Thermoplastics are recyclable materials that are used frequently today to create objects such as foam cups, polyethylene squeeze bottles, acrylic lenses and safety helmets. Their unique properties set them apart from the other two types of plastic, thermosets and elastomers. Heat and pressure cause the molecular structure of a thermoplastic to change, making it pliable and more useful.
Thermoplastics are the only type of plastic that can be welded. When heated to about 120 to 180 degrees Celsius, thermoplastics become pasty or liquid, and they can be molded and formed into different shapes. Each type of thermoplastic has its own properties, characteristics and welding temperature. They can withstand multiple heating and re-shaping, which makes them recyclable. Once the thermoplastic object has cooled down, the new form is set.
Types of thermoplastics include polyethylene (PE), polyvinyl chloride (PVC) and polystyrene (PS), which often are used for packaging. Other groups of thermoplastics are acrylics, fluoropolymers, polyesters, polyimides and nylons. All of these types can be melted down many times and re-shaped into different forms. For example, a foam cup is a thermoplastic material that can be heated and turned into a dish.
Nylon is a thermoplastic that resists abrasion and is self-lubricating. Often it is used to make ropes, fishing line and zippers. Acrylics are used to make goggles, windows and lenses because of their impact strength and transparency. Polyethylene is very strong and tends to resist impact, and so it is used to make buckets and toys. PVC is a very inexpensive plastic, commonly seen in floor tiles, hose pipes and cable coatings.
Thermoplastics are often used in place of metal, due to their strength, rigidity and impact resistance, along with their lightweight quality. Certain flame-retardant substances can be added to thermoplastics to make them fit the safety requirements in constructing aircraft and rail cars. When combined with materials such as glass or carbon, thermoplastics become even more dependable and typically have higher melt points than metal.
Thermoplastics can be modified by the addition of other properties. Adding fibers makes thermoplastics stronger and stiffer, while adding plasticizers make them more flexible. The use of lubricants makes thermoplastics easier to mold, while anti-oxidants make them more stable under higher temperatures and ultra-violet stabilizers give them sunlight resistance. Every time a thermoplastic is changed, it takes on different properties, creating a substance that can be used for a wide variety of purposes.