What is a polymer?

Luck is nothing without science

Luck can be a factor in developing new materials. However, although it is a significant element, it is far from being essential. Although many scientists were groping around in the dark in the early 20th century, it is no longer the case. Without going into the difficult details of macromolecular chemistry, manufacturing a plastic is the result of polymerisation, which is the process through which small molecules, such as carbon-based molecules extracted from oil, react with each other to create molecules with a higher mass. The presence of reagents and catalysts, combined with heat and pressure, are other essential factors for the formation of so-called macromolecular chains that give birth to a variety of polymers. It goes without saying that the "mad scientist" approach no longer has a place in this highly scientific industry.

Polymers: as old as time itself!

A polymer is a giant molecular structure. It is a macromolecule comprised of a long chain of smaller and identical molecules that are attached to each other like pearls on a necklace. Although the term "polymer" was coined at the end of the 19th century, this type of molecular structure exists in nature and has always been used by man. Amber, scales, resin from trees, wool, hair, the secretions of certain insects such as lacquer and silk, are plastics because they are mouldable. The cellulose found in trees, grass, flax, hemp and cotton is the most common of the natural polymers.

Better than nature

At the end of the 19th century, the scarcity of certain polymers or the simple desire to copy nature galvanised researchers, who were able to create artificial polymers by chemically transforming natural polymers. These were the first plastics, in the strictest sense of the word. Man created nitrocellulose (celluloid, artificial silk) to replace ivory, silk and materials with new properties that could one day find new applications, such as ebonite. Finally, synthetic polymers, that were mainly a result of petroleum chemistry, were increasingly used during and after the Second World War. Scientists no longer looked to nature for inspiration, but rather created new materials that were increasingly resistant to impacts, to temperatures and chemicals, that were lighter...and easier to mold.

Trade secret

Manufacturing synthetic polymers requires oil to be heated to approximately 400°C in a fractionating tower (the large and visible towers in refineries). After heating, the naphtha is collected from the top of the tower; it is a transparent liquid resulting from the condensation of oil. This liquid is essential in the manufacture of plastic. It is also used to produce dyes, fertilisers, cosmetics and various household products. Once they have been collected, the molecules extracted from the naphtha are broken down (cracking) with steam in a steam cracker. The naphtha and steam are combined and heated at 800°C, at which point the temperature is suddenly lowered to 400°C. The process creates small molecules. The molecules are made up of 2 to 7 carbon atoms and are called monomers. They are then subjected to reaction and linked together to form polymers, which are the beating heart of plastics.

Similar operations can be performed with natural gas due to its high ethane content; the gas is also one of the raw materials used to create plastics.

Two branches for a single family

A material is called "plastic" when it retains the desired shape after having been deformed by an external action such as heating. All plastic materials, be they natural or synthetic, are comprised of polymers. A polymer's properties depend on the nature of their basic molecules and the way in which they are interlinked. These structures serve to classify plastics into two distinct families, depending on their reaction to heat: thermoplastics and thermosetting plastics. The vast majority of polymers are thermoplastics (PVC, PET, polyamides, etc.). Once it has been manufactured, the polymer can be heated and re-shaped at will. The speed at which it can be done, and the possibility of re-using production waste or recycling them mean that they are often used. Thermosetting plastics (epoxies, phenolites, etc.), on the other hand, cannot be melted down and cannot therefore be deformed through the application of heat. On the contrary, in fact: the more they are heated, the more rigid they become./p>

Transformation !

Regardless of their family, polymers often take the form of pellets that are subsequently melted down and molded either by injection or extrusion. In the first case, the pellets are heated and inserted into an endless screw that pushes the melted polymer into a mold. The principle is relatively similar in the second case, the only difference being that the polymer ends up in a die which pushes it out as a filament yarn such as a fibre, for instance. Finally, the melted pellets can also be calendered (or rolled), an operation that consists of pushing the material between two cylinders to produce a film or a sheet.
Polymers can be molded, extruded, rolled or even mixed with solvents to produce glues or paints. In short, they come in all shapes, appearances and colours. Their intrinsic properties can even be amplified through a large range of additives that provide them with more or less flexibility and a texture suitable for their intended use.

So what are composite materials?

Finally, let us not forget composite materials which are also often a product of the chemical industry. A material is called a composite when it is comprised of at least two components whose respective properties complement each other to form a single material with improved properties. A composite material is comprised of reinforcement, in the form of fibres or strands, and a matrix made from a thermosetting resin. The reinforcement, which is usually carbon or glass although it can also be made from aramid, provides most of the mechanical properties. The resin acts as a binder and also contributes its basic mechanical properties. The reinforcement itself is flexible: it only becomes rigid when it is combined with the resin.

An industry rich with promise

Much like the computing industry, scientific research in the plastic industry does not let up. It is still a promising area in which extraordinary breakthroughs are sure to happen over the coming decades. Who would have imagined, barely 20 years ago, that plastics would one day conduct electricity? Plastics are an invitation to boldness. They can be insulating or conductive, light and resistant, flexible yet unbreakable, transparent or opaque. Some plastics, such as the so-called high performance plastics, have incredible properties such as resistance to temperatures above 250°C, resistance to wear and corrosion and, of course, their light weight. Organic resin composites are already in use in high-tech sectors such as the aerospace industry where they are used in wings that simple air friction can heat up to over 250°.

Intelligent plastics

Plastics are even becoming intelligent. For several years now, new types of products are being produced that straddle two industries: plastics and electronics. Plastronics has enabled the creation of high added value plastic systems that combine electric components that provide intelligence with plastic components that provide the mechanical functions. Finally, the so-called self-repairing plastics will enable materials to recover their original shape after being deformed. These polymers act like blood coagulating subsequent to an injury. It goes without saying that the automotive industry is extremely interested in these new properties.

Behind the scenes of success

Look around you. We live in a world filled with polymers. From the most basic to the most high-tech, all industries use them. In certain cases, such as in the automotive and sports equipment industries, they have become more than essential. Why are they so successful? Contrary to popular belief, most industries are interested in plastics for more than simply-budgetary reasons. While it is true that a great many polymers can be cheaply produced, it is not always the case. The key advantage of plastics is their light weight and their ability to take any shape. In certain fields, they have no competition. It would have been impossible to build the International Space Station without plastics. Weighing in at 400 tonnes, the ISS is far from a small structure. Without composite materials, it would be several dozen tonnes heavier.

Considering that it costs € 25,000 to send just one kilogramme into space, space agencies would have been crippled with debt. The automotive industry would not be the same either: thanks to plastics, vehicles have been slimmed down and the resulting fuel economy of 750 litres of fuel over their lifetime is quite an achievement. Of course, such technological advances are not made at the expense of safety, as in many cases polymers are more resistant than metal. After all, it is Kevlar, a synthetic polymer, which is used in the manufacture of bulletproof vests.