What Is a Thermoplastic Polymer?

By Susan Kristoff; Updated April 24, 2017
Polyethylene is a common thermoplastic polymer.

A thermoplastic polymer is a type of plastic that changes properties when heated and cooled. Thermoplastics become soft when heat is applied and have a smooth, hard finish when cooled. There are a wide range of available thermoplastic formulas that have been created for many different applications.

Basics

A thermoplastic polymer is made up of long, unlinked polymer molecules, generally with a high molecular weight. Because the molecular chains are unlinked, they rely on other interactions, such as dipole-dipole interactions, aromatic ring stacking, or Van der Waals forces. Thermoplastics generally form a crystalline structure when cooled below a certain temperature, resulting in a smooth surface finish and significant structural strength. Above this temperature, thermoplastics are elastic. As the temperature increases, thermoplastics gradually soften, eventually melting.

Blends

The material properties of a thermoplastic polymer can be adjusted to meet the needs of a specific application by blending the thermoplastic resin with other components. For example, shape memory polymer can be mixed with thermoplastic polymer to create a material that has shape memory characteristics, but retains the basic properties of the thermoplastic. Plasticizers can be added to a thermoplastic polymer to keep the material flexible at lower temperatures. This mixture is often used in plastic automobile body parts to prevent them from cracking during periods of cold temperatures.

Common Thermoplastic Polymers

Some of the most commonly found thermoplastic polymers include polyethylene, polypropylene, polyvinyl chloride (PVC), polystyrene, polytetrafluoroethylene (PTFE, commonly known as Teflon), Acrylonitrile butadiene styrene (ABS plastic), and polyamide (commonly known as nylon).

Recycling

Because thermoplastics can be melted and reused without any change in material properties, these polymers can be actively recycled. Beverage bottles and household containers with resin identification codes are generally thermoplastic polymers. These containers are ground into chips, melted, refined to remove impurities, and reused as reclaimed material.

Thermoplastic vs. Thermoset

Despite the similar names, thermoplastic polymers and thermoset polymers are very different materials. Thermoset polymers undergo an irreversible molecular change when sufficient heat is applied, whereas thermoplastic polymers can be heated and cooled over and over again. Thermoset polymers are used to create permanent structures and are used extensively in composite materials.

About the Author

Susan Kristoff has been writing engineering content for 13 years. Her articles have appeared on eHow.com, Suite101, her personal websites, and the websites of many ghostwriting clients. Kristoff's expertise includes design, structures, sensors, data acquisition, and fabrication.