Bakelite 111 years old

A milestone in this context was the development of initially semi-synthetic and later completely synthetic high-polymer substances (polymers), for which the German chemist Ernst Richard Escales (1863-1924) coined the word “Kunststoffe” (= “plastics”) in 1910: such products as film material and imitation mother of pearl could be made from celluloid based on nitrocellulose and camphor. Erinoid (galaltih) based on casein and formaldehyde became the epitome of costume jewellery.

For quite a long time, industry made use of such natural polymers as rubber, the resin from the Hevea brasiliensis tree that is native to South America, and shellac, which comes from the resin-like secretions of a lac bug (Laccifer lacca) that is native to South-East Asia. “About 150,000 of these tiny bugs take almost six months to produce enough resin for a pound of shellac” (Mark 1970, 79-80). The natural resin, which was in demand not only from the gramophone record industry but also from the electrical engineering industry as a non-conductive insulation lacquer that was a very welcome solution to problems there and which could be used as a bonding agent, sealing lacquer, varnish, polish, veneer, coating, putty and glue substitute, was therefore an expensive substance.

At the time, inadequately insulated electricity lines and power distributors endangered factory workers, while large amounts of electrical energy were lost to the environment as well. In addition to natural resins, apart from shellac, for example including hard rubber, rosin, copal, gutta-percha or amber, mineral compounds like glass, porcelain, plaster or chalk are also suitable insulators, without being thoroughly convincing. Many insulation materials failed to withstand the heat caused by a loose connection or short circuit, for instance (Brandenburger 1938, 20). And the rule in the production process was: parts moulded cold required long storage periods for setting, while parts moulded warm required long storage periods for cooling (Raubach 1960, 35). For this reason, production of the insulation components needed in huge quantities by the electrical engineering industry at the end of the 19^th century and the beginning of the 20^th century was a both lengthy and costly process.

In other words: limits were very soon reached at the qualitative and quantitative levels with the materials that were available. Shellac was unable to solve the problem either, for the reasons already outlined above, i.e. due to the lack of sufficient and affordable volumes. “An intensive search therefore began for good insulation materials, which were supposed at the same time to meet the requirements of being less fragile than glass and porcelain, shapeable without cutting, lightweight and cheaper than natural resins” (Raubach 1960, 34). Chemists tried out hundreds of alternative materials, including the thermoplastic indene/coumarone resins synthesised from coal tar and sulphuric acid by Rütgerswerke in Erkner near Berlin, which were invented by Gustav Kraemer (1842-1915) and Adolf Spilker (1863-1954) in 1890 (Collin 2003, 149, Collin 2010, 10, and Koßmehl 2010, 10). A genuine breakthrough was not made, however.

This was a challenge that appealed to the Belgian chemist Leo Hendrik Baekeland. He was born in Ghent on 14. November 1863 as the son of a cobbler and already attended evening lectures about technical chemistry at the industrial college there at the age of 14 on a scholarship provided by the city of Ghent authorities. When he left three years later, his report noted medals in physics and chemistry and confirmed that Baekeland had received his diploma in industrial chemistry “with distinction” (Collin 2007, 3). 

The promising young man then – in 1880 – immediately received the next grant from his home city, so that he could start studying natural sciences at Ghent University. Baekeland’s academic teacher for general chemistry was Professor Théodore Swarts (1839-1914), who was the successor to the German Professor Friedrich August Kekulé (1829-1896), who developed the classic structural theory in organic chemistry. 

In 1881, Baekeland was appointed to a position as as an assistant in Swart’s laboratory and finally completed his chemistry studies in 1884 by obtaining a doctorate “summa cum laude” at the tender age of 21. The next place where he made a name for himself was in the natural sciences faculty of the teacher’s training college in Bruges, where he was an assistant professor. 

In 1887, he was awarded a gold medal by the Belgian Academy of the Sciences as well as a travel grant in the context of a university competition for his scientific paper about the phenomena of electrolytical dissociation (Collin 2007, 5, and Braun 2010, 22). Baekeland used the grant for stays at universities in London, Oxford and Edinburgh as well as at Columbia University in New York with Professor Charles Frederick Chandler (1836-1925). The latter was so impressed by Baekeland’s skills, that he tried to persuade him to stay in the United States and work there as a scientist from then on. 

“Ghent University attempted to keep its gifted chemistry graduate in his home country and appointed him to be associate professor in its science faculty on 25. September 1889. However, Baekeland wanted to move to the country of his dreams and his role model Benjamin Franklin (1706-1790, editor’s note), who – like him – came from a poor background and worked his way up to being a world-famous statesman and scientist” (Collin 2007, 6). 

In Baekeland’s family it was a tradition to migrate to America, albeit in different circumstances: some of his ancestors, who eked out a living as cloth-makers and linen weavers, sank into poverty due to the triumphant success of cotton and left Flanders and their desperate situation there to try their luck in the USA (Collin 2007, 1). Leo Hendrik Baekeland’s situation was different – he was attracted by the safe prospect of money and a career, because he had a bright future as a chemist.

He and Professor Chandler shared a passion for photography, which Baekeland had developed while still at school and which he never lost. The young Baekeland obtained the necessary chemicals to prepare photographic plates. He managed to get hold of the silver salts that he could not afford to buy by dissolving the chain of a silver pocket watch – a present from his father – in nitric acid and by precipitating light-sensitive silver chloride from it with the help of hydrochloric acid (Collin 2007, 4). Later on, while still in Ghent, he invented a self-developing, dry photographic plate – in competition with Désiré van Monckhoven (1834-1882), a chemist who was a friend of his – and filed a patent application for it. To market it, Baekeland and his laboratory colleague Jules Emmanual Guequier (1848-1929) established the company “Baekeland en Co., Scheikundige Producten”, which was not to prove a success, however.

In New York, Baekeland now benefitted from Chandler’s contacts to America’s biggest supplier of photographic articles at the time – E & H. T. Anthony & Company – for which the professor published the “Photographic Bulletin”. In 1891, Baekeland got to know Richard A. Anthony, the co-owner of the company, who first of all made him a photochemical consultant and then employed him as a chemist. Baekeland left the company again after only two years, set himself up in business in New York as a consulting chemist and invented a highly sensitive photographic paper, which he gave the name “Velox Gaslight Paper” (the Latin word “velociter” means “fast”). Velox was “the first photographic paper onto which pictures could be copied with the help of artificial light” (Mark 1970, 79), i.e. that could be used in photographic laboratories irrespective of the natural light conditions. “The special silver chloride emulsion created for this purpose could be developed quickly too after exposure. Production began in 1893 at the company Nepera Chemical Company in Yonkers, N. Y., that he established with Leonhard Jacobi as financial backer. After initial sales problems, the company became very successful with its fast paper and further new developments and became a serious rival for the photographic market leader Eastman Kodak Company” (Collin 2007, 7). The company boss George Eastman (1854-1932), the inventor of the Kodak camera, therefore decided to buy the Velox photographic paper from Nepera and invited Baekeland to visit him in Rochester in 1899. “Baekeland accepted this invitation; he considered himself to be a hard-headed businessman and was determined to demand USD 50,000 and to accept no less than USD 25,000. Eastman offered him a million” (Mark 1970, 79; cf. Collin 2003, 149, and Collin 2007, 9), “half in cash and half in Eastman-Kodak shares” (Schmutzler 1993, 20); other sources talk about the no less impressive amount of USD 750,000 (Schäfke 1987, 12), about USD 25 million in current terms (Plastic Museum Association 2004, 16). The deal also committed Baekeland to avoiding the development and production of photographic chemicals for the next 20 years (Schmutzler 1993, 20, and Collin 2007, 9). 

“Baekeland returned to Ghent again as a rich man […]. He realised that he had left the people of this city behind him and had become an American. He decided never to come back again” (Collin 2007, 9). In the USA, he acquired the property Snug Rock in Yonkers on the Hudson River, an up-and-coming little town in the state of New York, remodelled it and set up a private research laboratory in one of the stable buildings. In order to increase his expertise, he went to Germany and signed up to study electrochemistry at Berlin-Charlottenburg Technical University in the winter term of 1900/1901. This short course of studies produced immediate results: in 1901, Baekeland and the US chemist Clinton Paul Townsend (1868-1931) succeeded in coming up with the “invention of an improved diaphragm cell for the electrolytical production of lye and chlorine from salt. On the basis of this, E[lon] H. Hooker (1869-1938, editor’s note) set up Hooker Electrochemical Company in Niagara Falls, which developed into the biggest electrochemical company in the world at the time with Baekeland as a consultant” (Braun 2010, 22; see also Collin 2003, 149, and Collin 2007, 10).

In 1904, he turned his private laboratory in Yonkers into a pilot plant, because he now focussed his research on the “attempt to synthesise artificial shellac, that was able to replace the natural product […]” (Mark 1970, 79) and represented a convincing alternative to the electrical engineering industry as an insulation material. Baekeland recalled his chemistry studies in Ghent, where his teacher Théodore Swarts had familiarised him with a synthetic resin that had been described for the first time by the German chemistry professor Adolf Baeyer (1835-1917), who taught in Strasbourg. The man who subsequently won the Nobel Prize had written in the “Reports by the German Chemistry Association” in 1872 that he had obtained a resin-like substance by mixing phenol with formaldehyde gas that was dissolved in water (Baeyer 1872, 1095 & 1099). He did not continue his experiments with it, however, because he found little to like about it. Mark 1970, 80 writes: 

“For Baeyer and the other chemists in the 19^th century, these resin-like reaction products were merely an annoying side effect. […] From the practical point of view, they were extremely tedious. They settled in the test tubes and retorts and made the vessels useless, because they did not dissolve. […] In their opinion, the synthetic production of resins ought to be avoided at all costs.” 

In Baekeland’s opinion, the “cement-like” nature (Fiell and Fiell 2009, 13) of the phenolic resin, a “hard, porous and insoluble grey substance” (Mark 1970, 80), was not necessarily a flaw; on the contrary, it was an indication of potential that needed to be exploited. Finishing touches were still needed, however, before he succeeded in developing the new substance into a viable material – more durable than wood, lighter than iron, more long-lasting than rubber and capable of controlling electricity (Collin 2007, 10) – gave it the name “Bakelite” and managed to file a patent application for it: 

“Instead of trying to prevent the reaction that caused phenol and formaldehyde to combine, Baekeland attempted to encourage it. Instead of allowing the mixture to cool, as soon as it had formed, he heated it up. To make certain that the higher temperatures kept it constantly in a liquid state, he applied pressure to the mixture. And, finally, he incorporated additives, in order to accelerate the entire process” (Mark 1970, 80). 

But let us take one thing at a time … It caused very few problems to obtain the basic phenol and formaldehyde substances, because what were involved were two waste products of the chemical industry:

• Phenol (chemical formula: C₆H₅OH) is a component of coal tar and was discovered in 1834 by the German chemist Friedrich Ferdinand Runge (1794-1867), who called it “carbolic acid”. The name “phenol” is in turn derived from the Greek word for “to shine” (“phainomai”) and is attributable to the fact that not only tar but also illuminating gas is produced when coal is heated in the absence of air (coking). This gas was used for street lighting – in Germany, for the first time in Berlin in September 1826, when 26 gas lanterns were brought into operation on Unter den Linden. Phenol is a colourless, crystalline solid, which dissolves easily in water. After being insignificant for a long time, it was later used as a disinfectant, before it attracted the attention of the plastics industry. Nowadays, more than 90 per cent of it is obtained via acid cleavage of its derivative cumene hydroperoxide (Hock’sche Phenolsynthese; more details can be found at Collin 2007, 27).

• Formaldehyde (methanal, chemical formula: HCOH) is an oxidation product of methyl alcohol in gas form, that was initially called wood alcohol. The latter is in turn a distillate of wood gas, which is produced when wood is heated up in the absence of air. The suffix “-aldehyde” reflects the dehydration of the alcohol, i.e. the removal of hydrogen atoms during oxidation. The prefix “form-“ is attributable to the fact that methanal can be converted into formic acid by oxidation. Formaldehyde was discovered in 1855 by the Russian chemist Alexander Mikhaylovich Butlerov (1828-1886). The aqueous solution known as formalin is what is used most, e.g. as a preservative. Formaldehyde is produced nowadays by catalytic gas phase oxidation of methanol (more details can be found at Collin 2007, 28).

What is produced when phenol and formaldehyde are combined is a substance with the chemical formula HOCH₂C₆H₄OH, which was unprecedented at Baekeland’s time: it is similar to neither of the two original substances and cannot be produced from any substance that can be found in nature. “It is as if a number of hairpins and a can opener were taken apart into their individual components and were then put back together again to make a complete, working colour television” (Mark 1970, 81). 

But how does this combination take place? What exactly happens in chemical terms? Anonymous 2010c, 78 explains: “Up to three formaldehyde molecules can attach to one phenol molecule. These two substances therefore form a spatially networked structure and thus a strong and resistant plastic”. This does not happen by itself, however; activating impulses are needed instead: “By carefully heating and compressing the mixture, Baekeland enabled the formaldehyde molecules to lose their oxygen atoms and the phenol rings to connect to each other via a carbon atom. Once this reaction started, the molecule grew into an enormous network of rings” (Mark 1970, 80). 

Since water is released as a by-product when phenol and formaldehyde react, the phenolic resin that is produced is known as a condensation polymer and the more common term “plastic” is avoided. However, the four letters “poly-“ that both terms share indicates the large number of molecules that have joined together in both cases to form a single macromolecule (Mark 1970: “Giant molecule”). What is probably the most prominent condensation polymer is, incidentally, the synthetic fibre polyamide 6.6, which is better known as nylon.

The molecule networks that are characteristic of phenolic resin at the chemical level are the reason for its central physical property of retaining its shape even if it is exposed to higher temperatures. It is this property that makes phenolic resin what is known as a thermoset, to distinguish it from thermoplastics: “Thermosets consist of molecule networks that are difficult to destroy, whereas thermoplastics consist of a large number of juxtaposed molecular chains. Since this arrangement is less resistant, thermoplastics can be melted or dissolved and also recycled” (Anonymous 2010c, 80). Phenolic resin, on the other hand, can be heated up to 300° before it chars, without softening (Brandenburger 1938, 20). 

So that phenol and formaldehyde molecules cross-link, additives are incorporated that initiate, maintain and strengthen condensation polymerisation. The outstanding feature of the additives, which are known as catalysts, is that they trigger and/or influence chemical reactions without participating in them themselves and therefore come out of them unchanged and unconsumed. Extremely different end products are created, depending on whether acid or alkali (basic) additives are used: “Acid catalysts lead to novolacs that do not set by themselves, while alkaline catalysts lead to self-setting resols” (Domininghaus 1969, 57). The catalogue published for the Bakelite anniversary exhibition says: “A distinction is made between two processes in the production of phenol-formaldehyde resins. The first possibility is the reaction with a surplus of phenol and an acid catalyst. What is produced here initially is a resin with the technical name ‘novolac’. Linear molecular chains are involved in this case, i.e. a meltable resin that is easy to process. A setting agent is needed to develop the material properties attributable to a stable molecular network. […] The second possibility is the process that […] operates with a surplus of formaldehyde and an alkaline catalyst. The end product does not melt” (Anonymous 2010c, 78). 

While Adolf Baeyer had worked exclusively with acids (Baeyer 1872, 25-26 & 1095-1096), Baekeland’s research included both acid and alkaline catalysis, so that he developed both basic types of phenolic resin as a result: 

• In acid catalysis, a meltable resin similar to shellac is produced, which Baekeland therefore gave the name “novolac” (stands for “new shellac”) (Brandenburger 1938, 24, and Collin 2007, 11). Novolac does not set by itself; amines have to be added first. Nowadays, it is standard practice to use “the ‘formaldehyde dispenser’ hexamethylentetramine (Urotropin)” as the setting agent (Collin 2007, 11; see also Schäfke 1987, 14). Moulded articles were originally produced from novolac; nowadays, the material is used for such applications as microelectronics and micromechanics (Anonymous 2010c, 78). 

• In alkaline catalysis, e.g. using lye or an ammonia solution, the phenolic resin goes through a kind of gradual growth process during the condensation polymerisation reaction – something that Baekeland himself divided up into three different stages: resol (A stage), resitol (B stage) and resit (C stage).

Resol forms “as an oily layer […] that […] hardens into a brittle compound when it cools down” (Raubach 1960, 42); it melts and is soluble. Under the influence of heat and the elimination of water, it becomes resitol, a rubber-like compound (ibid., 42), which no longer melts but swells and can be shaped. Under the influence of heat and pressure as well as the elimination of further water, resitol finally becomes resit, which neither dissolves nor melts nor can it be shaped. Resit therefore has to be considered the final stage (condensation polymer) of the phenolic resin. Resol and resitol are considered to be preliminary stages (oligocondensates). It goes without saying, however, that all three compounds can be processed industrially, depending on the purpose to which they are to be put: “By stopping the reaction when the required consistency has been reached, the manufacturer of the resin has many different possibilities, especially for forwarding the material to the manufacturers of the end products” (Anonymous 2010c, 78-79). 

Baekeland started the first tests to study and control the chemical reaction of phenol and formaldehyde in his private laboratory in Yonkers in 1905. Until then, “no-one […] had succeeded in producing flawless moulded parts, because the reaction between phenol and formaldehyde and, above all, the setting of the resins produced were uncontrollable under the conditions applied and led to blistered or porous products due to the release of condensation water. Baekeland therefore faced the challenge of developing a process for the production of homogeneous, hard, non-melting and insoluble reaction products from phenol and formaldehyde without pores or visible cavities (holes). The solution that Baekeland found was – in contrast to all his predecessors – to work under the simultaneous influence of heat and pressure at higher temperatures and thus to accelerate the reaction, to eliminate most of the condensation water and to set the end product ‘without bloating and becoming porous’. To this end, he constructed a reactor he called Old Faithful, in which he produced 180 litres of an amber-coloured, viscous phenolic resin compound for the first time on 20. June 1907” (Braun 2010, 24; cf. Collin 2003, 150, Raubach 1960, 37-39, and Brandenburger 1938, 24). 

In the final analysis, the simultaneous application of heat and pressure was therefore “the key feature of the Baekeland process” (Brandenburger 1938, 20) – the successful conversion of resitol into high-quality resit was the crucial breakthrough in the development of a material that was suitable for industrial production: 

“In contrast to earlier experiments with phenol/formaldehyde mixtures, the chemical reaction was […] relatively easy to control and to repeat successfully. The resin compound produced was blister-free at last too” (Fiell and Fiell 2009, 13). Baekeland “managed to carry out resin formation […] in such a way that it was possible to interrupt development into the insoluble, non-melting material at different times, i.e. at the times when it was suitable for combination with other substances or for moulding” (Brandenburger 1938, 19). Baekeland’s achievement was therefore less the discovery of phenolic resin – to all intents and purpose that was imminent – and more the controllability of the reaction process, as a result of which industrial production became possible and worthwhile, as Schäfke 1987, 12 writes. 

“Baekeland tested his set products to determine their insulation properties. The results were excellent. This therefore meant that the resin that was so urgently needed for insulation moulding compounds had been found at long last” (Raubach 1960, 39). In 1907, Baekeland then filed a total of seven US patents. The “heat and pressure” patent (US 942,699) that was filed on 13. July 1907, 111 years ago today, is considered to be the most important one. The innovative new phenolic resin was given the name “Bakelite”, which was also registered as a trademark.

It is not difficult to see that the inventor was thinking of himself when he chose this name, because there is not much of a phonetical difference between “Baekeland” and “Bakelite”: he added the first syllable of the Greek word for stone “lithos” – thus alluding to the strength of the thermoset material – to the first two syllables of his surname, “Baeke-“, simply leaving out the first “e” (Schäfke 1987, 12). Since what was involved was “the first genuine (= entirely synthetic, editor’s note) plastic, the first macromolecule deliberately created by mankind” (Mark 1970, 81), Bakelite for a long time came to be used by the general public as a synonym for all the plastics (Schäfke 1987, 12) that were to follow it, while the generic term “phenoplast” was introduced in the chemistry community in 1926 instead of “phenolic resin” (Braun 2010, 25, and Gamber 1926, 5). Incidentally: Baekeland’s pressure vessel “Old Faithful” was subsequently renamed the “Bakelizer” (Braun 2010, 24: “Bakelisator”).

(To be continued on the first of September 2018!)

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