12 MARCH 1937, Page 8

AN AGE OF PLASTICS

By F. SHERWOOD TAYLOR

THE discovery of a new class of material is a great event in human history. The use of wood, leather, bone, ivory, pottery, brick, plaster and metal dates back to the dawn of history. Glass came into use more than 3,000 years ago. In the three millennia preceding the last quarter of the nineteenth century, the methods of producing and working the old materials were vastly improved, but no new class of materials was discovered.

Plastics are strictly defined as including any substance which can be first shaped by forcing into a mould by pressure and then subsequently hardened. According to this definition clay and glass are plastics, but by common consent these ancient materials are excluded from our new category. Celluloid and hard rubber—vulcanite—are correctly called plastics, as also are the ivory-like substances made by com- pressing and heating casein, the curd of milk ; but the plastics of greatest interest today are the synthetic resins, of which bakelite is the type.

The scientific layman will find a definition by enumeration more interesting. The dark sealing-wax-like material of which his electric light switches and plugs are made is bakelite : the panels and control knobs of his wireless set are likely to be of the same stuff. The brightly coloured unbreak- able picnic-ware, imitation ivory, brightly coloured or trans- parent fountain-pens, umbrella-handles or dress-buckles which resemble glass or transparent horn, cheap spectacle- frames, and a host of trifles made of materials which look like poor relations of ivory—all these are made of plastics, of which more than a dozen kinds are now in use.

A complete list of uses for plastics would occupy most of this article : from accumulator cases and aircraft accessories it passes on through cocktail-shakers, Easter eggs, gear-wheels and furniture, to end up with vent-stoppers and wool-holders. Science, which provides with equanimity poison-gas and anaesthetics, in plastics has given us a fresh source both of rosary-beads and of poker-chips.

The only plastics known before 1906 were celluloid and vulcanite. Celluloid has always suffered from the defect of extreme inflammability, made as it is from gun-cotton and camphor. Both celluloid and vulcanite have the further fault of softening at a temperature near that of boiling water. In 1906 L. H. Baekeland discovered that if a mixture of phenol (the disinfectant carbolic acid) and formaldehyde (formalin) was heated with a little ammonia to about the temperature of boiling water, a substance rather like resin was produced. This resin softened like sealing-wax when heated, and so could be squeezed into a mould of any desired shape. But the central point of his discovery was that if the mould was heated to about 300° F. a further change in the " resin " took place : it hardened, and thereafter was unaffected by any reasonable degree of heat. So articles of bakelite, as the product was named, can be made by the very easy method" of moulding under pressure ; and, once moulded, will not soften again. The modern method of making a bakelite article is sub- stantially as above, with one important modification. The soft resinous mass is not used as such in the moulds, but is mixed with a large bulk of inert filler, such as wood flour or paper pulp. This at once decreases the cost of the material, prevents shrinking in the mould and, if the filler is a fibrous one, greatly increases its strength. If bakelite is incorporated with layers of cloth a material with a breaking strain of four or five tons per square inch can be obtained. This is strong enough for use as gear-wheels, which run with much less noise than those of metal.

A disadvantage of bakelite is its colour, which is brownish or yellowish, a fact which forbids its use for making bright- coloured translucent objects. Naturally, efforts were made to find a nearly colourless substance with the good points of bakelite. It was found that urea—a substance readily made from raw materials no more recondite than air, water and coke—would combine with formaldehyde and give a colourless and translucent resin which could be dyed or " filled " with bright-coloured pigments. From this and other more recent plastics, some of which are as waterwhite and transparent as glass, a host of ornamental trifles and household-ware is made.

The reason for the hardening of bakelite and its allies is interesting. The molecules or smallest particles of phenol are tiny rings about one fifteen hundred thousandth of a millimetre in diameter : the molecules of formaldehyde may be pictured as minute rods of much the same length. When the two are mixed and heated, the formaldehyde- rods link the phenol-rings together and so make short chains of perhaps half a dozen links. These chains, being much heavier than the original rings, are less easily moved by the atomic vibrations we call heat : consequently they form a solid mass, which softens only when heated to a temperature near that of boiling water.

But when this mass of short wriggling atomic chains is heated up to about 300° F., the linking process goes further. and comparatively long chains- are produced. The finished bakelite is an irregular tangle of minute thread-like chain- molecules held together by the small electrical attraction that such molecules have for each other. Heat-vibrations will not disentangle these larger 'chains, though at a high enough temperature the chains disintegrate and the material chars. The long-chain molecule is Nature's -recipe for strength. Wood, linen and cotton from plants, silk from insects, hair from mammals, are all made of long chain- molecules held together by electrical attraction.

The practical man will be less interested in the structure of bakelite than in its sales and its uses. If indeed this is to be the age of plastics, their raw material must be cheap, common and 'not -under control of any one nation or trust. The source of the-more important plastics is simple, namely, coal, air and water. Phenol is a coal-tar product : at the time when Baekeland first worked on this subject, the avail- able supply much exceeded the demand. It is not incon- ceivable that a large expansion of the plastics industry might cause a shortage of phenol ; particularly if there were a strong demand for benzol, from which phenol can be made.

But the bright-coloured and translucent plastics made from urea and formaldehyde are something of a marvel to chemist and layman alike, as being made from nothing more than coke, water and air. Nitrogen from air and hydrogen from water are forced by vast pressure to form ammonia, which, also under pressure, combines with carbon dioxide (a by-product in the above process) to make urea. Formaldehyde is made from air and methyl alcohol, which is itself made from carbon monoxide and hydrogen, which again are made by blowing steam over white-hot coke. Urea and formaldehyde combine to give our plastics. The price of air, coke and water assures the continual cheapness of plastics.

To what extent can plastics replace the older materials ? It is probable that plastics will be much improved by future research, but it is most unlikely that they will approach steel in tensile strength and it is certain that they will not approach it in toughness, hardness or resistance to wear. It is therefore certain that plastics will not replace metals for most engineering purposes. They will, however, very largely replace metal for a great variety of purposes for which great strength and resistance are not required, and most particularly for a thousand household articles, trays, doorplates, handles, fittings, &c. In the electrical industry bakelite is completely established. An insulator of great strength and capable of most accurate moulding could not be neglected.

Plastics are perfectly suitable for a great variety of purposes from which they are now aesthetically debarred. We do not like the look of plastic table-ware, though in lightness and strength and freedom from breakage, plastics infinitely excel pottery. Bakelite furniture, too, is light, strong, cheap and admirably suited for mass-production ; were tables and chairs scientific instruments, they would probably be made of plastics. But, to the eye of 1937 at any rate, there is an air of machine-finish and cheapness about this new material. A walk up Bond Street revealed no plastics except a couple of umbrella handles : Woolworths, on the other hand, was full of such articles. But it is just in the direction of increased beauty of appearance that we may expect research on plastics to have its best success. The industry is only of late rid of its childish ailments and it may well be that the Age of Iron, lamented by Hesiod, may give way to the Age of Plastics, which will not lack poets to proclaim its further degeneration.