What Are the Two Categories of Polymers?

From building Boeing 737s to manufacturing bulletproof vests, polymers are used for a plethora of applications. How a polymer behaves when exposed to heat is one of the key properties used to categorise these unique materials. Every polymer can be divided into two main categories – thermosets and thermoplastics. Below, we take a closer look at each:

Thermosets

Also known as thermosetting plastics, these materials have extremely high structural rigidity and can’t be reshaped or recycled after being set. This is due to the strength of the chemical bonds between each molecule, which makes the polymers heatproof. During processing and manufacturing, two-stage polymerisation is used to strengthen the chemical bonds and create a cross-linking pattern. As well as being heatproof, thermosets don’t dissolve in organic solvents. This makes them the polymer of choice for manufacturing heavy duty products.

Polyurethanes used to manufacture car parts, footwear and foam used in home furniture, is one example of a thermoset polymer. Epoxy resin used for aerospace components and marine vessel parts is another common use for thermoset polymers.  

Thermoplastics

Coveted for their versatility, thermoplastics can be repeatedly softened, melted down and reshaped when exposed to heat. Similarly, they solidify and harden when exposed to cold temperatures. Most thermoplastics are durable enough to withstand these processes multiple times before starting to degrade.

Around 80% of all plastics currently in circulation are classed as thermoplastics. This includes materials used to manufacture everyday commodities. For example, polypropylene, polyvinyl chloride (PVC) and polyethylene. As well as being used to manufacture grocery bags, packaging films and cable insulation, polyethylene improves the strength of bulletproof vests, without weighing down the wearer.

Engineering materials with exceptional strength and durability, such as nylons, polycarbonates and acetals, are also classed as thermoplastic polymers. Other examples include thermoplastic elastomers, also known as thermoplastic rubbers. These have rubber-like properties and are widely used for injection moulding applications.

Natural vs synthetic polymers

Another way to characterise polymers is by origin. From this perspective, polymers can be either natural or synthetic. Examples of natural polymers include cellulose, carbohydrates and proteins. More specifically, materials such as wool, cotton and silk. In comparison, synthetic polymers are artificially produced and derived from petroleum. They’re developed in laboratories by scientists and engineers, usually as part of a product development process.

Polymers on the global stage

Driving research and development of cancer therapies, combating the global plastic pollution crisis and improving the performance of space-grade plastics are just a few examples of why polymer characterisation matters. Want to know more about polymers? Find out more about the latest analytical methods for polymer characterisation, including cutting-edge chromatography techniques, in our complete guide, ‘Polymer Characterisation - Techniques, Types & Properties’.