Despite similar-sounding names, thermoset plastics and thermoplastics are completely different materials. Each one is suited to different types of plastic products and applications, depending on the individual properties and aesthetics required. They both have important properties that enable them to be moulded into highly bespoke shapes and designs, but there are many differences to understand alongside this similarity.

What is the difference between thermoset plastics and thermoplastics?

The difference between using thermoset plastics and thermoplastics to manufacture plastic components is that the former are permanently set in their physical and compound properties once they have undergone heat treatment. They do not melt into a liquid, nor deform if they are exposed to excess heat. This makes them incredibly robust and resistant to heat, chemicals and mechanical strength, although they can only be used for one application and are not recyclable.

Thermoplastics, on the other hand, are better known for their flexibility and reusability. The injection moulding and cooling process that they undergo to form the required plastic component is wholly reversible. This is because the structure of thermoplastic polymers is not the same as thermoset plastics. No chemical holding takes place during the heating and moulding process. Thermoplastics can be remoulded and reused multiple times without compromising their material properties or performance. Thermoplastics are not as robust as thermoset plastics but offer several different advantages instead.

Advantages of thermoplastic matrix composites compared to thermoset matrix composites

Thermoplastics are easy to mould and remould several times over, making them extremely flexible and recyclable. They adhere well to metals and other materials and offer high impact resistance and excellent electrical insulation. They are resistant to corrosion, chemicals and detergents, making them suitable for packaging and medical applications in particular. They are very versatile when it comes to colours, shapes, textures and finishes.

The superior strength of thermoset polymers, however, means that they are well suitable for applications requiring high levels of durability and resilience. They form a tough, rigid material that is resistant to high temperatures, chemicals and wear and tear. Thermoset plastics also offer excellent mechanical properties and are relatively

cost-effective to manufacture. They can be moulded into complex shapes and dimensions with pleasing aesthetics and finishes.

How to know if a polymer is a thermoset plastic?

A thermoset plastic polymer is one that can be turned into a new form through a chemical reaction known as curing. In the uncured form, thermoset plastic polymers are composed of small, unlinked monomers. These cross-link during the curing process to form longer molecular chains, which cause the material to solidify into the required shape and dimensions. A thermoset plastic will be rigid, strong and durable. It is not recyclable, however, as it is unable to revert back into a previous state of matter.

Examples of thermoset plastics and thermoplastics:

Common thermoset plastic polymers include:

• Polyurethanes
• Polypropylene
• Fluoropolymers
• Bismaleimide (BMI)
• Phenolics

They are used in such applications as signage, storage boxes, electrical plugs, pipelines, automotive parts, medical equipment, construction equipment kitchen appliances and toys.

Thermoplastics include the following commonly used materials:

• Polyethylene
• Polyvinyl Chloride (PVC)
• Acrylonitrile Butadiene Styrene (ABS)
• Polyamide (Nylon)
• Polystyrene

These materials are used for a variety of purposes like protecting delicate items during shipping, making plastic bags, clothes, and even insulating electric wires. They’re also handy for storing food safely and making strong containers for liquids that won’t get damaged easily.