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In this article, the uses and applications of each of these types of Plastics will be presented, including a summary of the relative advantages and limitations of each.

The primary difference between the two is that Thermoset is a material that strengthens when heated, but cannot be remolded or heated after the initial forming, while thermoplastics can be reheated, remolded, and cooled as necessary without causing any chemical changes. As a result of these physical and chemical properties, thermoplastic materials have low melting points while thermoset products can withstand higher temperature without loss of its structural integrity.

Despite the similarities in their names, thermoplastics and thermosetting plastics are different from each other with regard to their properties, applications and in how they are manufactured and processed. It is important for product designers to understand the differences in order to use the best option for their products.

What is the Difference between Thermoset and Thermoplastic?

Thermosetting plastics and thermoplastics are both polymers, but they behave differently when exposed to heat. Thermoplastics can melt under heat after curing while thermoset plastics retain their form and stay solid under heat once cured.

Because thermoplastics have a low melting point, they are ideal for applications that use recycled materials. Thermoset plastics, in contrast, are able to withstand high temperatures without losing their shape, making them more durable.

Thermoset Plastics

Thermoset plastics, also called thermosetting resin or thermosetting polymers, are typically liquid at room temperature and then harden once heated or with a chemical addition. They are usually produced using reaction injection moulding (RIM) or resin transfer moulding (RTM) and form permanent chemical bonds during the curing process. These chemical bonds between the monomer chains within the material, called crosslinks, hold the molecules in place and change the nature of the material, preventing it from melting and returning to a liquid state. Once heated, thermoset plastics are set into a specific form, although overheating can cause them to degrade without entering a fluid phase.

Thermoset plastics are ideal for use in situations where heat is a factor, such as with electronic housings and appliances or chemical processing equipment, due to their greater structural integrity and resistance to both heat and chemicals. Able to resist deformation and impact, common thermosets include epoxy resins, polyimide, and phenolic, which are often used in composites.

Pros

Thermoset plastics provide a wide range of benefits:

• Able to be moulded with different tolerances
• Allows for flexible product designs
• Improved structural integrity through variable wall thicknesses
• Typically cheaper than components fabricated from metals
• Superb electrical insulation properties
• Excellent heat resistance at high temperatures
• Corrosion resistant
• Strong dimensional stability
• Low thermal conductivity
• Cheaper setup and tooling costs than with thermoplastics
• High strength-to-weight ratio
• Water resistant
• Wide range of colours and surface finishes

Cons

Despite these many benefits, there are still some drawbacks with thermoset polymers:

• Cannot be reshaped or remoulded
• Cannot be recycled

Thermoplastics

Thermoplastics are resins that are solid at room temperature but become soft when heated and eventually become fluid as a result of crystal melting or from crossing the glass transition temperature (Tg).

Processing thermoplastics involves no chemical bonding and they can be poured into a mould to cool and solidify into the desired shape. Thermoplastics can be reheated, recycled and remoulded without affecting the material properties. As a result, these materials are used in processes including extrusion, thermoforming, and injection moulding.

Common thermoplastics include polyethylene (PE), polycarbonate (PC), and polyvinylchloride (PVC), polypropylene (PP), polystyrene (PS), and polyethylene theraphthalate (PET), with each having varied properties. However, generally speaking, thermoplastics tend to resist shrinking while offering good elasticity and strength. Used in applications including industrial machine components and plastic bags for retail, thermoplastics can soften, deform and lose some of their physical properties if exposed to high temperatures.

Pros

The benefits of thermoplastics include:

• Good adherence to metals
• High quality aesthetic finish
• Can be recycled and reshaped with little impact on material properties
• Resistant to chemicals and detergents
• Good electrical insulation
• High impact resistance
• Enhanced anti-slip properties
• Can create both rubbery and hardened crystalline surfaces
• Resists chipping
• Corrosion resistant

Cons

Despite these benefits, there are a few drawbacks with these materials:

• Not suited to all applications due to softening when heated
• Typically more expensive than thermosetting polymers

Applications

Due to their superb chemical resistance, structural robustness and thermal stability, thermoset plastics are used for a range of applications, meeting a variety of production specifications. Easier to form into different shapes than metals, thermoset polymers offer considerable consistency in their fabrication. As a result, they are widely used in sectors including adhesives and sealants, aerospace, defence, electrical, automotive, energy, and construction.

Applications for thermosetting polymers include:

• Pipes, fittings and cell covers for chemicals such as chlorine
• Housings and components for electrical or medical use
• Doors, panels and housings for heavy construction or transportation equipment
• Agricultural products including livestock feeding troughs
• Parts and components for vehicles, including tractors and military vehicles

Thermoplastics have found applications in a wide range of industries to create items including milk containers and piping. They are able to withstand corrosive conditions, making them a good substitute for metals, although they are limited in high temperature applications. As a result, these materials have found ready use in construction, electronics, medical, biomedical, food and beverage, chemical, automotive, plumbing and more industries.

Applications for thermoset plastics include:

• Ropes and belts
• Insulation for electrical cables
• Liquid storage
• Protective coverings for equipment