RUBBERMILL FOR MIXINGHARDRUBBERCOMPOUND
Hard Rubber (Ebonite) A. R. KEMPAND F. S.
31.4~31,Bell
Telephone Laboratories, New York,
A
N. Y.
LTHOUGH Charles Publication of information o n hard rubber &ion ( h e a t i n g with sulfur). has been lacking and is so widely scattered as to The term “hard r u b b e r ” iS Goodyear discovered the m x t widely used, and may mean process of vulcanization make difficult a survey of the subject. The a n y h a r d r u b b e r composiof s o f t r u b b e r with sulfur in 1839, it appears that Thomas Present PaJIer presents a resume O f the literature tion having a v u l c a n i z a t i o n Hancockwas the first, in 1843, to on hard rubber with pertinent information o n the coefficient between about 25 and note the f o r m a t i o n of a hard vulcanization process and compounding practice. 47. The vulcanization coefficient is expressed as the number and physical propertiesof the mablack hornlike substance as a The of units of weight of sulfur comOf heating strips Of rubber terial and methods of tests are also given. A d bined .with parts of rubber i n m o l t e n sulfur for a p r o longed period. The present vance in hard rubber field appears to have hydrocarbon. There is no tercommercial process of mixing lagged behind that of soft rubber, which indicates minology for describing t h e a n opportunity for additional research and deintermediate vulcanization prodlarge quantities of sulfur with ucts of rubber and sulfur ocvelopment rubber and heating the dough to effect vulcanization into hard curring between the vulcanizarubber w a s a c t i v e l y s t u d i e d tion coefficients of t h e u p p e r by Goodyear (18) who patented a process for making this limit of soft rubber and the lower limit of hard rubber which substance in 1851. The commercial manufacture of hard are about 4 and 25, respectively. Few rubber products are rubber started a few years later and increased rapidly to be- manufactured with vulcanization coefficients between these come an important branch of the rubber industry. limits. Certain so-called semi-hard rubber compositions may The chemical inertness, high strength, and good appear- be vulcanized to coefficients somewhat lower than 25. These ance of hard rubber have led to many of its uses. For ex- materials, however, generally lack chemical stability and ample, the handling of acids and other corrosive liquids and physical strength and are not to be considered hard rubber. gases in the chemical industry involves the use of equipment Hard rubber, like soft rubber, is compounded with other with hard rubber linings, piping, fittings, and similar parts. materials and may therefore contain varying amounts of In the manufacture of hard rubber dentures, syringes, storage modifying ingredients other than rubber and sulfur, introbattery cases, automobile steering wheels, fountain pens, duced for the purpose of obtaining desirable characteristics. combs, and the like, these same properties are brought into One, therefore, cannot set down fixed properties for this play. Recognition of the excellent dielectric properties and material. moisture resistance of hard rubber led to its early and conThough the terms “ebonite” and “hard rubber” are syntinued use for the insulation of telegraph, telephone, radio, onymous, ebonite is considered by some to mean a simple and other types of electrical equipment. basic rubber-sulfur composition which has been completely Rubber chemically saturated with sulfur as a result of vulcanized. Even in the case of ebonite the definition is not heating a mixture of these two substances is frequently called a complete one, for various types of rubber may be used, the “ebonite” from its resemblance to ebony wood. It is occa- amount of sulfur added may range from 30 to 50 per cent, and sionally called “vulcanite” because it is a product of vulcani- the temperature and time of vulcanization may vary widely. 141
142
INDUSTRIAL AND ENGINEERING CHEMISTRY
VULCANIZATION When a mixture of rubber and sulfur is heated, the sulfur present combines with the rubber in such a manner as to render i t unextractable with acetone. Ostwald (34) and later Harries (80) considered this change known as vulcanization to be due to adsorption of the sulfur by the rubber. This theory is untenable in view of the overwhelming evidence shown by numerous investigators (8, 22] 48, 44, 46, 49) that,
Vol. 27, No. 2
pound, the temperature coefficient was found to vary from 1.53 to 3.04. The commercial period of vulcanization of hard rubber generally ranges from about 15 minutes to 20 hours, depending upon the composition, the temperature employed] and the dimensions of the article. The hard rubber reaction liberates considerable heat. Perks (37), for example, showed that 3.5-cm. cylindrical specimens of rubber-sulfur mixtures when heated in a bath to 160' C. reach an internal temperature more than 100' above that of the bath, as a result of the heat liberated from the reaction. This heat is liberated suddenly a t a certain stage in the reaction and is accompanied by a vigorous evolution of hydrogen sulfide. Riding (38) vulcanized a 3.5-cm. cylinder of a 65-35 rubber-sulfur mixture a t 145' C. and obtained an internal temperature rise of about 60'. However, when vulcanizing at 135" C., the internal temperaturerise was only about 10'. When the vulcanizing temperature reaches 178' the sulfur commences to react by a process of substitution or dehydrogenation. This reaction becomes fairly rapid as the temperature exceeds 200', and copious amounts of hydrogen sulfide are given off. Therefore, in curing thick articles of ebonite, low temperatures and long periods of vulcanization must be used or the material becomes porous or converted t o a spongy brittle mass as a result of excessive internal temperature. Organic accelerators must therefore be used with caution in hard rubber, especially in the curing of thick articles of ebonite. Their use sometimes is attended with difficulties such as scorching, porosity, surface discoloration, and brittleness in the final product. Certain accelerators, however, are widely used, especially in press-vulcanized hard rubber articles which are so compounded as to lessen the dificulties attendnnt upon rapid curing. Recently Davies (12) has studied the relative efficiency of various CALENDERING COMPOUND FOR HARDRUBBERSHEET organic accelerators in promoting the vulcanization of ebonite. under suitable conditions of heating, sulfur adds chemically Glancy, Wright, and Oon (17) found that the use of various to the double bonds in the rubber hydrocarbon to the point of accelerators increases the rate of vulcanization of hard rubber saturation and then stops. This point corresponds to one a t 170" C. to a lesser degree than with soft rubber. sulfur atom added to the double bond in each CsHs group, Stevens and Stevens (45) vulcanized hard rubber a t 70' yielding a product ( C ~ H S Scontaining )~ 32.00 per cent sulfur and 100' C. for long periods of time, employing a large excess in chemical combination. Spence and Young (44) found of sulfur in the presence of ultra-accelerators. These authat gutta-percha and balata hydrocarbons react with sulfur thors have interpreted their results as showing that extensive in a similar manner to rubber. Whitby and Jane (49) heated substitution occurs under these conditions as judged by rubber for long periods with a large excess of sulfur in various "coefficients" in one case as high as 142.8. The composition solvents a t various temperatures and found that the acetone- with the high coefficient of 142.8 cited by the two Stevens insoluble product always contains close to 32.00 per cent of contained 100 parts of rubber, 20 parts of sulfur, 20 parts of combined sulfur. They also found that acetone-extracted zinc oxide, and 20 parts of zinc diethyldithiocarbamate. The ebonite dust (polyprene sulfide) is incapable of bringing about highest possible vulcanization coefficient in this case would vulcanization when mixed with crude rubber and heated, il- therefore be 20. The combination of sulfur with the zinc lustrating the firm bond which exists between the sulfur atoms salts must also be considered as introducing errors into the determination of sulfur combined with rubber. None of and the rubber molecule. The treatment of acetone-extracted soft vulcanized rubber these results, therefore, can be taken as evidence that substiwith bromine (42) or iodine chloride (27) results in the addi- tution occurred. In view of the low temperatures and lung tion of halogen equivalent to the unsaturated part of the rub- periods used by the Stevens for vulcanization, one would ber-sulfur complex as calculated from its combined sulfur scarcely expect substitution of sulfur to take place. Recently the use of selenium (1A) has been proposed for content which is further evidence of the chemical nature of the reaction of sulfur with rubber. accelerating the cure and improving the physical properties of Since sulfur reacts with rubber only very slowly a t room hard rubber. Blake (6) has found that ebonite cannot be temperatures, vulcanization of hard rubber is usually carried formed by the use of selenium alone out a t temperatures between 130' and 160' C. The temperaThe effect of the resin and nitrogeneous constituents on ture coefficient of the reaction velocity above 100' C. is the vulcanization of hard rubber has not been as carefully about 2.7 for each IO" rise in temperature (4).Davies (12) studied as in the case of soft rubber. Spence and Young found the temperature coefficient of hard rubber formation (4)showed that these nonhydrocarbon constituents were to be 2.52 a t 140" to 150' C . , 2.80 a t 150' to 160°, and 3.13 not essential in the vulcanization of hard rubber. Whitby's at 160' to 170' for a compound consisting of smoked sheet results (4.9) indicate that rubber from which the resin and 100, sulfur 50, zinc oxide 5, and stearic acid 0.5 parts. some of the protein had been extracted vulcanized to hard When various organic accelerators were added to this com- rubber a t a somewhat slower rate than unextracted rubber.
Fahruurg, 1933
1 N D lJ S T 11 1 A 12 A N D E N G 1 N E E I1 I N G C H E M I S T R Y
It can be said in a general way that the normal variations in the resin and protein content of crude rubbers of the better quality do not need to bo taken into account in the manufacture of hard rubber. Washed and dried caucho, which ordinarily contains upwards of 5 per cent resin and less than 0.1 per cent nitrogen, produces hard rubber of excellent quality. It is well known that cancho rubber produces a very inferior soft rubber as compared with Para, indicating that the elastic structure or "nerve" of the crude rubber is not so important in hard as in soft rubher manufacture. In view of the fact that soft, sticky, wild rubbers produce satisfactory hard rnhber (8Y), it might be surmised that nnrmal variations in milling of plantation rubber would not injure the quality of the resulting hard rubber product. Spence and Ward (43) found that long milling did not affect the rate of vulcanization of hmd rubber. Davies (If)found that excessive milling reduced the ultimate tensile strength of hard rnhber by about 20 per cent. Davies (12)also found that the effect of prolonged mastication after the addition of sulfur was more severe than overmastieation of the crude rubber alone. It is of general experience, however, that normal variation in milling time does not affect the quality of hard rubber. Blake (6) has snmmarized the literature on the heat of vulcanization of rubber. IIis own investigation of this suhject wns made by determining the heat of combustion of vulcanisates containing iip to 32 per cent sulfur. The differencesbetween the values found and those calculated were taken as the heat of reaction of sulfur with rubber. His results showed that 300 calories per gram of componnd were liberated in the formation of polyprene sulfide (CsH,S),. IJe found that the heat of vulcnnization increased in a linear fashion as tlie combined sulfur increased from 6 per cent to the highest value. Hada, Fukaya, and Nakajima (19) carried out a similar investigation hut considered the heat liberated as a result of the sulfur trioxide formation in the combustion rather than sulfur dioxide assumed by Blake. They found the heat of reaction increasing to over 600 calories per gram of compound a t 10 per cent combined sulfur content, decreasing to -40 calories a t a sulfur content of 28 per cent. The wide differences of these results from those of Blake would lead to the conelusion that there is need for further study of this important subject. Recently Jessnp and Cunimings (84) found 8 strictly linear relationship to hold between the heat of vulcanization and the combined sulfur content over the whole range. They obtained a value of 145 calories per gram of eoinpound as the heat liberated in the formation of polyprene sulfide. CXEMICAL PROPERTIES Hard rubber gradually softens upon heating and a t 100" C . it becomes quite flexible. Above this temperature various investigators (8, 15,47,50)have shown that hydrogen snlfide splits off from hard rubber iii increasing amounts with rise in temperatiire up to 265" C. Cuinrnings (8),for example, found that a vulcanized composition of 80 parts rubber with 20 park sulfur made from purified rubber lost about 1.7 per cent sulfur as hydrogen sulfide when heated for 8 hours from 105" to 265' C. while a 68-32 composition lost 10.4 per cent snlfur under the same conditions. The results of Cuminings show that each added increment of sulfur combined with rnbber from the composition (C~ofl~~S),, to (C&S),, shows an increasing degree of instability. The work of Hinrichsen and Iiindschcr (a$)and Wliithy and Jane (@) in removing sulfur from hard rubber by treatment with alcoholic potash and of Spence (41) by tlie use of metallic sodium leads to the same conclusion. Retween 260" and 280' C. hard rubber melts to a jet black
143
resin which on cooling is a hard brittle substance. This material becomes very plastic at about 80" C., possesses good adhesive properties, and is useful for fiIling defects in hard rubber parts. Bolas (7) mentions the use of this material as a binder in grinding wheels. Kernp ($6)found that vulcanizates with sulfur contents varying from 8 to 16 per cent become thermnplastic as a result of heating to high temperatures.
VULCANIZING EQUIP ME^ m n RODSAND TUBES
Midgley, Henne, and Shepard (YO) subjected ebonite to destructive distillation and identified various thiophenes and aromatic hydrocarbons in the products. The same authors (31)on tlie basis of this stndy proposed a structural formula for ebonite where sulfur is linked to a carbon at.om bearing a methyl group on the one side and to the next third carbon atom of the rubber chain on the otlier side. Eard rubber compositions nrith vulcanization coeflicients above 30 are very stable under ordinary conditions and show few signs of physical deterioration after many years. Dieterich and Gray (15) showed t.hat hard rubber was unaffected by heating 14 days in air at 70' C, When the heating w&s conducted for 60 bows a t 15O0, they found that considerable decrease in impact and transverse strengths had resulted. In general, it may be concluded that hard rubber retains its excellent physical characteristics unimpairod for many years under ordinary conditions of use. On exposure of hard rubber to sunlight or to light rich in ultraviolet rays, a film of sulfuric acid is formed on its surface. According to Fry and Porritt (fa)this acid is the result of oxidation of sulfnr in the polyprene sulfide complex. Evidence on this point has lieon obtained (4) by exposing an acetoneextracted sample of ebonite to sunlight; the removal of free d f n r did not affect the formation of acid on the surface. I t is also possible that the formation of siilfnric acid may result from ihe photochemical oxidation of the hydrogen sulfide which is split off from the polyprene sulfide. This susceptihility of hard rubber to light deterioration k an objectionahle property in its use for electrical insulation where light exposure is involved, since it results in greatly increased electrical conduction over the surface. Curtis (9) studied this effect from the eleetrieal standpoint and showed that, on removing the acid from the surface with dist.illed water, the high initial surface resistivity of hard ruhtier is restored. More research is needed to imnrove hard rubber from the standpoint of its resistance to the effect of sunlight.
? >
1 he excelleiit resistance of hard rubber to many chernicals is well known. In this respect it is much superior to soft rubber. Aside from rubber solvents, such as benzene, carbon tetrachloride, and strong oxidizing acids, such as nitric and sulfuric, hard rubber may be said to be chemically resistant. The chemical resistance of hard rubber, I;iowevcr, is limited n t temperatures above 65" C. (for further details, citations 1 and 14 sliould be consulted). COMPOUNDING Pure riibber-sulfur mixtures produce excelleiit l i d rulilm for sonle purposes. However, the reqoirerrrents of factory iirocessing and varied uses are such as to make desirable the addition of various compounding ingredicnts to meet specific iieeds.
pared witli mineral fillers (%). Ground hard rubber in 40mesh and finer sizes are used up to equal volumes on the rubber; in special e a s a even higher percentages are used. The effect of hard rubber dust addition on impact strength is shown in Table I. Reclaimed rubber is widely used in the manufacture of many hard rubber articles sinoe its use aids factory processing and effects economies in compounding. The addition of reclaimed rubber is a valuable aid in reducing excessive internal krnperature rise during vulcanisation. The effect of redairrred rubber on the impact strength of hard rubber is sirown in Table IT. Tanim XI. E I ~ Y X OF R a c ~ n m mRUBBEI~ ON IMPACT STBENQTH (4)
TAMLE I.
Rubber
%
70.0
Vuleaairation: 4-liour rme t o 149' C., 12 hourn st h Floating ieeiaiin of 85 per aent rubber .ontent. r ayecimen.
66.5 68.0 69.5
sB.0 52.5 49.0
*
Vulcsnizatiom: 4-liour rise to 141P C.. 12 hours at 50-meahdust from I t i g b - q d i t ~eorap. 1.27-om.speoimen.
14s"
1.27-em.
149'.
IIard rubber dust (3) is used either alone, a8 in dust presa molding, or in new mixtures. It facilitates mixing and milling operations and reduces excess shrinkage in the manufacture of rods, tubes, sheets, and molded parts. With the use of dust the possibility of "blowinig" during cure is greatly reduced (38). Hard rubber dust from low-gravity, brigiitfracture, clean hard rubber scrap can he used with comparatively little deleterious effect on physical properties as eom-
Such materials as oil auhstitute, mineral rubber, waxes, and vcgetablo oils are frequently added to hard rubber mixings t o obtain desired working properties. Additions, however, beyond a few per cent result in an objectionable reduction in the hardness of the final product. Table 111 shows the effect on cold flow and impact strength of adding 3 per cent of various commercial softeners to a 68-32 rubber-sulfur mixture vulcanized 12 liours at 150". The method of test appears later under physical properties. Lime and magnesia are sometimes used in small amounts to accelerate the wlcanization of hard rubber. There a p pears to he very little difference in the accelerating action of these materials on a volume basis as shown by Glancy (18).
February, 1933
I N D U S T R I A L A N D E N G I N E E R I N G CHE3ZISTRY
143
thi. purpose the use of many different instruments has been proposed but no definite testing procedure has been adopted. The durometer is a suitable instrument for rapid tests and has been employed (1-4) for tests a t 100". DaTjes (12) has investigated durometer measurements on hard rubber over the range of 10" t o 50" C. The hardness, like the resistance to TABLE111. EFFECTOF SOFTENERS ON IMPACT STRENGTH LXD COLDFLOW flow under compression, is greatest with the highest cure. SOFTEZER IUPACT STRENQTH (IZOD)" COLI> F L Ob ~ The addition of fillers (inorganic), such as whiting, aluminum Cm.-kg If m powder, and barytes, increases the hardness as would be ex2.44 0.04 None pected; addition of softeners has the opposite effect. 2.23 Zinc laurate 0.13 0.71 2.08 Hydrocarbon oil One of the most valuable tests for determining the tendency 2.08 0,15 Rosin oil I ) . 14 2.23 Raw linseed oil of a material t o break on being subjected to sudden shock is the impact resistance test. Special machines have been % made for this purpose. The Izod and Charpy types of im53.00 Smoked sheet ruhher pact testers are most widely used and have been described by 2 5 . IO0 Sulfur 19 00 Hard rubber i i u s ~ Werring (48). The test involves notching a 1.27-em. square 3.00 Softener --bar of hard rubber, placing it in the Jan's of the machine, and 100.no striking it with a weighted pendulum. Tables I, 11,111,and 1.27-cm. specimen. IV show the effect of hard rubber dust, reclaimed rubber, b 281 kg. per sq. cm.: 1.27-cm specimen. softeners, and combined sulfur on impact strength. Addie Vulcanization: 4-hour rise t o 149' C., 12 hours at 149' tions of mineral fillers beyond a few per cent on the rubber Fillers such as barytes, whiting, and clay are widely used reduce the impact strength of hard rubber. Hard rubber varies in tensile strength and elongation, det o obtain greater hardness and heat resistance and for pending on its degree of vulcanization and composition. Its economy. In producing colored hard rubber, there is the obvious tensile strength ranges from about 300 to 775 kg. per sq. em., difficulty of covering up its natural brownish hlack color the higher value being obtained for completely vulcanized which involves the use of a large proportion of coloring agents. ebonite. Glancy (16) studied the variation of tensile strength The chemical reaction of the sulfur with the pigmerit must also and elongation with combined sulfur in the case of various be considered. This inherent dark color is usually covered rubber-sulfur mixtures vulcanized a t 170". Compounding by adding a white pigment such as lithopone or zinc sulfide. generally results in a reduction in tensile strength associated The sulfides of zinc, mercury, cadmium, and antimony are with either an increase or a decrease in elongation, depending on the type of compounding ingredient. Pearsall (36) found frequently employed as pigments in hard rubber. In recent years considerable effort has been made to take that the elongation of hard rubber is approximately 20 per advantage of the high tinctorial power of organic lake colors cent at a vulcanization coefficient of 25 and decreases to 2 per cent a t a coefficient of 45. Davies (11) has studied the in hard rubber n-ith promising results (SB, 53). stress-strain relationship in hard rubber as affected by variation in composition and state of cure. PHYSICAL AND MECHANICAL PR0PERTIF:S The transverse breaking strength of hard rubber is not very As sulfur combines chemically with the rubber hydrocarbon, critical as regards showing the effect of variations in composithe density increases t o a maximum corresponding to the full tion. Various means are used for measuring this property saturation of the double bonds. Curtis, McPherson, and (38). The most common method is probably that of supScott ( I O ) determined the density of rubber-sulfur compounds porting a 1.27 X 1.27 X 12.7 em. bar of the material on knife a t 25" C. over the complete range between soft rubber and edges 10.2 cm. apart and applying a given load in a transverse direction to the center of the bar and testing a t about fully vulcanized hard rubber. Some commercial uses of hard rubber require that the ma- 21" C. Table IV gives values for transverse strength of terial shall offer high resistance to distortion under compres- various hard rubber compositions. sion strains a t temperatures up t o 49" C. A suitable test for this property involves subjecting a 1.27-cm. cube of the maELECTRICAL PROPERTIES terial to a constant pressure of 281 kg. per sq. em. a t a conHard rubber in the pure state has a dielectric constant a t stant temperature of 49" C. and measuring the deformation with a micrometer after 24 hours. Fully cured hard rubber 1000 cycles and 25" C. ranging from 2.7 to 3.0 ( I O ) . The free from softeners has a high resistance t o deformation. exact value depends on the state of cure, amount of free sulTable IV shows the effect of combined sulfur on physical fur, and purity of the rubber. Addition of fillers and pigproperties of hard rubber. Addition of mineral fillers de- ments, especially carbon black, increases the dielectric concreases this flow as would be expected, while softeners tend stant. The effect of temperature is quite marked (29, @), the dielectric constant increasing some 50 per cent between to increase cold flow. 65" and 145" C. The dielectric constant a t 1000 cycles and TABLEIV. EFFECTOF COMBINED SULFURON PHYSICAL 25' C. rises rapidly to a maximum value a t a point between PROPERTIES OF HARDRUBBER (4) 12 and 15per cent combined sulfur ( I O , 26,28,69,40). These IZOD TRANSCOMmaximum values are shifted t o correspond with other sulfurCOMPOSITIONa COLD IMPACT VERSE BINED DESSITY4T rubber ratios as a result of changes in the temperature or Riihber Sulfur FLOW STREXGTR STRENGTH SULFUi? 25' c. % % Mm. Cm.-kg. K o . / s q . cm. % frequency of measurement (69, 40). 72 2s 0.12 4.0 975 27.6 1.131 The power factor of ebonite a t 60 to 3000 cycles ranges be70 30 0.15 4.0 1000 29.2 1.146 tween 0.3 to 0.8 per cent a t 25°C. At 300,000 cycles the 68 32 0.09 3.9 1060 30.4 1.163 65 35 0.12 3.7 1095 31.8 1.183 values range between 0.7 to 0.9. The power factor a t 25" C. a Vulcanization: 4-hour rise to 149' C., 16 hours a t 149O. and 1000 t o 3000 cycles when plotted against vulcanization coefficient over the whole rubber-sulfur range show peak values Frequently it is desirable to determine the hardness of of 7 t o 8 per cent. The maximum values lie between vulcanihard rubber comDositions a t various temneratures. For zation coefficients of 13 and 17 (10, 26, 28,29, SO). Both
Light-calcined magnesia is, hoviever, most commonly used. Davies (12) has shown that the accelerating action of magncsium carbonate is very similar in magnitude to that exhibited by organic accelerators.
INDUSTRIAL AND ENGINEERING
146
temperature and frequency shift the position of this peak value on the curve for percentage combined sulfur vs. power factor (29, 40). The power factor of pure hard rubber is generally increased by additions of other ingredients. Plotting volume resistivity (ohm-cm.) against combined sulfur content shows a steady increase with an abrupt rise to a peak occurring between 20 and 30 per cent, then sharply decreasing a t 32 per cent sulfur. The resistivity of hard rubber having vulcanization coefficients between 25 and 43 is 1 x 1OI6 to 3 X 10l6ohm-cm. (10). Hard rubber possesses a high dielectric strength. The value for ebonite ranges between 100,000 and 150,000 volts per mm., depending on the particular composition (55). Commercial grades of filled hard rubber are generally lower than ebonite in dielectric strength (58). When thin sheets of hard rubber are soaked in water for very long periods, equilibrium is approached and the absorption of water slows down to an undetectable rate. The ultimate amount of water absorbed varies with the composition of the hard rubber as can be seen in Table V. In the case of ebonite mixtures this water absorption does not affect the appearance of the material or seriously affect its electrical properties. Table V gives the water absorption of hard rubber when immersed for long periods in distilled water and its effect on electrical properties.
CHEMISTRY
Vol. 27, No. 2
LITERATURE CITED (1) Anonymous, Chem. & Met. Eng., 33, 627 (1926). (1A) Anonymous, Vanderbilt News, 3, 4 (1933). (2) Bacon, J.Phys. Chem., 32, 801 (1928). (3) Bath, I n d i a Rubber J., 79, 935 (1930) : 80, 67 (1930). (4) Bell Telephone Lab., unpublished work. (5) Blake, IND. ENQ.CHEM.,22, 737 (1930). (6) Ibid., 26, 1283 (1934) Arts, 28, 763 (1880). (7) Bolas, J . Roy. SOC. (8) Cummings, Bur. Standards J. Research, 9, 163 (1932). (9) Curtis, Bur. Standards, Bull. 11, 402 (1914).
(IO) Curtis, McPherson, and Scott, Bur. Standards, Sci. Paper 560 (1927). (11) (12) (13) (14) (15) (16) (17) (18) (19)
Davies, Inst. Rubber I n d . Trans., 9, 130 (1933). Ihid., 10, 176 (1934).
Dieterich and Gray, IND.ENQ.CHEM.,18, 428 (1926). Fritz and Hoover, Am. SOC.Testing Materials, Symposium on Rubber Preprint, pp. 79-90 (March 9, 1932). Fry and Porritt, India Rubber J.,78, 307 (1929). Glancy, ISD.EXG.CHEY.,16, 359 (1924). Glancy, Wright, and Oon, IND. ESQ.CHEM.,18, 7 3 (1926). Goodyear, Nelson, U. S.Patent 8075 (1851). Hada, Fukaya, and Nakajima, J. Rubber SOC.J a p a n , 2, 389
(1931); Rubber Chem. Tech., 4, 507 (1931). (20) Harries, Ber., 49, 1196 (1916). (21) Herrmann, Bell Lab. Record, 13, 45 (1934). (22) Hinrichsen and Kindscher, Ber., 46, 1291 (1913); Kolloid-Z., 10, 146 (1912). (23) Hutin, Caoutchouc & gutta-percha, 21, 12, 290 (1924). (24) Jessup and Cummings, Bur. Standards J. Research, 12, 357 (1934). (25) Kemp, U. S.Patent 1,638,535 (1927). (26) Kemp, U. S.Patent 1,656,737 (1928). TABLE V. EFFECTOF MOISTURE ON ELECTRICAL PROPERTIES(27) Kemp, Bishop, and Lackner, IND. EXQ.CHEM.,20, 427 (1928). OF HARDRUBBER (4) (28) Kimura, Aizawa, Takeuchi, J . Inst. Elec. Engrs. (Japan), 1928, 1274-7. Mors- TIME SPECIFIC (29) Kitchin, IND. ENCI. CHEM.,24, 549 (1932). TORE OF INDUCTIVE SPECIFIC POWER ABIMCAPACITYb REEIBTIVITY F A C T O R b (30) Midgley, Henne, and Shepard, J. Am. Chem. SOC.,54, 2953 MATERIAL“SORBED MERBION Dry Wet Dry Wet Dry Wet (1932). % Days Ohm-cm. X 10-15 % % (31) Ibid., 56, 1326 (1934). Ebonite (75-25) 0 . 2 8 315 2.8 2.9 20 10 0.8 0.9 (32) Morgan, I n d i a Rubber World, 88, 39 (1933). 0.8 0.6 3.0 20 10 Ebonite (70-tO) 0 . 2 3 315 2.9 (33) Naunton, Inst. Rubber I n d . Trans., 4, 68 (1928). Hardrubber 1.56 315 3.0 4.0 20 8 1.3 1.4 (34) Ostwald, Kolloid-Z., 6, 136 (1910). Sheets 1 mm. thick immersed in distilled water. (35) Patterson, Rayner, and Kinnes, J. Inst. Elec. Engrs. (London) b Test conditions: 1000 c cles per second and 25’ C. 50, 254 (1913); I n d i a Rubber J.,62, 27 (1913). 0 Composition of hard ruxber: smoked sheets, 28.5; reclaimed rubber, (36) Pearsall, I n d i a Rubber World, 77, 7 0 (1927). 18.5. sulfur 15.0. paraffin 2.0. hard rubber dust, 35.0; mineral rubber, 2.0; ’carbon hiack, 6.5; and &apde.ia, 0.5 (total, 100). (37) Perks, J. SOC.Chem. Ind., 45, 142T (1926). (38) Riding, Inst. Rubber I n d . Trans., 6, 230 (1930). (39) Schumacher and Ferguson, IND.ENQ.CHEM.,21, 158 (1929). (40) Scott, McPherson, and Curtis, Bur. Standards J. Research, 11, Schumacher and Ferguson (39) showed that moisture dif173 (1933). fuses somewhat slower through hard than through soft rubber. (41) Spence, U. S.Patent 1,235,850 (1917). They studied the rates of diffusion of various rubber compo- (42) Spence and Scott, Kolloid-Z., 8, 308 (1911). (43) Spence and Ward, Ibid., 11, 274 (1912). sitions and found that the rate does not vary much with com- (44) Spence and Young, Ibid., 11, 28 (1912); 13, 265 (1913). position. Recently Herrmann (21) has determined the rate (45) Stevens and Stevens, J . SOC.Chem. Ind., 48, 5 5 T (1929). for various hard rubbers and obtained an average value of (46) Weber, “Chemistry of India Rubber,” p. 91, London, 1902. 1.5 X gram per sq. cm. per hour per mm. of mercury (47) Webster and Porrit, I n d i a Rubber J . , 79, 239 (1930). (48) Werring, Proc. Am. SOC.Testing Materials, 26, 634 (1926). when measuring the loss of weight in a cell with water as well (49) Whitby and Jane, Trans. Roy. SOC.Can., 111,20, 121 (1926). as salt solutions on one side of the hard rubber diaphragm (50) Wolesensky, Bur. Standards J. Research, 4, 501 (1930).
and P206on the other. The effective diameter of the cell used was 4 cm. and the specimen thickness was 15 to 20 mils.
RECICIVED October 10, 1934. Presented before the Division of Rubber Chemistry at the 87th Meeting of the American Chemical Society, St. Petersburg, Fla., March 25 to 30, 1934.
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THE
MONSANTO CHEMICAL COMPANY, MONSANTO, ILL.
