Introduction to Thermoplastics
- Thermoplastics are a type of polymer material that can be melted and reformed multiple times without undergoing significant chemical changes.
- They have a high molecular weight and are composed of long chains of repeating units.
- Thermoplastics exhibit excellent flexibility and can be easily molded into various shapes.
- They possess good impact resistance and can withstand a wide range of temperatures.
- Unlike thermosetting plastics, thermoplastics can be recycled and reused.
Applications of Thermoplastics
- Thermoplastics are widely used in the automotive industry for manufacturing components such as bumpers, dashboards, and interior trims.
- They are commonly employed in the construction sector for producing pipes, insulation materials, and roofing membranes.
- Thermoplastics find extensive applications in the packaging industry for creating bottles, containers, and films.
- They are utilised in the electrical and electronics field for manufacturing connectors, cables, and housings.
- Thermoplastics are also used in the healthcare sector for producing medical devices, implants, and drug delivery systems.
Types of Thermoplastics
- Polyethylene (PE) is a thermoplastic known for its high strength, chemical resistance, and low cost.
- Polypropylene (PP) is a versatile thermoplastic with excellent chemical resistance and high melting point.
- Polyvinyl chloride (PVC) is a widely used thermoplastic known for its durability, flame retardancy, and electrical insulation properties.
- Polystyrene (PS) is a lightweight thermoplastic commonly used in packaging and insulation applications.
- Polyethylene terephthalate (PET) is a thermoplastic with high clarity and excellent barrier properties, making it suitable for beverage bottles and food packaging.
Processing Techniques for Thermoplastics
- Injection molding is a commonly used technique for mass-producing thermoplastic parts with complex shapes.
- Extrusion is a process that involves forcing molten thermoplastic through a die to create continuous profiles, sheets, or films.
- Blow molding is used to produce hollow thermoplastic products such as bottles and containers by inflating a molten tube of plastic.
- Thermoforming involves heating a thermoplastic sheet and shaping it over a mold to create various products like trays, cups, and blister packaging.
- Welding is a technique used to join thermoplastic parts together by melting the surfaces and allowing them to fuse.
Advantages and Limitations of Thermoplastics
Advantages:
- Thermoplastics can be easily processed and molded into complex shapes.
- They have good chemical resistance and can withstand harsh environments.
- Thermoplastics can be recycled and reused, contributing to sustainability.
- They exhibit excellent electrical insulation properties.
- Thermoplastics offer a wide range of mechanical properties to suit different applications.
Limitations:
- Some thermoplastics have lower heat resistance compared to thermosetting plastics.
- They may have lower strength and stiffness compared to metals.
- Thermoplastics can deform under high temperatures or prolonged exposure to UV radiation.
- Certain thermoplastics may be more prone to chemical attack or degradation.
- The cost of some high-performance thermoplastics can be relatively high.
This article needs additional citations for verification. (March 2021) |
A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains associate by intermolecular forces, which weaken rapidly with increased temperature, yielding a viscous liquid. In this state, thermoplastics may be reshaped, and are typically used to produce parts by various polymer processing techniques such as injection molding, compression molding, calendering, and extrusion. Thermoplastics differ from thermosetting polymers (or "thermosets"), which form irreversible chemical bonds during the curing process. Thermosets do not melt when heated, but typically decompose and do not reform upon cooling.
Above its glass transition temperature and below its melting point, the physical properties of a thermoplastic change drastically without an associated phase change. Some thermoplastics do not fully crystallize below the glass transition temperature, retaining some or all of their amorphous characteristics. Amorphous and semi-amorphous plastics are used when high optical clarity is necessary, as light is scattered strongly by crystallites larger than its wavelength. Amorphous and semi-amorphous plastics are less resistant to chemical attack and environmental stress cracking because they lack a crystalline structure.
Brittleness can be decreased with the addition of plasticizers, which increases the mobility of amorphous chain segments to effectively lower the glass transition temperature. Modification of the polymer through copolymerization or through the addition of non-reactive side chains to monomers before polymerization can also lower it. Before these techniques were employed, plastic automobile parts would often crack when exposed to cold temperatures. These are linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling.
thermo- + plastic
thermoplastic (not comparable)
