| Property | Thermoplastic Plastics | Thermosetting Plastics |
|---|---|---|
| Definition | Polymers that soften on heating and harden on cooling. The process is reversible. | Polymers that harden irreversibly upon heating due to cross-linking. Cannot be reshaped after curing. |
| Molecular Structure | Linear or branched polymer chains with weak intermolecular forces (van der Waals or hydrogen bonds). | Three-dimensional network structure formed by strong covalent cross-links between chains. |
| Behavior on Heating | Softens and melts when heated; can be remolded and recycled. | Does not soften on heating; decomposes or burns at high temperatures. |
| Reprocessability | Can be repeatedly melted and reshaped (recyclable by melting). | Cannot be remelted or reshaped after initial curing (not recyclable by melting). |
| Mechanical Strength | Generally lower strength and rigidity; more flexible and ductile. | High strength, rigidity, and dimensional stability due to cross-linking. |
| Solubility | Soluble in suitable organic solvents before shaping. | Insoluble after curing; only swells in solvents. |
| Examples | Polyethylene (PE), Polypropylene (PP), Polyvinyl Chloride (PVC), Polystyrene (PS), Nylon, ABS | Phenolic resins (Bakelite), Epoxy resins, Melamine formaldehyde, Polyurethane, Urea-formaldehyde |
| Processing Methods | Injection molding, extrusion, blow molding, thermoforming | Compression molding, transfer molding, casting (curing required) |
| Heat Resistance | Lower heat resistance; deforms at moderate temperatures. | High heat resistance; maintains shape at elevated temperatures. |
| Chemical Resistance | Moderate; depends on polymer type. | Excellent resistance to chemicals and solvents due to cross-linked structure. |
| Applications | Pipes, bottles, films, cables, toys, packaging, automotive parts | Electrical insulators, adhesives, coatings, laminates, kitchenware (handles), circuit boards |
Note: Thermoplastics are ideal for recycling and mass production, while thermosets are preferred for high-performance, heat-resistant applications in engineering.