Thermoset Resins vs. Thermoplastics: Choosing the Right Polymer

Thermoset resins and thermoplastics are two types of polymer resins used in various products. Thermoplastic resins are commonly used in unreinforced forms, such as pet and food storage containers, and are used in fiber-reinforced composites (FRP) for structural composites. 

We regularly interact with thermoplastic polymer resins because of their widespread use. Most thermoplastic resins are used in their unreinforced state, when the resin is molded into the desired shape without any additional reinforcement for added strength.

Some widespread thermoplastic resins and the goods they enable are:

Pet – Beverage containers

Containers for food storage made of polypropylene

Lenses made of polycarbonate safety glass

PBT: Playthings for Toddlers

Windows framed in vinyl

Produce bags made of polyethylene

PVC-Piping, or Piping

Armrests on Planes Made with PEI

Shoes Made From Nylon

Reinforcement in the form of short, discontinuous fibers is common in thermoplastic materials. To a lesser extent, carbon fiber is also used. The mechanical properties are improved, and the material can be classified as a fiber-reinforced composite, although the resulting strength is significantly lower than that of continuous fiber-reinforced composites.

FRP composites typically involve reinforcing fibers of a quarter-inch or higher in length. Recently, structural composite materials made from continuous fiber and thermoplastic resins have become increasingly common. Thermoplastic composites have a few benefits and drawbacks over thermoset composites.​

Thermoplastic Composites’ Many Benefits

Thermoplastic composites benefit from two primary benefits. The first is that, compared to equivalent thermoset composites, many thermoplastic resins offer superior impact resistance.

The gap in durability can be as much as ten times as great.

The capacity to reform is another great benefit of thermoplastic composites. You have to keep in mind that raw thermoplastic composites are solid at room temperature. A reinforcing fiber undergoes a physical change rather than a chemical reaction when subjected to heat and pressure during the impregnation process.

Because of this, thermoplastic composites can be easily remolded into different forms. It is possible to provide a curved shape to a straight rod of pultruded thermoplastic composite by applying heat and reshaping it. Thermosetting resins cannot be used for this purpose. This opens up the possibility of recycling the thermoplastic composite when its useful life is over. (Although promising, this is still in the experimental stages and not available to the public.)

Thermoset Resins’ Features and Advantages

In conventional fiber-reinforced polymer composites (FRP composites), the structural fiber is held securely in place by a thermosetting resin matrix. These are some examples of thermosetting resin:

Resin Polyester

Epoxy phenolic urethane and vinyl ester resin

Polyester resins, followed by vinyl ester and epoxy, are the most widely used thermosetting resins today. Uncured thermosetting resins are liquid at ambient temperature, which is one reason why they are so widely used. Reinforcing fibers like fiberglass, carbon fiber, or Kevlar can be impregnated with ease.

As was previously noted, working with a liquid resin at room temperature is convenient. Using a vacuum or positive pressure pump, laminators efficiently eliminate all air from the production environment, allowing for quick product production. Production utilizing Sealing Molds In addition to their inexpensive raw material costs and simple production, thermosetting resins can display high-quality features.

Thermoset resins have the following characteristics:

High tolerance to chemicals and solvents.

High-temperature and heat-resistance

Resistance to fatigue

Customized pliability

Superb bonding

The polishing, painting, etc., are top-notch.

The uncured molecules of a thermoset resin are chemically cross-linked in a catalytic reaction. By undergoing this exothermic chemical reaction, the resin solidifies and forms extraordinarily strong bonds with its constituent molecules.

After being catalyzed, a thermosetting resin cannot be undone or reshaped. A thermoset composite is a material that cannot be altered after it has been produced. As a result, collecting and recycling thermoset composites is a daunting task. Although thermoset resins are not recyclable in and of themselves, some innovative businesses have found ways to pyrolize the resin out of the reinforcement fiber, making it usable again.

Problems with Thermoplastics

It’s much trickier to pass off thermoplastic resin as reinforcing fiber because it’s always solid. To impregnate fibers, the resin must be heated to its melting point, pressure is needed, and the composite must be cooled while still under pressure. This is very different from the standard thermoset composite production method, and it is also very complicated. Many costly tools, techniques, and pieces of equipment are required. Unfortunately, here is where thermoplastic composites really fall short.

There is ongoing development in thermoset and thermoplastic materials. Both have their uses and advantages, and neither will be phased out in the near future of composites.