History of Plastics
In the period between the Wars, there was a huge increase in the polymer industry (large molecules, which we call plastics), its later development being very interconnected with petrochemical. Man has always used natural polymers (silk, wool, cellulose…), but the chemical interest in polymers dates back to the early 19th century. At this point there were attempts to chemically modify natural polymers to give them other uses and properties, and some examples have been mentioned in previous posts. The first non-natural polymer was cellulose nitrate, manufactured in 1862, by the nitration of the natural cellulose polymer. Celluloid, which was cellulose nitrate mixed with camphor to become more malleable, it was used to replace ivory in billiard balls and piano keys, later it was used to produce movie films. However, it is highly flammable and had to be replaced. Other examples of modified synthetic polymers include cellulose acetate used for waterproofing the fabrics used in aircraft manufacturing in World War I, semi-synthetic fibre, films in the photographic industry, as well as vulcanized rubber. The first 100% synthetic polymer, i.e. man-made from small molecules, was bakelite, introduced in 1909 and developed to substitute a missing natural product that is still used today. Although the reaction was discovered some 20 years earlier, a very systematic and careful study was needed to conveniently control its manufacture. In the 1930s and 40s, the development of high-pressure technology and chemical polymerization theories led to several other polymers like nylon and polyethylene in the market. Polyethylene is probably the most produced plastic. This polymer was first prepared in Britain in 1934 in the ICI’s laboratories. The industrial production began five years later, almost at the beginning of World War II. Its first application was as an insulation in the electrical wires of the military radars. Given their importance in the war and the difficulty of working efficiently if polyethylene was not available, it is often said that polyethylene was the plastic that won the war. This was only the beginning of an industry that allowed us to have access to a great variety of new materials with unique characteristics, and to what we owe regarding the way we live and its contribution to the development of science and technology.
The first successful attempts to produce a synthetic plastic owe to Leo Baekeland, a Belgian chemist who in 1909 patented the preparation of the first fully synthetic polymer he called bakelite. This polymer, which is a phenol formaldehyde resin, has been developed to replace a natural product, Shellac resin, which is out of stock. After the reaction was discovered, it took nearly about 20 years for a very systematic and careful study to conveniently control its manufacture. Due to its insulating properties, bakelite has not only been extensively used in the electrical industry, but also for everyday use and for jewellery. Many of these objects are now sought after by collectors and are exhibited in museums. Interestingly, Andy Warhol adored bakelite objects, when he died in 1987 his collection hit record prices at Sotherby’s.
The first man-made plastics were obtained through the modification of natural polymers such as cellulose or proteins – this is the case with celluloid. Another example is natural rubber, which has to undergo transformations in order to be used. In fact, natural rubber loses its elasticity and becomes sticky when heated. This is because it is constituted by the polyisoprene chains at high temperatures and they are interlaced, slide over each other and do not return to the original status. Charles Goodyear slightly solved this problem by chance. He was an inventor and for many years investigated how to keep rubber elastic at high temperatures. For 10 years he worked without any success since the investigations were done moderately at random as little was known about the molecular structure. Until one day in 1839, he accidentally dropped a mixture of natural rubber and sulphur into a hot oven. When the mixture cooled a little he found that despite the heat, the rubber showed elasticity. Today we know that the sulphur will bind to the polyisoprene chains interconnecting them and forming these a three-dimensional network. The sulphur bridges between chains prevent the molecules from sliding at high temperatures and thus maintaining the elasticity of rubber. This process is called rubber vulcanization and is still used today, with vulcanized rubber mainly used in the tire manufacturing.
The investigation leading to the discovery of nylon was carried out by W. Carothers and his collaborators in DuPont laboratories. At that time, it was already acknowledged that wool and silk were proteins and the molecular structure of such was known. As they intended to produce fibres, they tried to synthesize new polymers with certain similarities to the proteins of silk and wool. Carothers and his group produced several nylons using different amines and organic acid derivatives (the molecules they used as building blocks and attached to one and other to provide the long molecules of the fibre). The nylon first used in toothbrushes was in 1938, but it did not spark great interest. However, when it was used to replace (very expensive) silk in ladies’ socks in 1939, it was a huge success. It is later also used for manufacturing clothing.
When World War II began, it was preferable to produce parachutes, ropes, and other materials needed by the military due to the limited amount of nylon… nylon socks were not a priority. Given their shortage, they were highly sought after, high in value, and used as an exchange currency. It was not until the 1950s that production of nylon was sufficient to meet the demand for socks. In the following image you can see an advertisement promoting socks after the war. However, despite being widely used as fibre, it can be shaped in other forms and is used to replace metal parts in some machines. This type of application results from the fact that it is strong, rigid, abrasion resistant and poorly reactive. The use of nylon in clothes did not interest consumers at first. As it is hydrophobic (not “liking” water), nylon fabrics did not absorb moisture or permeate through it, thus making these fabrics become irritating. There had been thoughts to produce a new fibre, but it would have been expensive and there were already machines developed for nylon fibres and were not adaptable to other fibres. The solution was not a new fibre, but a new technology to process nylon. There has been a development to produce finer fibres and to remove their lustre and make them look more pleasant and more similar to natural fibres. The characteristics of the wire were also changed by introducing a large number of loops, which allow the fibre to remain waterproof, as they are thin enough not to let the liquid water pass through but rather allow the fibre to “breathe” with a pathway for water vapour in between the loops. This new fibre, softer and more textured than cotton, was called Tactel.