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Thermoset vs Thermoplastic: Definition and Differences

Thermosets and Thermoplastics are classes of polymers that are large molecules formed by the chemical linking of monomers. As we talk about these two, we’ll find multiple similarities between them, but there are certain differences as well. ‘Thermoplastics’ was a common name in the injection molding and parts manufacturing industry until ‘Thermosets’ happened.

Thermosets and resins, when combined together, serve as a great alternative to metal and thermoplastics in plastic fabrication processes. Some processes or products specifically require thermoplastics, while others require thermosets. There are products/processes that can put either to use.

Thermosets and Thermoplastics: Definitions

Thermosets vs. Thermoplastics

To better understand these polymers, we need to study their characteristics, behavior, and unique properties. Here, we are discussing these in detail one by one.

Thermoplastics

Thermoplastics are polymers that can be softened, melted, and remolded into different shapes multiple times. These shift forms from solids to liquids when heated and liquids to solids once cooled down. Their versatility is what widens their use case.

Chemically, these constitute long-chain polymers that are held together by weak intermolecular forces called van der Waals forces. This is what makes them easily change their state of matter.

Certain properties of thermoplastics are tabulated below:-

Melting point150°C (302°F) – Above 250°C (482°F) (depending upon the thermoplastic)
FlexibilityMore flexible than alternatives
RecyclabilityEasily recyclable
TransparencyIt can be made transparent

A few examples of thermoplastics are polyethylene, polypropylene, and polyethylene terephthalate (PET). These are generally used in industries such as injection molding, automotive, packaging, and construction. 

When we talk about thermoplastics, they can be modified easily to suit the needs. A few of these can be made resilient to UV rays and Flame. There are also shape-memory thermoplastics that get back to their original form once heated.

shape memory thermoplastics

Thermosets

Thermosets are a class of polymers that undergo a chemical reaction during molding that produces a three-dimensional network structure. They can be distinguished from thermoplastics by their cross-linked structure, which does not allow them to change shape or form. In thermosets, crosslinking gives the material improved mechanical, thermal, and chemical qualities.

Through the process of cross-linking, thermosets create a web of covalent bonds between polymer chains. During the curing process, which frequently uses heat or chemical catalysts, crosslinking takes place.

The curing process usually requires heat energy; some thermosets can cure at room temperature, while others may require higher temperatures. A chemical initiator or catalyst can also be applied during the curing part. For example, epoxy resins use amine-based hardeners as curing agents, and polybenzoxazine is a rare case that cures without any catalyst.

Certain properties of thermosets are listed below

  1. Thermosets can usually withstand high temperatures. 
  2. They are commonly known for their strength and resistance
  3. Chemicals or catalysts don’t have much effect on their composition
  4. They also stay intact when it comes to heavy loads.
  5. Thermosets are usually resistant to solvents.

A few popular kinds of thermosets are epoxy resins, polyurethanes, phenolic resins, melamine formaldehyde, etc. These are currently used in industries like aerospace, automotive, electronics, etc.

Vulcanized rubber is thermosetting plastic and one of the strongest materials known. Melamine-formaldehyde resins, a type of thermoset, are used in the production of melamine tableware.

Although thermosets have several benefits, they also have a few problems. They are irreversible and non-recyclable. Their non-biodegradability is also a major concern.  They are also brittle, and their usage is limited when it comes to requiring something flexible.

Thermosets and Thermoplastics, Definitions

Thermosets and Thermoplastics: Differences

Thermoplastics and thermosets are similar plastic polymers but vary greatly when compared on certain bases. Here, we are going to explain and explore a few of those.

Melting point

The melting point of polymers like thermosetting and thermoplastics is an important basis for differentiating them. Their behavior under heat determines their diverse properties and potential applications.  

Thermosetting plastics or thermosets get their name from their ability to withstand heat. The only time thermosets have any reaction toward heat is when they are curing or cross-linking. These polymers are indifferent to any heating post-curing.

Thermoplastics, for that matter, have a low melting point and can be molded and remolded when exposed to heat. This aids the recyclability of this material. Their application is limited in the areas that require functionality despite high temperatures.

Aesthetics

Beyond functional considerations, the one significant thing when it comes to differentiating thermoplastics and thermosetting plastics is aesthetics. Thermosets, due to their covalent cross-linking, have rigid and intricate surfaces. This intricate detailing becomes a supporting characteristic in industries like automotive and consumer electronics.

The only time we can add color to thermosets is before molding. The color goes directly on the mold, which facilitates better bond formation between paints and plastics. This process provides thermosets with resistance to flaking, cracking, etc.

Thermosets are also adequate for low and high-gloss finishes. Painted thermosets also provide the opportunity to infuse intricate details like logos.

Thermoplastics, on the other hand, provide high-quality finishes. Their ability to melt and reshape contributes greatly to their aesthetic abilities. Thermoplastics can be tinted over and over and show a perfect balance of functionality and aesthetics. 

The surface finish of thermoplastics is easily alterable through various techniques like extrusions and 3D printing. These can adapt to either matte or gloss finishes as per the desired aesthetic outcome. Moreover, the transparency and translucency of thermoplastics make these a perfect fit for applications in lighting fixtures, electronic devices, and eyewear.

Corrosion resistance

It is estimated that various industries, like chemical processing plants, have had to pay significant prices because of corrosion. Thermosets do exhibit high corrosion resistance due to their structure. Epoxy resins, for example, are used as a coating in places where corrosion protection is a requirement.

The inherent rigidity can be a cause of concern in certain places where flexibility is crucial for corrosion protection. Additionally, some thermosets may lose their functionality when exposed to UV rays for a long time, which limits their outdoor application.

If we talk of thermoplastics, they offer great endurance and flexibility. This factor makes their applications possible in places like pipes and tanks to automotive. Polypropylene and PVC, for example, are widely used in the construction industry for their corrosion-resistant properties.

Even though we can use thermoplastics in multiple places, factors such as molecular weight and chemical composition can influence their performance. A few thermoplastics may even be susceptible to stress cracking, which ultimately affects their corrosion resistance. For application in industries like chemical, marine, oil, and gas, thermosets are a better choice of material.

Durability

Durability is exceptionally important when we discuss the usage of polymers in industries like electronics and cars. Both thermosets and thermoplastics are used in these industries but in different areas because of their different endurance capabilities.

Indifference towards heat after curing makes thermosets one of the stronger plastic polymers. Their covalent cross-linking is what favors this exceptional heat resistance. Not just heat, thermosets show exceptional resistance to chemicals also.

Thermosets are lightweight while being strength-providing and tough. They also support reinforcing materials like carbon and fiberglass. These are strong enough not to be affected by volcano lava.

When we talk of thermoplastics, their structural integrity is not as great as that of thermosets. They are also not very stable to prolonged UV light, but UV protectors can be added. Their durability can be affected by gradual wear and tear.

They are not extremely resistant to heat or chemicals but still manage to work fine in certain places. Their durability lies in their ability to absorb and distribute impact energy. Thermoplastics are suitable mainly for packaging materials, consumer goods, and automotive materials of certain kinds. 

If we talk mechanically, we can say any thermoset, as a polymer, is more durable than thermoplastic.

Machine And Parameters For Injection Molding

Due to their different properties, their usage for injection molding (which they are both suitable for) has different specifications. They require different machines and have different parameters for this process.

As we take thermoplastics into account, standard screw-type injection molding machines with high injection pressure are required. These machines are also supposed to have both heated barrels and molds to ensure adequate melting and flowing of plastic.

Thermosets, on the other hand, need specialized transfer or compression molding machines. They employ lower pressure quantity compared to thermoplastics. Here, only molds are heated to facilitate the curing process. 

Coming to parameters, thermoplastics employ high temperatures (150-300°C) and pressure (50-200 MPa) compared to thermosetting plastics(80-150°C, 10-50 MPa, respectively). Thermoplastic injection molding occurs much faster(10-30 secs) than thermoset injection molding (several minutes to a few hours). This happens because thermosets take ample time to cure.

Thermosets and Thermoplastics: Applications

Thermosets and thermoplastics shine wonderfully with their own strengths. Let’s sort out the confusion regarding what to use and where.

Thermosets

  • Automotive industry: Thermosets can be used in engine parts, electrical insulation, brake pads, and other automotive components. They are perfect for under-the-hood applications because of their exceptional dimensional stability and capacity to tolerate high temperatures. 
  • Electrical and electronic sectors: Because thermosets have superior insulating qualities, they are usually employed in the electrical and electronic sectors. For example, epoxy resins are frequently used in electronic applications.
  • Oil and gas sector: Harsh circumstances, such as exposure to corrosive chemicals and high temperatures, are part of the oil and gas sector. Thermosets, like epoxy coatings and composite materials, are used in storage tanks, offshore structures, and pipelines.
  • Medical equipment and devices: Materials used in the medical field frequently need to be biocompatible, sterilizable, and resistant to repeated washing and disinfection procedures. Thermosets meet these specifications and are employed in a variety of applications, such as equipment housings and implanted devices.
  • Building and Infrastructure: Thermosets are used in construction at several places. For example, composites are utilized in pipelines, building materials, and bridge components.
Thermosets and Thermoplastics, Applications

Thermoplastics

  • Packaging sector: In the Packaging sector, cost-effectiveness and flexibility are important qualities, so thermoplastics are the choice. Because they can be easily molded, materials like polyethylene and polypropylene can be commonly seen for packaging films, bottles, and containers. Also, thermoplastics’ being recyclable fits nicely with the increased focus on environmentally responsible and sustainable packaging options.
  • Consumer Electronics: Materials with good aesthetics and light weight are in high demand when we talk about consumer electronics. Electrochromic polymers such as polycarbonate and ABS (acrylonitrile butadiene styrene) are majorly utilized in electronic device production. Their durability is what guarantees the safety of sensitive internal components, and their moldability permits elaborate designs.
  • Transportation: Thermoplastics possess properties like lightweight, good durability, and prevention from corrosion, which makes these useful in the transportation sector. The common examples are polycarbonate (PC), used for automotive lenses and taillights, and ABS, used for car interiors and dashboards.
  • Kids’ Toys: Various kid’s toys are usually made of thermoplastics. Their moldability and recyclability make thermoplastics the choice for this purpose. Polyethylene(PE) is a thermoplastic that is employed for this purpose.
  • Sporting Goods: Sports goods manufacturers often rely on thermoplastics for the production of equipment and gear. All the lightweight components of sports goods, helmets, and protective padding are of thermoplastics. The ability to tailor the material properties to specific performance requirements makes thermoplastics the ideal choice.
  • Textile and clothing: Synthetic fibers and fabrics composed of thermoplastics are used in the textile industry. Polyester, nylon, and spandex are examples of thermoplastics that are usually utilized. Thermoplastic fibers can be melt-spun for the creation of fabrics with specific properties like moisture-wicking, elasticity, and resistance to wrinkles.
Thermoplastics, Applications

Conclusion

Thermosets and thermoplastics both have their own strengths and weaknesses. They have their own unique properties that are specifically beneficial at certain times.

There are various ongoing research studies to better these two polymers. Scientists are working on producing biodegradable thermoplastics from sustainable sources like sugarcane or maize starch. These substances provide a more environmentally friendly substitute for conventional thermoplastics derived from petroleum.

The right material must be chosen based on the particular needs of the project and the desired qualities. The creation of hybrid materials, which offer customized solutions that incorporate the best aspects of both worlds, blurs the boundaries between these two categories as technology develops. 

The dynamic interaction between thermosets and thermoplastics is still reshaping material science, impacting sustainable practices and innovation. For more information on our services and similar topics, contact us.

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