Plastic has become such an essential part of our lifestyle, common material for producing end-use parts and products, from consumer products to medical devices. It’s second nature to accept a plastic item and not think about the material at all – and get rid of it within minutes. Humans produce 380 million plenty of plastic every year. And 50% of that are single-use; items we buy and throw away within minutes sometimes. But how are plastic parts made?
A variety of plastics manufacturing processes have been developed to cover a wide range of applications, part geometries, and kinds of plastics. For any product designer and engineer working in development, it’s critical to be familiar with the manufacturing options available today and the new developments that signal how parts will be made tomorrow.
This guide provides a summary of the most common plastics manufacturing processes for producing plastic parts and guidelines to help you select the best option for your application.
What are Plastics Made of?
Most of the plastics in use today are made from hydrocarbons, organic molecules containing entirely carbon and hydrogen. These hydrocarbons are derived from materials of biological origin occurring within Earth’s crust, referred to as fossil fuels. Fossil fuels are created from the petrified, buried remains of plants and animals that existed many years ago. Some samples of fossil fuels are:
Crude oil
Also known as liquid petroleum. It’s often found in oil sands (tar sands), underground reservoirs, and within the gaps and pores of sedimentary rocks. It’s often obtained by drilling on land or at sea, or by opencast mining. Plastics production is responsible for about 5% of oil production worldwide.
Natural gas
Also known as methane gas. Counting on where it’s located underground, gas is classified as either conventional or unconventional. The traditional type can be found in permeable bedrocks or blended into oil reservoirs and can be extracted using ordinary drilling techniques. On the opposite hand, unconventional gas extraction requires special techniques such as fracking, since the regular drilling techniques are often too costly and difficult.
Coal
It may be a solid, carbon-rich rock that’s classified into four types based on its carbon content: lignite, sub-bituminous, bituminous, and anthracite. Coal extraction is completed by either underground mining, which utilizes machines to mine coal from deep underground seams, or surface mining, which scrapes layers of soil to urge to the coal deposits. It is not that commonly used in Western countries but is used relatively frequently in China.
Plastics Manufacturing Process
This section will cover everything you would like to know about the entire plastics manufacturing process, starting from raw material extraction up to its fabrication.
Extraction of Raw Materials
The overwhelming majority of plastic produced is made of fossil fuels. Therefore, extracting petroleum, gas, and sometimes coal from the bottom is the first step.
Refinement
Fossil fuels are sent to refineries where they’re converted into different petroleum products, like gasoline, asphalt, jet fuel, waxes, and lubricating oils. This is the part where the building blocks of plastic, ethane, and propane, are also created.
The crude oil will be heated in a furnace before being vaporized and sent to a fractional distillation tower. The distillation tower features a temperature gradient, with the top being colder than the bottom. Based on their boiling point (the temperature at which the phase shift from liquid to gas happens) and weight, the liquids, and gases within the tower get segregated. The vapors of the lighter fractions, like gasoline and petroleum gas, drift to the top of the tower, while the heavier ones, like residual fuel oil, remain at the bottom.
All of those fractions in the tower contain hydrocarbons with a comparable amount of carbon atoms, with smaller molecules marching to the top. Gas liquids (NGL), like ethane and propane, also with naphtha are the most essential feedstock for the plastics manufacturing process. However, to be useful, these hydrocarbons have to be sent to a cracker plant and undergo a procedure named cracking.
Cracking
By utilizing heat, pressure, and sometimes catalysts, the complicated hydrocarbons are weakened into simpler, low molecular mass alkenes/alkanes. This process is vital because it transforms the abovementioned ethane into ethylene, also as propane into propylene. There exist two sorts of cracking: steam cracking and catalytic cracking.
The steam cracking process is administered in steam crackers, which are extremely complex and energy-intensive facilities. This is where the chemicals are first mixed with steam and then heated to 1430-1610 degrees Fahrenheit inside a tubular reactor. In order to prevent the feedstock from forming carbon, which could happen at such temperatures, it’s being sent through the furnace’s pipes very fast and at very low pressure.
The catalytic cracking process doesn’t require such high temperatures or pressure due to the presence of the catalyst. First, within the reaction phase, the feedstock is contacted by a catalyst at temperatures of roughly 900 degrees Fahrenheit, and therefore the cracking reaction occurs. Product proportions are determined by the temperature, the duration, and therefore the catalyst.
Polymerization
In polymerization, monomers are linked together by a reaction in order to form polymers. This will be achieved by either addition, which ends up in all of the monomer’s atoms being present in the polymer, or by condensation, which ends up in the formation of a tiny molecule byproduct.
Plastic Fabrication
Fabrication is the last step of the plastics manufacturing process, in which the plastic gets its final form. So, to make it easier to transport, plastic resins are most often further processed into pellets. These pellets are then reshaped to be crafted into various plastic products. It’s always a good idea to start out with a 3D printed plastics prototype.
