Introduction
Plastics are synthetic polymers made of various monomeric units. We use plastics in almost every field of life. All plastics do not have the same type of arrangement of monomeric units. In some monomeric units, the arrangement is linear, whereas in others, it is cross-linked. Polythene is an example of a plastic. It is used for making commonly used polythene bags. Plastic can be classified as thermoplastic and thermosetting Plastic. Keep reading to know more details about thermoplastic.
What is Plastic?
Plastic is a polymer consisting of synthetic or semisynthetic organic compounds. Some plastic can be shaped when soft and then harden to keep the given shape.
Types of Polymers
1. Based on molecular force
Elastomer
Fibres
Thermoplastic
Thermosetting plastic
2. Based on occurrence
Natural
Semi-synthetic
Synthetic
3. Based on structure
Linear
Branched
Cross-linked
4. Based on thermal behaviour
Thermoplastic
Thermosetting plastic
What is Thermoplastic?
Thermoplastic is a plastic that has a strong force of attraction. These types of plastic become soft on heating and become hard on cooling. These types of plastic can be reshaped and remelted into a variety of shapes.
Common examples of thermoplastic are polyester, Teflon, polystyrene, and polypropylene.
Types of Thermoplastics
There are various types of thermoplastics. Below is the list of some thermoplastics.
Polyethylene terephthalate (PET) is one of the most easily recyclable plastics and it has excellent moisture and a barrier.
Polyvinyl chloride (PVC) is constituted by the polymerization of vinyl chloride. It is versatile plastic and used for packaging and the paper industries. It is resistant to wear and tear.
Polypropylene (PP) is made of polymerization of propane. It is a partially crystalline and nonpolar compound. This polymer is produced by the chain growth polymerization reaction.
High-density polyethylene (HDPE) is formed by the polymerization of ethylene. It exhibits less branching that's why it has a high density.
Low-density polyethylene (LDPE) is also made by polymerization of ethylene but it shows less branching than high-density polyethylene.
What is Thermosetting Plastic?
Thermosetting plastic is a polymer that is obtained by irreversible stiffening a solid soft and liquid prepolymer. Thermosetting plastic is also known as a thermoset. Examples of thermosetting plastics are bakelite and vulcanised rubber.
Types of Thermosetting Plastic
Listed below are some of the thermosetting plastics.
Epoxy Resin - These types of plastic contain an epoxide group. These are formed by the reaction of two or more compounds and emit heat and change the material from liquid to granular solid.
Melamine Formaldehyde - These types of plastics are obtained by polymerization of the monomer unit called formaldehyde with melamine. It hardens when heated after the setting can't be changed to a different shape.
Polyester Resin - Polyester resin is formed by the reaction of organic acids and polyhydric alcohols.
Urea-formaldehyde - Urea formaldehyde is formed by the polymerization of urea and methanol. These types of polymers have more hardness and high modulus.
Difference Between Thermoplastic and Thermosetting Plastic
Conclusion
Plastics are polymers of organic compounds. These can be divided into various types. The two most important types of plastics are thermoplastic and thermosetting plastics. This classification is based on the thermal behaviour of plastics. Thermoplastics are used for manufacturing toys, combs, and various types of containers as they can be remould after heating. Thermosetting plastics are used for making electrical switches, handles of various utensils, etc. as these plastics don’t soften on heating.
FAQs on Thermoplastic and Thermosetting Plastic
1. What are thermoplastics? Please provide some common examples.
A thermoplastic is a type of polymer that becomes soft and mouldable when heated and hardens upon cooling. This process is reversible, meaning they can be reheated and reshaped multiple times without significant chemical change. Their polymer chains are held together by weak intermolecular forces. Common examples include:
- Polyethylene (PE): Used in plastic bags and bottles.
- Polyvinyl Chloride (PVC): Used for pipes, window frames, and electrical wire insulation.
- Polypropylene (PP): Found in containers, car parts, and carpets.
- Polystyrene (PS): Used for packaging foam and disposable cups.
2. What are thermosetting plastics, and where are they typically used?
Thermosetting plastics, or thermosets, are polymers that, once heated and cured, become permanently hard and rigid. This process involves forming strong, irreversible chemical bonds (cross-links) between polymer chains. They do not soften upon reheating and will char or decompose at very high temperatures. Key examples and their uses include:
- Bakelite: Used for electrical switches, plugs, and handles for cookware due to its high heat resistance.
- Melamine Formaldehyde: Used to make durable and unbreakable dinnerware.
- Epoxy Resins: Used as strong adhesives, coatings, and in the manufacturing of electronic circuit boards.
3. What is the fundamental difference between a thermoplastic and a thermosetting plastic?
The fundamental difference lies in their behaviour upon heating, which is dictated by their molecular structure. Thermoplastics can be repeatedly softened by heat and hardened by cooling, while thermosetting plastics undergo an irreversible chemical change upon initial heating and cannot be remelted. Key differences include:
- Structure: Thermoplastics have linear or slightly branched polymer chains with weak intermolecular forces. Thermosets have a rigid, three-dimensional network structure with strong covalent cross-links.
- Reversibility: The heating/cooling cycle is reversible for thermoplastics but irreversible for thermosets.
- Recyclability: Thermoplastics are generally recyclable, whereas thermosetting plastics are not.
- Hardness: Thermosets are typically harder, stronger, and more brittle than thermoplastics.
4. Why can thermoplastics be repeatedly remoulded while thermosetting plastics cannot?
This is due to their internal bonding. In thermoplastics, the long polymer chains are held together by weak intermolecular forces (like van der Waals forces). When heated, there is enough thermal energy to overcome these weak forces, allowing the chains to slide past one another, making the material soft and mouldable. In thermosetting plastics, heating during production causes strong, permanent covalent bonds called cross-links to form between the chains. These cross-links create a single, giant, rigid molecule that cannot be broken by reheating, which is why the plastic does not melt but decomposes at high temperatures.
5. How does the molecular structure of thermosetting plastics contribute to their high heat resistance?
The high heat resistance of thermosetting plastics comes from their extensive cross-linked, three-dimensional network structure. Unlike the separable chains in thermoplastics, the polymer chains in a thermoset are locked in place by strong, stable covalent bonds. A significant amount of thermal energy is required to break these covalent bonds, far more than what is needed to overcome the weak intermolecular forces in thermoplastics. As a result, thermosets maintain their structural integrity and hardness at high temperatures where thermoplastics would soften and melt.
6. In which applications are thermosetting plastics preferred over thermoplastics, and why?
Thermosetting plastics are preferred in applications that demand high structural integrity, dimensional stability, and resistance to heat and chemicals. Because they do not soften when heated, they are ideal for:
- Electrical Components: Materials like Bakelite are used for switches and insulators because they don't deform under the heat generated by electrical currents.
- Automotive Parts: Used for components near the engine or in brake systems that must withstand high operating temperatures.
- Cookware Handles: They provide a heat-resistant grip that remains rigid even when the pan is hot.
- Strong Adhesives: Epoxy resins form powerful, temperature-resistant bonds for industrial and construction use.
7. Are plastics like PVC and Bakelite good conductors of heat and electricity?
No, both PVC (a thermoplastic) and Bakelite (a thermosetting plastic) are poor conductors of heat and electricity. This property makes them excellent electrical insulators. The electrons in these polymers are tightly held within covalent bonds and are not free to move and carry an electric current. This is precisely why PVC is widely used for insulating electrical wires and cables, and Bakelite is used for making electrical switches, plugs, and circuit boards.
