1106
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 19, No. 10
Synthetic Resins By A. V. H. Mory BAKELITB CORPORATION, BLOOYBIELD, N. J.
HEREVER the internal-combustion engine, in its present high state of development, is at work for the wealth and comfort of mankind-in automobile, airplane, motor boat-there, rendering indispensable service, will be found synthetic products which are classed with the synthetic resins but which possess a combination of properties unlike and superior to those of other resinous products, natural or synthetic. These products, the phenol condensation products, or more specifically, to employ the terminology of their inventor, the phenol resinoids, represent an outstanding achievement of chemical science and are one of chemistry's important contributions to our present-day industrial development. I n the automotive field they serve to the practical exclusion of other synthetic resin products. A brief consideration of the character of their service, and of their origin, their various forms, and their properties should therefore be of interest to those who have not followed closely the rapid development of these unique and highly important plastic materials. Examination of a well-known automobile reveals the following parts, each made wholly or in some measure of a phenol resinoid product:
W
Starting motor armature (impregnated with phenol resinoid varnish) Ignition coil shell Distributor contact breaker bushing Rotor Distributor head Generator brush holder stud insulation Carbon brushes Generator cut-out relay Lighting switch-back insulation Back-up and stop light terminal insulation
Vibrator horn insulation Fan idler gear Timing gear Water pump shaft coupling Accelerator button Control lever knob Steering gear control cover Horn button Vanity case Smoking case
It will be seen that certain of these parts serve as electrical insulators while others have purely mechanical uses; all must possess mechanical strength, rigidity, and resistance to wear, and these, together with satisfactory electrical properties, must persist relatively unimpaired under exposure to heat and to oils, water, and atmospheric attack. Furthermore, the material thus qualifying must lend itself to being fashioned accurately and cheaply into the various forms required. I n the early days of the automobile the electrical system was insulated with materials which, though good as insulators, gave no end of trouble from softening under heat. It was at about this juncture that the phenol resinoids became available. Rigid, unsoftened even to the temperature of charring, of high insulating value, easily fashioned, strong and enduring, the phenol resinoids, along with rubber and the alloy steels, may be said to have made possible the modern automotive vehicle, with its quantity production and trouble-free service. That any one product, or group of related products, should be able to meet such broad and exacting specifications is in itself noteworthy. Nature has produced no such versatile material nor had organic synthesis up to 1905, when L. H. Baekeland in his laboratory in Yonkers, N. Y., undertook the chemical investigation of the condensation products of phenol and formaldehyde, embracing their many reactions, each engendering a very different product while starting from the same chemical substances as raw materials. The Story i n Brief Intelligent, painstaking, persistent research is the price that Nature exacts of him who would learn her innermost
secrets. Baekeland paid the price and was rewarded with the secret of the control of the phenol-formaldehyde reactions. The story is not new, but it will remain a n inspiration. It is here briefly told in language drawn freely from the researcher's own words. This puazling problem had received attention from various chemists ever since about 1871, when Adolf Baeyer and his pupils, in studying the reaction of acetaldehyde upon phenols, had noticed that sometimes resinous bodies were produced. These substances escaped further chemical identification, and proved useless. Other products, not resinous but crystalline and soluble, were obtained under slightly different conditions by other investigators, starting from the same original substances. By a very similar synthesis a shellac substitute, or a product resembling natural resins, was obtained. These resinous substances had the main characteristics of natural resins-via., fusibility and solubility in the usual solvents. Sometimes infusible and insoluble resins were formed, which were totally worthless as no practical method had been devised to control their production or utilization, nor were the conditions known under which they were happening, as unexpectedly different results appeared while working under seemingly similar conditions. I n February, 1909, Dr. Baekeland gave before the New CHEMICAL SOCIETY a rhsumC York Section of the AMERICAN of his work, which was published' in the newly instituted and was later separately industrial journal of the SOCIETY, disclosed by the publication of his patents filed in 1907. From about that time, or a year earlier, dates the beginning here in the United States of a new industry which has since spread to other countries, and which is based upon the production and utilization of the so-called phenol resinoids, best known under the trade-mark Bakelite. General Characteristics and Applications
Although possessing a resinous appearance, the phenol resinoids are decidedly different from the natural resins or from the earlier-known artificial phenol resins, both of which are fusible and soluble in the appropriate organic solvents. The phenol resinoids in their hard, fully polymerized state are infusible and insoluble, are unaffected by oils, practically impervious to water, unattacked by organic and dilute mineral acids, are affected little by strong hydrofluoric and hydrochloric acids, though they are gradually disintegrated by relatively strong nitric and sulfuric acids and by the alkalies. Another characteristic of the phenol resinoids is their unusual hardness and tensile strength, far superior to that of amber, one of the hardest and strongest of natural resins. If' made with ammonia as a catalyst or with substances equivalent to ammonia, they have the color of natural amber; under other conditions they can be produced colorless, or they may be obtained in various colors by the use of suitable dyes and pigments. These properties early suggested an obvious application, the manufacture of jewelry or other ornamental articles, which has been practiced rather extensively in different parts of the world. But these are merely their minor uses. Possessing high insulation value. as well as mechanical strength and resistance to heat, 'they have found incomparably more important applications in the various electrical and mechanical arts, where 1
THISJOURNAL, 1, 149 (1909); see also page 545.
October, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
they have introduced entireIy new possibilities, and set a new standard among plastics. As ordinarily prepared, phenol resinoids do not have the flexibility or elasticity of rubber or celluloid. On the contrary, they are rigid and remain so up to temperatures a t which the older plastics are either liquefied or destroyed. Furthermore, the ease with which they can be molded rapidly and with extreme accuracy to unchanging shapes and dimensions has brought forth endless applications. The possession of such properties explains the extensive use of phenol resinoid products in wireless telegraphy, radio, telephones, electric-lamp sockets, motors, dynamos, and in general in any electric equipment which is to be subjected to heat, moisture, chemical agents, atmospheric influences, or great strain, electrical or mech:tnical. For like reason they have found increasing usefulness in purely mechanical ways, including such exacting service as that required by transmission gears, in which silence is added to strength and endurance, or by airplane propellers, stronger than wood and unshattered by the bullets of the enemy. Compounded with abrasives, they make grinding wheels; on the other hand, when molded in admixture Kith graphite they serve as self-lubricating bearings. The R e a c t i o n Controlled and Its P r o d u c t Utilized
Baekeland’s control of the chemical reaction between phenol and formaldehyde was brought about by: (1) The use of ammonia as a catalyst. (2) The use of other bases in unlimited proportion.
(3) The joint use of heat and pressure for controlling and accelerating the reaction either with or without ammonia or other bases.
Industrial utilization of the resinoid thus produced was made possible by: (1) Addition of fibrous materials which gave increased resistance t o shock and stresses. ( 2 ) Introduction of the two-step resin, the first step of which is the production of a fusible phenol resin, and the second the transformation of the fusible resin into the infusible resinoid through reaction with paraformaldehyde, hexamethylenetetramine, or other substance containing the active methylene group. (3) Control of the reaction between the phenols and formaldehyde so as t o stop a t the so-called “A” stage, producing a resinous intermediary product, which is still fusible and soluble and can be stored as such for further use, but which is potentially reactive and therefore is promptly transformed on further heating into the fusible, insoluble, resinoid.
To the field opened by Baekeland contributions were early made by other workers, including Aylesworth, Redman, Keith, and Brock, each furthering the industrial development begun and also carried forward by Baekeland. Of I n c i d e n t a l and Academic Interest The chemical constitution of the resinoids is still more or less a matter of conjecture, but Baekeland and Bender have more recently thrown some light on this subject.2 Dr. Bender has prepared a diagram briefly setting forth in their proper relation to each other and to their common raw materials the products of chief interest which may be obtained by the interaction and condensation of phenol and formaldehyde. With his permission this diagram is here reproduced. As Found on the M a r k e t The principal phenol resinoid products employed as raw materials by the fabricator of finished parts such as those used in the construction of automotive vehicles are these: SO-CALLED TRANSPARENT MATERIALS-These are polymerized,
or hardened, phenol resinoids designated as phenol resinoid 2
THISJOURNAL, 17, 225 (1925).
1107
“C,” either in the natural, clear, amber-like state or prepared with colors or pigments. They are ordinarily available in the form of blocks, rods, or forms roughly approximating the objects into which they are later to be fashioned. They contribute little in the construction of automotive vehicles beyond providing a n occasional ornamental touch such as that given by the decorative shift lever ball. MOLDINGMATERIALS-These ordinarily consist of fusible phenol resin intimately incorporated with a fibrous filler-wood flour, cotton flock, asbestos-and enough of a methylene body, such as paraformaldehyde, hexamethylenetetramine, or other substance containing the active methylene group, t o give in effect a potentially reactive resin, or resinoid of the “A” type. The molding materials are in the form of powders or plastic sheet. At a temperature given by 100 t o 150 pounds of steam and P h e n o l R e s i n s and P h e n o l R e s i n o i d s T h e reaction between phenols a n d aldehydes will take a n y one of t h e following paths, according t o conditions: (1) DIRECTRESINOIDROUTE (2) INDIRECTRESINOIDROUTE (“One-step”) (“Two-step”) Theoretical or excess (a) Excess phenol pres- ( b ) Excess catalyst aldehyde present; either ent, either with or present (preferably alwith or without catawithout catalyst kalies), followed b y neulyst (preferably basic) (preferably mineral tralization a n d heating acid)
I
\
\
I
J.
\
Fusible phenol resins (”Novolak” or “two-step” resins)
\
\
I’
Addition of aldehyde in nresence of Eatalyst (generally basic)
\
I
J.
Fusible phenol alcohol resins (DeLaire type)
‘Removal of excess phenol a n d heating t o high tem-
.’
I
peratures Addition of or addition of strong aldehyde in mineral acids Dresence of catalyst (generally Saiiretin resins (Kleeburg type) basic)
.+
\ Addi’tion of aldehyde, basic catalyst, a n d a little
Resinoid, “A” T y p e
I
Heated
Resinoii, “B” T y p e (mixture of “A” a n d “C” types; point a t which jell stage begins) Heated
RESINOID,“C” TYPE
under a ton of pressure to the square inch, they become plastic and flow into every recess of the mold. The resinoid “A” meanwhile undergoes transformation into the infusible “C” type, or polymerized resinoid, binding the fibrous filler into a compact mass having greater resistance t o shock than the polymerized resinoid alone. Metal inserts may be firmly embedded in the molding operation, and every detail of the steel mold finds its counterpart in the molded object, Letters are imprinted with clean-cut fidelity, and a highly polished mold gives a highly polished piece, finished except for the removal of the ‘?in,’’ or thin remnant of extruded material. Thus does accurate molding, requiring but a few minutes in all, insure quantity production of replaceable parts a t a minimum of labor cost. The distributor head of a modern internal-combustion engine well illustrates the advantages of emhedding metallic inserts during the molding operation. I n fact, these advantages may be considered the outstanding manufacturing achievement of the phenol resinoids, in that superiority in the finished product has been achieved along with economy in production, for thus in a very few minutes is accomplished what with plastic materials formerly employed at times required many minutes, or even hours, consumed in hand assembly of metallic parts and in other finishing operations. It will be understood t h a t economy in all such molding operations presupposes quantity production because of the high cost of steel molds of accurate design and requisite strength and
1108
INDUSTRIAL AND ENGINEERING CHEMISTRY P r o p e r t i e s of P h e n o l R e a i n o i d P r o d u c t s LAMINATED PHENOLRESINOID PURE POLYMERIZED RESIXOID Paper Fabric
Mechanical properties: Tensile strength, pounds per square inch
5000-11,000
8700-22,000
8500-12,000
__ = _ _
Vol. 19, No. 10 MOLDEDPHENOL RESINOID Wood-flour filler Asbestos filler (Figure 8 test piece) 3500-6500 3500-5000 (h-ew test piece) 6000-12 000 5000-10,000
-I----
0.5-25
5-25
10-65 ,000-30,000
Compression strength, square inch
pounds
Hardness: Brinell Sf Gedcope Electrical properties: Dielectric strength, volts per mil Dielectric constant Power factor,. Der _ cent (at one million cycles)
per
26,000-33,000
1-11
5000-10,000
(Parallel to laminations) 20,000-45,000 20,000-45,000 18,000-36,000 (Perpendicular to laminations)
18,000-36,000
35,000-47,000
30-45 75-110
35-45 84-94
250-700 4 5-7
750- 1300 4,5-6
0 2-3
1.5-5
33-38 60-67
30-38 78-92
250-500 4.5-6
250-700 4.5-7 5
2-7
1 5-7
Volume resistance, ohms per cubic centimeter lO’Q-lOL? 10’0-10’2 10’0-10’’ 10’0-10’4 Deteriorating agencies: Age Improves rather than deteriorates with age Heat Infusible; withstands Infusible; withstands heat u p t o charring of cellulose 500’ F. (260’ C.) filler without charring Sunlight No effect other than No effect on electrical properties surface reddening Mineral oils a n d gasoline KO effect on a n y phenol resinoid product Animal a n d vegetable oils No effect on a n y phenol resinoid product Water: Intermittent wetting No permanent effect; amount absorbed depends on time of immersion Continuous immersion for 24 hours (specimen 1 X 1 X l / g inch) 0.05-0.017, 0.2-1, 0 7 ~ 0.2-2.07~ 0.05-0.27, Organic and dilute mineral acids Little or no effect except from water absorbed Strong hydrochloric a n d hydrofluoric acids Little or no effect Deteriorate through attack on cellulose filler Strong sulfuric a n d nitric acids Alkalies
1-6
5000-12,000
Disintegrate the resinoid and therefore all resinoid products Mild alkalies soften and strong alkalies rapidly disintegrate all resinoid products
hardness. Rut where is there greater demand than in the automotive industry for quantity production and replaceable parts? Molding materials for special uses are prepared with fillers appropriate to each use. Thus, powdered mica is employed for special “low-loss” materials and graphite for self-lubricating material, while by a modification of the molding process abrasive particles are securely and enduringly bound together. VARNISHES, OR SOLUTIONS OF “A” TYPERGsmorD-’I’hese are employed principally in the coating and impregnating of paper and cloth, which, being freed from solvent and submitted t o suitable temperature and pressure produce the so-called laminated stock, characterized by strength and toughness. Laminated resinoid is prepared in the form of plates varying in thickness from a few thousandths of a n inch t o several inches and, particularly in the case of the paper laminated, in the form of rods and tubes of various shapes and sizes. A variety of paper laminated having special interest is punching stock, which, as its name implies, must be tough. It ordinarily owes its toughness to a low resinoid content, but more recently there has been developed a flexible punching stock of high resinoid content, possessing thereby improved electrical properties. Cotton fabric of various weaves and weights and, to some extent, linen fabric are employed when even greater toughness is required. Of special interest here is canvas gear stock, from which silent gears are cut, though gears are also molded from layers of impregnated canvas so cut and assembled as to obtain greater uniformity of texture along with economy of material. Phenol resinoid varnish is used also in coil impregnation, as is well illustrated by the starting motor armature, which is thus made resistant t o heat, shock, oils, and moisture. A use little t o be suspected from appearance is found in the carbon brushes made of graphite, in which phenol resinoid varnish is employed as the binding agent. FLEXIBLE VARNISHES,LACQUERS, AND ENAMELS-These are modified “A” type resinoid in suitable solvents, which, either plain or with pigment, are employed as tank linings, wire insulation, and as protective coatings generally. A special use is found in the manufacture of a very enduring, water-resisting sand paper. MISCELLANEOUS PRODUCTS-These include resinoids for special uses; notably as the binder in grinding wheels and as a component of the cement employed in lamp basing. To the parts sent us by the automobile manufacturer might be added an electric lamp, the glass bulb and metal base of which are united by resinoid basing cement, giving improved strength and resistance t o the heat developed by the tungsten filament. Horn commutators, the bars of which are insulated and rigidly bound together by phenol resinoid molding material, are also of interest. A list of parts not unlike those found on the automobile might be given for the airplane and motor boat. The airplane pro-
38-42 76-95 150-500 4.5-7.5 5-20 (mica filler 0 . 5 0.7) 108-10’0 1nfusi:le; withstands 500 F. (260° C.) without charring
0.05-0.
170
Gradually deteriorates through attack on filler
peller, already mentioned, with its spread of 9 feet and weight of 100 pounds, is molded from phenol resinoid-impregnated canvas. Indirect Contributions
Phenol resinoid products, besides entering bodily as a structural material, contribute in other important, though indirect, ways to automotive construction. The grinding wheels whose abrasive particles are bound together by phenol resinoid give increased speed and longer wear in snagging and fashioning operations, and ball bearings in which the steel balls move in retaining rings of phenol resinoid laminated make possible speeds hitherto unattainable. The sandpaper that has its abrasive particles securely held and its paper back made tough and water-resistant by flexible phenol resinoid varnish saves time in preparing the car body for painting and in the subsequent rubbing down of each succeeding dried coat. This operation is best conducted in running water, which plainly is impossible with other than water-proof sandpaper. Also, phenol resinoid products contribute indirectly through performing service as important parts of electric and other machinery employed in the construction of automotive mechanisms. But let us consider somewhat in detail the properties that have given the phenol resinoids their present degree of importance in industry (see table). Future Possibilities The future possibilities of synthetic resins other than phenol resinoids would appear from present indications to lie largely in the field of protective coatings. Long strides are being taken these days in the production of varnishes and enamels, and synthetic resins, including the phenol resinoids, may confidently be expected to become factors of increasing importance in this field. As yet, however, no resins have appeared which seriously menace the present supremacy of the phenol resinoids in the field of plastics. There are resins which harden with heat, but not with the speed and the finish that would enable them to compete commercially. It would be idle, of course, to deny the possibility that even better resins may become available
October, 1927
I X D USTRIAL A N D EiVGINEERING CHEMISTRY
as the result of continued research, but present expectation centers rather on the further improvement of the phenol resinoids, with their adaptation and extension to new uses. The electrical field still has much to profit from their use, but the greatest opportunity appears to lie in the mechanical field. This applies to automotive vehicles as well as to industry in general. There are those of reputed conservative judgment who predict the use of laminated resinoid for automobile bodies. Certain it is, there are parts now fashioned of wood or of metal which with quantity production may be made cheaper and better of phenol resinoid products.
1109
Special uses will call for products of special and improved properties. Increased mechanical strength and resistance to shock, improved resistance to heat, lower water absorption on long immersion, greater dielectric strength, lower loss in high-frequency insulation-these are some of the improvements research has provided for special uses, while present indications point with favor to air-drying paints and varnishes among resinoid products of the future, and the development of flexible resinoid products is still further extending the field of usefulness of these outstanding examples of American achievement in the field of organic synthesis.
Coated Textiles’ By Hamilton Bradshawz E. I.DU
P O N T DE
NEMOURS & COMPANY,%’ILMINGTON,
HIS paper is intended to give very briefly an idea of the extent t o which the coated textile industry is a chemical industry and its problems chemical problems. During nearly fifteen years’ contact with the manufacture of coated textiles, the writer has had a growing appreciation of the manifold ways in which chemistry serves this industry and the possibilities of further development along purely chemical lines. Fifteen years ago our chemical work consisted largely of control analyses of raw materials and our experimental work was chiefly an attempt to make new combinations of the usual ingredients. During the last five or ten years the growth of the science of colloid chemistry and the development of methods of utilizing this science in industrial research have made possible a much more scientific attack on the problems of this industry. It is of considerable interest that the conipany by which the writer is eniployed has recently shown its appreciation of the importance of increasing our knowledge of the colloid chemistry of such materials as nitrocellulose and rubber by embarking on a program of fundamental research in colloid chemistry, particularly of nitrocellulose dispersions. It is hoped that the efforts of three or four carefully selected men of recognized ability in this field will result in many important contributions to existing scientific knowledge. There are three principal types of coated textiles, differing in the nature of the coating applied to the fabric. The three basic materials used are pyroxylin, linseed oil, and rubber. The writer has been interested chiefly in the pyroxylin and rubber types, and consequently will have more to say about these than about the linseed-oil product.
T
1926 were upholstered with this material, and the writer has been told that there is a growing demand for artificial leather for several makes of cars which have not been using it for several years. The reason for this is the difficulty of getting an adequate and uniform supply of real leather. In a great many cars in which real leather is used for the seats, the pyroxylin-coated product is used elsewhere-for example, the door panels and kick boards. Rather recently it has become popular for the instrument board and for the curtains of closed cars. A large amount of it is used for the side walls and head linings of taxicabs. I n many cases i t is not used as a substitute for real leather, but as a distinctive material vith its own peculiar advantages. I n a number of cars marketed in recent years, i t has been the practice to make the artificial leather exactly match the real leather in color and pattern. As an illustration of the fine appearance and quality of artificial leather, a recent experience with a popular sport roadster might be mentioned. Having been interested in artificial leather for many years, the writer feels pretty well acquainted Mith most of the little tricks of distinguishing it from real leather. In this case, however, it was absolutely impossible to tell in what parts of the car the real leather and the artificial leather had been used, until a corner was turned up here and there, and the back of the goods examined. The principal seat was found to be upholstered in real leather, whereas artificial leather had been used on the rumble seat and the panels. The appearance and feel seemed abqolutely identical. Lime a n d coal
Artificial Leather
The term “artificial leather” is usually applied to the pyroxylin-coated product, although this designation is frequently very misleading. When the product is embossed in leather grains it very closely resembles real leather, but for many purposes there is no intention of imitating leather and conventional designs of great variety are used. The largest consumption of artificial leather in the automobile industry is for upholstery. About 90 per cent of the open cars made in a
Contrlbution No 6 from t h e D u Pout Experimental Station Assistant Chemical Director.
-3 +JH2
J.
Linseed-Oil Materials
This group includes the large industry of oilcloth manufacture, which has little application in an automobile, but several varieties of top materials have also been made with linseed-oil coatings and they have been of consiclerahle importance in this field.
DEL.
Calcium carbide
4
Acetylene Molasses
Sodium chloride
Acetic acid
Alcohol-+Ethyl
XaOH
acetate
I A
J.
Solvents
+ Clz
LA--
1
s2
Ammonia Sulfur
R a w linters
4
HNOD HzSOd L i
J.
Purified cotton
Mixed acid
A- - . - - - :
.1
Pigment
Pyroxylin
c
ARl’lFICriL
Casto? oil
LEATHER
The significance of the manufacture of artificial leather as a chemical industry is shown by the simple chart which has been prepared to shorn the number of chemical industries which contribute to this product. The solvents come from molasses and from lime and coal, the latter forming the raw
