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People use plastics every day, and for the past 50 or 60 years, the use of plastics has expanded into nearly all aspects of our lives. In the end, plastics are so versatile that they have completely replaced wood and metal in many applications.

There are some 45 unique types of plastic materials, with more than a dozen variations each. However, one key difference can help you understand which will work for your goal: thermoset plastics and thermoplastic plastics. In this article, we’ll cover the difference between the two categories of plastic and compare their properties.

What Are Thermosets?

Thermosetting plastic, also known as thermosetting polymers, starts out as liquid resins at room temperature. However, upon heating or chemical dosing of additives, these polymers harden. The production process usually involves one of two manufacturing processes:

1. Resin transfer molding (RTM) is a molding process in which the resin is injected under pressure into a mold cavity, thus creating parts of two finished surfaces.
2. Reaction injection molding (RIM) is a molding process in which active plastic liquids are mixed under high pressure and injected into a mold to react and polymerize.

During these processes, a cross-linking reaction occurs between polymers in the material, forming an irreversible and molecularly unbreakable bond. After the initial curing process, thermosets gain high-heat resistance and high impact resistance, which makes them perfect for maintaining structural integrity at higher temperatures.

This means that thermoset plastics don’t melt when exposed to heat. However, excessive heat may compromise the material in other ways, as some may even combust. There are several different types of thermosets, including phenolics, silicone, epoxy resins, polyurethane, and melamine.

What Are Thermoplastics?

Unlike thermosets, which are liquid resins at room temperature, thermoplastic polymers are solids that soften upon heating until they eventually become liquid. Unlike thermosets, the manufacturing process of thermoplastic materials doesn’t involve any chemical bonding.

Thermoplastics start out their journey as resin pellets that are melted and formed into many shapes by injection molding, thermoforming, or extrusion. Since there’s no chemical bonding, and the material is pretty resistant to shrinking, the main characteristic of thermoplastic materials are that they can be reheated, remolded, and recycled without compromising the molecular integrity of the material.

Some of the most common thermoplastic materials are acrylic, polycarbonate, polyethylene, polystyrene, polypropylene, polyvinyl chloride (PVC), polyethylene terephthalate, and Teflon. It’s worth noting that each of these materials has different properties, which also means that their range of application varies from one industry to another.

Differences Between Thermosets and Thermoplastics

Despite their similarities, thermoplastic and thermoset polymers have different physical properties.

Melting Point

The main difference between these two categories of plastic materials lies in their respective thermal properties. Thermoplastic materials aren’t really resistant to high temperatures, and they have a pretty low-melting point compared to thermoset materials, whose degradation temperature is much lower than their melting point.

This makes thermoplastics recyclable, as you can reheat them to form an entirely different product if desired. However, that’s not the case with thermoset resins, which, once cured, won’t change their shape once subject to heat.

Aesthetics and Finish

Thermoplastics are often associated with a high-quality finish, but they can’t really match the finish produced by thermosetting RIM and RTM manufacturing processes. The injection molding associated with thermosetting materials allows for an in-mold painting process, which creates a strong chemical bond between the paint and plastic.

This produces an exceptional surface finish with excellent pain adhesion that prevents chipping and cracking. Additionally, achieving low- and high-gloss surface finishes on thermosets is much more affordable compared to thermoplastic. Don’t try polishing these at higher speeds, as the friction will melt the surfaces of thermoplastics.

Corrosion Resistance

When we talk about corrosion with plastic materials, we’re not discussing typical oxidation that’s associated with metal corrosion that produces rust but rather exposure to different plastic corrosive agents. That’s why it’s important to select the right material for your application and product design. Admittedly, both materials are highly corrosion resistant, but thermoplastics are more resilient to different types of chemical environments than thermosets.

Durability

Durability and thermal resistance are important material properties for products such as electrical insulation, appliance housing, and automotive and aerospace parts. These are all made with thermoset materials, which are considerably more durable compared to thermoplastics.

Thermosets have exceptionally high strength and deformation resistance while being relatively lightweight at the same time. These can be reinforced with composite materials, such as carbon or fiberglass, which results in greater dimensional stability.

Cost

Several different factors affect the overall manufacturing costs of plastic parts, regardless of which of these two types of material you use. The material itself is certainly a contributing factor, but there’s also a matter of labor costs, tooling, manufacturing time, and finishing operations.

That’s why it’s important to consider the costs associated with the production of the part before choosing the material. Generally speaking, thermoplastics are often more affordable than thermosets, but thermosets obviously offer more in terms of physical and chemical properties that could potentially make them cheaper in the long run.

Applications of Thermosets and Thermoplastics

The differences between thermosets and thermoplastics play a crucial role in their respective applications. However, the type of plastic you should use is mostly dictated by your project requirements. If your project requires high-temperature resistance, thermoset materials should be your choice. Likewise, if you need better corrosion resistance, then thermoplastics might be more suitable.

Thermosets are typically a more economical solution compared to metals, especially due to the easier formation of complex shapes and high-temperature resistance. This makes thermosets great for applications like electrical housing, panels, medical equipment, parts manufacturing, and chemical processing equipment.

Thermoplastics are better suited for industrial machine equipment, such as clamping knobs and lobed knobs, as well as electrical insulation, lab equipment, gas tanks, piping systems, and non-stick cookware. They’re also a good substitute for metal, not because of their structural integrity but because of their chemical resistance.

Thermoset Plastic vs. Thermoplastics

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The main difference between thermosets and thermoplastics is how they respond to heat, which ultimately plays a crucial role in material selection. If you want to learn more about different types of materials, such as plastics and steels (including stainless steel varieties) visit our online store or call our team to find products suited for your next manufacturing project.