Plastic is a polymer, chains of simple organic chemicals (monomers), linked together in long chains. The monomers are synthesized in refineries, from oil. The linking of the monomers in the polymer chain is done inside polymerization reactors until the desirable average molecular weight is achieved for the polymer. Then dyes and other additives are added to the molten polymer and the material is extruded into filament, granules or flakes and cooled.
Plastics are sold in these forms as raw materials to the various manufacturers. Recycled plastic can be molten and re-extruded or directly crushed into granules or torn into flakes.
Plastic products are made out of raw plastic using a host of moulding techniques which always involve mixing and melting of the raw material inside a screw extruder.
Most plastic molecules are just hydrogen and carbon atoms, or mostly hydrogen and carbon with some oxygen, sulfur, nitrogen or chlorine atoms as well. They take advantage of the ability of carbon atoms to bond their electrons together in long flexible chains in order to create long flexible molecules.
When we combine monomers, we generate polymers or plastics.The plastic production process begins by heating the hydrocarbons in a “cracking process.” The resulting resins may be molded or formed to produce several different kinds of plastic products with application in many major markets.
Processes Used In Plastic Making-
Organic substances, in chemistry, refer to substances containing carbon. Carbon has a very useful electronic configuration which allows it to bond easily with 4 atoms at once.
The basic organic molecules, alkanes, alkenes and alkynes, contain only carbon and hydrogen. However, many other ‘functional groups’, can be added to the carbon chain to change the properties of the substance. For example, oxygen, nitrogen, sulphur or chlorine. However the vast majority of plastics do not contain the latter two.
If you aren’t familiar with the structure of organic compounds, here is an example:
The above substance is polyester. The brackets and subscript ’n’ around this diagram représentant the fact that this is a single unit of polyester, which is repeated in a chain to create the full fabric. As you can see, there is only carbon, hydrogen and oxygen in polyester (the three elements most common in the human body). The overall structure is reasonably complex, with two standard methyl links, two ester groups, and an aromatic ring (benzene).
So, where do the elements and substances, that make up plastics like polyester, come from?
The answer is, of course, from fossil fuels. Crude oil, petroleum, coal, and natural gas are entirely composed of these organic substances, and plastics are made by utilising various chemical processes, with chemicals from fossil fuels.
Fossil fuels, in turn, are made of dead and compressed organic matter (this time referring to things that were previously alive, like trees).
So if you were to go way back into the history of the atoms in that pair of polyester underwear you’re wearing, they might have been part of a dinosaur, or a huge tree.
Now Enough About Plastic Making Process, Let us talk about how plastic is molded into various shapes.
Plastic Molding Processes-
The main process used to form plastics. A heated plastic compound is forced continuously through a forming die made in the desired shape (like squeezing toothpaste from a tube, it produces a long, usually narrow, continuous product).
The formed plastic cools under blown air or in a water bath and hardens on a moving belt. Rods, tubes, pipes, Slinkys, and sheet and thin film (such as food wraps) are extruded then coiled or cut to desired lengths.
Plastic fibers also are made by an extrusion process. Liquid resin is squeezed through thousands of tiny holes called spinnerets to produce the fine threads from which plastic fabrics are woven.
Injection Molding –
It is the second most widely used process to form plastics. The plastic compound, heated to a semifluid state, is squirted into a mold under great pressure and hardens quickly. The mold then opens and the part is released. This process can be repeated as many times as necessary and is particularly suited to mass production methods. Injection molding is used for a wide variety of plastic products, from small cups and toys to large objects weighing 30 pounds or more.
Pressure is used to form hollow objects, such as the soda pop bottle or two-gallon milk bottle, in a direct or indirect method. In the direct blow-molding method, a partially shaped, heated plastic form is inserted into a mold. Air is blown into the form, forcing it to expand to the shape of the mold. In the indirect method, a plastic sheet or special shape is heated then clamped between a die and a cover. Air is forced between the plastic and the cover and presses the material into the shape of the die.