Polymers and research: a continuous interaction
Since the discovery of synthetic materials, it has been customary to associate polymers with plastics. In the collective unconscious, these two words are perfect synonyms. This is not wrong since all materials in the synthetic plastics family are polymers, but there are also natural polymers. First of all, it is important to know that a polymer is nothing more than a large molecule made up of a repeating chain of small molecules otherwise known as monomers. And, just like the chemical industry, nature is very good at producing monomers and assembling them into polymers.
Man's use of natural polymers can be traced back to more than 3,000 years before our era
These include plant fibres, cellulose, animal sinews, wool, leather, and more - materials that man has been taming since the Stone Age. Ötzi, for example, the mummy discovered in the 1990s in the Ötztal Alps (hence the nickname Ötzi) in Italy, was carrying an axe at the time of his death, the flint tip of which was glued to the handle with birch pitch.
3,200 years before our time, the use of polymers such as pitch, a natural glue made from tree resin, had already been mastered. In Central America, there are also traces of the use of a kind of gum made from rubber derived from the resin of the rubber tree around 1,600 B.C.
In Western countries, the first applications of this natural rubber only emerged in the 17th century.
In 1839, the American Charles Goodyear discovered the rubber vulcanisation process by chance. This made it possible to transform the relatively liquid sap of the Hevea tree into an elastic rubber whose use is still very widespread, particularly in tyres and soles (see our article https://plastic-lemag.com/Lart-dexploiter-linattendu).
Bakelite: a historic invention
Bakelite was the first synthetic polymer in history. It was invented by Leo Baekeland, a Belgian-American chemist who was researching a new electrical insulating material. It was to be very successful in the first half of the 20th century. This thermosetting polymer (which, once heated and moulded, retains its final shape) consists of benzene (a hydrocarbon) and solvents. It was the first plastic to be produced and marketed on a very large scale. It was found in telephones, radios, household appliances (hoovers, hair dryers, etc.), costume jewellery and, above all, in light switches.
The luxury brand Rolls Royce even boasted that it was used in the finishings in the interior of its vehicles, as this material was perceived as being at the cutting edge of modernity and chic. It paved the way for the chemical plastics industry to develop new polymers with ever more astonishing qualities in the years that followed.
Bakelite, the first synthetic polymer in history, was to enjoy considerable success in the early 20th century.
The title of first synthetic polymer in history is sometimes claimed by Parkesine, invented in the early 1860s. It consists of a mixture of cellulose nitrate, a natural element derived from plants, and an animal oil. It is therefore an artificial polymer, obtained by chemically modifying natural elements. It cannot be called a synthetic polymer. Unlike Bakelite, its success did not meet the expectations of Alexander Parkes, its English inventor. The reason for this was his desire to reduce production costs, which undermined the quality of his material. But his discovery was not accidental, since the American John Wesley Hyatt improved it by introducing camphor, an organic compound derived from the camphor tree, and collodion, an antiseptic. This new polymer, which he named celluloid, was to have a much more enviable destiny.
It was the middle of the American Civil War (1861-1864) and the North was subjecting the South to an economic blockade, which concerned ivory in particular: a precious material used to make billiard balls, a very popular game at the time.
Celluloid, invented as a substitute for ivory, was until recently used to manufacture table tennis balls.
The winner was John Wesley Hyatt. The success of celluloid was not to be based solely on billiard balls. It was used to make almost everything that was previously made of ivory: combs, cutlery handles, piano keys, false teeth, dolls that are now highly prized by collectors and, of course, the photographic films that made Kodak's fortune. However, this polymer had the defect of being highly flammable. With the arrival of new polymers considered less "dangerous", it was gradually replaced until it fell into disuse. About ten years ago, however, it was still produced to make table tennis balls, but in 2013 the International Table Tennis Federation decided to switch over to polypropylene.
1920s: plastics also had their roaring twenties
In the 1920s, the chemical and petroleum industries were booming and saw polymers as future materials to be improved and developed. As drilling and refining techniques improved, oil became an increasingly important energy source. At the same time, the growth of the automotive industry required an ever-increasing amount of fuel. However, once the oil had been refined into fuel, lighter, gaseous fractions such as naphtha remained, which no one knew what to do with at the time. Subsequently, chemists mainly used naphtha as the basis for designing new materials: polymers.
The First World War did not lead to any major advances in the field, and it actually hindered the development of these new materials.
After the marketing of Bakelite at the end of the 1900s, it was not until about twenty years later that new synthetic polymers appeared. The invention of PVC is a perfect example of this. It was discovered in 1835 when a French chemist noticed that a white paste appeared on a bottle containing vinyl chloride, a mixture of ethane, potassium hydroxide and ethanol, that had been exposed to light for a very long time. The story could have ended there if, at the beginning of the 20th century, a Russian chemist had not finally taken an interest in this discovery. He tried to use this paste, which was not yet called PVC (polyvinyl chloride), to manufacture objects. His efforts were in vain and the war and the Russian revolution put an end to his ambitions. It was not until 1926 that the American B.F. Goodrich succeeded in stabilising the polymer by adding additives. Now flexible and easier to manufacture, PVC would really take off in the following decade.
Today, it is still one of the stars of the polymer family. In its rigid form, it is used, among other things, to make sewage pipes (40% of PVC production is used for these pipes), credit cards and bathtubs and washbasins. In its flexible form, it is also used in floor and wall coverings. It is also the polymer used to make the famous vinyl records that were thought to be dead and buried for several decades and are now making a comeback.
PVC is a polymer widely used in the construction industry and is also the material used to make vinyl records.
The story of PMMA (polymethyl methacrylate) has a lot in common with that of PVC as it was discovered long before it was even commercialised. It dates back to the end of the 19th century when a German chemist succeeded in polymerising methyl methacrylate into a solid, highly transparent polymer. Long before polycarbonate, for example, it was the first organic glass in history.
This was a significant discovery, but it did not interest many people at the time because the synthesis of methyl methacrylate (the monomer) was complicated and very expensive, and its applications appeared to be very limited. The First World War did not help matters. PMMA also experienced a revival in the 1920s and was first marketed as an organic safety glass by the British company ICI. In 1940, the first contact lenses appeared. During the Second World War, it was used to manufacture turrets for bomber aircraft because it was considered less dangerous than glass for the eyes of machine gunners in the event of enemy attacks. This polymer was chosen for its optical qualities by manufacturers of illuminated signs. The furniture industry and its designers love it for its ease of moulding and for its ability to enhance their work.
1930s and 1940s: polymers during war time
The 1930s were years of uncertainty resulting from the international tensions that would lead to the Second World War. And for good reason, the looming world conflict was going to push nations to find new materials, particularly to make up for the possible shortages inherent to each armed conflict. For Germany, there was greater urgency as it was gradually cutting itself off from the world and had lost all its colonies in the First World War. It was thus unable to access latex to produce rubber or gutta percha, a natural polymer close to its cousin rubber and also derived from an exotic tree: palaquium gutta. With its chemical industry already at the cutting edge, Germany relied on the skills of its researchers to quickly find substitutes for natural materials. It was not the only country to do so, as the British and the Americans also accelerated their research. At the time, the main concern was to find new materials to make weapons and defence systems more effective.
The 1930s and 1940s were boom years for polymers. The urgency to find new materials in wartime accelerated their development.
Most of the polymers still in widespread use today were finalised in the 1930s and 1940s. Interestingly, although their respective formulas (or at least their embryonic forms) had sometimes been known for several decades, they were not always in use. Industrialists did not consider it useful to refine their research with a view to marketing them.
This technological evolution experienced in the 1930s/1940s within the world of chemistry is in every way comparable to that experienced by digital technology from the 1980s onwards.
The birth of a king
Surprisingly, while many monomers were already polymerised, the simplest of them all - ethylene - was not. Its polymerisation seemed impossible because it required pressures that were unlikely to be achieved mechanically. A British team succeeded in 1935 and synthesised the polymer that is still most widely used today: polyethylene. It was soon put into production and used to seal submarine cables as an efficient replacement for gutta percha.
It was also used to insulate the high-frequency cables of the first radars, devices that were absolutely crucial to the Allied victory.
Without polyethylene, it would have been much more difficult to develop the radars that played a major role in the Allied victory.
After the war, new applications were found in packaging, initially for shampoos starting in the 1950s. It was the basis for the design of the famous Tupperware boxes, and then gradually found its way into our cars, planes, films and, of course, all kinds of containers.
Plastics also become guardian angels
Other stars of the field, polyamides (some of which are better known by their commercial name of Nylon) were developed during the war years. They were also discovered in the 1910s, but the polymer chains were too short to be spun. This is an important detail, since polyamides were created to find a substitute for natural silk, the production of which was costly and even uncertain due to the high propensity of silkworms to fall ill.
Although the paternity of woven polyamide goes to the American Dupont de Nemours in the 1930s, the German IG Farben was also working on this material and succeeded in launching its production in the early 1940s. In the United States, its first application was in toothbrush bristles, but due to the conflict, it was mainly used to make parachute strings and canvases in both Germany and the United States, as well as aircraft tyre carcasses.
During the 1944 landings, all the GIs' parachutes were made of polyamide. Its lightness, strength and low coefficient of friction made the parachutes safer and saved a considerable number of lives. Without this polymer, the D-Day landings would have been very different and possibly even have ended very differently, as it would have been impossible to manufacture thousands of parachutes from silk as had been the case until then. At the end of the war, parachute production obviously fell, but polyamides continued their rise and were woven into stockings and lingerie that gradually became popular clothing among women around the world.
Today, the polyamide family is made up of more than a dozen members, depending on the composition of their warp, and some are biobased, such as Rislan, a castor oil-based polyamide that is used to manufacture sanitary equipment, medical devices and clamps, among other things. Others, such as Kevlar, are decidedly high-tech and are much more recent, having been commercialised in 1971. It was developed by Stephanie Kwolek, an American chemist working for DuPont, who wanted to develop a new fibre to improve the structure of tyres. This fibre, five times stronger and much lighter than steel, resistant to shocks and tugging, and capable of withstanding heat of 400°, was soon to find a number of good uses, notably in bulletproof vests. Today, it can be found in pilot suits, gloves, sporting goods, boat sails, brake linings and, of course, tyres.
The recently discovered polyamide was used to make the thousands of parachutes needed for the 1944 landings.
Silicones, namely polyurethane, styrene butadiene, PTFE (polytetrafluoroethylene, better known as Teflon) were also developed during the Second World War and all found their first applications in the military. PTFE, for example, was the only material capable of withstanding the extremely corrosive acids used in the processing of uranium 235. It was used to make the seals in the first atomic bombs that ended the Pacific War in 1945. Polyurethane was developed by the German company Bayer, which was looking for a substitute for American nylon. In the early years of the war, the company mixed water with urethanes and obtained a foam that was initially used to insulate submarines and combat aircraft.
The second world war was a catalyst for the chemical industry. Both sides developed new polymers that would become indispensable in the following decades as they found new applications.