HARD RUBBER
_____ HENRY PETERS, Bell
-.
Telephone
Laboratories, Inc., Murray Hill, N. J .
a
HE previous review of the literature ( 3 2 ) covered the developments of hard rubber for the period 1946 to 1947. This present survey is a continuation of the literature published during the past year, 1948. The attached bibliography deals mostly with papers and patents pertaining t o industrial use and manufacture of hard rubber articles. While technical papers are few in number, the British continue to contribute their share to the investigation of compounding, and physical and chemical properties of hard rubber. FUNDAMENTAL STUDIES
Fisher, Sewton, Norman, and Scott (16) investigated nine different accelerators in ebonite compounds and found them to be effective as accelerators but less effective as compared to soft rubber vulcanizates. Nevertheless, they increase resistance to plastic yield and to sir-elling in liquids; they decrease impact strength and increase dielectric loss a t normal temperature. Zinc and magnesium oxides do not function as activators in accelerated hard rubber mixes. Butyraldehyde aniline plus magnesium oxide was the most effective combination for reducing the vulcanization period without risk of overheating due to the exothermic hard rubber reaction. Numajiri (36) has found thnt by increasing the amount of tetramethylthiuram monosulfide in hard rubber, the time taken to develop the highest temperature in curing the mixture is greatly shortened, although a saturation point seems to exist in this connection. Furthermore, i t was found that the development of tensile strength, hardness, and the increase in the percentage of combined sulfur in the product were faster with samples containing more accelerator. I n a recent publication (49) it has been reported that Vandex, which is finely divided selenium, acts as a nonscorching accelerator to impart toughness without brittleness in hard rubber. Mixtures containing 45 parts of sulfur and 1, 2, and 5 parts of Vandex on 100 parts of rubber were cured a t 149 O C. in from 3 to 10 hours. I n all cases, time required to scorch a t 100” C. was in excess of 300 minutes. Scott (98)has investigated the rubber sulfur ratio and found that an increase in sulfur in ebonite causes the yield temperature to rise to a maximum and then fall. Prolonged vulcanization causes hardening with little increase in combined sulfur. Srvciling in solvents and oils increases rapidly as the degree of vulcanization is reduced. Selker and Kemp (39) have studied sulfur linkages in natural and GR-S ebonites and found that they had lost one third of their combined sulfur on methyl iodide reaction a t 24’ C. to yield a product of trimethylsulfonium iodide. S o evidence was obtained for the presence of polysulfide in natural ebonite containing 32% sulfur. Fisher (16j has shoLvn the influence of various proportions of magnesium carbonate on an ebonite mix of 32y0 sulfur. Properties reported include ash, total sulfur, acetone extract, free sulfur, densitj-, coeficient of linear expansion, plastic yield, Young’s modulus, cross-brenking strength and elongation, tensile strengt,h and elongation, machining properties, permittivity and power factor, electrical breakdown, surface and volume rejistivity, surface deterioration, water absorption, swelling in organic liquids, and inflammability. Fisher, Scott, and TKlloti (is)have compared ebonite compounds made from xho!e iatex and purified rubber having a high and low protein content, respectively. Permittivity and power factor at 10Qc::cle= per second are somewhat improved for puriiied rubbers, otherwise no technical useful advantage was
gained with regard to breakdown strength, volume and surface resistivity, or stability to light. I n an article by Dock and Porritt (14) on the absorption spcctrum of ebonite, they have shown that strong absorption commences in the blue and extends to the violet end of the visible spectrum. I n samples 0.05 mm. thick, strong absorption starts around 5200 A. Fisher and Scott ( 1 7 ) have investigated the influence of light absorbent pigments on electrical surface deterioration during exposure to light. Pigments such as gas black, ferric oxide, and lead titanate were incorporated into ebonite and exposed to daylight and mercury vapor lamp. These pigments increased the final equilibrium resistivity but not sufficiently tr! be of any practical value. Chatterjee contributed two papers ( 7 , 8); the first deals with dielectric properties of some solid insulating materials a t 750 mc. per second. A modified Lecher wire method was used and a dielectric constant of 2.6 and a loss factor of 0.31 was obtained for ebonite. The second paper deals with the dielectric constant of some solid insulating nntcrinls a t ultrashort v-aves. Ebonite i r i the form of 1- to 2-cni. thick slabs was measured over a wave lrngth range of 140 to 57.7 cm. using the Lecher wire method. i value of 3.1 was obt:iined a t the high frequency and the valur~ increased with a decrease in frequency. I n a s h d y of GR-S rubber dealing with polymer structure gel content, processing, compounding, calendering, and vulcanization, Bishop (3) concluded that the physical properties of GR-S hard rubber are not greatly inferior to those of natural rubber with the exception of machinability, punching, and drilling. \-dues are given for impact, cold flow,transverse strength, tmsile, and elongation. Clark and Cheyney ( 1 0 ) carried out some compounding studiey to improve compression properties of cellular ebonites derived from nitrile synthetic rubber. Sulfur content, blowing agents, accelerators, plasticizers, fillers, and rubber breakdown wercinvestigated. BlovAng agents and selected plasticizers tend trb have a substantial effect. Rostler ( 3 7 ) investigated rubber compounds ranging from soft co hard rubber prepared from natural rubber, GR-S, and butadiene-acrylonitrile copolymer. Data are given for tensile strength, elongation, and hardness before and after aging. Satural rubber containing 10 to 15Y0sulfur has a minimum tensile strength whereas GR-S and butadiene-acrylonitrile increase in tensile strength with increase in sulfur content. CHEMICAL AND PHYSICAL TESTING
Hammond and ;\lorley (24) have compared the accur:icie> of the perchloric acid, Carius, and fusion methods of estirmiting total sulfur in soft rubber and ebonite. The Carius method is best; the perchloric mid method is unsuitable for ebonite. Bridgman ( 6 ) devised a rough compression method and investigated 177 substances including ebonite a t 40,000 kg. per square cm. Church and Wayne (9) originated a dilatomctcr method for determining the cubic coeficient of thermal exparision of ebonite. The apparatus is able to determine the coefficicnt within 0.000001 per C. BOOKS AND REVIEWS
A number of books and review articles have been published which relate directly or indirectly t o hard rubber. “Hard Rubber and Plastics Handbook” (1 ), a valuable book, inc!:i:lrs
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INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
October 1949
tolerances, weights, and standard sizes for sheets, rods, and tubes. A book ( 2 ) dealing with compounding, physical properties, and industrial applications is of interest. A comprehensive tabulation ( 2 6 ) is given for the physical and chemical properties of natural ebonite. Dawson (12) discusses his review of the rubber industry in Germany during the period of 1939 t o 1945. Most of i t pertains to soft rubber, b u t some of i t covers hard rubber made from Buna S and Buna S. A review of the rheological properties of dielectrics including ebonite is discussed by Lethersich (SI); Malm’s review ( 3 2 ) covers the 1946 t o 1947 period. A review by Tudor ( 4 1 ) deals with a periodical and patent survey for 1947 with 27 references. INDUSTRIAL PRODUCTS AND USES
Utilizing mold design and pressure, Stepukhovich ( 4 0 ) has developed a rapid method for vulcanizing rubber to ebonite while Wildschut and Houwink ( 4 4 ) have compared hard rubber with Bakelite and steel as a material of construction. Hirano and Oda (26)have developed a psuedo ebonite from crude rubber rondensed with formaldehyde. A United States patent (29, relates t o a procedure for making hard rubber articles from synthetic and natural rubber in the presence of an inert gas. Three patents (80-28) were granted for the use of hard rubber In accumulators and two patents ( I f , 4 2 ) covered the use of hard rubber in storage batteries. Randall ( 3 6 ) discussed the importance of reclaim in hard rubber. The use of expanded hard rubber as a bonding agent for wood, heat insulator, and as a lightweight with good tensile strength is the subject of patents (27, 28). I n a British patent ( 2 3 ) the cellular structure in ebonite may be formed from a gas producing substance, ferrous oxalate. Miscellaneous patents cover the use of hard rubber in such items as combs (5, S 3 ) , umbrella containers ( 4 ) , fountain pens ( I S ) , ebonite base for self-sealing fuel tznk (19), surgical goods (SO), and insecticidal fumigants ( 3 4 ) . LITERATURE CITED
(1) iniericari Hard Rubber Co., Xew Ynrk, ”Hard Rubber and
Plastics Handbook,” 1948. ( 2 ) Barron, H., “Modern Rubber Chemistry,” pp. 295-302, New York, D. Van Nostrand Co., 1948. (3) Bishop, W. S..Bell Labs. Rec., 26, 55--7 (1945).
Bossart, A,, Brit. Patent 595,884 (Jan. 2, 1948). ( 5 ) Brant, E. H., Ibid., 605,626 (-4ug. 11, 1948). (6) Bridgman, P. W., Proc. Am. Acad. A,.ts Sci., 76, 71-87 (1948). (7) Chatterjee, S.II., Ibid., 574,320 (Jan. 1, 1946). Hammond, G. L., and Jlorley, J. F., J . R u h b u Research. 17, 131-3 (1948). Hirano, S., and Oda, I?., J . SOC.Chem. I n d . J a p a n , 47, 3.73-4 (1944). IND. ENG.CHEM.,40, 1891-903 (1948). ,Jablonsky, R., Brit. Patent 598,769 (Mar. 10, 1948’1. Ibid., 607,213-4 (Sept. 8, 1948). Kirby, R. A,, U. S. Patent 2,449,390 (Sept. 14, 1948). Lessard, E. L., Can. Patent 450,8013. Lethersich, JV., Electrician, 141, 39G (1948) : Elec. ZCei~ieU (London),142, 932 (1948). lfalm, F. S.,IND.ENG.CHEM.,40, 1773-936 (1948). hlonet, F. C., Monet, R. C., and Alonet, R. C., Brit. I’lristics Fed. Abs., 3,45 (1948);French Patent 919,99S(Doc. 16,1946). Murray, C. W. (to U. S. of -4merica as represented by the Secretary of Agr.), U. S. Patent 2,440,751 (May 4, 1949). Numajiri, S.,J . SOC.Chem. Ind. J a p a n , 44, 80G-8 (1941). Randall, R. L., Rubber Age, 63, 475 (1945). Rostler, F. S., I n d i a Rubber World, 117,493-7 (1948). Scott, J. R., J . Rubber Research, 17, 170-5 (1948). Selker, bl. L., and Kemp, A. R., IND.ENG.CHEX.,40, 1470-3 (1918). Stepukhovich. A. D., J . Applied Chem. (U.S.S.R.), 22, 110-14 (1947). Tudor, R. J., Ann. Rep?. Progress RuhSer Teciinol., 1947 (11). pp. 125-8. United States Rubber Co., Brit. Patent 603,323 (June 23, 1948). Vanderbilt Co., R. T., Vanderbilt News, 14, Sos. 1 and 9 (1945). Wildschut, A. J., and Houwink, R., Mededeel. Rubber-Sticht.. DeZft, No. 23 (1941). RECEIVED .July 16, 1949.
Stainless Steels and Other Ferrous Alloys ___
31. €1. BROWN AND W. B. DELONG, Engineering Research Laboratory, E. I . du Pont de Nemoitrs & Company, rnc., Wilmington, Del.
A
LTHOUGH still relatively young as materials of construction, the stainless steels have earned for themselves a permanent place in the industrial scheme. Production of these alloys has increased by a factor of 10 since 1934 and currently stands a t approximately 500,000 tons of ingots per year ( 1 1 ) . This figure is small (less than 1%) compared to the total steel production, b u t represents a sizable quantity of premium-priced material. The unusual properties of these alloys have obviouily justified their continued use in spite of t,heir high cost. Similari:\, the amount of published research that appears annually certainly exceeds 1% of that published on the ferrous materials.
Investigators are apparent,ly not convinced that still more unique properties cannot be developed by continued research on these alloy systems. A symposium on evaluation methods for staiiiiess steels was held a t the 1949 annual meeting of the American Society for Testing 1Iaterials. Although the papers presented have not yet been published, they contributed significantly to existing knowledge of (1) the potcntialities and limitations of the estralowv-carbon (0.03% carbon maximum) stainless grades, (2) comparative results and factors influencing data obtained by the comnionly used evaluation methods for predicting susceptibility
