastic in their creation.