Polymers: Material with the Most Rapid Innovation and Discovery

Today the materials science basics topic is the third and final unique class of materials, polymers. Before we jump into polymers if you are not familiar with materials science you should read that article.

Previously we talked about metallic and ceramic materials; and this week we are talking about polymeric materials. The more common term for polymers is plastics. So the words polymer or plastics mean the same thing.

History of Polymers

Similar to metals and ceramics, the word polymer comes from Greek words. Are you sensing a theme here? However, unlike ceramics and metals, it actually comes from two words. The first word poly- means many and the second part of the word -mer means many parts. And this is definitely a fitting name for plastics because the most basic definition of a polymer is a substance that has a molecular structure consisting entirely of a large number of similar units bonded together in a repeating order. Polymers are the more up and coming class of materials, especially as they are being used a lot in composite materials their first use dates back pretty far.

When most people think of polymers or plastics they think of synthetic polymers. And credit the discovery of polymers to Leo Baekeland who invented a polymer he named Bakelite, in 1907. This was in fact the first invention of a completely synthetic polymer. However, almost half a century earlier in 1869 John Wesley Hyatt developed a semi-synthetic polymer by harvesting the natural material, cellulose from the cotton fiber with camphor, an organic compound to create a polymer.

Despite all of these innovative discoveries in modern history, the first example of human beings using polymers was in 3000 B.C. During this time, people in ancient Asian civilizations wrapped children in silk bundles, and silk fiber is a natural polymer. Polymers can be natural or synthetic. Natural polymers are polymers that are naturally occurring in the world and synthetic polymers are man-made polymers.

Types of Polymers and Their Properties

There are three major categories of polymers which includes elastomers, thermoplastics, and thermosets

Elastomers

Elastomers are polymers that can be stretched repeatedly. They can also be stretched to great lengths without a negative effect on their properties. The most common type of elastomers are rubbers. A good example of an elastomer is a rubber band. Think about how stretchy rubber bands are and how frequently they are stretched and restretched without breaking.

Elastomers are able to do this because there are very weak intermolecular forces between the chains of the polymers

Thermoplastics

Conversely, thermoplastics are polymers that become soft at higher temperatures and hard at lower temperatures. Thermoplastics can usually undergo many cycles of heating and cooling without an effect on their properties. This is what makes thermoplastics great material for everyday items because they can be recycled and reused. Think about water bottles.

Thermosets

Lastly, the final type of polymer is a thermoset. Thermosets are polymers that are irreversibly hardened by curing of a soft solid or viscous liquid prepolymer or resin. Thermosets are typically the strongest type of polymer which is why they are used in many applications when a load is going to be applied like boat hull or sports equipment.

If you want to learn more about any of the specific types of plastics let me know down below in the comments

Processing Polymeric Materials

Compared to metals and ceramics polymeric materials, specifically synthetic plastics are one a newer class of materials and as such their applications in the world are growing rapidly.

Due to the differences in the polymer properties, the type of polymer and the application of the polymer affects the processing method. There are too many polymer processing methods to list them all but just to name a few:

• Blow-molding is the technique used to make water bottles.
• Thermoforming is used to make car parts.
• Extrusion can produce parts like pipes or small pellets that are then used in other applications. Polymer fibers are made via process called melt spinning. The manufactured fibers are used to make fibers that go into textiles or materials like the filters in N95 masks.

Those are just a couple of the many processing techniques for plastics in this brief introduction to polymeric materials.