Polypropylene is the second most profitable polymer in history. Its thermoplastic nature and low production techniques are the main reasons behind its popularity.
Look around yourself right now. What do you see? You may be sitting in your room on a plastic chair, comfortably holding your plastic smartphone or laptop and eating chips out of a plastic packet. By now, you probably understand where I’m going with this. Plastic is all around us, and whether we like it or not, it is perhaps the most important discovery of the 21st century.
The introduction of plastics into our lives has changed them in immeasurable ways. Whether it is the low cost of products or their durability; everything has improved with the rise of the plastic empire. Although this plastic has slowly started to create environmental issues worldwide at an alarming rate, researchers are continually working to create a substitute that will be safe and biodegradable at the same time.
What is polypropylene?
Polypropylene is a plastic polymer. A polymer is a chemical substance with a molecular composition that looks like a chain. The chain is made of many identical links, called monomers. The number of monomers in a single polymer chain can range from less than a hundred to hundreds of thousands. Propene (IUPAC) or propylene (common name) is the monomer or basic building block of polypropylene. It a simple unsaturated hydrocarbon containing three carbon atoms and six hydrogen atoms, as well as a double bond between any two of the carbon atoms.
The history of polypropylene goes back to the 1960s when two American chemists, Robert Banks and J. Paul Hogan, first found a way to polymerize polyethene. The end product from their process was astonishing. This led to heavy research in the manufacturing techniques of polypropylene. Today propylene occupies the largest share in the polymers market, and it is the second most profitable polymer in history after polyethene. Its global market in 2016 stood at over 71 billion USD (Cresana), and this number is expected to cross the 100 billion mark by 2020. So, what are the reasons that make it so useful and profitable?
How is polypropylene manufactured?
Polymers are primarily produced from their respective monomers through two kinds of production techniques: Step-growth polymerization and Chain-growth polymerization. For the manufacture of polypropylene, we use the latter. Polymerization techniques are generally quite slow and require catalysts to speed up production. For the polypropylene, Ziegler-Natta or metallocene catalysts are used. Today, due to extensive research, many different types of catalysts and production techniques are available for making polypropylene. As such, the proprietary costs aren’t very high.
The manufacturing technique can be either gas phase or liquid phase. The gas phase method involves a fluidized bed, or a continuous flow stirred reactor. The monomer is fused at very high temperatures and allowed to flow over a bed of catalyst where the polymerization takes place. The liquid phase process involves a slurry or solution of the monomer, along with droplets of the catalyst. As this mixture is rapidly agitated, the catalyst reacts with the monomers, polymerizing them into the required product. This process is similar to the micelle formation technique. The reactors used in the process are simple batch or continuous reactors that do not require a high capital investment.
Where is propylene obtained from?
Plastic polymers are generally derived from low to medium molecular weight hydrocarbons. These hydrocarbons are retrieved from natural gas or crude oil. The fractional distillation of these fossil fuels differentiates them into various carbon-based entities based on their volatility, which in turn depends on their molecular mass. One such fraction yields monomers, such as ethylene and propylene, which are later used to form their respective polymers. As these chemicals are the byproduct of an already booming industry, their production occurs on a very large scale, which makes them available at relatively lower prices.
What properties of polypropylene make it so special?
Polypropylene, like most other plastics, does not react with acidic or basic solutions. It’s not easily oxidized and is also resistant to fats and organic solvents. Its chemical resistance is much greater than wood or metal, which is one of its most important properties, making it an invaluable industrial resource.
The thermal properties of any polymer basically dictates its relevance in the market. Most industries deal with chemicals and solutions at high or low temperatures, and the relevant polymer needs to be compatible in such working environments to be of any real use. The melting point of commercial polypropylene is about 165°C, which is good enough for holding fluids and gases at manufacturing plants.
Polypropylene is a thermoplastic polymer, which means that it will melt at temperatures higher than its melting point, but solidify to its original composition upon cooling down. This is different from thermosetting polymers that set to a fixed temperature once they’re cooled down from their melting point. If their temperatures are raised once again, they tend to become charred. The thermoplastic nature of polypropylene allows it to be injection molded into any shape, which also makes it recyclable, to some degree.
A Final Word
Polypropylene is used in the manufacture of household and industrial appliances, which makes its market much wider. With stricter environmental norms, cutting a tree for wood and mining metals has become really tough. As such, the polypropylene market has a great opportunity to capture the void created by the decrease in use of these conventional materials.
The global production of polypropylene polymer in 2016 stood at more than 73 million tons, and with rising population and consumption trends, this number will grow exponentially in the future. Demand from the automotive, construction and disposable consumer products industries will drive the demand for all plastics, and as such, the future for polypropylene looks very bright!
- The Essential Chemical Industry
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