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Thermosets vs. Thermoplastics

Once, “thermoplastic” was the last word in injection molding and parts manufacturing. However, that word has been replaced by one which sounds similar but contains a world of difference: thermoset.

Recently, thermoset plastics and resins have emerged as an attractive alternative to both thermoplastics and other traditional ingredients such as metal and wood. While thermoplastics continue to have their use for certain products and in certain situations, thermoset often provides a number of advantages aesthetically, structurally, and in regards to cost and labor.

It is important to understand the differences between thermosets and thermoplastics in order to choose the ideal material for your next manufacturing project.

What are Thermoplastics?

A thermoplastic, also called a thermosetting plastic, is any plastic material which melts into a soft, pliable form above a certain temperature and solidifies upon cooling. Thermoplastics can be re-melted and re-shaped any number of times. They are usually stored in the form of pellets prior to the molding process.

Common examples of thermoplastics include acrylic, polyester, polypropylene, polystyrene, nylon and Teflon. These materials see a wide variety of use in manufacturing products from clothing and non-stick cookware to carpets and laboratory equipment.

Thermoplastic Injection Molding

Thermoplastics have seen common use in the injection molding process as they produce parts that are flexible, accurate and have aesthetically pleasing surface finishes. Thermoplastics are also valued for their recyclability, as products created from them can be re-melted and formed into different shapes via the injection molding process. This has led to the popularity of thermoplastics in the toy, furniture and clothing industries, as it allows parts to be recycled and reformed after suffering damage, wear and tear.

The process of thermoplastic injection molding begins with the creation of a mold, usually from metal such as steel or aluminum. The thermoplastic resin is then melted into liquid form in a heated barrel before it is injected into the mold to cool as a solid. Once the part has fully set and cured, it is removed from the mold and the process is complete.

However, thermoplastic injection molding requires high heat and high pressure in order to successfully create parts. For this reason, it is not always a cost-effective solution, especially for orders that require a high number of parts to be produced. Thermoplastics are also ineffective for parts which are regularly exposed to extreme heat or rapidly varying temperatures, because of their ability to melt.

What are Thermosets?

In contrast to thermoplastics, thermosets (alternately known as thermosetting plastics or thermosetting polymers) are materials which remain in a permanent solid state after being cured one time. Polymers within the material cross-link during the curing process to perform an unbreakable, irreversible bond. This means that thermosets will not melt even when exposed to extremely high temperatures.

Common examples of thermoset plastics and polymers include epoxy, silicone, polyurethane and phenolic. In addition, some materials such as polyester can occur in both thermoplastic and thermoset versions. Unlike thermoplastic pellets, the components of thermoset polymers are stored in liquid form, usually in large tanks or containers.

Different thermosets provide different advantages when used as a production material. For example, epoxies are highly elastic, tough and resistant to many chemicals while phenolic is highly flame resistant. For a more in depth at the benefits of one popular thermoset, polyurethane, see our article here.

Advantages of Thermosets vs. Thermoplastics

Thermoset plastics and polymers provide a number of advantages when compared to other materials, including thermoplastics. The most obvious benefit when compared to thermoplastics is that thermosets do not melt when exposed to heat. Additionally, they do not deform, warp or lose their shape in extreme cold temperatures either. This makes them ideal for any parts or machinery that will be used in extreme climates or environments which experience regular variations in temperature.

However, this is far from the only advantage which thermosets provide over thermoplastics. Thermosets are low-viscosity and easy to work with because they exist in liquid form at room temperature, meaning that no application of heat is required. They also carry a lower health hazard than thermoplastics, as no potentially toxic fumes such as styrene are released during the molding process.

Injection molding utilizing thermosetting polymers can be carried out using far less heat and pressure than is necessary when using thermoplastics. Because of this, thermoset injection molding (which includes reaction injection molding (RIM) and long fiber injection molding (LFI) can be carried out at a far lower cost. Molds for the process are cost-effective and easy to manufacture; they can be made from a number of materials including aluminum, kirksite alloys, nickel, epoxy, silicone and fiberglass.

Reaction injection molding utilizing thermosets is a time-efficient process as well as a cost-efficient one. Cycle times for the completion of a single part range from one to several minutes. In addition, the ease of mold construction allows the prototype development to be completed rapidly. A working prototype of a desired part can usually be created within 3 to 15 days.

Structural Advantages

Thermosets have excellent “flowability,” meaning that they easily and effortlessly fill every crevice and corner of the mold. This allows for the creation both of larger overall parts and of geometric shapes far more complex and detailed than anything that can be produced with metal or thermoplastics. This is yet another way that choosing thermoset injection molding help you save money. Instead of producing each small part individually and joining them together later, as is traditionally done when using metal, parts can be combined into one larger, more complex whole right in the mold itself.

Additionally, thermosets have all of the light weight and flexibility which made thermoplastics so popular while adding strength, toughness, durability and impact resistance. They are dimensionally stable and structurally sound, experiencing little to no shrinkage when removed from the mold. Thermosetting polymers are also easily strengthened further via the addition of reinforcing materials such as fiberglass, carbon and Kevlar. Romeo RIM’s signature Long Fiber Injection (LFI) molding technology utilizes glass fibers combined with thermoset resin to create an interior fiber “skeleton” of unequaled strength and resilience.

Parts created via thermoset injection molding can have varied wall thickness across a single part, something which is impossible to do with other materials and processes. At Romeo RIM, we have the capability to produce walls as thin as 0.25 inches and as thick as 1.125 inches across a single part.

Thermoset polymers possess excellent resistance to a number of environmental factors above and beyond simply high and low temperatures. Thermosets can survive exposure to the elements without breaking, warping or scratching. They are also resistant to a number of chemicals including both organic and inorganic acids. Many thermosets, such as polyurethane, are also water-resistant, dielectric, and radiopaque, allowing them to be used in the creation of watercraft, insulation, medical equipment and a number of other products.

The encapsulation of inserts is a simple, no-fuss process with thermoset injection molding. Some of the inserts we at Romeo RIM have successfully encapsulated into our thermoset polymer products include steel, aluminum, glass, wood and even electronic sensors.

Aesthetic Advantages

Choosing thermosets does not mean sacrificing the high-quality finish for which thermoplastics are traditionally known. Romeo RIM’s reaction injection molding and long fiber injection molding, both of which utilize thermoset polymers, offer the unique opportunity for in-mold painting (IMP).

In the IMP process, the mold is sprayed directly with gel coat or paint before the injection of the thermoset. This creates unbreakable bonds between the surface and the paint; this excellent adhesion prevents chipping, flaking and cracking even in paint jobs regularly exposed to the elements. This makes thermosets an excellent choice for materials which frequently experience extreme weather or dirty conditions, such as truck cabins and construction machinery.

We are able to provide you with either low- or high-gloss Class A finishes straight out of the mold – a similar result to painted metal at a fraction of the price and manufacturing time. Painted thermosets such as polyurethane can also mimic finely detailed textures, including stone, wood and metal.

The extreme detailing which thermosets’ “flowability” provides also allows for the smallest of aesthetic touches, such as the addition of branding or logos on the product.

Overall, while thermoplastics still prove beneficial in certain situations, thermosets provide a greater number of advantages and are useful for a far wider range of products and parts. Romeo RIM produces high-quality thermoset products in industries ranging from transportation and construction to personal spas. Contact us today to learn more about how thermoset polymers are ideal for your next project!