Thermoplastics are plastic made from polymer resins that become liquid when heated and hard when cooled. They are recyclable and come in many types, including polyurethane, polypropylene, polycarbonate, and acrylic. They differ from thermosetting plastics and elastomers and can be made more pliable with plasticizers. They are used in everyday life, such as in sports equipment, toys, car parts, water bottles, and bulletproof vests.
A thermoplastic (sometimes written as thermoplastic) is a type of plastic made from polymer resins that becomes a homogenized liquid when heated and hard when cooled. When frozen, however, a thermoplastic becomes glass-like and prone to fracture. These characteristics, which give the material its name, are reversible. That is, it can be reheated, reshaped, and frozen repeatedly. This quality also makes thermoplastic materials recyclable.
There are dozens of types of thermoplastics, with each type varying in crystalline organization and density. Some commonly produced types today are polyurethane, polypropylene, polycarbonate, and acrylic. Celluloid, considered the first thermoplastic, made its appearance in the mid-1800s and reigned over the industry for about 100 years. During its peak production, it was used as a substitute for ivory. Today it is used to make guitar picks.
Sometimes, thermoplastics are confused with thermosetting plastics. While they may look the same, they actually have very different properties. While thermoplastics can be melted into a liquid and cooled into a solid, thermoset plastics chemically deteriorate when subjected to heat. Ironically, however, thermosetting plastics tend to be more durable when allowed to cool than many thermoplastics.
Thermoplastics also differ from elastomers, although some consider both. While many thermoplastics can be stretched to a certain extent, they generally tend to resist and stay in the shape they are stretched to. Elastomers, as the name suggests, bounce back. However, adding plasticizers to the melt can make a thermoplastic more pliable. Indeed, this is usually the case when a thermoplastic material is used for injection molding or plastic extrusion.
The specific action of a plasticizer is to lower the material’s glass transition temperature (Tg), which is the point at which it becomes brittle when cooled and soft when heated. The Tg varies with each type of thermoplastic and is dictated by its crystallization structure. However, Tg can also be adjusted by introducing a thermoplastic into a copolymer, such as polystyrene. Until the use of plasticizers, some molded thermoplastic parts were prone to cracking in cold weather.
Thermoplastics have been around for a long time, but today they are a huge component of everyday life. For example, acrylonitrile butadiene styrene (ABS) is a type of thermoplastic used to make sports equipment, toys (for example, LEGO® blocks), and various car parts. Polycarbonate is used to make compact discs (CDs), water bottles, food containers, and eyeglass lenses, among other things. Polyethylene is probably the most commonly encountered thermoplastic and is used to make shampoo bottles, plastic grocery bags, and even bulletproof vests.
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