The specifics of how plastic is made depends on what kind it is and what it will be used for, but the basic steps are the same. Plastic is made using a variety of chemical and refining processes that turn single molecules called monomers into long chains called polymers. After this happens, the polymers can be molded or shaped into whatever the end product is.
The main types of raw materials used to make plastic are fossil products, such as crude oil and natural gas, though it can also be made from other things like soy, corn and hemp. These contain compounds called hydrocarbons that can be used to make monomers, which can then be processed to make plastic. This is usually done by cracking, in which the hydrocarbons are either heated to extreme temperatures or chemically treated to break them down into monomers like ethylene or styrene.
Polymerization and Polycondensation
Once the monomers are extracted, they have to be chemically treated to make them bond together and form long polymer chains. This is normally done either through 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 byproduct like water.
During either process, different types of monomers are usually mixed together to form resin with different characteristics. They may also be mixed with other additives, like flame retardants or plasticizers, which make the end product less brittle. The resulting resins from both processes can be sold in liquid form or ground down into pellets or powder and then sold to plastic manufacturing companies.
Thermoplastics and Thermosets
The polymers can then be processed into either thermoplastics or thermosets. Thermoplastics melt when they reach a certain temperature, but are hard when they cool, while thermosets get harder as they get warmer, but can only be heated up and allowed to set once. If they're heated again, they burn. The difference between them usually comes down to the monomers used to make the resin and the structure that the polymers form while being processed: while thermoplastics form into chains of alternating hard and malleable sections, thermosets form hard, interlocked bonds.
Thermoplastics are usually processed by various forms of molding or extrusion. Molding is done by heating up resin and injecting it into a mold or blowing air into a softened tube of resin that's inserted into a mold to make it take 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 make it form a certain shape, and is used to make things like straws, fibers for weaving, and pipes. Thermoplastics can also be calendered, in which they're melted and then pressed between big rollers to make long sheets of plastic, like those used to make flooring.
Thermosets can be molded as well, though the molds are often pressurized to encourage the polymers to link more closely, which makes the end product more durable. They are also sometimes treated with a chemical before molding to make the polymers combine thoroughly. The first process is usually used to make things that need to be strong, but are made for consumer use, like phones and sports equipment, while the second is used to make stronger things like machine or vehicle parts. This type of plastic can also be coated onto other materials, like paper or fabric, and then heated and pressed together to make fuses, gaskets, and electronic circuit boards in a process called laminating.