The Differences of Thermoset Plastics and Thermoplastics

January 24, 2014
The Differences of Thermoset Plastics and Thermoplastics

Plastics have been used dating back to 1600 BC for a wide variety of things. Below we will discuss two types of plastics used in modern day that are commonly found in everyday life and manufacturing.


A thermoplastic is a type of plastic made from polymer resins that becomes a homogenised liquid when heated and hard when cooled. When frozen, however, a thermoplastic becomes glass-like and subject to fracture. These characteristics are reversible and can be reheated, reshaped, and frozen repeatedly making thermoplastics recyclable.

There are many kinds of thermoplastics, with each type varying in crystalline organisation and density. Some common types produced today are polyurethane, polypropylene, polycarbonate, and acrylic. Celluloid, considered the first thermoplastic, made its appearance in the mid-1800s and reigned in the industry for approximately 100 years. During its prime, it was used as a substitute for ivory and today is used to make guitar picks, electrical insulation, non-stick coating of cookware and milk jugs to name only a few.

Adding a plasticiser to thermoplastics lowers the material’s glass transition temperature (Tg), which is the point it becomes brittle when cooled and soft when heated. Tg differs with each type of thermoplastic and is dictated by its crystallisation structure. Tg can also be adjusted by introducing a thermoplastic into a copolymer, such as polystyrene. Until the use of plasticizers, some molded thermoplastic parts were vulnerable to cracking in cold weather.

Thermoset Plastics

Sometimes, thermoplastics are confused with thermosetting plastics. Although they may sound the same, they actually possess very different properties. Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form. Thermosetting resin may be contrasted with thermoplastic polymers which are commonly produced in pellets and shaped into their final product form by melting and pressing or injection molding.

Thermoset plastics are generally stronger than thermoplastic materials due to a three dimensional network of bonds (cross-linking), and are also better suited to high-temperature applications up to the decomposition temperature.

Some examples of thermoset plastics include, epoxy resin adhesives, laminates for work surfaces, electrical fittings and any part that needs to be strong and heat resistant like those needed in manufacturing or processing.