Difference Between Thermoplastic and Thermosetting Plastic

 Main Difference – Thermoplastic vs Thermosetting Plastic

Thermosetting and thermoplastics are two different classes of polymers, which are differentiated based on their behavior in the presence of heat. The main difference between thermoplastic and thermosetting plastic is, thermoplastic materials have low melting points; therefore, they can be remoulded or recycled by exposing it to heat. Unlike thermoplastic, thermosetting plastic can withstand high temperatures without losing its rigidity. Therefore, thermosetting materials cannot be reformed, remoulded or recycled by applying heat.

What is Thermoplastic

Thermoplastic is a class of polymer, which can be easily melted or softened by providing heat in order to recycle the material. Therefore, these polymers are generally produced in one step and then converted into the required article at a subsequent process. Furthermore, thermoplastics have covalent interactions between monomer molecules and secondary weak van der Waal interactions between polymer chains. This weak bonds can be broken by heat, and change its molecular structure. The Figure 1. and 2. illustrate the changes that occur in intermolecular interactions of thermoplastic in the presence of heat.

The softened thermoplastic can be placed in a mould, and then cooled to give the desired shape. When it cools significantly below its glass transition temperature (Tg), weak Van der Waal bonds in between monomer chains will form reversibly to make the material rigid and usable as a formed article. Therefore, this type of polymers can be readily recycled or remoulded, because each time it is reheated, it can be reshaped into a new article. Acrylic, Acrylonitrile Butadiene Styrene, Nylon, Polybenzimidazole, Polycarbonate, Polypropylene, Polystyrene, Teflon, Polyvinyl Chloride, etc. are several examples of thermoplastic materials. Among these thermoplastics, some materials such as Polybenzimidazole, Teflon, etc. have exceptional thermal stability because of their high melting points.

What is Thermosetting Plastic

Unlike thermoplastics, thermosetting plastics have superior properties like high thermal stability, high rigidity, high dimensional stability, resistant to creep or deformation under load, high electrical and thermal insulating properties, etc. This is simply because thermosetting plastics are highly cross-linked polymers that have a three-dimensional network of covalently bonded atoms. The strong cross-linked structure shows resistance to higher temperatures which provides greater thermal stability than thermoplastics. Therefore, these materials cannot be recycled, remoulded, or reformed upon heating. The Figure 3. and 4. illustrate the changes that occur in intermolecular interactions of thermosetting polymers under high temperatures.Thermosetting plastic will become softer with the presence of heat, but it will not be able to shape or form to any greater extent, and will definitely not flow. Typical examples of thermosetting plastics are,

Phenolic resins that occur as a reaction between phenols with aldehydes. These plastics are generally used for electrical fittings, radio and television cabinets, buckles, handles, etc. Phenolic are dark in color. Therefore, it is difficult to obtain a wide range of colors.

Amino resins that are formed by the reaction between formaldehyde and either urea or melamine. These polymers can be used to manufacture lightweight tableware. Unlike phenolics, the amino resins are transparent. So they can be filled and colored using light pastel shades.

Epoxy resins that are synthesized from glycol and dihalides. These resins are excessively used as surface coatings.

Difference Between Thermoplastic and Thermosetting Plastic

Intermolecular Interactions

Thermoplastic has covalent bonds between monomers and weak van der Waal interactions between monomer chains.

Thermosetting Plastic has strong cross-links and a 3D network of covalently bonded atoms. The stiffness of plastic increases with the number of cross-links in the structure.

Synthesis

Thermoplastic is synthesised by addition polymerization.

Thermosetting Plastic is synthesised by condensation polymerization.

Processing Methods

Thermoplastic is processed by injection moulding, extrusion process, blow moulding, thermoforming process, and rotational moulding.

Thermosetting Plastic is processed by compression moulding, reaction injection moulding.

Molecular Weight

Thermoplastic is lower in molecular weight, compared to thermosetting plastic. 

Thermosetting Plastic is high in molecular weight.

Physical Properties

Examples

Thermoplastic include Nylon, Acrylic, Polystyrene, Polyvinyl chloride, Polyethylene, Teflon, etc.

Thermosetting Plastic include Phenolic, Epoxy, Amino, Polyurethane, Bakelite, Vulcanized rubber, etc.

Reference

Cowie, J. M. G.; Polymers: Chemistry and Physics of Modern Materials, Intertext Books, 1973.

Ward, I.M.; Hadley,D.; An introduction to the Mechanical Properties of Solid Polymers, Wiley, 1993.