bluuebunny/crossref_metadata_2025 huggingface dataset:
Equivalent Effects of Time and Temperature in the Shear Creep and Recovery of Elastomers
Authors: Conant F. S. , Hall G. L. , Lyons W. James
Published: February 2011

An explicit relationship is set forth for the time-temperature dependence of the viscoelastic phenomena in superelastic polymers. An empirical equation that was found to represent adequately the above-mentioned relationship over the entire multiple-temperature curve is of the form: logtc=[Cα/(T−b)]+Cβ. Experimental verification is given for the equivalent influence of time and temperature on the creep and recovery of compounds based on Hevea, GR-S, Neoprene-GN, Butaprene, and Butyl rubber. A comparison of the empirical equation with that of a theoretical reaction-rate equation of Tobolsky and Eyring indicates a temperature dependence of the energy of activation.
Tetramethylthiuram Disulfide Vulcanization of Extracted Rubber. III. Short-Path Distillation of TMTD and Its Reaction Products from Rubber
Authors: Craig David , Juve A. E. , Davidson W. L.
Published: February 2011

During the course of this study we have found short-path distillation to be an especially useful procedure for separating volatile substances from macromolecular weight materials. For this reason and because the still which we have used most frequently has some rather novel features, it seems appropriate to devote the third paper of the series to a general description of our technique. Figure 1 is a schematic drawing of the still. Tube A is the heater tube, to the outside of which the samples in sheeted out form are attached by means of copper wire. The heater tube contains about 30 cc. of a liquid whose boiling point is the temperature at which the distillation is to be conducted. The liquid is boiled by an internal heating element regulated by means of a variable transformer. The leads H to the heating element enter through a rubber stopper in the upper end of the heater tube which is open to the atmosphere through flask G. For low-boiling heater liquids such as methanol, a condenser must be attached to the upper end of the heater tube. For the work described in the present series of papers, Cellosolve, b.p. 133° C, was used as the heater liquid. Tube B of Figure 1 is the condenser tube. Ordinarily, air cooling is sufficient to condense such materials as the usual rubber antioxidants, softeners, accelerators, fat acids, sulfur, etc. For special purposes, tube B is cooled by wrapping it with rubber tubing through which tap water was circulated or it is cooled with dry ice. The gap of this still, i.e., the distance from the heater tube to the condenser tube, is about 2 cm. The U-tube C, made of 1.25-inch glass tubing, constitutes a trap. It usually has been cooled with dry ice and acetone in I. That U-tube is connected to a booster pump D through a second dry-Ice trap. The pressure usually used has been less than 0.01 mm. and has been measured by a McCleod gage attached to E below the dry ice trap F. Where higher pressures have been used, the vacuum source has usually not included the booster pump.
Molecular Structure of Styrene-Butadiene Copolymers. Dynamic Mechanical Measurements
Authors: Nielsen L. E. , Buchdahl Rolf , Claver G. C.
Published: February 2011

The dynamic shear modulus, mechanical damping, swelling properties in benzene, and infrared spectra have been determined on a series of styrene-butadiene copolymers which were prepared under a variety of polymerization conditions. Evidence is presented which indicates it may be possible to prepare a poly-butadiene rubber which retains its rubberlike properties down to −120° C. Materials of the same overall composition were often found to differ greatly in structure as determined by these experimental methods. Many of these differences can be explained in terms of various types of heterogeneity found in the copolymers. The temperature of maximum mechanical damping is primarily determined by the composition of the copolymer, whereas the width of the damping peak is related to the heterogeneity of the material. The work reported here is part of an investigation of the differences in physical properaties of polymers of like composition that occur as a result of changes in polymerization conditions.
Butadiene-Styrene Resinous Copolymers
Authors: D'Ianni J. D. , Hess L. D. , Mast W. C.
Published: February 2011

Although high-styrene resins have become of great commercial importance during the past 5 years (approximately 25,000,000 pounds manufactured in 1949), comparatively little information on the polymerization processes or any systematic review of their properties can be found in the technical literature. The object of the present paper is to supply such information. A series of butadiene-styrene copolymers with charging ratios of 50/50, 40/60, 30/70, 20/80, and 10/90 was prepared. Polystyrene, prepared under the same conditions, was included as a control. Properties of the latexes and resins obtained, presented in a systematic manner, were found to be largely dependent on the monomer ratio employed in the polymerization. for the first time a coherent picture is presented of the entire plastic range of the styrene-butadiene resins. This should encourage the further development of this large and expanding field, which includes such applications as natural and synthetic rubber reinforcing, impact resistant compositions, protective coatings, and latex paints.
Polysulfide Polymers
Authors: Fettes E. M. , Jorczak J. S.
Published: February 2011

The chemistry of the condensation polymerization is reviewed briefly. The structures of the polymeric products as well as the effects of copolymerization, cross-linking, end groups, and molecular weight upon polymer properties are discussed. The composition and properties of the commercial crude rubbers, water dispersions, and liquid polymers are presented together with ideas on the mechanism of their vulcanization. The reason for the odor of polysulfide polymers is discussed. Some information is presented on solvent resistance, stress relaxation, and other characteristics of the polymers. Applications for the different types of products are summarized.
The Rubber Hydrocarbon in Freshly Tapped Hevea Latex
Authors: Bloomfield George F.
Published: February 2011

The rubber hydrocarbon in latex as it leaves the tree is already a high polymer, with a broad distribution of molecular weight ranging from several millions to below 100,000, with the major part of the hydrocarbon in the higher molecular weight ranges. Changes in the hydrocarbon subsequent to its leaving the tree tend to be degradative, but may also involve cross-linking reactions leading to changes in plasticity. Structural changes in rubber attributed to restricted cross-linking have a greater influence on plasticity than on solution viscosity. A gel component (probably microgel) present in the freshly tapped hydrocarbon is of considerable importance in determining the hardness of raw rubber, but greatly complicates the interpretation of viscometric data, of which evaluation by the equation: [η]=5.02×10−4 M0.67 only appears to be valid for gel-free rubber fractions. Plasticity and intrinsic viscosity cannot, therefore, be generally correlated, although the plasticity is influenced by the spread of the molecular-weight distribution into lower molecular weight regions. The presence of a high proportion of microgel in latex of untapped trees and of branches remote from the tapping panel of trees in regular tapping, and the presence of combined oxygen in the low-molecular fractions of rubber hydrocarbon obtained from both normal and microgel latexes may be of interest in connection with questions of biosynthesis and metabolism of the rubber hydrocarbon of Hevea brasiliensis.
The Application of Rubber in the Quantitative Determination of Ozone
Authors: Bradley C. E. , Haagen-Smit A. J.
Published: February 2011

A convenient rubber cracking test for ozone is described. This method serves not only as a rapid, positive means of identifying ozone in complex gas mixtures but also gives close approximation to the quantity present. Application of the method in determining ozone in heavy smog atmosphere is shown. The high ozone concentration in these tests is attributed to ozone formation under the catalytic action of nitrogen oxides and sunlight.
Radical Mechanisms in Saturated and Olefinic Systems. II. Disubstitutive Carbon-Carbon Cross-Linking by Tertiary Alkoxy Radicals in Isoprenic Olefins and Rubber
Authors: Farmer E. H. , Moore C. G.
Published: February 2011

The high degree of dehydrogenation effected by tert.-butoxy radicals at the α-methylenic groups of olefins enables these radicals to be used for the carbon-to-carbon cross-linking of unsaturated carbon chains, and especially of the polyisoprenic chains of natural rubber. Such cross-linking amounts to a vulcanization process in which the connecting links between chain molecules are just C—C bonds, which may be expected to have appropriate attributes. An examination has first been made of the cross-linking produced by tert.- butoxy radicals (from di-tert.-butyl peroxide) at 140° between the short iso-prenic chains in 1-methylcyclohexene, 4-methylhept-3-ene, 2,6-dimethylocta-2, 6-diene, and digeranyl. Cross-linking proceeds efficiently in each case, and the points of union in these isoprene units which become directly joined are not confined to original α-methylenic carbon atoms. Where the reagent radicals are in considerable deficit, e.g., one per two or three of the isoprene units present, those olefin molecules which are attacked become linked together mostly by single unions to form aggregates containing two, three or four molecules; but in the tetraisoprenic olefins the extent to which more than one union is formed between some of the directly linked molecules becomes appreciable. In natural rubber, cross-linking occurs smoothly and to nearly the full extent corresponding to the (in practice restricted) proportion of peroxidic reagent employed. Good vulcanizates can be so obtained in which the tensile stength is found to increase towards a maximum and then to decline rapidly as the degree of cross-linking steadily increases. Thus to obtain vulcanizates of the optimum physical characteristics, the degree of cross-linking must be suitably chosen. The role of the peroxidic reagent is almost entirely non-additive and non-degradative.
The Effect of Sulfur on the Oxidation of Sodium-Butadiene Rubbers
Authors: Kuzminskii˘ A. S. , Degteva T. G. , Lapteva K. A. , Lezhnev N. N.
Published: February 2011

In the vulcanization of rubber and in the service performance of vulcanized rubber products, oxygen and free sulfur are always present. Consequently it is important to know the effect of sulfur on the oxidation of rubber. The present work is devoted to an investigation of the oxidation of a sodium-butadiene polymer in the presence of sulfur. Dogadkin and his associates established the fact that oxygen has an influence on the nature of the structural changes of rubber during vulcanization. The present authors have shown that any sulfur which is chemically combined with rubber does not appreciably affect the kinetics of its oxidation, and that free sulfur, in solution in rubber, interferes with autocatalytic oxidation. The higher the concentration of sulfur, the greater is this interference (see Figure 1). Introduction of sulfur into rubber during autocatalysis does not prevent the autocatalytic process, but hinders it noticeably (see Figure 2). The introduction of a secondary aromatic amine has been observed to arrest the process altogether. This behavior of sulfur can be explained by its ability to react with intermediate oxidation products, since the rate of combination of sulfur is practically constant (see Figure 3).
Elastic Modulus and Swelling of Butyl Vulcanizates. Influence of Fillers
Authors: Zapp R. L. , Guth Eugene
Published: February 2011

The reinforcing of elastomeric vulcanizates by filler particles has been studied with Butyl rubber, a polymer of limited unsaturation. This limited unsaturation enables a comparison to be made of filler reinforcement in materials having a constant concentration of chemical cross-links, because excess curing agents can be added without increasing the state of cure byond a certain limit. Under such conditions differences in the adsorptive powers of fillers do not result in variations in the ultimate state of vulcanization. Reinforcement in this paper was defined as the ability of a pigment to enhance the elastic or equilibrium stress (at constant elongation) of a vulcanized specimen. Equilibrium stress at 50 per cent elongation was determined on a triple-beam balance, and the internal energy and entropy components of stress were determined. The entropy component of stress was found to conform more closely to the classical viscosity analog equation for reinforcement, where only the volume concentration of filler and not the surface area is the controlling factor. It was observed that carbon blacks, especially those of finer particle size, produced a greater internal energy contribution to stress than did mineral fillers, which appeared as a function of the total pigment surface added. The increase in stress observed with mineral fillers was due largely to entropy contributions. Another manifestation of reinforcement was shown to be the restriction of volume swelling of a network (in a good solvent) in the presence of pigments. Carbon blacks showed the greatest restriction of swelling capacity, and in distinction to stress behavior, this restriction was solely a function of the total surface area of carbon black present, regardless of type. With mineral fillers, far less restriction was observed, and in one case an increase in swelling was noted. This can be attributed to poor bonding, which results in voids. The photomicrograph of clay particles in a thin stretched section of Butyl shows this effect in Figure 21. The role of surface forces in the case of carbon blacks has been further demonstrated through measurements of the elastic properties of swollen rubber. The reinforcing nature of carbon black is maintained in a swollen network, while the weak bonds between the polymer and a mineral filler are destroyed when the chains are separated by the imbibed solvent, and the stress then approaches that of an unloaded compound.
Statistical Kinetics of Hevea Rubber Cyclization
Authors: Gordon M.
Published: February 2011

Rubber cyclization provides a useful illustration of statistical effects intervening in the reactions of long-chain polymers. Analogously to known cyclizations of simple diisoprenic terpenes, each individual cyclization act links two adjacent isoprene units in the rubber chain into a six-membered ring. However, some of the units remain stranded between neighboring rings and escape cyclization for want of a partner. Thus the final polymer has a copolymer structure of 86.5 per cent of diisoprenic rings and 13.5 per cent of uncyclized monisoprenic units. This result is derived from a statistical theory of Flory, and has previously found accurate experimental verification. The bearing of this statistical effect on the reaction kinetics has now been studied for the first time. Dilatometric experiments on rubber emulsions in sulfuric acid have shown that the cyclization reaction conforms in the main with a statistical cyclization law much better than with a first-order equation uncorrected for the survival of stranded units. High accuracy was required for this experimental distinction, whose importance lies in the implicit proof that the polymer units participate in the rate-determining transition complex, in accordance with the accepted proton transfer mechanism. A kinetic proof has incidentally been furnished for the fact that the rubber polymer contains long chains of identical units. When handled by an emulsion technique, this polymer can provide a useful “model compound” for its simpler terpene analogs. Certain rate abnormalities have been observed, including an induction period of reduced rate, probably connected with diffusion effects. A small volume change subsequent to the cyclization reaction may reflect a prototropic double-bond shift. The activation energy and entropy are found to be lower than in previous work, an effect traced in part to a curvature of the Arrhenius plot. The known dependence of cyclization rate on Hammett's acidity function H0 is quantitatively confirmed.
Modern Views on the Chemistry of Vulcanization Changes. I. Nature of the Reaction between Sulfur and Olefins
Authors: Farmer E. Harold , Shipley F. W.
Published: February 2011

At the present time it is taken for granted that in all kinds of linear high polymers, natural or artificial, true polymers or polycondensation products, the establishment of cross-links between adjacent thread molecules is in itself sufficient to transform the physical properties of the material, producing a state which can be collated with the vulcanized state in rubber. Yet in most of these instances—and particularly in the case of vulcanization of natural and synthetic rubbers by sulfur, by peroxides, and by other reagents—the idea that the vulcanized products with their characteristic toughness, swelling capacity, elasticity, etc., derive their special qualities from the mere formation (by one means or another) of connecting links between the original linear molecules still remains a matter of hypothesis. The sulfur-vulcanization process as applied to rubber presents many interesting and very elaborate features, especially those connected with its capacity for being accelerated by a host of similar and dissimilar organic substances, and for being retarded, reversed, delicately controlled, etc. Hence, it is of considerable interest to find out by experiment exactly what sulfur does to the rubber when the two are heated together (either alone or in the presence of different types of accessory reagents) and, thence, to discover whether the production of good vulcanized properties actually depends on the production of chemical cross-links, or on certain kinds of chemical cross-links, or on a judicious combination of cross-linking and mere sulfuration (the latter possibly assisting the establishment of van der Waals forces between molecules as an auxiliary factor) ; or whether, as some physical chemists have been inclined to allege, it results from a state of physical association between molecules which has little or nothing to do with cross-linking. The present series of communications describes recent experimental advances in this subject; it is necessary to explain at the outset that the method of experimental approach adopted has of necessity, owing to the formidable molecular magnitude of even unvulcanized rubber, been by way of the response to vulcanization treatment of comparatively simple olefinic compounds. This approach has thus involved in the first place a study of the chemistry of simple sulfur-olefin reactivity, which was previously never carried far.
Modern Views on the Chemistry of Vulcanization Changes. II. Role of Hydrogen Sulfide
Authors: Naylor Ralph F.
Published: February 2011

1. The normal addition of hydrogen sulfide to olefins is catalyzed by very small proportions of sulfur, but the rate of addition is too slow to provide a satisfactory basis for the hydrogen sulfide-actuated mechanism of vulcanization. 2. The main products of the sulfur-catalyzed (polar) reaction of hydrogen sulfide with polyisoprenes are substituted pentamethylene sulfides, derived by intramolecular normal addition of the initially formed monothiols. 3. The main products of the ultraviolet light-catalyzed (radical) reaction of hydrogen sulfide with polyisoprenes are monothiols and substituted pentamethylene sulfides, the latter derived by intramolecular abnormal addition. 4. The resemblance of the cyclic sulfides obtained by reaction of free sulfur with polyisoprenes to the products of polar hydrogen sulfide addition (as opposed to the products of the radical-type addition) supports the hypothesis that, in the sulfur-olefin reaction, the radical reaction chain is terminated by the capture of a hydrogen atom by an RS* radical, the thiol so formed adding intramolecularly in a polar reaction catalyzed by sulfur.
Peroxidation in Relation to Olefinic Structure
Authors: Farmer E. Harold
Published: February 2011

The process of autoxidation among olefinic substances comprises two major phenomena, that of the incorporation of molecules of oxygen (peroxidation), and that of secondary change (peroxide breakdown) during which the peroxide groups formed by this incorporation act as oxidizing agents for adjacent unsaturated centers. Interest may, accordingly, be directed towards two quite distinct but composite themes, viz. : (1) the nature of the mechanism by which the oxygen molecules are incorporated, the positions they take up in different kinds of organic molecules, and the effect of their introduction in causing (or not causing) specific types of molecule-linking, and (2) the inherent stability or instability of the peroxide groups in different molecules and its structural cause, the mechanism of breakdown of the peroxidic groups and the way this is influenced by light, heat, or catalytic influences, and finally the manner of utilization of the “active” oxygen given up by the decomposing peroxide groups in forming (by inter- or intramolecular reaction) new oxygeno-groups or, alternatively, in bringing about some small or large degree of scission of the carbon chains. Wherever the peroxido-olefins have a moderately high degree of stability, and they are consequently isolable in tolerably pure condition, no serious difficulty attends the systematic study of their thermal, photo-, or catalyzed decomposition, although as yet but little systematic work has been done in this field : but where their degree of unstability is very high, deductions concerning the character of the peroxido-olefinic structures produced and of their breakdown mechanisms have to be made (at any rate in the first place) from the nature of the secondary autoxidation products actually isolated in practice, and there is then grave danger of erroneous conclusions being drawn. Of course, many autoxidation products are extremely complex in character, and where this is the case the difficulty of correlating breakdown products with their peroxidic precursors is greatly increased. Therefore in prosecuting autoxidation studies, especially those directed towards determining the mechanism of reaction, it is very desirable to have as general guide a detailed knowledge of the structure and breakdown behavior of all the various distinctive types of organic peroxide which are capable of existence, and the following survey represents in the main a contribution in this direction.
Friedel-Crafts Catalysts and Polymerization
Authors: Evans A. G. , Meadows G. W. , Polanyi M.
Published: February 2011

In an earlier communication, evidence was given on which the following conclusion was based. In the dimerization of diisobutene and the polymerization of isobutene, it is essential that a trace of some third component, X, shall be present in addition to the monomer and the Friedel-Crafts catalyst, in order that the reaction shall proceed at an appreciable rate. It was suggested then that this third component was probably water. We have continued this line of investigation by studying the boron trifluoride-catalyzed polymerization of isobutene in the gas phase, using high-vacuum technique. The polymerization reaction was followed by mixing the boron trifluoride and the isobutene in the gas phase and measuring the fall in pressure with time. We may summarize the results as follows:
Molecular Weight and Polydispersivity of Rubber by Diffusion Measurements
Authors: Pasynskii A. G. , Gatovskaya T. V.
Published: February 2011

The study of diffusion in solutions of natural rubber (light crepe) by Lamm's method showed that even with a concentration of 0.1 per cent the normalized experimental diffusion curves diverge from the ideal Gaussian curve (Figure 1), in that they are characterized by a marked asymmetry and an excess of the maximal ordinate. It follows from an analysis of the experimental curves by the method of moments (up to moments of the fourth order) that they belong to Type IV Pearson curves, that is, to asymmetrical distribution curves with asymptotic branches. The determination of the perturbation multiplier enables us to calculate the course of the experimental curves with a fair degree of accuracy. The physical cause of asymmetry of the diffusion curves is the difference in the rate of diffusion to both sides of the interface (of the polymer into the solvent and back) due to a marked intermolecular interaction in the solution of the polymer at a given concentration. With a decrease of the concentration or of the molecular weight of the dissolved substance, the asymmetry of the diffusion curves becomes less pronounced. However, this asymmetry does not preclude the computation of the average diffusion coefficient D from the standard deviation of the curve. It can, indeed, be shown that the probable error does not exceed 1 per cent. The average value found for natural rubber in carbon tetrachloride is D20°=0.71×10−7 sq. cm. per sec.
Preparation and Properties of Rubberlike High Polymers. II. Polymerization of Mixtures in Bulk
Authors: Koningsberger C. , Salomon G.
Published: February 2011

Mixtures of butadiene and dimethylbutadiene with varying quantities of styrene and acrylonitrile were copolymerized under various catalytic conditions at 100° C. The formation of cyclic dimers from dienes and vinyl compounds is, in some cases, much more pronounced than the dimerization of the dienes alone. Since the latter is also a kind of Diels-Alder reaction, a series with increasing dienophilic properties can be established from a comparison of the yields of cyclic dimers. From solubility and swelling experiments it is evident that the polymers prepared from butadiene and the vinyl compounds and those from dimethylbutadiene and acrylonitrile are true copolymers. The mechanical properties of the copolymers from butadiene and increasing amounts of a vinyl compound change gradually from those of a rubber to those of the polyvinyl compound. The copolymers from a mixture containing 30 per cent styrene or acrylonitrile are very similar to Buna-S and Perbunan, respectively. Copolymers of the same composition from dimethylbutadiene and acrylonitrile, on the other hand, form a new class of thermoplastics with a much higher temperature of elasticity.
Preparation and Properties of Rubberlike High Polymers. III. Polymerization of Mixtures in Emulsion
Authors: Salomon G. , Koningsberger C.
Published: February 2011

The copolymerization in emulsion of butadiene with varying proportions of styrene and acrylonitrile and of dimethylbutadiene with the latter vinyl compound was studied on a laboratory scale. An essential difference between polymeric vinyl compounds and polydienes is the olefinic character of the latter, which leads to typical secondary changes in the polymers originally formed during the completion of the reaction. Such changes are of fundamental importance for the ultimate mechanical properties of polymers and copolymers based on dienes. After a brief discussion of the general theoretical line of thought serving as a base for our experiments, the influence of various factors on the rate of polymerization is pointed out and demonstrated by experiments. The changes in the nitrogen content of copolymers from acrylonitrile and the yields as a function of the reaction time also were studied. From an investigation of some physical properties, such as solubility and swelling, the existence of true. Copolymers (of unknown irregularity) is established. Copolymers from dimethylbutadiene and acrylonitrile represent a new class of olefinic thermoplastics resembling gutta-percha.
The State of Polydispersion of Hevea Latex. II.
Authors: Hessels J. H. E.
Published: February 2011

The influence of the degree of dispersion in latex on the composition and properties of the rubber was studied in detail by means of a series of latices, the mean particle size of which ranged from 1.1 to 0.15µ in diameter. These fractions were first obtained by centrifugation of preserved latex, and the degree of distribution was measured by photomicrographic analysis and by sedimentation. This method of fractionation yields latices and rubbers with compositions which differ widely. With decrease in the size of the particles, their surface area per unit of rubber increases, and the percentage of nonrubber components which is adsorbed irreversibly or which is dissolved in the serum increases greatly. On the contrary, the degree of polymerization decreases with decrease in the diameter of the particles. This may be explained by the fact that, in the beginning, the polymerization of the globules is relatively low, and that it progresses under the influence of a catalyst present in the serum. In brief, then, systematic dispersoidal analysis of Hevea latex is of prime importance in the plantation rubber industry.
The Thermoelastic Properties of Rubber
Authors: Meyer Kurt H. , Van der Wyk A. J. A.
Published: February 2011

In an earlier communication, Meyer, von Susich and Valkó showed that within certain limits of extension (100 to 300 per cent) and at constant elongation, the stress in a rubber sample is proportional to the absolute temperature. Within these limits, the stress is therefore analogous to the pressure of an ideal gas, which at constant volume is likewise proportional to the absolute temperature. Such behavior of rubber or of any other rubberlike substances is said to be ideal. However, a sample of rubber which exhibits ideal behavior at elongations of 100 per cent and higher deviates from this ideal behavior at elongations below 100 per cent and greater than 500 per cent. One of the reasons for such deviations at high elongations has already been discussed in an earlier publication. As a result of extension, rubber tends to crystallize. The resulting crystallites do not contribute to the elastic stress, but if the temperature is raised, they fuse and thereby increase the tension, which then increases more rapidly than is the case with an ideal rubber. Deviations from ideal behavior at small deformations have not yet been studied thoroughly, so it is these deviations which are the first subject of discussion in the present paper. First of all the experimental facts will be presented.
The Protection of Rubber against Oxygen by a Deactivating Effect
Authors: le Bras Jean , Hildenbrand René
Published: February 2011

It has already been shown by one of the authors that certain substances protect vulcanized rubber against deterioration by oxidation and yet have practically no retarding effect on its rate of oxidation. The mechanism of the action of these agents is, therefore, different from that of antioxygenic agents, and it has been called a deactivating effect. The first substance which was found to manifest this hitherto unrecognized effect was mercaptobenzimidazole. The attempt has been made to gain a better understanding of the conditions under which mercaptobenzimidazole is active, both alone and in the presence of an antioxygenic substance. It was first found that mercaptobenzimidazole, in contrast to most antioxygenic agents, has no protective action against aging in the case of simple rubber sulfur vulcanizates, i.e., vulcanizates which do not contain any other ingredients which are ordinarily added, notably accelerators, zinc oxide and plasticizers. Systematic experiments with these various types of ingredients show the indispensable part played by zinc oxide, in view of which it may be assumed that a zinc salt is formed during vulcanization by reaction of the zinc oxide with the acid group of the thiol. As a matter of fact, when zinc mercaptobenzimidazolate is added to a rubber-sulfur mixture, it protects the vulcanizate from aging. Furthermore, if the reaction of mercaptobenzimidazole with zinc oxide is rendered impossible by replacing the hydrogen of the SH group by a radical, there is no longer any protective effect. 2-Methylmercaptobenzimidazole, for example, shows no protective action under any conditions.
The Interaction between Rubber and Liquids. VIII. A New Examination of the Thermodynamic Properties of the System Rubber ± Benzene
Authors: Gee Geoffrey , Orr W. J. C.
Published: February 2011

New vapor pressure data are reported for rubber-benzene mixtures, and used to calculate thermodynamic functions for the system. The heat of dilution is comparable with that measured calorimetrically for a polyisoprene of low molecular weight. Comparing the results with the available theoretical calculations it is shown that a significant contribution to the entropy and heat of dilution of polymer solutions at low concentrations results from the occurrence of polymer-polymer contacts within individual molecules due to statistical kinking. Our thanks are due to J. L. Bolland, (Miss) J. Ferry, and H. P. Koch for the experimental assistance acknowledged in the text. The work described in this paper forms part of the program of fundamental research on rubber undertaken by the Board of the British Rubber Producers' Research Association.
Modifications of Chlorinated Rubber Brought about by Some Organic Bases. Piperidine
Authors: Jarrijon André , Lepetit Francis
Published: February 2011

By virtue of certain characteristics, among others its resistance to chemical reagents, which is one of its most valuable properties, chlorinated rubber has already found a wide field of applications. It is curious, however, that some materials which are only slightly corrosive are capable of affecting it, e.g., water and certain organic bases, the basicities of which are considerably lower than the basicity of potassium hydroxide or of sodium hydroxide.
Role of Carbon in Oxidation of GR-S Vulcanizates
Authors: Winn Hugh , Shelton J. Reid , Turnbull David
Published: February 2011

1. Carbon black is a catalyst for the oxidation of GR-S vulcanizates. The increased rate of oxygen absorption with increased loading is, however, a function of surface area rather than weight. Different types of carbons show different degrees of activity for a given surface area; the furnace carbons studied were, for example, only 55 per cent as active as channel black in promoting oxidation. 2. The rate constant for the initial rapid absorption of oxygen by GR-S tread stocks is independent of carbon loading. The presence of carbon is, however, essential to activate the centers involved in this initial stage, and the number of activated centers increases with carbon loadings, so that the amount of oxygen absorbed in a given time is also increased. 3. The second or linear stage of oxygen absorption involves two types of reaction with the remaining oxidizable centers in the polymer: a reaction with centers not under the catalytic influence of the carbon black, and a reaction catalyzed by carbon. 4. A theoretical equation was presented which permits the calculation of oxygen absorption by stocks containing either furnace- or channel-type carbons with various surface areas and loadings. The validity of the theory on which the derivation was based is supported by the quantitative correlation of calculated and observed rates of oxygen absorption for stocks containing carbons of both types, with surface areas ranging from 3.7 to 15.7 acres per pound and with loadings of 0 to 75 parts per 100 parts of GR-S. 5. The additional oxygen absorbed at higher loadings of carbon was shown to produce a correspondingly greater deterioration of physical properties.
The Permeability of Rubberlike Substances to Gases
Authors: Van Amerongen G. J.
Published: February 2011

The measurements of the permeability of various elastomers to hydrogen which have been described make particularly evident the following points. The permeability values of Perbunan, Neoprene and Oppanol are from one-third to one-eighth those of natural rubber. The higher the percentage of combined sulfur in natural rubber, the lower the permeability. The addition of a plasticizing agent has only a small effect on the permeability. The addition of progressively greater percentages of inorganic or organic fillers brings about a disproportionately great reduction in permeability. Among mixtures of natural rubber with other compounding ingredients, three mixtures in particular are noteworthy for their low permeability: (1) A mixture of equal parts of natural rubber and Oppanol (polyisobutylene). (2) A mixture of rubber with 15–20 per cent by vol. of bentonite, prepared by starting with latex. (3) A combination of these two types of mixtures (1) and (2). Finally it was proved experimentally that stretched rubber has a lower permeability than the corresponding unstretched rubber, probably as a result of crystallization of the stretched rubber.
The Permeability of Different Rubbers to Gases and Its Relation to Diffusivity and Solubility
Authors: van Amerongen G. J.
Published: February 2011

Since the permeability of rubberlike substances to gases is related to the solubility and rate of diffusion of the gases in those materials, these individual values should be known. The permeability of a membrane was measured manometrically and the diffusivity was derived from the time lag of the permeation. The solubility of the gas was computed from the permeability and the diffusivity; the solubility was found by direct measurement. In this way eight different gases were tested with nine elastomers at different temperatures. The permeability of a membrane to a given gas is not affected by the presence of a second gas. The differences in permeability of different elastomers to a given gas are caused mainly by differences in rate of diffusion and only in a very minor degree to differences in solubility. Differences in permeability of the same elastomer to different gases are caused not only by differences in rate of diffusion but also by differences in solubility. A linear relationship was found between the logarithm of the solubilities of different gases in natural rubber and their critical temperatures, so the higher the critical temperature of a gas, the better it dissolves. The presence of polar groups in an elastomer reduces the solubility of nonpolar gases and increases the solubility of polar gases in the elastomer. The various rubbers behave towards gases like organic liquids. The activation energy of the diffusion and the heat of solution were calculated from the temperature function of the diffusivity and the solubility. As the diameter of the molecule of the gas increases, the rate of diffusion decreases, while the activation energy of the diffusion becomes greater. The presence of polar groups and methyl groups in elastomers causes low rate of diffusion, which involves a great activation energy of diffusion. It is presumed that the activation energy of the diffusion is required to separate the rubber molecules for the displacement of the gas molecules. The attempt to elucidate the constant D0 in the equation D=D0 exp (−E/RT)—which proves to be a function of the activation energy of the diffusion E—by reference to one of the formulas published in the literature failed. An empirical formula was derived whereby D0 is directly related to the activation energy E.
Correlation of Tensile Strength with Brittle Points of Vulcanized Diene Polymers
Authors: Borders A. M. , Juve R. D.
Published: February 2011

For several years work has been carried on here to evaluate a large number of diene polymers and copolymers as rubberlike materials. The writers have observed that changes in polymer composition which result in improved tensile strength and crack-growth resistance of the vulcanizate cause an increase in low temperature stiffness and a rise in brittle point. This generalization seems to apply to tensile values measured at elevated temperatures as well as to those at room temperature. For example, a butadiene copolymer of dichlorostyrene can be made which, as a tread type of vulcanizate, exhibits a tensile strength of over 1500 pounds per square inch at 93° C, in comparison with 800 to 1000 pounds per square inch for GR-S in the same test tread formula at the same temperature. The brittle point of the butadiene-dichlorostyrene rubber, however, is −35° C or higher. GR-S treads in the same test have brittle points between − 55° and −60° C. Probably of greater practical importance is the fact that the vulcanizate with the higher brittle point is stiffer at temperatures well above the brittle point. The purpose of this investigation was to determine to what extent the maximum tensile strength of tread stocks of several synthetic rubbers varies with the temperature difference between the brittle point and the tensile testing temperature of each rubber. These data can then be used to judge the validity and extent of the general observation that changes in copolymer composition which increase strength also raise the brittle point.
Properties of Hard Rubber. XIX. Effect of Temperature on Cross-Breaking Strength and Elongation
Authors: Willott W. H.
Published: February 2011

In a series of cross-breaking tests carried out on hard rubber during hot weather, the values of the breaking elongation were higher than was expected, although the cross-breaking strength was of the usual order. It was thought that the high temperature might account for these results by making the hard rubber more plastic. The following experiments were, therefore, performed to investigate the effect of small changes of temperature, such as are encountered at different times of the year, on the cross-breaking strength and elongation. Test-pieces of standard size (75 × 25 × 5 mm.) were cut from a sheet of hard rubber of the composition: 68 per cent rubber, 32 per cent sulfur, which had been vulcanized for 5 hours at 155° C. They were immersed in a beaker of water and kept at the required temperature for about 15 minutes, when they were judged to have attained a steady temperature. The tests were carried out on an Avery fabric-testing machine fitted with special clamps to give a three-point loading test, the distance between the supporting knife-edges being 50.4 mm. (2 in.). These clamps were heated to the temperature of the specimens by means of an electric radiator. The specimens were tested as soon as possible after they had been removed from the water, so that the change of temperature during the test was reduced as far as possible. The standard conditions already laid down, were observed.
State of Cure of Neoprene Vulcanizates. Measurement by the T-50 Test
Authors: Forman D. B. , Radcliff R. R.
Published: February 2011

Generally the physical properties of elastomer vulcanizates are considered to depend on their states of cure. Although many tests for measuring the state of cure have been developed, none are completely satisfactory. Some of them fail to distinguish between the physical or chemical effects of compounding ingredients, others are too laborious to be of practical value. The T-50 test developed by Gibbons, Gerke, and Tingey for natural rubber vulcanizates eliminates some of these difficulties and further reduces the number of tests required for production control. The T-50 test is based on the retraction of a stretched and frozen specimen with an increase in temperature. The temperature at which the sample retracts to 50 per cent of its initial frozen elongation is termed the T-50 value. From a physical standpoint the test is sensitive, precise, and easily performed. From a chemical standpoint the original workers as well as Vila showed that, for any specific natural rubber composition, the T-50 value correlates with the amount of combined sulfur. Since the state of cure of a rubber vulcanizate is frequently discussed in terms of combined sulfur, the T-50 test offers a correlation of the state of cure with combined sulfur without the necessity for involved chemical analyses.
Mechanical Processing of Carbon Blacks. Resultant Effects in GR-S Compounds
Authors: Dobbin R. E. , Rossman R. P.
Published: February 2011

It was suggested that carbon blacks owe some of their characteristic properties to a tendency for individual particles to cluster into chainlike groupings or secondary aggregates. Results of mechanical processing experiments show that application of mechanical work altered or destroyed secondary aggregates. This conclusion was made since resistance to compression had been permanently overcome. Analytical measurements confirmed the supposition that secondary aggregates had been altered or destroyed, since oil absorption and liquid retention values markedly decreased with mechanical work. Finally, properties of compounded GR-S stocks were seriously altered—namely, smoothness of milled stock, high modulus, and enhanced electrical conductivity. It is concluded that these properties were originally caused by the presence of secondary aggregates or structure units. Alternative interpretations of these data are possible—namely, it might be concluded that it was not possible to disperse the densified material to the same extent as the original carbon black. However, this hypothesis contends that a large particle size material is being dispersed. Therefore, a decrease in tensile strength should have been noted. There is also some meager evidence suggesting that the chemical nature or activity of the carbon black surface was altered, so that its contribution to modulus was limited. It is believed, however, that most of the evidence offered by the data presented here preponderantly supports the structure theory of high modulus blacks. The authors consider these results as preliminary in the study of the structure properties of carbon blacks. They appear to be of sufficient interest to be brought to the attention of those studying reinforcement. Data available at present do not permit an interpretation of the contribution of structure to properties of “smooth-out” modulus and electrical conductivity of compounded rubber stocks.
Determination of Polystyrene in GR-S Rubber
Authors: Kolthoff I. M. , Lee T. S. , Carr C. W.
Published: February 2011

A convenient procedure for the determination of polystyrene in GR-S is given. The method depends upon degradation of the GR-S by tert-butyl hydroperoxide in the presence of a trace of osmium tetroxide. Polystyrene is not attacked and is separated by precipitation with ethanol.