Sign in. For Suppliers. Matmatch Suppliers. Case Studies. Thermoplastics and thermosetting polymers are types of plastic that undergo different production processes and yield a variety of properties depending on the constituent materials and production method. The terms thermoplastic and thermoset stand for how a material is or can be processed under a changed temperature [1].
The main physical difference is how they respond to high temperatures. When heated to their melting point, thermoplastics soften into a liquid form. Therefore, the curing process is reversible, which means that they can be remoulded and recycled.
On the other hand, thermoset polymers form a crosslinked structure during the curing process, preventing them from being melted and remoulded. As an analogy, think of thermosets like concrete, once they have set, they can never go back to the liquid form irreversible process. While thermoplastics are like water, they can transition between ice and water with the application or removal of heat reversible process.
A thermoplastic is a resin that is solid at room temperature but becomes plastic and soft upon heating , flowing due to crystal melting or by virtue of crossing the glass transition temperature T g.
Upon processing, usually via injection-moulding or blow-moulding-like processes, thermoplastics take the shape of the mould within which they are poured as melt, and cool to solidify into the desired shape. The significant aspect of thermoplastics is their reversibility , the ability to undergo reheating, melt again, and change shape. This allows for additional processing of the same material, even after being prepared as a solid.
Processes such as extrusion, thermoforming, and injection moulding rely on such resin behaviour. However, like any other material, thermoplastics have their limitations. If subjected to extremely high temperatures, the material may unwantedly soften, deform, and lose some of its physical properties [2]. A thermosetting resin, or thermosetting polymer, is generally a liquid material at room temperature which hardens irreversibly upon heating or chemical addition.
When it is placed in a mould and heated, the thermoset solidifies into the specified shape, but this solidification process includes the formation of certain bonds, called crosslinks , that hold the molecules in place and change the basic nature of the material, preventing it from melting.
As a result, a thermoset, as opposed to a thermoplastic, cannot return to its initial phase, rendering the process irreversible. Thermosets, upon heating, become set , fixed in a specific form. During overheating, thermosets tend to degrade without entering a fluid phase. Processes such as compression moulding, resin transfer moulding, pultrusion, hand lay-up, and filament winding depend on thermosetting polymer behaviour.
Some common thermosets include epoxy , polyimide , and phenolic, many of which are significant in composites [2]. Thermosets and thermoplastics differ in various ways in terms of their behaviour, but all those diverging properties result from an underlying, fundamental difference in their chemical structure.
This underlying difference can be noticed in how thermoset resins, throughout the length of their polymer chain, have particular spots that can be chemically activated to be part of chemical bonding reactions with neighbouring polymer molecules.
Since all thermosets carry such chemically reactive spots, it is often the case that all kinds of thermosets have the tendency to connect to one another. Such a process of forming chemical links across different thermosetting molecules is called crosslinking or curing. Upon curing, formed crosslinks not only confine the polymer molecules from moving but also the atoms inside those molecules are impeded to a greater degree than intermolecular attractions.
Another way of observing the behavioural difference between thermosets and thermoplastics is via their molecular weight. As we compare both polymer types, thermosets stand out in how their molecular weight drastically increases upon curing. Thermoplastics are known to have higher molecular weight values than uncured thermosets. However, when crosslinking occurs between two thermosets, a polymer network is formed of molecular weight almost double the weight when the two were separate.
As the number of linked molecules increases, the molecular weight continues to rise, exceeding that of thermoplastics. This drastic increase in molecular weight causes major changes in material properties, such as an increased melting point.
With a continuous increase in molecular weight due to crosslinking, the melting point can rise and reach a point that exceeds the decomposition point. In that case, a thermoset polymer would have a very high molecular weight that it would decompose before it can melt, which defines why thermoset processing is irreversible [2].
Thermoplastics generally provide high strength, flexibility and are resistant to shrinkage, depending on the type of resin the polymer in melted liquid form. They are versatile materials that can be used for anything from plastic carrier bags to high-stress bearings and precision mechanical parts. Thermosets generally yield higher chemical and heat resistance, as well as a stronger structure that does not deform easily. Here is a list showing the difference between thermoplastics and thermosets in terms of features and properties.
Notice the effect of crosslinking as an underlying factor in diverting those materials from one another. Flexible and elastic. Each requires different manufacturing methods, equipment and processing, as well as design considerations. Yulex Pure natural rubber is a thermoset type of polymer system. That is, in order to reach maximum physical properties and performance the material needs two things: a curing agent vulcanizer and heat to drive curing, which causes the elastomer chains molecular structure of the rubber to cross link.
Once these types of polymers are cured and cross linked, they remain linked, never returning to an unlinked form. Both Yulex Pure latex emulsion and dry solid are thermoset type elastomers, and both require a curing agent to be used and heat to drive the cross linking. Thermoform elastomer polymer systems, also called melt-processable and reprocessable do not require curing agents to achieve their physical properties but do require heat to soften them during manufacturing, then once cooled are ready to go.
They can be reused multiple times by grinding the used material up into small pellets, melted and usually injected into a mold or over another material over molding. There are certain disadvantages to the use of thermosets whereas the material properties are not as developed as those of thermoplastics. The low initial viscosity of materials results in flash and the need for secondary operations.
Also, low tensile strength and ductility tend to result in parts that require designs with thick walls. The compounds used in thermosets are reactive systems, which can impact the useful shelf life. Batch processes may exhibit greater variation and less consistency from lot-to-lot. High levels of some filler in the materials may result in excessive tool wear.
The product quality is dependent upon the degree of crosslinking established during the molding cycle. The rigidity of the material can result in product failure when used in high in vibration applications. Thermosetting polymers are built from various types of material that serve key roles and applications in the plastics fabrication industry. Composite thermoset materials consist of a matrix and a dispersed, fibrous, or continuous second phase. Casting resins include a catalyst or hardener.
Thermoset electrical resins and electronic-grade products are used in potting or encapsulating compounds, conductive adhesives, and dielectric sealants. Thermal compounds are designed to form a thermally conductive layer on a substrate, either between components or within a finished electronic product. Thermoset purging compounds are used to clean molding machines between runs of different colors or compositions.
Gap filling products are used to fill in gaps or spaces between two surfaces to be bonded or sealed. Specific types of thermoset materials that are in use within the plastics fabrication industry include the following:.
As discussed earlier, plastics are widely recognized as real-world applications of the use of chemistry. From plastic containers, bottles, and life-saving medical devices to aerospace components , plastics are a material that is used in applications all around us.
Thermoplastic polymers are one such type of plastic which is known for its versatility and recyclability. Thermoplastic polymers form when repeating units called monomers link into chains or branches. Thermoplastic pellets soften when heated and become more fluid as more heat is administered.
There are a variety of thermoplastic resins that offer various performance benefits, but the majority of materials commonly used offer high strength, shrink-resistance, and easy flexibility. Depending on the resin, thermoplastics can serve low-stress applications such as plastic bags or can be used in high-stress mechanical parts. Examples of thermoplastic polymers include polyethylene, PVC, and nylon. Image credit: Adams Plastics. In polluted, acidic, environments such as may be found in modern cities, steel piping systems are often vulnerable to rust or corrosion and therefore need special provisions for corrosion protection.
The cost associated with protecting steel piping systems that are exposed to these harsh environments can be expensive. Thermoplastics are considered to be a favorable substitute to minimize these costs.
Certain properties of thermoplastics that make them a suitable substitute material are:. Polyethylene gas tanks are used to transport natural gas for use in residential and commercial applications. Other common applications for thermoplastics include high-pressure polyethylene to encapsulate rigid objects like electrical equipment.
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