The key difference between thermoplastic and thermoset is that thermoplastic can be melted into any shape and re-used whereas thermosets have a permanent shape and cannot be recycled into new forms of plastic.
Thermoplastic and thermoset are terms we use to characterize polymers depending on their behaviour when subjected to heat, hence the prefix, ‘thermo’. Polymers are large molecules containing repeating subunits.
CONTENTS
1. Overview and Key Difference
2. What is Thermoplastic
3. What is Thermoset
4. Side by Side Comparison – Thermoplastic vs Thermoset in Tabular Form
5. Summary
What is Thermoplastic?
We call thermoplastics ‘Thermo-softening Plastics’ because we can melt down this material at high temperatures and can cool to gain back solid form. Thermoplastics are generally of high molecular weight. The polymer chains are linked together via intermolecular forces. We can easily break down these intermolecular forces if we supply sufficient energy. This explains why this polymer is moldable and will melt upon heating. When we provide enough energy to get rid of the intermolecular forces that hold the polymer as a solid, we can see the solid melting. When we cool it back, it gives off heat and re-forms the intermolecular forces, making it a solid. Therefore, the process is reversible.
Figure 01: Thermoplastics
Once the polymer is melted, we can mould it into different shapes; upon re-cooling, we can obtain different products as well. Thermoplastics also show different physical properties between the melting point and the temperature at which solid crystals are formed. Moreover, we can observe that they possess a rubbery nature between those temperatures. Some common thermoplastics include Nylon, Teflon, Polyethylene and Polystyrene.
What is Thermoset?
We call thermosets ‘Thermosetting Plastics’. They are able to withstand high temperatures without melting. We can obtain this property by toughening or hardening the soft and viscous pre-polymer through the introduction of cross-links between polymer chains. These links are introduced at chemically active sites (unsaturation etc.) with the aid of a chemical reaction. In common, we know this process as ‘curing’ and we can initiate it by heating the material above 200˚C, UV radiation, high energy electron beams and using additives. The cross links are stable chemical bonds. Once the polymer is cross-liked, it gets a very rigid and strong 3D structure, which refuses to melt upon heating. Therefore, this process is irreversible converting the soft starting material into a thermally stable polymer network.
Figure 02: Comparison of Thermoplastic and Thermoset Elastomers
During the process of cross-linking, the molecular weight of the polymer increases; hence the melting point increases. Once the melting point goes above the ambient temperature, the material remains solid. When we heat up thermosets to uncontrollably high temperatures, they decompose instead of melting due to reaching the decomposition point before the melting point. Some common examples of thermosets include Polyester Fibreglass, Polyurethanes, Vulcanized Rubber, Bakelite, and Melamine.
What is the Difference Between Thermoplastic and Thermoset?
Thermoplastic and thermosets are two types of polymer materials. The key difference between thermoplastic and thermoset is that it is possible to melt thermoplastic into any shape and re-use it whereas thermosets have a permanent shape and are not recyclable into new forms of plastic. Moreover, thermoplastics are moldable while thermoset is brittle. When comparing the strength, thermosets are stronger than thermoplastics, sometimes about 10 times stronger.
Summary – Thermoplastic vs Thermoset
Thermoplastic and thermoset are polymers. The key difference between thermoplastic and thermoset is that it is possible to melt thermoplastic into any shape and re-use it whereas thermosets have a permanent shape and are not recyclable into new forms of plastic.
Reference:
1. Helmenstine, Anne Marie. “Thermosetting Plastic Definition.” ThoughtCo, May. 8, 2019, Available here.
2. Johnson, Todd. “Thermoplastic vs. Thermoset Resins.” ThoughtCo, Jan. 12, 2019, Available here.
Image Courtesy:
1.”Colorful coils of thermoplastic options for 3d pens” By Your Best Digs (CC BY 2.0) via Flickr
2. “Thermoplastic elastomer TPE” By LaurensvanLieshout – Own work (CC BY-SA 3.0) via Commons Wikimedia