HARD RUBBER HENRY PETERS, Bell Telephone Laboratories, Inc., Murray Hill,N . J.
As judged by the literature, the general trend during the past year on the subject
ment of upper wind and air. Onazote expanded ebonite 1 inch thick is used as a cover for the sonde. Even though a temperature of -75” C. may be encountered, the thermal protection in conjunction with thp heat generated in t h e thermionic valves is sufficient t o maintain the internal temperature a t a reasonable level. The effect of acids and salts on hard rubber has been quantitatively determined by Rondberg (41). Loss of weight of ebonite after 8 weeks a t 20” C. in 25% sulfuric acid was 0.03; in commercial hydrochloric acid, 0.14; in 6% hydrofluoric acid, 1.62; in saturated sodium sulfate, 0.17; in 30% acetic acid, 0.37; and in sodium chloride 0.30%. Figures are given for swelling in organic solvents and nTater. Birsten ( 1 1 ) gives a n interesting account of natural and synthetic ebonites suitable for protecting metals against nitric acid within certain limits of concentration and temperature.
of hard rubber has been toward de-emphasis of fundamental research and more emphasis on use. Plastics, through substitution, continue to make gains in the field of hard rubber. A renewed interest is again show-nin the use of latex ebonite for industrial applications. The patent situation appears to be unusually active and the interest in synthetic hard rubbers continues to increase.
T
H I S annual review of 1951, like the previous one (39),is a summary of the work carried out in the field of hard rub-
ber. Lethersich (8.4) investigated the mechanical properties of dielectrics a t high temperatures. Tests made a t temperatures approaching the softening point showed that creep properties resembled those a t room temperature. The acceptable applied stress is considerably less a t elevated temperatures. The main feature is the absence of secondary creep (true viscous flow) even at temperatures a t which t h e material became rubberlike. The materials investigated were ebonite, polyethylene, polystyrene, and polymethyl methacrylate. Lethersich ( 5 5 ) also investigated the static and dynamic rheological properties of the same materials. Static tests of shear-strain-time relationships have been made in continuation of w-ork described previously ( 3 2 ) . Studies of dynamic modulus in shear and loss angle have been made over a wide range of frequencies by two methods ( 3 3 ) . Hard rubber made from reclaim rubber is still under investigation. Jackson (2‘7) recently prepared hard rubber from natural, Buna S, and Buna N types as well as reclaim rubbers and found it was necessary t o incorporate large amounts of sulfur. T h e results involving tensile strength, cold flow, heat distortion, elongation, impact, electrical properties, flexural strength, and resistance t o attack by corrosion are tabulated. In t h e relevant literature there are few references t o t h e making of ebonite directly from latex. One of t h e few processes which has been developed technically is Beckmann’s, whereby it is possible t o vulcanize a wet gel or coagulum into a microporous ebonite which in turn can be used for accumulator partitions. RIeanwhile the flow-casting process and the casting method Kith heatsensitive latex have been developed for making sample moldings ( 4 7 ) . T h e flow-casting method has been described together with the mechanical properties of latex ebonite and its applications. CHEMICAL AND PHYSICAL TESTING
Kreft (29) has studied the effect of temperature on the dielectric properties of certain insulants a t decimeter wave lengths. His new resonance method is capable of measuring the properties of the material by t h e reaction of a special measurement conductor on a primary conductor. Power factor and permittivity determinations on six dielectrics, including ebonite for a range of wave lengths of 10 t o 75 em. and a temperature of 20” t o 80” C., are reported. The power factor increases strongly nTith temperatures, but t h e permittivity shows only small variations. Measurement of the internal friction of plastic linings subjected to flexings was undertaken by Lienard ( 3 6 ) . The method was applied t o expanded ebonite. The shock-absorbing capacity or the ratio of energy lost in the course of each oscillation cycle t o the total energy of oscillation does not vary appreciably m-ith the amplitude; it is proportional t o the square of the thickness of the ebonite and decreases slightly when the frequency increases. Jones (R8) has developed a radar-sonde system for the measure-
BOOKS AND REVIEWS
Several books and review articles have been published which deal directly or indirectly mith hard rubber. The American Society for Testing Materials (4)has described in great detail its testing procedures for synthetic and natural hard rubbers. Two references ( 2 , 3 ) deal with the growth of t h e hard rubber industry during the past 100 years; one of these refers t o an anniversary edition of a handbook containing valuable chemical, electrical, and physical data. A review (8) of the history and development of rayon and artificial fiber industries includes a section on the use of ebonite for spinning machines. Dating as far back m 1880, a n interesting historical account (SO) is given for the protection of metals against acids using ebonite as the protective covering. The composition and grades of ebonite manufactured for use in the electrical industry are outlined ( 2 4 ) and routine physical and chemical tests are fully described. This report (46)is a compilation of work which because of the war was not published as the regular annual report of t h e Rubber Research Institute of Malaya; it includes oil absorption of hard rubber. Various phases and a p plications of hard rubber are summarized in two reviews (16, 17) having 14 and 19 references, respectively. The “Rubber Trade Directory of Great Britain” (44)continues t o serve as an encyclopedia for t h e soft and hard rubber industry. The “Chemical Engineering Catalog’’ (13) and the “Handbook of Chemistry” ( 2 6 )contain some vital information pertaining t o the physical and chemical properties of hard rubber. The ever-increasing demand for new compounds and for the testing of hard rubber is the subject of one of t h e chapters in LeBras’ most recent technical book (SI). T o a lesser extent the subject of hard rubber is referred t o in Meyer’s book (58) on high polymers. Another publication ( 2 1 ) deals primarily with the derivatives of hard rubber. INDUSTRIAL PRODUCTS AND USES
A novel application ( 4 6 ) involves the use of ebonite coating, produced by flame spraying in almost the same manner as polyethylene coating. Thick or thin coatings adhere well t o sheet iron and light-weight metals. Expanded ebonite (16) as a thermal insulating material and as a barrier t o water transmission continues t o be a subject of much interest. A percentage tolerance system 2344
October 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
based on accumulated variables inherent in mold distortion, production processes, and materials is the topic of one investigation ($6).A hard porous rubberlike product (48)is the result of a reaction between urea, formaldehyde, and zinc chloride in a sodium hydroxide solution of casein. Substitutions are constantly taking place and hard rubber in some applications has fallen by the wayside. In the fmt instance (14) a battery case for use with a miner’s lamp is now being made with polyethylene instead of ebonite. Greater efficiency, durability, and reduction in weight are claimed for this material. I n another application ( 3 7 ) polystyrene has been used in water meters since 1938. Again, it is claimed that this plastic is lighter and smoother, attracts less dirt, and is more resistant t o water absorption. In the case of battery separators (18, 19), a polyvinyl plastic known as Pormax is considered to be superior t o wood or ebonite because it is nonbrittle and more superior t o acids. Bennett (10) has given an interesting resume pertaining to the application of synthetic enamels t o hard rubber steering wheels. A cost analysis (41)is shown for articles made from latex ebonite in comparison with those produced from rubber ebonite and Bakelite. Lead as an acid-resistant lining in metal containers can be suitably replaced with ebonite (43). I n the textile and printing industry ( 7 ) metal rolls, covered with soft rubber, depend upon ebonite as the bonding medium. Three patents (9, 21,$3) were granted for the use of hard rubber in batteries: The first involves the use of ebonite separators made from latex-sulfur mixture, the second relates to a microporous ebonite battery separator having a resistance of 0.045 ohm per square inch, and the third refers to separators for electric, secondary batteries. A patent (12) involving a procedure for the preparation of hard rubber from a solution containing asbestos fibers and sulfur has possibilities. Miscellaneous patents cover the use of hard rubber in such items as teat cups far milking machines ( I ) , a cigar holder having a hard rubber mouthpiece of special construction (6),ebonite printing plates for printing figure registers ( 6 ) , a hard rubber impeller for centrifugal pumps (ZOO), and a buoyant disk of expanded ebonite (40). LITERATURE CITED
(1) Akkerman, J. J., Netherlands Patent 67,911 (July 4, 1951). (2)Am. Hard Rubber Co., “Ace Hard Rubber and Plastics Handbook,” 100th anniversary ed., 1951. (3)Am. Hard Rubber Co., Rubber Age, 70, 33942 (1951). (4)Am. Sac. Testing Materials, Philadelphia, Pa., “Standards on Rubber Products,” 1951. (5) Angert, J. J., U. S. Patent 2,532,531(May 12, 1950). (6) Axmacher, F. E., and Licentia Patent, Verwaltungs, Ger. Patent 805,161 (Aug. 3,1951). (7) Basu, B., Rubber I n d i a , 1, No. 2, 14-17 (1949). (8) Beecham, A., Trans. Plastics Inst., 19, No.37,66-89 (1951).
2345
Behrman, A. S., Brit. Patent 647,142(1951). Bennett, H. R., Rubber Age, 69,437-8 (1951). Birsten, V. M.,Rev. ghn. caoutchouc, 28, 67 (1951). Bremant, A,, French Patent 967,143 (1950). Chem. Engineering Catalog, New York, Reinhold Publishing Corp., 1950-51. Concordia Electric Safety Lamp Co. and Mineral Laboratories,
Brit.Plastics, 24,2-4 (1951). Cooper, A., Trans. I n s t . Rubber Ind., 27,84-100 (1951). Davis, B. L., Ann. Rept. Progress Rubber Technol., 13, 81-3 (1949).
Davnes. H.A.. Ibid.. 14.95-7 (1950). Elictric Storage Battery Co., Chem. E n g . News, 29, 1246 (1951); Tires, 32,No. 8,57(1951).
Ibid., 38,NO.8,38,57-62(1951). Foreman, W. E., and Dexine Rubber and Ebonite, Ltd., Brit. Patent 652,840,652,840-1 (Feb. 5, 1951). French Rubber Institut, Rue Scheffer, Paris 16e, France,
“Annual Report of the Rubber Industry and Its Derivatives,”
1950.
Fuller, L., Szper, J. A,, and Valery Dry Accumulators, Ltd., Ibid., 649,866(July 1, 1951). Greenup, H. W.,and Green, V. M., U. S.Patent 2,587,631(Jan. 9,1951).
Halls, E.E., EEec. Mfr., 6,213-16 (1950);B r i t . A h . , B11, 1285 (1960).
Hamevious, W.L., Products Eng., 22, 124-5 (1951). Hodgman, C. D., “Handbook of Chemistry and Physics,” 32nd ed., Cleveland, Ohio, Chemical Rubber Publishing Co., 1951. Jackson, E. D., Rubber Age, 69,200 (1951). Jones, F. E.,Hooper, J. E. N., and Alder, N. L., Proc. I n s t . Elec. Eng., 98,Part 11, 464,480,483 (1951). Kreft, W., Fernmeldetechz, 3,203(1950). Lacollonge, M. P., Rubber, 7, 66-7 (1951). (31) LeBras, J . , “ElBments de science et de teohnoligie der caoutchouc,” published for French Rubber Inst. by Soci6t6 d’Editions Techniques Coloniales, Paris, France, 1950. (32)Lethersich, W.,British Elec. and Allied Ind. Research Assoc., Rept. R e f . L/T 171 (1947). (33)Ibid., L/T 212 (1950). (34)Ibid., L/T 242 (1950). (35)Ibid., L/T 250 (1951). (36)Lienard, A., Rev. g6n. caoutchouc, 28,443 (1951). (37) Meterfabriek Dordrecht, Plastica, 4,190-3 (1951). (38) Meyer, K. H., “Natural and Synthetic High Polymers,” 2nd ed., New York, Interscience Publishers, 1951. (39) Peters, H., IND.ENG.CHEM.,43, 2256-7 (1951). (40)Pfleumer, H., U.S. Patent 2,540,831(June 2, 1951). (41) Rondberg, C.J., Ingenieur (Utrecht), 60, M K 88-9 (1948). (42)Rotgans, G. E., and Gerritsen, J. C., Rubber-Stichting, Delft, Holland, Commun. 158 (1950). (43)RubberIndia, 3,No.6,18 (1951). (44) Rubber Trade Directory of Great Britain, London, England, Maclaren and Sons, Ltd., 1950. (45) Sharp, C. T., Report of Rubber Research Inst. of Malaya for the Period January 1941 to August 1945. (46) Soci6t6 de Revetements Plastiques, I n d . Plastiques, Mod., 3,No. 4,9(1951). (47)Van’T Wout, J. W. F., Der Latex, 33-4 (1951). (48)Yoshinaga, H., J . SOC.Rubber I n d . , J a p a n , 20, 157-9 (1947). RECEIVED for review July 16, 1952.
ACCEPTED July 16, 1952.
