Plastics are made from fossil products or other materials that contain hydrocarbons. Monomers are extracted and chemically treated to form long polymer chains through polymerization or polycondensation. The resulting resins can be transformed into thermoplastics or thermosets, which can be molded or extruded to make various products. Thermosets can also be coated onto other materials in a process called lamination.
The specifics of how the plastic is made depend on what type it is and what it will be used for, but the basic steps are the same. Plastics are made using a variety of chemical and refining processes that transform single molecules called monomers into long chains called polymers. After this happens, the polymers can be shaped or molded into whatever the final product is.
Raw material
The main types of raw materials used to make plastics are fossil products, such as crude oil and natural gas, although they can also be made from other things such as soybeans, corn and hemp. These contain compounds called hydrocarbons that can be used to make monomers, which can then be processed to make plastics. This is usually done by cracking, where hydrocarbons are heated to extreme temperatures or chemically treated to break them down into monomers such as ethylene or styrene.
Polymerization and Polycondensation
Once extracted, the monomers must be chemically treated to make them bond together and form long polymer chains. This is normally done by polymerization or polycondensation. In the first process, the monomers are mixed with another chemical that acts as a catalyst and causes them to combine with each other, forming a resin. In the second, the monomers are processed in such a way that they combine with each other and release a by-product such as water.
During both processes, different types of monomers are usually mixed to form a resin with different characteristics. They can also be mixed with other additives, such as flame retardants or plasticizers, which make the final product less brittle. The resins resulting from both processes can be sold in liquid form or ground into pellets or powder and then sold to plastic manufacturing companies.
Thermoplastics and Thermosets
The polymers can then be transformed into thermoplastics or thermosets. Thermoplastics melt when they reach a certain temperature, but are hard when they cool, while thermosets get harder as they heat up, but can only be heated and allowed to harden once. If they are heated again, they burn. The difference between them usually comes down to the monomers used to make the resin and the structure the polymers form during processing: While thermoplastics form in chains of alternating tough, malleable sections, thermosets form tough, interconnected bonds.
Thermoplastic processing
Thermoplastics are usually processed by various forms of molding or extrusion. Molding is done by heating the resin and injecting it into a mold or by blowing air into a tube of softened resin which is placed into a mold to give it a shape. These processes are used to make things like toys, containers, and soda bottles. Extrusion is done by pushing the resin through a mold to give it a certain shape and is used to make things like straws, weaving fibers and pipes. Thermoplastics can also be calendered, in which they are melted and then pressed between large rollers to make long sheets of plastic, such as those used to make flooring.
Thermosetting processing
Thermosets can also be molded, although the molds are often pressurized to encourage the polymers to bond more tightly, which makes for a more durable end product. Sometimes they are also treated with a chemical before molding to make the polymers combine completely. The former process is usually used to make items that need to be durable, but are made for consumer use, such as phones and sports equipment, while the latter is used to make more durable items such as machine or vehicle parts. This type of plastic can also be coated onto other materials, such as paper or fabric, and then heated and pressed together to make fuses, gaskets and electronic circuits in a process called lamination.
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