Plastic is used in items as different as toys and remote controls
Have you ever wondered why items as different as dolls and remote controls can both be made out of the same material? The glasses you see through, shoes you wear, and pen you use are all likely made of plastic
. Plastic can be easily molded into different shapes. This ability allows plastics to be found in so many products. We know that plastic shows up everywhere. Now it’s time to explore why.
Plastics are modern, man-made materials that can be molded into different shapes
We use the word plastic to refer to a range of synthetic
, or man-made, materials. Plastic is lightweight, durable, and inexpensive. We often use plastics as a replacement for other types of materials. For example, vinyl, a plastic product, is often used to replace more expensive leather
. Some furniture, shoes, and clothes are made of vinyl.
We also use plastic as a replacement for glass
. Some examples are plastic water bottles and plastic lenses for your glasses. Compared to glass, plastic is lighter and will not break. Plastic can be a replacement for wood
. Some people use plastic instead of paper bags, because plastic is strong and does not absorb moisture. Finally, we use plastic to replace steel
, because it is lightweight and durable. Some companies make plastic silverware instead of stainless steel silverware or plastic parts instead of steel parts for cars.
We use plastics to make some things that just cannot be made with other materials. There are lots of different kinds of plastics. Just remember that all plastics share some key properties
Plasticity, the ability to change shape when force is applied, is a key behavior
The word plastic comes from the Greek word plastikos
. Plastikos means capable of being shaped or molded. Plasticity - the ability to permanently change shape when a force is applied - is a behavior all plastics have. Because they easily deform under compressive stress, plastics can be made into almost any shape imaginable.
Plastic has the properties we want in a product. As good insulators
, plastics conserve energy. This property is useful in refrigerators and air conditioners. The containers inside your refrigerator are also likely made of plastic. This plastic does not react
with your food. It keeps air out and food fresh. It is also transparent so you can see the food. Many plastics are lighter today. Plastic bottles, for example, are 25 percent lighter than they were in the 1970s.
Another important property is durability
. Plastics are made to last. Their chemical bonds slowly degrade in nature. Plastic bottles can last between 450 and 1000 years. That means that a bottle you drank out of today could still be around in the year 3000! A plastic toy will not break when dropped and the plastic parts of your refrigerator are going to last.
Plastics are carbon-based polymers
What makes something a plastic? Well, all plastics are carbon-based polymers. Every plastic is a polymer
: a long chain of molecules that repeat. There are lots of other polymers in the world. DNA, the building block of all life, and proteins are both polymers. The difference is that plastic polymers are mostly made of carbon
Most plastic is made from oil and natural gas
It is amazing to see the final products that are made out of different raw materials. For example, you might know that paper (even toilet paper!) is made from trees. Metals come from ores often found in rocks. But did you know that most plastic is made out of oil and natural gas? We refer to oil and natural gas as fossil fuels
. They are the remains of plants and animals that lived millions of years ago. We don’t just use these fossil fuels to power machines and heat our homes. We use parts of these fossil fuels to produce plastic.
Plastics contain other materials that affect their properties
Plastics can also contain other organic or inorganic compounds. Most plastics used today have had a filler, plasticizer, or colorant added. Fillers
enhance the properties of plastic. Flame retardants, for example, are added to make plastic less flammable. Fillers are also used to lower the cost of production. Plasticizers
are oily compounds that reduce how rigid plastic is. Colorants
change the color of plastic.
Plastics can be classified by their structure and behavior
There are many different kinds of plastics. Two important groups to know are thermoplastics
. Thermoplastics do not go through a chemical change when made. They can be melted and remolded. Polystyrene, which we know as styrofoam
, and nylon are both thermoplastics. Most of the plastics we use are thermoplastics.
Thermosets do undergo a chemical change. Consequently, they cannot return to their original state. Making a thermoset plastic is like baking a cake. The molded plastic or the “cake” is the final product. It cannot return to what it was before.
A few additional methods for grouping this material include deciding if the plastic is natural or manmade. You can also categorize plastics by how degradable they are.
We have changed natural plastics and invented synthetic ones
The history of plastic includes examples of many common plastics. To improve this material, humans have changed plastic in many ways. Plastic’s development has three main parts. First, over 5,000 years ago, natural plastic substances were used. The first chewing gum was actually a natural plastic made from the tar of birch trees. Yum! Ancient Mesoamericans would make balls and sandals from natural rubber.
Then, beginning in the Middle Ages, humans began chemically changing natural plastics. People of this time made a type of plastic by treating cattle horns with lye. During the Industrial Revolution, vulcanization
was invented. Vulcanization is a chemical process to harden rubber. After vulcanization, the plastic has greater chemical resistance and a smooth, soft surface. Vulcanization allows rubber to be used as a material for tires on bikes and motorcycles.
The last major plastic development was the creation of completely man-made plastics. The first man-made plastic dates back to 1856. This plastic, called Parkesine at the time, but celluloid in modern times, is made of cellulose (wood fibers) and nitrate. The cellulose nitrate is dissolved in solvent, then hardened. It forms an elastic, transparent material which can be molded when heated. Buttons and combs are made of parkesine. Bakelite, invented in 1907, was the first synthetic plastic. Synthetic means unnatural. Synthetic plastics are made out of fossil fuels rather than plants or animals.
Many plastics used today are man-made. The most popular include: polystyrene
, and nylon
. Polystyrene is used to make disposable cutlery and for protective packaging. Fabric often contains polyester. Nylon is found in cloth, cookware, screws, and bolts.
Plastics are molded into the durable, diverse items we desire
Over time, the role of plastics in our world has grown immensely. People used to make simple toys and trinkets out of plastic. Now, it plastic is found in a majority of everyday items. Perhaps you were just sitting on a plastic chair or reaching into your plastically-insulated fridge. It is obvious that this material shows up everywhere. Plastics are molded into the durable, diverse items we need and want.