General Introduction to Plastics
Plastics are a group of synthetic or semi-synthetic materials that are malleable and can be molded into a variety of shapes when heated. They are typically organic polymers of high molecular mass and often contain other substances to improve their properties and performance. The term plastic is derived from the Greek word plastikos, which means capable of being shaped or molded. Plastics are versatile materials, used in a wide range of applications and products in almost every aspect of modern life. Plastics are lightweight and durable, corrosion-resistant, easily formed into a variety of shapes and sizes, and have many different properties depending on the type of material.
Types of Plastics
There are many different types of plastics, each with their own unique properties, uses and advantages. Depending on the application, different types of plastics may be used for various purposes. Thermosetting plastics and thermoplastics, both of which are processed in different ways, are two of the most common types of plastics available. Other common types of plastics include acrylics, polypropylene, polyvinyl chloride (PVC), polyethylene, polycarbonate, nylon, and polyurethane.
Thermosetting plastics are plastics that undergo an irreversible chemical change when subjected to heat, pressure, or the presence of a catalyst. Once hardened, the material retains its shape even when heated. Thermosetting plastics are typically used in construction, automotive parts, insulation, and molds.
Thermoplastics are plastics that can be melted down and re-shaped multiple times. They are formed through plastic molding and do not undergo a chemical change during the process. Thermoplastics are used in a wide variety of applications, including medical devices, packaging materials, automotive parts, and toys.
Properties of Plastics
The physical and chemical properties of plastics are determined by their composition, structure, and additives. Common physical properties of plastics include strength, hardness, flexibility, stiffness, heat resistance, and electrical insulation. Common chemical properties of plastics include flame retardancy, weatherability, chemical resistivity, and UV protection.
Plastics are also known for their electrical insulation, meaning they do not conduct electricity. This makes them ideal for use in electrical components and applications where electrical insulation is required.
Processing Plastics
Plastics may be processed using a variety of methods, including extrusion, injection molding, blow molding, rotational molding, and thermoforming. Each method has its own advantages, depending on the desired shape and procedures for the part being manufactured.
In extrusion, a plastic is pushed through an extruder, or die, which is a tool used to create a shape from a material. The plastic emerges from the die in the desired shape and may then be cooled, cut, and further processed.
In injection molding, melted plastic is forced into a mold cavity in the desired shape, then cooled and ejected from the mold. Blow molding is similar to injection molding, except the melted plastic is blown into the mold cavity.
Rotational molding is a process in which a powder or liquid is placed in a mold and then spun at a high speed to melt the material and form it into the desired shape. Thermoforming is a process in which a sheet of plastic is heated and then molded into the desired shape.
Common Applications of Plastics
The most common applications of plastics include packaging, construction, and consumer products. Plastics are extensively used in packaging, such as bags, bottles, containers, and food wrappers, as well as electrical components and circuit boards. Plastics are used in the construction of buildings, bridges, and other structures, and in consumer products such as medical devices, furniture, consumer electronics, toys, and appliances. Plastics are also used in many industrial applications, including automobiles, aircraft, and marine vessels.
