elastomers - American Chemical Society

Reconstruction Finance Corp., Washington, D. C.. The Government has revoked consumption controls on rubber, and this action permits competition betwee...
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Ofice of Synthetic Rubber, Reconstruction Finance Corp., Washington, D . C .

that combine complete resistance to ozone; excellent resistance to abrasion, heat, sunlight, and weather; unusually good flex life and resistance to crack growth; and low water absorption. It is a chlorosulfonated polyethylene (polyethene) and contains 27.5% chlorine and 1.5% sulfur. The elastomer can be vulcanized with magnesia, litharge, tribasic lead maleate (Tri-Mal); sulfur-type accelerator, Tetrone A, mercaptobenzothiazole (Captax), d i p h e n y 1g u a n id i n e; a n d organic acids, Staybelite resin, and wood rosin. I t s uses will include tire treads, weather stripping, coated fabrics, footwear, wire and cable insulation, and many others (SO, 36,

The Government has revoked consumption controls on rubber, and this action permits competition between natural and synthetic rubber. Technically classified natural rubber is beginning to show promise. A completely new synthetic rubber, Hypalon S-2, has made its appearance. It is a chlorosulfonated polyethylene and is vulcanizable, shows complete resistance to ozone, and has excellent weathering and other characteristics. GR-S with only about 10%of styrene gives very good low-temperature properties. Oil-extended and plasticized highMooney GR-S continues its rapid progress, producing tires that are as good as “cold” GR-S and sometimes better. In tire testing, the weight method is said to give better results than measurements of depth of tread markings. Studies are progressing on reinforcement and bonding by carbon black, low-temperature tests, and accelerated and other tests with ozone.


HE United States Government last June revoked all consumption controls on natural rubber; this action permits free competition between natural rubber and synthetic rubber, as stated in a report of the Crude Rubber Committee, Rubber Manufacturers Association, Inc., New York, N. Y. (41). The producers of natural rubber now have the responsibility of supplying the American consumer with the product he wants. Low grades even under contract have been altogether too general. The manufacturing industry is oonfident of the important future position of synthetic rubber, and believes that the future of the natural rubber industry will be best served by emphasizing uniformity, cleanliness, proper grading, and good packing. The price of natural rubber a t this time was around 33 cents a pound and that of GR-S was 23 cents a pound. An interesting discussion of the economics, production, and consumption of natural and synthetic rubbers has been published (38). The results with technically classified natural rubber are very encouraging ( 1 1 3 ) . The current method reduces considerably the rate of vulcanization. Reviews and discussion of the methods are given (64, 114). The reports of the Rubber Research Institute of Malaya for January 1941 to August 1945, and for September 1945 to December 1948, cover work of the Soils, Botanical, Pathological, and Chemical Divisions (141). Eleven specific branches of the rubber industry and general repork on planting, rubber derivatives, synthetic rubber, and machinery are discussed in a book issued by the Institution of the Rubber Industry (46). Leaves of kok-saghyz plants were painted daily with a 1% solution of CI4-labeled sucrose containing a small amount of glucose, and the rook, which were suspended in a moist-air chamber, were tapped for latex daily (113). The GI4 appeared in the latex within the first 10 days of the experiment, and its main location in the rubber proper was proved by isolation of the purified rubber and determination of its C14activity. Tropical soils vary widely in fertility depending on the parent rock, but generally they are poor in the mineral nutrient elements bhat plants require (133). Work has been done to show the requirements of added minerals to balance the tree’s nutritional supply. NEW SYNTHETIC RUBBERS

Hypalon S 2 is a new elastomer that is stated to be the most durable ever offered for use in the rubber industry (176). It is supplied in a white, spongy, matted form which can be processed with conventional rubber machinery and cured into products

166). Side chains in monomers converted into elastomers raise transition temperatures but low-temperature flexibility cannot be materially improved in this way (118). The polymer from 2heptyl-1,a-butadiene showed transition temperature of -83” C., and that from ktertbuty1-1,3-butadienewas +20° C. OTHER SYNTHETIC RUBBERS

High purity 1,3-b~tadiene-2,3-C’~ has been prepared in four steps from methylene-labeled succinic acid (96). There are four types of neoprenes and of these, one “crystallizes” fast (in hours), and the others in weeks, months, and years (108). Preparation of solutions and their uses are described. They can be cured a t 60’ C. or on standing a t room temperature. An improved Neoprene Type WRT is a modification of Type W but is crystallization-resistant (138). A book on neoprene applications in engineering design has been published (93). I n the polymerization of 2,3-difluoro-1,3-butadiene and 2chloro-3-fluoro-1,3-butadienethe net effect of the introduction of fluorine into butadiene was shown to decrease the cold resistance by a considerable amount, leaving the tensile properties and solvent resistance relatively unchanged (173). A book has been published on the engineering properties of silicon rubbers (160). A literature review has been given on silicone rubber (61). Polyethyl acrylate can be vulcanized with reagents which cause the removal of ethyl alcohol through a Claisen type of condensation, the ester group going out with an alpha-hydrogen atom from another group (149). The alcohol can be recovered in a high vacuum a t high temperatures, but ordinarily it remains as a plasticizer. The corresponding polyethyl methacrylate, which has a methyl group in place of the hydrogen, does not react a t all. RUBBER DERIVATIVES

A thiol, preferably CSHBSH,reacts with a stripped elastomer latex, yielding an addition elastomer that will cure but will not cyclize or resinify on heating a t 250’ to 275’ 0. in the absence of air (169). The thiol reacts selectively with vinyl side groups but not with the chain double bonds. Homogeneous and elastic solids were produced by heating a mixture of smoked sheet, resorcinol, and hexamethylenetetramine




for 7 days a t 65" C. ( S I ) . The two chief components are bonded chemically by an addition reaction. Chlorinated rubber is prepared by passing gaseous chlorine into stabilized and strongly acidified Hevea latpx (3). A high acidity prevents the formation of hypochlorous acid and improves the mechanical stability of the latex. Reactive and nonreactive chlorine atoms were determined in chlorinated rubber by treatment with aniline (4). The first stage of chlorination, in which hydrochloric acid is evolved, is a substitution presumably on the CH2 adjacent to the double bond. Addition next occurs, followed after 3 C1 per CEHe have been added by the formation of CCl, structures. OIL-PLASTICIZED POLYMERS

The direction of polymerization toward rubber polymers followed by sufficient swelling with oil to make them plastic should produce rubbers equal to those made by polymerizing in the presence of modifiers (179). A method of measuring the length of a s a ollen test piece 30 nim. long and 1 mm. in rross section is proposed, especially because it is suitable for rubber of high hardnesR, and for factory control testing (164). Tires made of the neir copolymer-oil mixtures have given better service than tires made either of standard GR-S or of GR-Smade by the low-temperature process (63, 176). Higher proportions of fillers and pigments can be incorporated in the copolymer-oil mixtures than in the standard GR-S mixtures. Composition data obtained by the more rapid refractive index-density-molecular weight method are given for oils ( 8 8 ) . The determinationof thehydrocarbon type of petroleum products is made by the refractive index, with a long list of hydrocarbons and their refractive indices (137). A critical review and discussion oi the background and present developments are given concerning the production of butadiene-styrene copolymer-petroleum oil mixtures by latex compounding, with many facts, a large amount of experimental data not hitherto published, many tables and graphs, and 86 references (136). There have been suggested two codes of symbols and specifications for petroleum products that are used as plasticizers for rubber, based on chemical characteristics easily measured in any laboratory-a four-symbol code for exact research work and a three-symbol code for broad general classification and commercial usage (136). POLYMERIZATION

I n a redox cuxnene hydroperoxide-iron-wgar iecipe a t 0" arid 30" C., dihydroxyacetone was the most effective sugar (80, 81). Ferrous sulfide-cumene hydroperoxide wab also viorked into a good recipe of polymerization. The only reliable method for evaluating the ielative efficiency of an initiator system is to determine the rate of polymerization per particle of latex formed (107). Monomer reactivity ratios have been determined for the copolymerization of butadiene with methyl methacrylate, butyl acrylate, methacrylonitrile, and vinylidene chloride in emulsion a t 5" C. (174). The rate of polymerization increased with the purification of the monomers in the systems of isoprene and 2,3-dimethylbutadiene and copolymerization with styrene a t - 18' C. in emulsion, and approximately quantitative 1,4 addition was obtained with polyisoprene and with polydimethylbutadiene (117). The modifier (mixed tertiary mercaptans, MTM) disappeared very rapidly for isoprene and dimethylbutadiene but very slowly for butadiene. A general review has been written of synthetic rubber polymerization practices, including some history of GR-S, theories of initiation, oil-resistant types, and Alfiii polymers ( I S ) . A mixture of sodium dimethyldithiocarbamate and sodium polysulfide is a polymerization stopping agent for both hot and cold GR-S (7).

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Indian C'rgptostegia gra,idi$oru latex is best coagulated with 0.5% of soap solution, which is more economical than the l a r p ~ proportion of Ealt required ( 1 2 3 ) . Studies have also been matic: of coagulation with Hevea latex. Blends containing 70% or more of natural rubber latex l i d 1itt)leeffect, on the stress-strain properties of the films of the mixture; cold GR-Slatices gave higher stress-strain values of natural rubber blends than did standard hot GR-S latices; and the physical properties of a natural rubber stock are superior to thosc of any of the synthetic rubber latices eo far tested (121). The relative values of recent methods of testing latex have boen critically discussed and thr conclusion is reached that no avnilable tests of chemical stability are capable of predicting the suitability of latex for all applications (111). The review includes the latest methods of preparing latex concentrates and a descript,ion of the concentrate prepared by a ne7y electrodecantation process. Several new low-temperature synthetic latices have been developed, some of which are polymerized to 50% solids and heat concentrated to 6070 solids (6Y). Ot'her new latices include those containing 110 permanent elect'rolyte and emulsified with volatile base soaps. By the use of cotton fabric h:tving a positive charge and reinforced latex, stronger adhesion can be obtained than with untreated fabric and ordinary latex (119). Positive charge on the cot,t,onis obtained by treatment in t'he known way wit'h a cationic soap in dilute solution, and the reinforced latex is prepared by the method of LeBras and Picrini. TYith synthetic resins formed in situ, rubber in latex is reinforced and a tensile strength of 460 kg. per sq. em. (6550 pounds per uq. inch) has been obtained (130). Reinforced latex rubber hss been used for the manufactlure of convej-or belts (186). h series of tests was carried out on clonal and seedling rubher during 4 years and it was found that the main differences attributahlr to clonal origin are considerable difference8 in mechanical stability of the latex, inverse differences in viscosity, and unrelated differences in potassium hydroxide value (78). TTlth a somewhat new apparatus i t was found that plotting the time factor of the mechanical stability against the concentration of :I surface-active substance gives a curve which is reproducible and offers a means of measuring indirectly but on a quantitat>ive bask :in\. change resulting froin the addition or removal of the surface-active substance (98). Sodium fluotitanate is valuablc as a ptilling agent. for natural latex and GR-8 latices (89). A study has been made on the preparation of aqueous susp i s i o n s of zinc oxide for adtlition to latex compounds ( 7 6 ) . The effevt of several materials added to latex on the zinc oxide stabilitj. is: Fatty acid and sulfonic acid soaps have only a slight influeiic~;sequestering agents and sodium phosphates and silic>:ites have R atabilizing effect; a,nd ammonium salts and amines have a r c d destabilizing effect ( 6 9 ) . description is given of 11 greiiC many commercial synthetic es of C. S. manufacture anti their properties, and similarly of commercial water-soluble and dispersible flexible synthetic materials (185). It has been shown that by the proper choice of styrene cont'ent (approximately 10% bound), GR-S foam rubber can be made that is superior to Hevea foam in subzero properties ( 1 6 6 ) . Zinc phenylethyldithiocarbamate is a particularly good accelerator in products molded from latex, and makes possible drying a t the optimum range of 60" to '70" C. and complete vulcanization in 1 hour a t 100' C. (86). Hammer-milled glass fiber of suihble particle dimensions in foamed-rubber latices thickens such mixtures and is valuable as a foam stabilizer, and as the proportion of glass fiber is increased the time of gelation becomes progressively shorter (17). Films cast from vulcanized Hevea latex were much more permeable t'o water vapor, sorbed considerably less water, and had IL greater negative temperature dependence of permeability t,ha.n uncompounded or dry vulcmimd films (26).

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O n e of Largest Vulcanizers Ever Constructed in ilkron


Osmotic and viscometric data for fractionated fresh riaturd rubbers show that normally tapped rubber, not only as it leaves the tree, but also in dried freshly coagulated latex and smoked sheet 1 year old, comprises a series of polymer homologs in the molecular weight range of 50,000 to over 3,000,000 (31, $2). At least 60% of the hydrocarbon has an intrinsic viscosity higher than 6, which corresponds to molecular weights exceeding 1,300,000, with a substantial proportion exceeding 2,500,000. No appreciable proportion of any components of molecular weight, sufficiently low to classify them as viscous liquids was found. A gel component, probably microgel, present in the freshly tapped rubber hydrocarbon is of considerable importance in its effect on the hardness of the raw rubber and complicates greatly the interpretation of viscometric data. Benzidine added to the latex gave a hardened rubber. Data are also given for oxygenated rubber. The major differences in polymer structure of cold GR-S as compared with standard GR-S appear to be: a narrower molecular weight distribution with less soupy polymer, a slight increase in crystallization tendency, and an increase in homogeneity of the polymer composition (11). As the number of divinylbenzene units or potential cross-linking sites per molecule is increased, there is a rapid decrease in the molecular weight exponent as the divinylbenzene concentration approaches one cross-linking unit per molecule (76). This method does not provide an absolute means for measurement of cross linking, but it is of significance as a measure of the degree of cross linking in soluble polymers and is helpful in the production of polymers of maximum chain length without gelation. When natural rubber and a- and 8-gutta-percha are in the amorphous state, their infrared spectra are very similar but not identical; in the crystalline state marked differences appear (161). With natural rubber, rubber hydrochlorides, chlorinated rubber hydrochlorides, chlorinated rubber, cyclized rubber, and rubbersilver salt complexes, infrared spec’tra obtained are between 5.7

and 14 microns (144). By means of infrared absorption alkali metal-catalyzed butadiene polymers had a higher proportion of butadiene residues in the 1,2-~onfiguration, 45 to 50%, than emulsion polybutadiene, 18 to 23% (100). The second-order transition temperature of sodium-catalyzed polybutadiene polymerized a t 30’ C. was -45’ C., whereas the 75’ C. polybutadiene had a value of - 64’ C. X-ray studies show that 8-polychloroprene has the cis configuration of a-gutta-percha, and p-polychloroprene has the trans configuration of 8-gutta-percha ( 7 3 ) . PHYSICAL PROPERTIES

The strain (elongation) at a fixed stress (5 kg. per sq. em.) is uniquely related to the load required to produce an elongation of 100% of pure gum natural rubber vulcanizates (19). The second constant of the Mooney equation for the stress-strain curve does not vary greatly from rubber to rubber. An apparatus has been described for measuring the pliant flow of rubberlike materials, which should be useful in studying the properties and behavior of tires and mechanical goods (16). Relationship between molecular structure and physical properties has been discussed, showing that the chemical nature of the monomer units determines the intermolecular forces and influences especially the temperature range in which rubber elasticity is exhibited, the swelling in organic liquids, and the permeability of gases (68). Molecular weight distribution is most significant for permeability. Measurements of the conductivity of a rubber produot, component part of the product, or experimental sample when new are not a reliable criterion of the static effects later (71). Methods are given which measure the capacity of a rubber product or experimental sample to “bleed off” self-generated or imposed electrostatic voltage. A new “electrostatic probe” and associated equipment have been described for measuring and recording the changes in electrical potential of the rubber batch in the Banbury mixer (66).



By this means the breakdown of the rubber and the state of incorporation of the pigment, oils, and other ingredients can be followed without raising the ram. The change in anisotropy with elongation has been found for iiatural rubber and for several synthetic rubbers (169). Unmturated rubbers have a large principal susceptibility perpendicular to the direction of stretching, because of the presence of olefinic double bonch. The differences between natuial rubber and polybutadiene are attributed to the presence of unsaturated side groups caused by 1,Saddition in polybutadiene The real part of the reduced dynamic rigidity, plotted against the reduced frequency, gives a single composite curve for data over wide ranges of frequency and temperature; this is true also for the imaginary part of the rigidity or the dynamic viscosity (49). -4simple apparatus for determining the dynamic properties of elastomers in shear a t audio-frequencies was appraised (68). Typical values of shear modulus and viscosity for natural rubber, Butyl, and silicone rubber have been given, both a t room conditions and a t 150" F. Frequencies of test range from 100 to 5250 cycles per second, the shear moduli from 0.5 X 106 to 480 X 106 dynes per sq. em. and the viscosities from 20 to 75,000 poises. Dynamic properties over a wide range of frequencies, employing both a horizontal pendulum method and a tuning-fork method, have also been published (154). A number of useful approximate relations can be deiived by investigation of the mathematical structure of the integrals relating the distribution of relaxation times to the observed properties and by examination of the behavior of certain particular relaxation time distributions ( 5 ) . Attempts to correlate dynamic and static data on the basis of t b general theory have been reaYonably successful. I n another article the measurement of dynamic properties of rubber has been well discussed (99). A study of the softening of rubber by applied stress haa increased our theoretical knowledge of reinforcement, and softening by stress is due primarily to breakage of attachments between filler and rubber, while the linkages between rubber molecules formed through carbon particles are of two kinds, of which the stronger type is chemisorptive attachments x hich remain unbroken by stressing and thr rwaker are van der Waals type (go). There are machines that inea~iireand autoniatically record the load-deflection characteristics of vibration-coutrol mountings, that measure hysteresij and dynamic modulus of elastomers, vibration machines, and rotational fatigue machines (138). The conclusion is that under prolonged constant strain a t a low temperature greater than that of the second-order transition, all elastomers studied crystallize more or less, and the crystallization depresses the stress (103). Butadiene-styrene copolymers with 8.7 and 16.0% of styrene yield vulcanixates which have stable compression sets considerably lo^ er than the compression set of the standard GR-S vulcanizates, and are useful for gaskets for low-temperature service (106). Nonlinear vibration Characteristics are readily observed for tread stocks of both Hevea and synthetic rubbers in the mechanical range of frequencies ( 6 2 ) . Measurements of the nonlinearity over a range of temperatures suggest that the vibration elicits structural changes in the rubber analogous to those observed in the rheology of rubber solutions and raw rubber. Permeability can be reduced to one third its value for an unloaded vulcanizate by the incorporation of 20% by volume of commercial mica or powdered aluminum (16'7). Determinationsweremadeat -36O, -26", -17.5',and - 2 " C . , the changes were followed dilatometrically, and a maximum rate of Crystallization was found at about -26' C. for raw natural rubber (143). Experimental data for the extension of butadienestyrene polymers vulcanized 7 to 40 minutes at 143' C. showed almost exactly the linear relation predicted by the theory previously derived: S = E ( L - l ) , where S = stress, E = elastic moduIus, and L = rP1atiw length on extension, enrh function

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passing through two maxima a b the vulcanization time i p increased from 7 to 40 minutes (9). On the basis of thermodynamics and of the elmticity theory of large &rains, an equation has been derived for the reinforcement energy-that is, the energy of the filler-rubber mixture less that of the separate components (130). The reinforcement energy it regarded as a negative measure of reinforcement, and its component terms (elastic and surface energies) are established. I n the screw-extrusion machine, at zero discharge, the mechanism for rubberlike materials ia one of viscous shearing, ltratl rubberlike materials behave as viscous but highly thixotropii liquids ( l a g ) . An empirical relationship between permeability and 6olubiht.l has been determined (109). Natural rubber was found to transmit less vibrational force than any of the other rubbers tested in the range of frequenciefrom 25 to 2000 cycles per second; moreover, its transmissibilitj was practically constant over this range of frequencies (106) From observations, a bask for the mathematical relation between the different moduli under each set of testing conditiollwas established empirically (84). 9 general equation was derived, from which approximate values of the material constantcan be calculated by taking into account the imposed statir strain, the Rhape factor, and the dynarnir stiffening. CHEMICAL PROPERTIES

Polybutadiene, prepared by emulsion polymerization, thi I mixed with di-Prt-butyl peroxide foi 15 minutes at 180' C., I < rubbery and has a high degree of rebound, low tensile strength and only 25% elongation (37). When baked for up to 10 days a t 250" C. it is converted into a hard rigid material, the density 0' which increases from 0.91 to 1.01, solvent swelling drops from 200% to zero, and the second-order transition point rises froin -85" to about 160' C. and then disappears. Polybutadiene, ptepared with sodium as the catalyat, changes in physical propertie+ nith baking at a rate four times as fast as does the emulsion poli mer. CARBON BLACh

The unitornuty of dispersion of carbon black in rubber is determined better by autoradiography than by the usual t e n d ( > sti ength, elongation, and modulus values (79). The carJxm black is prepared by being degassed and heated with C1402io, 5.5 hours at 900" to 1000° C. A relationship has been found between the modulus, oil absorption, and ultimate analysis of carbon black (160). Resiptivity test reveals differences between blacks of the same type and therefore i t is a simple and sensitive test for characterizing b l a c b and should be uqeful for quality control of production and foi specification purposes (91). Electron microscope photograph., of carbon black--rubber mixes demonstrate the aggregation of carbon and its associated gel rubber (83). I n the formation of bound polymer, the temperature has a large effect; higher temperatures increase the amount of binding when carbon black loadings are low, and it was found that the polymer of higher molecular weight is preferentially bound duriiip mill mixing ( 4 7 ) . Carbon blacks in general rapidly respond to mixing, and the chainlike aggregates characteristic of reinforciw carbon blacks observed under the electron microscope are practically unchanged after mixing with rubber (Qs), There is some experience that oil-type furnace blacks disperse more easily than the channel blacks. Good correlation is obtained between electron micrographs and light transmittance measurements of dilule solutions of the compounds ( 5 3 ) . The method provider a simple way for the measurement of carbon black dispersion E research or control work. Differences in milling conditions cause Pignificant variationp 111 the dispersion of SRF blacks in Butyl rubber and recent work ha. placed inch cliffeienceq on a morc quantitative basis (68) Anal)


October 1952


sis of phenomena has led to the conclusion that they may be interpreted a~ evidence of pigmentpolymer association. A general report on the carbon black industry shows that 840,OOO short tons were produced in this country in 1951 (163). A review of the reinforcement of rubber by carbon black has been published, with 43 references (66). I n a mid-century review of rubber carbons it is stated that the electron microscope lifted the veil of carbon black’s closely guarded secret of reinforcement and carbon black technology moved from the qualitative to the quantitative (26). NONBLACK PIGMENTS


Pigments contribute to the reinforcement of rubber, one effect being purely mechanical and resulting in the rubber functioning a t a higher elongation than the compound as a whole, a second being due to the absorption of the rubber to hold it securely to the pigment particle, and the third and most important effect appearing to be an organizational effect which permits more efficient cross bonding of the molecules during vulcanization (178). Titanium dioxide pigments of the rutile crystalline structure have greater tinting and opacifying strengths than anatase oxides, but the anastase pigments are “whiter” (27). The nonwater-dispersible types form the most stable pigment-in-water dispersionfl. TIRES AND TUBES

The weight method was found to be more sensitive than the depth method in the tread wear of tires (169). Natural rubber treads containing channel black wore faster as the temperature increased, whereas synthetic rubber treads containing furnace blacks wore faster as the temperature decreased. The rubber and the black in the construction of a tire tread act independently with respect to tread wear, and the advantage of the weight method far outweighs its somewhat lower precision; this method becomes almost indispensable for a valid comparison of treads of different design (94). All measurements taken during a test run are incorporated in a single rating of tread wear for each tire, based on either loss in nonskid depth at constant mileage or miles to tire baldness (168). A method for determining the resistance of the bond between tire cord and rubber stock to fatigue is dwcribed (87). The test cords under tension are subjected to rapid cyclic flexing on a special apparatus and the adhesion is determined by the familiar H pull-out test. The results correlate well with road performance. The chapter on “Tire and Tube Manufacturing Practice,” taken from a new book, “Machinery and Equipment for Rubber and Plastics,” Volume I, is a fine concise description with charts (14). The torsional shear spring called Flexitor has been developed for the independent suspension of the nondriven wheels of road vehicles, such as trailers (108). fi


In a report of the 1950 meeting of the International Organization for Standardization (Third Meeting of Committee, ISO/ TC/45), the types of testing methods discussed include hardness, tension stress-strain, abrasion, ply adhesion, resistance to tearing, aging, flex cracking, rubber-to-metal bonding, and dynamic behavior (23). In “Methods of Testing Raw Rubber and Unvulcanized Compounded Rubber” and “Methods of Mixing and Vulcanizing Rubber Test Compounds,” chapters are on viscosity, plasticity and recovery, scorching rate ,equilibrium water-vapor absorption, mixing procedures, storage of mixed stocks, and vulcanizing procedure (28, 29). There has also been published an excellent long review of analytical methods pertaining to natural and synthetic rubbers (16).


For a test for crystallization effectsin rubbers an apparatus is described for testing a standard dumbbell with a 100-pound load in a cold box for 24 hours (10). The refractive index at 25O C. of GR-5 Type 452 was 1.5349 t o 1.5352, with a mean of 1.53507, from which the bound styrene is determined (6). There is a recording torsion pendulum for the measurement of the dynamic mechanical properties of plastics and rubbers (116). Through testing several abrasion resistance machines, the results with the Lambourn abrader (Dunlop Rubber, Ltd., England) were the most promising, especially with GR-S stocks (1). Ply adhesion depends on the rate of separation and experimental errors are 80 large that, for a specified rate of stripping of 1 inch per minute, no significant difference in adhesion is likely to be found in the range of 0.2 to 5 inches per minute (94). Belt flexing can be defined by time for crack initiation and time for crack propagation (S2). When a steel screen wm used as the test surface on a National Bureau of Standards abrader, the 41 O F. GR-S vulcanieate showed the higher wear resistance corresponding to that reported for road tests (B), In an article on “Mechanical Rubber Goods, with Special Emphasis on Latest Designs and Testing Methods for Automotive Park,” tests are given at temperatures m Ion- ap -65OF. (66). A brass electrode attached to the specimen by vulcanization never gave a measurable contact resistance (116). The best type of electrode which could be applied to an already vulcanized sample was tin foil attached to the sample by colloidal graphite. It was found necessary to clear the whole surface of some higher resistivity samples to avoid surface leakage effects. In a study of the physical properties of natural and synthrtic rubber materials a t low temperatures, a torsional apparatus and a hardness indentation tester have been found to be essentially equivalent for use in evaluating the stiffness characteristics of elastomers over a range of low temperatures (86). There are individual advantages in each apparatus that would determine the choice t o be made in selecting a test method for a particular spwification. Various low temperature test procedures were studied and tested by several laboratories in cooperation with the Synthetic Rubber Division of Reconstruction Finance Corp. (67). The first group of test8 included methods of determining flexibility, extensibility, and temperature retraction, and the second provided a means of classification by compression set, stress relaxation, hardness, and rate of retraction. At the present time the T-R, Gehman, compression-set, and rate-of-retraction te& appear most desirable. A low-temperature flexibility tester has been described for use down to 80’ F. for showing temperatureof stiffening, temperature a t which the specimen becomes rigid, and rate of stifFening (126). The best procedure for hardness testing is to use a zero load and a pressor foot (148). This method is embodied in the revised British Standard Method and in the recommendations of Committee ISO/TC/45-Rubber. Details are given for the quantitative determination of natural rubber hydrocarbon by refractive index measurements The old method of determining the rubber hydrocarbon by bromination has been reworked critically and found to be of real service, using benzene as tho chief solvent with the addition of chloroform which inhibits substitution of bromine (60). In the residue from vulcanized rubber after ignition, zinc is determined gravimetrically as the anthranilate, and magnesium colorimetrically in the filtrate by means of Thiazole Yellow (64). The quantitative determination of minute amounts of copper in rubber compounds was developed colorimetrically after surveying 61 references (18). Copper in natural rubber is determined quantitatively by the depth of color of a nonfading copper-carbamate complex in carbon tetrachloride solution (101). A 0.01% solution of zinc dibeneyldithiocarbamate in carbon tetrachloride selectively extracts copper from acid solutions containing rel-





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Meter Room of Synthetic Rubber Plant

atively large amounts of most other metals, and the soluble copper in the extract is determined colorimetrically (98). A new method has been devised for the identification of accelerators and antioxidants in vulcanizates by infrared spectroscopy (95). They cannot be identified in the spectrum of a vulcanizate or its acetone extract, and must be separated chromatographically from the extract. Conductometric titration procedures can be utilized for the analysis of GR-S latices containing either fatty or rosin acid soaps (97). I n the presence of free alkali an indirect titration method is reliable, and should be used whenever the presence of free alkali is suspected or detected. COMPOUNDING A h D VULCANIZIKG

Following earlier work on the quality of estate rubber, it is proposed to supplement the old test with a test at a different state of cure and to construct the whole vulcanization curve as an exponential function of time (166). I n this way it is possible to deduce from the measurements of two moduli a limiting modulus which serves to characterize the stiffness of the vulcanizate, and a constant representing the time required for curing the particular rubber. A general discussion on the meaning of terms related to curing is given, including vulcanization, state of cure, times for equivalent cure, optimum cure, and technical rate and level of cure (146). Air-Banbury treatment of high viscosity GR-S and other synthetic rubbers is an effective means of plasticizing them into processible stocks (131). Cold compression set was chosen as a criterion for evaluating 181 plasticizers in GR-S gasket stocks to be used at low temperatures (104). Ten gave excellent results with respect to compression set a t -35" C., volatility, and lou extractability: some of them are di-Zethylhesyl adipate, di-

butoxyethyl adipate, dioctyl sebacate, and tri-2-ethylhexyl phosphate. Volume expansions of ten to fifteen fold can be realized by the use of p,p'-oxybis-( benzenesulfonyl hydrazide) which in the range of 130" to 160" C. produces nitrogen for blowing, andleaves a nontoxic, odorless, nonstaining polymeric residue (70). A n e x rotary seal has been designed for high-speed and high-pressure applications (88). For the vulcanization of Neoprene Type W, Permalux, Retarder JT3 and 2-PVIT in the presence of sulfur are efficient accelerators (55). They are unique in that the processing safety of stocks containing them is easily controlled by the type and amount of metallic oxides used without affecting the properties of the vulcanizates. The modulus a t 100% elongation can be used as a good practical measure of the state of cure in pure gum natural rubber vulcanizates (50). Formerly six employees were used, but now with the new machine for drying rubber cement on top stock with infrared only one is used; drying is accomplished in 18 seconds a t a speed of 15 feet per minute (139). AGIhG. INCLbDIWG OZONE CRACKING

Methods are given for the use of rubber products in the tropics and of accelerating aging to assess their behavior when in service in the tropics (167). The use of' a dark pigment, though raising the average temperature, reduces the penetration of light and hence the depth to which oxidation catalyzed by light occurs. The stability on exposure to sunlight of cellular rubber made from latex is greatly improved by nickel dibutyldithiocarbamate, which increases the resistance to flex cracking of GR-S vulcanizates, but not by incorporation in the dry way (184). Kickel compounds are not used extensively in elastomers, only nickel dibutyldithiocarbamate being in commercial development as a

October 1952



stabilizer for a number of elastomers (178). I n neoprene nickel salts inhibit the degrading effects of heat, light, and oxygen. They protect GR-S against oxygen and ozone, and show a definite effect for natural rubber. They also enhance the softening activity of aryl and alkyl mercaptans in natural rubber. Carbon blacks repress Bolymer gel formation, which is associated with their behavior in repressing the oxidative scission reaction (163). By proper formulation it is possible to produce stocks with adequate uncured storage stability (146). No vulcanizing agents are used, GR-S or nitrile rubber, mixed as cool as practicable, becomes harder in a given time than after having been mixed hot. GR-S gives satisfactory service for pipe-joint rings, and it is believed that synthetic rubber is superior to natural rubber for them (177). A review and discussion are given of various problems involved in the protection of films, coated fabrics, and plied and laminated products, which contain fabrics and(or) plasticizers which act as nutrients for fungi (171). With respect to resistance to oxidation after vulcanization, salt-acid and alum as coagulants are essentially the same (1.99). Coagulation of Hevea latex (ammonia preserved) by sulfuric acid and by zinc sulfate gave the most stable rubber. For a simple approximate method of measurement, sheets are vulcanized and cellophane is applied t o the smooth surface; the rubber sheet is allowed to remain stretched in a room or outdoors, then the time is entered when cracks can easily be seen under a low-powered microscope (39). It is generally accepted among rubber technologists that ozone stands alone as the cause of exposure check cracking of rubber, and authors of a paper fromLos Angeles concur in this opinion (8). The concentration of ozone in the atmosphere in the Los Angeles area is very high as compared to that in the rest of the country. Frosting is the final product of the slow oxidation of the rubber hydrocarbon produced or catalyzed by ozone (1%’). I n a nondestructive aging test for rubber, the samples are exposed to heat, light, air, and ozone; the degree of deterioration is indicated by an increase of elongation of samples that become cracked and by a decrease of elongation for samples that become hard when heated (162). For a study of the factors affecting the weathering of rubberlike materials, a new test chamber has been built with control of ozone, humidity, light, and temperature from -50” to 100’ C. (61). In an investigation of the cracking of natural rubber and GR-S in ozone a t different temperatures and elongations, it was found that natural rubber compounds cracked a t lower temperatures and elongations than either regular GR-S or cold GR-S compounds (42). For each temperature there exists an elongation below which no sample cracked; this elongation is termed the “cracking threshold” for this temperature. Synthetic rubber was first and best in a large series of tests of 139 protective coatings on steel panel specimens tested by complete sea water and atmospheric exposure in the Panama Canal Zone (110).

In a method of ozone crack depth analysis for rubber the crack depth is measured in a cross section made normal to the length of the cracks by using a 20 X microscope, and real service is found in noting the life of sample vulcanizates over hours of time (142). Carbon black, regardless of type, particle size, structure, and physical properties imparted, does not affect the rate or degree of checking or cracking in natural rubber or low temperature GR-S compounds when subjected to weather or ozone exposure (1.87). Natural rubber will withstand much longer periods of exposure than the synthetic polymer studied. The selection of a polymer, such as natural rubber, GR-S, neoprene, or Butyl rubber, has a marked influence on ozone resistance of automotive rubber products (181). Unless a polymer is handled and compounded properly, good ozone resistance is not obtained, and rubber cured under strain cracks faster than when cured a t rest. Explorative studies have been made a t the New York Naval Shipyard with the ultimate objective of developing an accelerated


ozone aging test for elastomers based primarily on compositional changes rather than on the conventional variations in physical characteristics ( 2 ) . Infrared spectrograms of films cast from treated solutions show progressive intensification of clearly defined absorption bands a t 2.9 and 5.8 mu, reflecting the functional groups hydroxyl and carboxyl, respectively. Neither the presence of accelerators nor their influence on the modulus of fully cured neoprene vulcanizates affects ozone resistance (168). The addition of fillers impairs ozone resistance in proportion t o the amount used, and unsaturated oils and their derivatives, as well as wood rosin, are beneficial to ozone resistance. ADHESION

A panel discussion on rubber-to-metal bonding was presented a t Los Angeles, with questions and answers (156). There was a Chicago Rubber Group Symposium on rubber-to-metal bonding, covering development, classification, and use of adhesives, single adhesives, a table of uses, with questions and answers (73). For a given loading, acidic carbon blacks in rubber-to-metal cements give the strongest bonds (164). RECLAIMED RUBBER

In comparison with natural rubber and cold GR-S Neoprene Type G-N-A appears to be the most satisfactory t o blend with reclaim, and blends in which half of the elastomer content is derived from neoprene appear t o be the most attractive (170). A test formula for testing Butyl reclaimed rubber has been adopted by the Technical Committee of the Rubber Reclaimers’ Association (34). A panel discussion with questions and answers on the general topic of reclaimed rubber has been held (74). GENERAL

The Stacomizer continuous hydraulic press may enable substantial advapces to be made in the dewatering, working, and compounding of rubber; processing is characterized by low power input, tremendous pressure, and ease of temperature control (77). For the waste disposal a t a synthetic rubber plant (Polymer Corp., Ltd., Sarnia, Canada), various processes and wastes are discussed for a plant comprising butadiene, styrene, isobutylene, GR-S, and Butyl rubber (46). Tires, tubes, tank track blocks and bushings, tank bogie wheels and bands, and idler wheels; mechanical rubber goods; insulated wire and cable; coated fabrics; hard rubber products; rubber cement and sealants, are all listed, described, and pictured as Army Ordnance mechanical rubber goods (138). A new synthetic rubber powder for rubber roads mixes freely with asphalt, and has been used in test installations in the Middle West (140). A survey is given on the use of rubber in bituminous pavements from 1945 to 1951, with 128 references (36). There has been described the library of the Division of Rubber Chemistry, AMERICAN CHEMICAL SOCIETY,in which Betty Jo Clinebell is the librarian, in the Bierce Library, University of Akron (182). The Dayton Rubber Co. has an interesting Foreign Technical Service Division (90). Unique plans were made beginning in >larch 1932, and the company has helped companies abroad, although not in Germany. “Strategy in Rubber Research” is the title of the Charles Goodyear Medal award address, presented before the Division of Rubber Chemistry, AMERICANCHEMICAL SOCIETY in 1951, by W. C. Geer (67). “Operational research in the rubber industry’’ is defined a8 a scientific method of providing arrangements with data on which to base executive decisions (147). Typical results of surveys of product quality are given to show the extraordinarily great variability in the properties and performance of similar products manufactured b y different companies.



The engineer’s approach to rubber is discussed with some of the difFiculties that face the engineer in using rubber in the highly stressed state, and other examples of rubber in engineering (180). Selected rubber references for the mechanical engineer cover processing, manufacturing, equipment, testing, properties, and new applications, with 40 references (161). A book on vibration and shock insulation has been written for the practicing engineer (40). This book is the first large study of the subject, and analyzes the causes of vibration and shock, and evaluates the use of natural and synthetic rubbers and other materials for designing resilient mounts or isolators. The Deutsche Kautschuk Gevellschaft (German Rubber Society), originally founded in 1926 and inactive since 1945, was reactivated in October 1951 Erich Conrad, Leverkusen, is president.



(1) Adams, J. W., Reynolds, J. A., Messer, W. E., and Howland,

L. H., India Rubber World, 124, 584 (1951); Rubber Age (N. Y . ) ,69, 581 (1951). (2) Allison, A. R., and Stanley, I. J., Anal. Chem.,24, 630 (1952). (3) Amerongen, G. J. van, IND. ENG.CHEM.,43,2535-40 (1951). (4) Amerongen, G. J. van, Konigsberger, C., and Salomon, G., J. Polyner Sei., 5,639-52 (1950). (5) Andrews, R. D., IND. ENG.CHEM.,44,707-15 (1952). (6) Arnold, A., Madorsky, I., and Wood, L. A., Anal. Chem., 23,1656-9 (1951). (7) Autlfinger, G. J., and Lufter, C. H., Rubber Age (N. Y , ) , 70,753 (1952) Abstract. (8) Bartel, A. W., and Temple, J. W., IND. ENG.CHEM.,44,857-61 (1952). (9) Bartenev, G. M., and Vishnitskaya, L. A., Zhur. Tekh. Fiz., 20,858-65 (1950). (10) Beatty, J. R., India Rubber World, 125,438-9 (1952). (11) Beatty, J. R., and Zwicker, B. M. G., IND. ENG.C m x , 44, 742-52 (1952). (12) Beaudry, J. T., Rubber Age ( N . Y . ) ,69,429-32 (1951). (13) Bebb, R. L., Carr, E. L., and Wakefield, L. B., IND.ENG. CHEM.,44,72430 (1952). (14) Beebe, P., Blank, A. C., and Vogt, W. W., India Rubber World,125, 709-13, 720 (1952); “Machinery and Equipment for Rubber and Plastics,” ed. by R. G. Seaman and A. M. Merrill, New York, I n d i a Rubber World, 1952. (15) Bekk, J., Kautschuku. Ghmmi, 4,250-3 (1951). (16) Bekkedahl, N., Anal. Chem., 24,279-93 (1952). (17) Bennett, B., and McFadden, G. H., India Rubber World, 125.51-2,60 (1951). (18) Bie, G. J. van der, Rubber Age ( N . Y . ) ,69,309-15 (1951). (19) Blackwell, R. F., Trans. Inst. Rubber I d . , 28,75-84 (1952). (20) Blanchard. A. F.. and Parkinson. D.. IND.ENO. CHEW.44. 799-812 (1952). Bloomfield, G. F., J . Rubber Research Inst. Malaya, 13, Commun. No. 271, 1-17 (1931). Bloomfield, G. F., Rubber Chena. and Technol., 24, 737 (1951). Blow, C. M., and Newton, R. G., Trans. Inst. Rubber I n d . , 27, 166-74 (1951). Borroff, E. M., Elliott, R., and Wake, W. C., J . Rubber Research, 20,42-5 (1951). Bowler, W. W., IND.ENG.CHEV.,44,787-91 (1952). Braendle, H. A., Rubber Age ( N . Y . ) ,70,609-16 (1952) Breckley, J., Ibid., 70, 597-605 (1952). Brit. Standard, 1673: 1951, Pt. 3. Brit. Standard, 1674: 1951. Brooks, R. E., Strain, D. E., and McAlevy, A., Rubber Age (N. Y . ) ,70,751 (1952) Abstract. Brackner, Z., and Schay, G., Acta Chim. Hung., 1,163-7 (1951) (in English). Buist, J. M., and Williams, G. E., Trans. Inst. Rubber I d . . 27,209-22 (1951). Burns, J. C., and Storey, E. B., IND.ENG.CHEM.,44, 825-30 (1952). Busenberg, E. B., Rubber Age ( N . Y.), 70,608 (1952). Busse, W. F., and Smook, M. A., Ibid., 70, 751-2 (1952) Abstract. Clinebell, B. J., and Straka, L. E., Ibid., 70,69-73 (1951). Coffman, J. A., IND.ENG.CHEM., 44,1413-28 (1952). Cox, J. T., Jr., Chem. Eng. News, 30,20-1 (1952). Crabtree, J., and Erickson, R. H., India Rubbey World, 125, 719-20 (1952). Crede, C. E., “Vibration and Shock Insulation,” New York, John Wiley & Sons, 1952. .



Vol. 44, No. 10

(41) Crude Rubber Committee, Rubber Manufacturers Association, Inc., India Rubber World, 126,364, 373 (1952). (42) Cuthbertson, G. R., and Dunnom, D. D., IND.ENG.CHEM., 44,834-7 (1952). (43) Dannenberg, E. M., Ibid., 44,813-8 (1952). (44) Deutsche Kautschuk Gesellschaft, Rubber Age ( N . Y . ) , 70, 494 (1952). (45) Dougan, L. D., and Bell, J. C., S~wagea i d I n d . Wastes, 23, 181-7 (1951). (46) Drakeley, T. J., ed., “Annual Report on the Progress of Rubber Technology,” 1950, Vol. XIV, London, Institution of the Rubber Industry, 1951. ENG.CHEM., (47) Duke, J., Taft, W. K., and Kolthoff, I. M., IND. 43,2885-92 (1951). (48) Fanning, R. J., and Bekkedahl, N.. Anal. Chem., 23, 1653-6 (1951). (49) Ferry, J. D., Fitzgerald, E. R., Grandine, L. D., Jr., and Williams, M. L., IND. ENG.CHEX.,44,703-6 (1952). (50) Fletcher, R‘. P., Gee, G., and Mori-ell, S. H., Trans. I m t . Rubber I d . , 28,8592 (1952). (51) Ford, E. W., and Cooper, L. V., India Rubber World, 124, 6968,701; 125,5540 (1951). (52) Ford, F. P., and Gessler, A. M., IND.ENG.CHEM.,44, 81924 (1952). (53) Ford, F. P., and hlottlau, A. Y . ,Rubber Age (Y. Y.), 70,457-63 (1952). (54) Fiey, H., Anul. Chim.Acta, 5,313-16 (1951). (55) Fritz, F. H., and Mayo, L. R., INTI. ENG.CaEnr., 44, 831-3 (1952). (56) Fuller, H. J., Econ. Botany, 5 , 311-37 (1951). (57) Geer, W. C., IND. ENG.CHEM.,43,2436-40 (1951). (58) Gehman, S.D., Ibid., 44,730-9 (1962). (59) Gils, G. E. van, India Rubber World, 125,317-21 (1951). (60) Gowans, W. J., and Clark, F. E., Anal. Chem., 24, 529-33 (1952). (61) Gregory, J. B., Rubber Age ( N . Y.1, 70,211-15 (1951). (62) Gui, K. E., Wilkinson, C. S., Jr., and Gehmibn, S. D., IND. ENG.CHEM.,44,72&3 (1952). (63) Harrington, H. D., Weinstock, K. V., Legge, N. R., aud Storey. E, B., India Rubber World, 124,435-42,571-5 (1951). (64) Harrison, H. C., India Rubber J.,122,313-14 (1952). (65) Haushalter, F. L., India Rubber World, 125,1814 (1951). (66) Havenhill, R. S.,Carlson, L. E., Emery, H. F., and Rankin, J. J,, Trans. Inst. Rubber Ind., 27,339-63 (1951). (67) Helin, A. F., and Labbe, B. G., India Rubber World, 126, 227-31,365-8 (1952). (68) Hopkins, I. L., Trans. Am. SOC.Mech. Engrs., 73, 195-204 (1951); Rubber Chem. and Technol., 24,507-19 (1951). (69) IXodand, L. H., Neklutin, V. C., Brown, R. W., and Werner, H. G., IND.ENG.CHEM., 44,762-9 (1952). (70) Hunter, B. A, and Schoene, D. L., Ibid.,44,119--22 (1952). (71) Hurry, J. A., Bolt, T. D., and French, W. E., India Rubber World, 124, 689-95 (1951). (72) Iguchi, M., J . SOC.Chem. Ind., Japan, 45, Suppl. binding, 424B (1942) (in German). (73) India Rubber World, 125, 590-6 (1952) 174) Ibid.. DD. 726-30. (75) Johnson, B. L., and Wolfangel, 11. D., INn. ENG.CHEW,44, 752-6 (1952). (76) Jones, H. C., and Klaman, C. A., Eubber Age ( N . Y . ) , 70, 325-32 (1951). (77) Keane, J. D., and Bickel, F. W., Ibid., 71,349-51 (1952). (781 Kidder, G. A.. India Rubber World. 124,563-6. 699-701 (1951). (79) Kirshenbaum, D., Hoffman, C. W.,and Ckosse, A. V., Anal. Chem.. 23.1440-5 (1951). (80) Kolthoff, I.‘M,, and Rledalia, A . I., ,I. PoEymer Scd., 6, 189207 (1951). (81) Kolthoff, I. XI., Medalia, A. I., slid I-ouse, M., Ibid., 6, 93--109 (1951). (82) Kurtz, S. S., Jr., and Maitin, C‘ C., Kubbci Age (W. Y . ) , 70, 753 (1952) Ibstract. (83) Ladd, W. .i.. and Ladd, M. W., INL). CNG.CHEM.,43, 2564-8 (1951). (84) Leontein, S. G., Trans. Inst. Rubbo I d . , 28, 27-72 (1952). (85) Lepetit, F., Rev. g h . caoutchouc,28,492 8 (1951). (86) Lichtman, ,J. Z., and Chatten, C. K., Anal. Chem., 24, 812-18 (1952). (87) Lyons, W.J., Ibid.,23,1255-9 (1951). (88) McCuistion, T. J., India Rubber World, 125,575-8 (1952). (89) McFadden, G. H., and Bennett, B., Rubber Age ( N . Y.), 70, 748-50 (1952). (90) McXenna, J. J., India Rubber World, 125,714-16 (1952). (91) RlcKinney, J. E., and Roth, F. L., IND. ENG.CHXM., 44,159-63 (1952). (92) Madge, E. W., Collier, H. M., and Duckworth, I. H., Trans. Inst. Rubber I d . , 28,15-26 (1952).

October 1952



(93) Malcomson, R. W., Mech. Eng., 73,627-32,643 (1951); “Neoprene Applications in Engineering Design,” E. I. du Pont de Nemours & Co.. Inc.. Wilminnton. Del. (94) Mandel, J., Steel,’ M. ‘N., and-Stiehler, R. D., IND.ENG. CHEM.,43,2901-8 (1951). (95) Mann, J., Trans. Inst. RubberInd., 27,232-48 (1951). (96) Mann. K. M., and Nystrom, R. F., J . Am. Chem. Soc., 73, 5894-5 (1952). (97) . . Maron, S. H.. Ulevitch. I. N.. and Elder, M. E., Anal. Chem., 24, 1068-70 (1952). (98) Martens, R. I., and Githens, R. E., Sr., Ibid., 24, 991-3 (1952). (99) Marvin, R. S., IND. ENG.CHEM.,44, 696-702 (1952). (100) Meyer, A. W., Hampton, R. R., and Davison, J. A., J . Am. Chem. Soc., 74,2294-6 (1952). (101) Milliken, L. T., Rubber A g e ( N . Y.), 71,64-66 (1952). (102) Mitchell, A., Ibid., 71, 67-70 (1952). (103) Mooney, M., and Wolstenholme, W. E., IND.ENG.CHEM.,44, 335-42 (1952). (104) Morris, R. E., and Hollister, J. W., Rubber Age (N. Y,), 70, 195-203 (1951). (105) Morris, R. E., Hollister, J. W., and Shew, F. L., IND.ENG. CHEM.,43,2496-500 (1951). (106) Morris, R. E., James, R. R., and Synder, H. L., Ibid., 43, 2540-7 (1951). (107) Morton, M., Salatiello, P. P., and Landfield, H., Ibid., 44, 739-42 (1952). (108) Moulton, A. E., Trans. Inst. Rubber Ind., 27,313-24 (1951). (109) Mueller, W. J., Rubber A g e (N. Y.), 70,752 (1952)Abstract. (110) Mundt, H. W., and Thompson, L. J., Corrosion, 7, 376 (1951). (111) Murphy, E. A., IND. ENG.CHEM.,44,756-62 (1952). (112) Neiman, M. B., Prokof’ev, A. A., and Shantarovich, P. S., Doklady Akad. Nauk. S.S.S.R., 78,367-70 (1951). (113) Newton, R. G., India-Rubber J., 122,340,343 (1952). (114) Newton, R. G., News Sheet, 1, Introduction and General Explanation, International Rubber Research Board, London, 1951. (115) Nielsen, L. E., Rev. Sci. Instruments, 22, 690-3 (1951). (116) Norman, R. H., Trans. Inst. RubberInd., 27,276-89 (1951). (117) Orr, R. J., and Williams, H. L., Can. J . Chem., 30, 108-23 (1952). (118) Overberger, C. G., Arond, L. H., Wiley, R. H., and Garrett, R. R., J. Polymer Sci., 7,431-5, discussion, 435-41 (1951). (119) Piccini, I., Rev. gdn. caoutchouc, 28,317-20 (1951). (120) Ibid., pp. 570-6. (121) Pierson, R. M., Coleman, R. J., Rogers, T. H., Jr., Peabody, D. W., and D’Ianni, J. D., IND.ENG. CHEM.,44, 769-74 (1952). (122) Pigott, W. T., Trans. Am. SOC.Mech. Engrs., 73, 947 (1951). (123) Pillai, A, K. M., Rubber India, 3, No. 5, 9-15, No. 6, 7-9, 12 (1951). (124) Pinazzi, C., Rev. gdn. caoutchouc, 28,567-70 (1951). (125) Pinazzi, C., and Piccini, I., Ibid., 28,321-3 (1951). (126) Pollack, M. A,, Emmett, R. A., and Cobbe, A. G., Rubber A g e (N. Y.), 69,713-17 (1951). (127) Popp, G. E., and Harbison, L., IND. ENG.CHEM.,44, 837-40 (1952). (128) Radcliff, R. R., I n d i a Rubber World, 125,311-14 (1951). (129) Rao, N. V. C., Winn, H., and Shelton, J. R., IND.ENG.CHEM., 44, 576-80 (1952). (130) Rehner, J., Jr., J . Polymer Sci., 7, 519-36 (1951). (131) Reioh, M. H., Taft, W. K., and Laundrie, R. W., Rubber A g e (N. Y.), 70,55-62 (1951). (132) Reinsmith, G., and Kahn, I., India Rubber World, 126, 219-23, 226 (1952). (133) Rhines; C. E., McGavack, J., and Linke, C. J., Rubber Age ( N . Y.), 70,467-74 (1952). (134) Rorden, H. C., and Grieco, A., J . Applied Phys., 22, 842-5 (1951). (135) Rostler, F. S., Rubber Age ( N . Y,), 69,559-78 (1951). (136) Ibid., 71,223-8 (1952). (137) Rostler, F. S., and White, R. M., Ibid., 70,73547 (1952). (138) Rubber A g e ( N . Y . ) ,70,475-6 (1952).


(139) Ibid., p. 618. (140) Ibid., 71, 97 (1952). (141) Rubber Research Institute of Malaya, Report for Period September 1945 to December 1948 [C.A., 45, 9289-93 (1951)l; for Period January 1941 to August 1945. [C.A., 45,4955-7 (1951)l. (142) Rugg, J. S., Anal. Chem., 24,818-21 (1952). (143) Russell, E. W., Trans. Faraday SOC.,47,539-52 (1951). (144) Salomon, G., van der Schee, A. C., Ketelaar, J. A. A., and van Eyk, B. J., Discussions Faraday Soc., 1950, No. 9,291-9. (145) Schade, J. W., India Rubber WorEd, 126,67-72 (1952). (146) Schroeder, C. H., Ibid,, 125,53-4 (1951). (147) Scott, J. R., J . Rubber Research, 20,63-70 (1951). (148) Scott, J. R., Trans. Inst. Rubber Ind., 27,249-63 (1951). (149) Semegen, S. T., and Wakelin, J. H., Rubber Age ( N . Y.), 71, 57-63 (1952). (150) Servais, P. C., Mech. Eng., 73, 63943 (1951); Engineering Properties of Silicon Rubber,” Dow Corning Corp., Midland, Mich. (151) Shader, R. E., and Turner, R. M., India Rubber World, 125, 440-2 (1952); Rubber Age (N. Y.), 70,343-5 (1951). (152) Shaw, R. F., and Adams, 8. R., Anal. Chem., 23, 1649-52 (1951). (153) Shearon, W. H., Jr., Reinke, R. A., and Ruble, T. A,, IND. ENG.CHEM.,44, 685-94 (1952). (154) Sheehan, G. M., Kraus, G., and Conciatori, A. B., Ibid., 44, 580-2 (1952). (155) Shor, F., Akers, J., Reynolds, B., and French, F. J., India Rubber World, 125, 196-9 (1951): Rubber Age ( N . Y . ) , 70,204-10 (1951). (156) Smook, M. A., Roche, I. D., Clark, W. B., and Youngquist, 0. G., Rubber Age ( N . Y . ) , 70,751 (1952)Abstract. (157) Soden, A. L., and Wake, W. C., Trans. Inst. Rubber Ind., 27, 223-31 (1951). (158) Stechert, D. G., andBolt, T. D., Anal. Chem., 23, 1641 (1951). (159) Stiehler. R. D.. Steel, M. N., and Mandel, J., Trans. Inst. RubberInd., 27,298-312 (1951). (160) Studebaker, M. L., Rubber Age ( N . Y . ) , 70,752 (1952)Abstract. (161) Sutherland, G. B. B. M., and Jones, A. V., Discussions Faraday SOC.,1950, NO.9,281-90. (162) Swaney, M. W., and Barnes, F. W. (to Standard Oil Development Co.), U. s. Patent 2,556,856 (June 12, 1951). (163) Sweitzer, C. W., and Lyon, F., IND.ENG.CHEM.,44, 125-31 (1952). (164) Takano, Y., J. SOC.Rubber Ind., Japan, 22,36-7 (1949). (165) Talalay, L., and Talalay, A,, IND.ENG. CHEM.,44, 791-5 (1952). (166) Thirion, P., Rev. gdn. caoutchouc, 28,563-6 (1951). (167) Ibid., pp., 684-91. (168) Thompson, D. C., Baker, R. H., and Brownlow, R. W., IND. ENG.CHEM.,44,850-6 (1952). (169) Toor, E. W., and Selwood, P. W., J . Am. Chem. Soc., 74, 2364-68 (1952). (170) Torrenoe, M. F., and Schwartz, H. G., Rubber A g e ( N . Y.), 71,357-60 (1952). (171) Treichler, R., Ibid., 69,579-80 (1951). (172) Verbanc, J. J., IND. ENG.CHEM.,44, 1023-7 (1952). (173) Wakefield, L. B., Ibid., 43,2363-6 (1951). (174) Walling, C., and Davison, J. A,, J . Am. Chem. Soc., 73, 5736-8 (1951). (175) Warner, R. R., Rubber Age ( N . Y , ) ,71,205-21 (1952). (176) Weinstock, K. V., Baker, L. M., and Jones, D. H., Ibid., 70, 333-8 (1951). (177) White, W. L., J . Am. Water Works Assoc., 43,872-6 (1951). (178) Williams, I.,I n d i a Rubber World, 126,359-63 (1952). (179) Williams, I., Rubber Age ( N . Y,), 70,753 (1952) Abstract. (180) Willis, A. H., Trans. Inst. Rubber Ind., 27,264-75 (1951). (181) Winkelmann, H. A., IND. ENG.CHEM.,44,841-50 (1952). (182) Wolf, R. F., India Rubber World, 125, 582-4 (1952). (183) Zwicker, B. M. G., IND. ENG.CHEM.,44,774-86 (1952). RECEIVED for review

J u l y 14, 1952

ACCEPTEDJ u l y 15, 1952.