Journal & Proceedings of the Royal Society of New South Wales, vol. 152, part 2, 2019, pp. 242–250. ISSN 0035-9173/19/020242-09 Polymers: a historical perspective Robert Burford, FRSN Emeritus Professor, School of Chemical Engineering, UNSW Sydney Email: [email protected] Abstract This commissioned paper outlines the emergence of new forms of synthetics and plastics as our under- standing of polymer chemistry has advanced. Synopsis phenols and styrene are “polymerised” to olymers have been ubiquitous since form thermosets,1 including phenol for- simple gaseous molecules began to form maldehyde “Bakelite” thermosets, but are P 2 life-giving organic structures many millions also present in thermoplastics including of years ago. Today, we rely upon proteins polystyrene and related materials such as comprising twenty amino acids, as well as styrene acrylonitrile (SAN) and ABS.3 The DNA and RNA with many fewer nucleic manufacture of Bakelite is often viewed as acids. Similarly, many fibres and plants the birth of the synthetic polymer industry. comprise carbohydrate polymers: we and The enormous growth both in diversity and other animals use these and protein-based volume of thermoplastics is a feature of the polymers for our diet. Hence, organic earth’s 20th century, dismissively called the “plastics surface has an enormous diversity of natu- age.” Again, important but sometimes ser- rally occurring polymers, sometimes called endipitous discoveries are a feature of this macromolecules. period, but the associated large-scale produc- Today, these continue to feed and clothe tion introduced multinational corporations us, and much more, but the beginning of originating mainly in Europe, the US and man-made materials might be considered Japan. to be the transition from entirely natural From the late 1930s, polymers based on materials to either substitutes or modified ethylene and propylene, gases formed from macromolecules. This period might be clas- “cracking”4 of naphtha or ethane/propane, sified as the “precursor age” of synthetic have become commonplace. Their versatility polymers. It originates from the early 19th and low cost have led to packaging and other century and is an exciting period of amateur single-use modes, which, in the absence of science, entrepreneurship and considerable careful social behaviour, contribute mark- skulduggery. A theme that continues today edly to unacceptable waste. This period of is the replacement of conventional materials commoditisation is characterised by a transi- with improved or cheaper substitutes. tion from gleeful acceptance from the 1940s The second period relates to entirely syn- to the ’60s to misgivings and apprehension thetic polymers which have as raw materials in the 21st century. small molecules that arise from processing of coal or oil. Aromatic compounds such as 3 Acrylonitrile butadiene styrene 242 Journal & Proceedings of the Royal Society of New South Wales Burford — Polymers: a historical perspective The First Age of Polymers In this environment the opportunity for The beginnings of human exploitation of entrepreneurial inventors to make and sell natural polymers might date from the use of new and desirable articles was compelling, timber, including fire, many millennia ago. and examples described below either replace The use of natural fibres including various scarce natural substances, or introduce new wools is another prehistoric example. materials with novel properties. In this age, More recently, the creative application of much work was conducted by energetic and an isolated polymer might start from the creative, but somewhat uneducated, ama- recreational use of coagulated rubber from teurs. Hevea braziliensis by the Aztecs and others Although the primary focus in this paper in Mesoamerica, as observed by Europeans is on plastics and to a lesser extent thermo- in the 15th and 16th centuries. setting materials, the exploitation of natural The history of rubber is fascinating, as it rubber illustrates several common themes. combines great wealth with slavery, not just Natural rubber was available from South in South America, but in South East Asia America in the 18th century, and those con- and in Africa. This was convincingly broad- trolling the plantations and essentially slave cast by the late Professor Peter Mason (1979). labour were becoming enviably wealthy. It is also documented extensively, for Opera houses, trams, electricity and much example in Stahl (1984) and Fenichell else was built in the Amazon beside a deci- (1996). This latter text provides excellent mated native population. Saplings of these case studies that are drawn upon elsewhere “rubber trees” were smuggled from South in this paper. America and the survivors propagated in Here the emphasis is placed upon the Kew Gardens. These in turn became the deliberate manufacture of either new but forebears of the globally distributed rubber modified materials that can be processed plantations: pest species replacing native to take on desired forms, or, later, entirely trees. new synthetic polymers (predominating in The next chapter was the need to make the Second Age). In many ways, however, synthetic rubber to overcome the difficul- synthetic polymers cannot match natural ties in sea transport of natural rubber to the materials and this remains an aspiration. UK and the US. The project was one of the The industrial age can be characterised underappreciated technical achievements of not only by the harnessing of energy via the WW2. When I worked at the Australian Syn- steam engine, but also the mass conversion thetic Rubber Company in the 1970s, secret of raw materials into refined or intricately codes both for raw materials and products, a produced products such as woven cotton legacy of the war, were still being used! and woollen garments. An examination of The transformation from a soft flowing any technology museum will reveal a mul- and impure material to one that might be tiplicity of complex machines designed to more valuable and useful was beset with tech- value-add starting materials into consumer nical challenges. Such challenges had to be articles. overcome with a combination of mechanical changes as well as chemical modifications. 243 Journal & Proceedings of the Royal Society of New South Wales Burford — Polymers: a historical perspective Natural rubber comprises cis poly iso- for invention of a credible substitute. Gun prene, with (as we now know) a molecular cotton (cellulose nitrate) was already known. weight of about 106 atomic mass units. Such Admixtures in solvent (collodion) were a high molecular weight makes the material developed by John Hyatt in the 1860s to hard to process (“tough as boots”) and with encase wood pulp and bone mixtures. Ulti- poor adhesion qualities, which limits its fur- mately a suitable substitute was realised and ther deployment. This was addressed using the prototype remains (although the prize a crude masticator known as the Hancock was not awarded), but Hyatt’s main discov- “pickle,” akin to a torture instrument with ery was to follow. multiple arrays of intermeshing teeth. The This was the addition of camphor to nitro- modified rubber was a marked improvement cellulose to make the material malleable, and on the naphtha-dissolved rubber used by millable into a thin coherent mass. This Charles Macintosh in the 1820s to water- product — celluloid — patented in 1869, proof garments. became the key product of the American Soon after, Charles Goodyear sought to Celanese Corporation, and celluloid formed improve the properties of “India Rubber” the basis of photographic film technology (named from the Caribbean Indies and and greatly affected both the photographic from the ability of the polymer to erase and movie industries. Hyatt himself left to pencil markings) with essentially no knowl- begin the hotel company that bears his name edge of chemistry at all. He tried numerous to the present time. experiments with little success over more In assisting the Powerhouse Museum con- than a decade, with Goodyear in and out of servation team in Sydney, I’ve had the oppor- debtor’s courts and prisons. It was however tunity to learn of the polymers available from the entirely accidental exposure of rubber about 1880 to the 1940s (from the Penfold latex to spilt sulphur on a stove that led to collection,5 amassed on a global tour) and crosslinking, or vulcanisation, a technol- to the present time. A surprisingly small ogy still conducted today. Despite his 1844 number of polymer families existed, but in patent, Goodyear died impoverished. This a diversity of manifestations. Many forms of is a representative example of an important ivory substitutes were available, sometimes and enduring but accidental discovery. with casein (milk protein) derived polymers. A second important discovery was the Celluloid materials, either cellulose nitrate modification of cellulose ester to render the or acetate, were also well represented. The material both transparent and malleable. The former are dangerously unstable, whilst the origins are fascinating and relevant. The Vic- acetate also loses acetic acid to leave brittle torian era was largely decorated with ivory: cellulosic residues. This is a major concern piano keys, hairbrushes, knife handles and much else. Particularly challenging items were billiard balls, those having the best 5 During the period 1929–55, the Powerhouse “click” made from the middle, clear grained Museum director Arthur de Raymond Penfold became section of