bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevention of Ozone Attack on Rubber by Use of Waxes
Authors: Ferris S. W. , Kurtz S. S. , Sweely J. S.
Published: February 2011

The tendency for stretched rubber, when subjected to outdoor exposure, to form cracks perpendicular to the direction of stress was originally known as suncracking. The work of Newton showed that light was not necessary and identified ozone as the causative agent. That ozone is the principal factor there seems to be no doubt, but we cannot assert that it is the sole factor. Some test specimens, for example, have been found to crack in the shade, but not in the sun, and some investigators suspect that certain atmospheric pollutants may have a modifying effect. It has been known since 1881 that addition of wax to the rubber compound will provide protection against this type cracking. Garvey and Emmett found that oils or oil-like materials would also effect improvement, but by far the major portion of work has been done with petroleum waxes. The two broad classes of petroleum waxes are paraffin and microcrystalline. The value of the literature—and this applies to many fields other than ozone cracking—is sharply limited by the tendency to characterize waxes as either paraffin wax or microcrystalline wax. As a matter of fact, the composition of petroleum waxes is complex, so that there are large differences in composition between different paraffin waxes and different microcrystalline waxes, with resultant differences in their performance when added to rubber.
Stress-Strain Relation in Rubber Blocks under Compression. I
Authors: Schay Géza , Ször Péter
Published: February 2011

For the stress-strain relation of differently shaped rubber blocks submitted to compression, an equation of general applicability is deduced, starting from the idea that compression work must be done also against the tension arising through the increase of the free surface. In this equation the stress is not a function of the compression ratio only, but of the ratio of the fixed to the free surface as well. Besides the shear modulus of the block's substance, this equation involves a single empirical constant which changes only slightly with the shape of the block's cross section. The validity of the equation obtained was tested by measurements performed by the authors on cylinders as well as by data on quadratic prisms published in previous literature. The calculated values are in good agreement with the experimental data within the limits of experimental error.
Measurement of the Isothermal Volume Dilation Accompanying the Unilateral Extension of Rubber
Authors: Hewitt Fred G. , Anthony Robert L.
Published: February 2011

The fractional increase in volume accompanying the isothermal extension of soft gum rubber was measured for four rubber samples at mean extensions of 14, 33, and 51%. The chain molecular weights Mc of the four samples were 5500, 5100, 4400, and 3000, with an estimated uncertainty of about 10% in each value of Mc. The observed fractional increase in volume ranged from 3.2×10−5 to 142×10−5, the latter value being observed for the sample of lowest chain molecular weight and at the extension of 51%. The experimental results for each sample have been represented by theoretical curves based on Gee's expression for the fractional increase in volume as a function of the sample extension. The theoretical curves exhibit good agreement with those of Gee, Stern, and Treloar. The process of fitting the theoretical curves to the experimental points constituted a determination of Young's modulus E for each rubber specimen. As a check on the experimental results, and also on the theory employed, determinations of E were also made by two additional methods, namely, from rough stess-strain curves, and from the relation E=3γρRT/Mc. With one exception, the internal agreement between the three determinations of E for the four different samples was satisfactory. The exception noted can probably be ascribed to the use of too small a value of Mc for the sample of lowest chain molecular weight.
Scattering of Light in Crystalline Polymers. I. Formation and Melting of the Crystalline Phase in Neoprene
Authors: Trapeznikova O. N. , Smirnova G. E.
Published: February 2011

The process of formation and melting of neoprene crystallites was investigated by the polarized light scattering method. Conclusions about the nonreversibility of the crystallization and melting processes were drawn on the basis of angular distribution measurements of depolarized and polarized components of light scattered from polymer films. The appearance of a relatively small number of large crystallites is characteristic for the initiation of crystallization; further development of crystallization is accompanied by a decrease in the size of the crystallites. All crystallites disappear simultaneously during the melting process. The size of the crystallites determined by microphotography corresponds approximately to the particle size determined by the formula for isotropic, spherical particles. A method for the determination of the melting range of crystalline polymers is proposed.
Compatibility as the Basic Factor in the Adhesion of High Molecular Weight Materials
Authors: Alekseenko V. I. , Bogoslavskaya L. A. , Mishustin I. U.
Published: February 2011

1. Relationships were established between the bond strength of joints made from rubber with fabric, leather, or rubber with physical property data from the films made from the mixtures of the adhesive with the rubber from which the vulcanizates were made. 2. The effect of the chemical structure of the adhesive on the bond strength is established. 3. Nairit-NT, mainly the trans isomer of poly-1,4-chloroprene and chemically closely related to gutta percha (trans polyisoprene) gives a good adhesive cement for bonding rubber to fabric, leather, or rubber. It makes chemical surface treatment unnecessary. This new adhesive gives good bonding to SKS-30. Similar results were obtained with cement made from gutta percha; however, bonding strength to SKN-40 rubber was much higher.
The Structure of Gels. IX. Effects of Plasticizers on the Physical Properties of Styrene Butadiene Rubber
Authors: Zverev M. P. , Zubov P. I.
Published: February 2011

1. The glass and flow temperatures and the strength and relative extension of rubber depend not only on the concentration of the plasticizer but also on its molecular structure. 2. Styrene butadiene rubber plasticized with nonpolar plasticizers has higher glass and flow transition temperatures than rubber plasticized with polar substances. The same relationships are found for the strength and relative extension of vulcanizates of this rubber. 3. Nonpolar plasticizers also weaken intramolecular interaction to a greater extent than polar plasticizers.
The Photovulcanization of Butyl and SKB (Polybutadiene) Rubbers
Authors: Zuev Yu S.
Published: February 2011

It is known that the mechanical properties of raw and vulcanized rubbers change markedly under the action of light in which not only oxidation processes but also photovulcanization processes in which sulfur is involved play an essential part. In view of the wide interest shown lately in questions of radiation vulcanization of polymers, as well as the possibility of reducing the photodegradation effect upon the mechanical properties of some polymers, we made studies of the photovulcanization of butyl rubber (degradation by irradiation) and SKB (polybutadiene) rubber (structure formation by irradiation). The study was made on films 200µ thick of purified butyl rubber with a molecular weight of about 42,000 and an unsaturation of about 1%. Both ordinary (twice crystallized) sulfur and radioactive S35 were used. The films obtained from a solution of rubber plus sulfur on cellophane were irradiated with a PRK-7 lamp through a Pyrex glass light filter and distilled water at a distance of 25 cm. Then determinations were made of the absorption spectrum and the static modulus 30 minutes and 24 hours after applying the load. The amount of free sulfur remaining in samples extracted previously was determined from the intensity of the S35 radiation. SKB not containing PBNA was reprecipitated from a benzene solution. When films of SKB (200µ thick) were irradiated, the light filters UFS-1, ZhS-4 and OS-5 were used. After the irradiation of the SKB films their static modulus was determined 30 minutes after the application of the load. When we irradiated butyl rubber containing 0.25 to 2.5% sulfur, we observed a distinct photovulcanization optimum (see Figure 1) in the modulus as a function of irradiation time like that which occurs in thermal vulcanization, and an optimum of the photovulcanization rate as a function of sulfur concentration.
The Nature of Optimum Vulcanization in Natural Rubber
Authors: Kuzminskiĭ A. S. , Chertkova V. F.
Published: February 2011

The vulcanization of natural rubber is accompanied by a considerable change in mechanical properties as the vulcanizate is formed. With sulfur as the vulcanizing agent an optimum is observed in the change in tensile strength and other physical properties. In many studies the presence of an optimum vulcanization has been considered as the result of the superimposition of two processes: (1) the structure-forming action of sulfur and (2) the degrading action of the oxygen, which causes a reversion of vulcanizates. We have established2 that the oxidative degradation of natural rubber in the vulcanization process proceeds extremely slowly and cannot have any substantial effect on the tensile strength of vulcanizates. To resolve the question as to the true causes of the reversion of vulcanizates in “overvulcanization”, several series of experiments were set up. In the first series the mobility of sulfur bonds was studied in natural rubber vulcanizates containing various accelerators by the use of the sulfur radio-isotope S35 with a method described earlier. The results of these experiments shown in Figure 1 indicate the “concentration” of mobile links in the vulcanizate to change proportionately with the change in tensile strength and the maximum density of mobile polysulfide links thus corresponds to optimum vulcanization according to tensile strength. The modulus likewise changes during the course of vulcanization, proportionately to the density of the intermolecular crosslinks formed. The formation of a complex three-dimensional network proceeds continually through all the various stages of the process up to the optimum. The increase in network density in the vulcanizates being formed, up to the optimum, is accompanied by a steady substantial rise in tensile strength. Further vulcanization, however, causes a decrease in network density and a drop in tensile strength. In a second series of experiments with vulcanizates at various stages of the process the polysulfide bonds were removed by extraction with sodium sulfite. When this occurred a decrease in the tensile strength of the vulcanizates was observed, which was especially marked at optimum vulcanization (Figure 2, Curve 2). In a third series of experiments, vulcanization was achieved with tetramethylthiuram disulfide (TMTD) without added sulfur. It is known that TMTD forms monosulfide bonds in rubber which are stable under the usual vulcanization conditions (a temperature of 143° C). Figure 2 (Curve 3) shows that no reversion is observed in vulcanization with TMTD.
Vulcanization of Elastomers. 21. Vulcanization of Natural Rubber with Thiuram Disulfides. VI
Authors: Scheele Walter , Hummel Klaus
Published: February 2011

Bound sulfur in a pure thiuram vulcanizate increases relatively rapidly at first at all temperatures, reaches a poorly defined maximum at about 27 to 30%, independent of temperature, and then recedes slightly to reach a limiting value of 25% also independent of temperature, based on the original thiuram disulfide. The rise in sulfur content at the start points to a temperature-independent limiting value of 33%. It is shown that the combination of sulfur in this region initially follows a first order reaction, and goes at the same rate as the reduction in concentration of thiuram disulfide. It can be seen from the above that sulfur may be combined in thiuram vulcanization without simultaneous crosslinking. The dithiocarbamate formation increases rapidly in the region of longer vulcanization times, after the maximum in bound sulfur has been reached, without further combination of sulfur with the vulcanizate. The rate constants for thiuram decrease, for dithiocarbamate increase and for sulfur combination were calculated. The temperature dependence of each of these reactions has practically the same activation energy, 23 kcal/mole. The bound sulfur content of the vulcanizates in pure thiuram vulcanizations is no criterion of the state of vulcanization.
The Reactions of Amines and Sulfur with Olefins. IV. The Chemical and Thermal Decompositions of N,N′-Thiobisamines and Their Reactions with Olefins
Authors: Saville R. W.
Published: February 2011

Parts I–III of this series described the use of combinations of secondary amine and sulfur and of N,N′-thiobisdiethylamine Et2N⋅S⋅NEt2 as olefinic sulfurating agents. The introduction of N,N′-thiobisamines, (RR′N)2Sx, as vulcanizing agents for rubber justifies a more detailed study of their properties.
Polybutadienes of Controlled Cis, Trans and Vinyl Structures
Authors: Short J. N. , Kraus G. , Zelinski R. P. , Naylor F. E.
Published: February 2011

The physical properties of polybutadiene vulcanizates have been measured as a function of polymer microstructure. Although the over-all properties of any one polybutadiene are determined by the relative ratio of cis, trans and vinyl units in the polymer chain, marked changes in physical properties do not occur until a relatively pure configuration is approached or unless the raw polymer displays crystallinity. Thus, polybutadienes containing more than 85 per cent cis, trans or vinyl units are characteristically different from each other and the differences are accentuated as the isomeric forms approach 100 per cent of a given configuration. Polybutadiene of 95 per cent cis configuration displays very low heat generation and high resilience (equaling natural rubber in these properties) and excellent abrasion resistance. trans-Polybutadiene (90 per cent), a crystalline plastic in the raw state, becomes rubbery after vulcanization. Gum vulcanizates possess high tensile strength, and tread stocks display high modulus and tensile strength, high hardness and fair hysteresis properties. Vulcanizates of amorphous 94 per cent vinyl polybutadiene are characterized by fair tensile properties, low hysteresis, and poor low temperature properties. Crystalline syndiotactic polybutadiene, 70 per cent vinly, displays much higher gum and tread tensile strengths than its amorphous counterpart. Amorphous polybutadienes containing less than 70–80 per cent of any one configuration are generally similar in most properties, and resemble emulsion polybutadiene in many respects. The wide range of properties of the various polybutadienes makes them suitable for many applications. cis-Polybutadiene is an excellent tire rubber, which has given as much as 40 per cent greater abrasion resistance than natural rubber in passenger tire tests. Heavy duty 10:00 × 20 truck tires fabricated with a 1:1 blend of cis-polybutadiene and natural rubber in the treads have given slightly better abrasion ratings and lower running temperatures than control tires fabricated entirely from natural rubber. Amorphous 80 per cent cis-polybutadiene has been found to possess exceptionally good low temperature properties, far superior to present arctic-type unsaturated elastomers, trans-Polybutadienes by virtue of their high modulus, high tensile strength, and high hardness could be utilized in the preparation of hard rubber goods, floor tiles, and shoe soles. While none of these polybutadienes is yet available commercially, their unusual properties and potential applicability in many areas should lead to their manufacture in the future.
Infrared Spectra of Cured and Uncured Rubbers
Authors: Blokh G. A. , Mal'nev A. F.
Published: February 2011

The newest physical-chemical methods of research enlarge the scope of study of the vulcanization process. There is a possibility of studying the structure changes during vulcanization of rubber by the application of infrared spectroscopy. Infrared rays are selectively absorbed. Therefore the infrared absorption spectrum can be used as a characteristic property of a substance and could be used for analytical purposes. The large spectral range of the infrared rays indicates their importance for the study of the properties and structure of substances; this makes possible the determination of the moments of inertia of atomic nuclei and molecules, isotopic mass, arrangement and strength of atomic bonds in the molecule and the frequencies of their vibrations. By knowing the frequencies for pure substances, molecular analyses of complicated mixtures of various organic rubbers, accelerators and other substances could be performed. The study of linear absorption spectra is the basis of the spectrographic method in the infrared region. Since the frequencies of near infrared radiation correspond to the characteristic frequencies of the atoms in the molecules, this method could be used to obtain interesting information concerning the structure of organic molecules, the chemical structure of high molecular weight compounds, the determination of the presence of specific groups or atoms in the rubber molecule, the character of the bonds between these groups and the order of arrangement of the individual chain links. This is true because the position of the absorption bands, which are specific for a given group of atoms, is practically the same for the different combinations in which the group occurs. The complicated process of polymerization of diene and vinyl compounds and the structure of different types of rubbers can be investigated with the aid of infrared spectroscopy. For example, Table I lists the characteristic absorption frequencies in the infrared region for some important chemical combinations.
Effect of Primary Molecular Weight on the Dynamic Properties of Cured Rubber
Authors: Kuvshinskiĭ E. V. , Fomicheva M. M.
Published: February 2011

1. Studied were the moduli of resilience and rebound elasticity of the vulcanized rubbers made from fractions of butadiene-styrene rubber “SKS-30-A” at temperatures of 20, 60, and 100° C in the region of molecular weights from 45,000 to 620,000 with various degrees of vulcanization (with variation in the pseudoequilibrium modulus from 5 to 70 kg/cm2). 2. The dynamic modulus of resilience is little dependent on the molecular weight of the original rubber both at room temperature and at higher temperatures. 3. At higher temperatures the elasticity of vulcanized rubber is mainly determined by the degree of vulcanization, the measure of which is the pseudo-equilibrium modulus, and is little dependent on the initial molecular weight. At low temperatures (20° C) elasticity increases with the degree of vulcanization, but it increases at different rates for vulcanized rubbers made from fractions with different molecular weights. At 20° C the increase in the degree of vulcanization increases the elasticity of vulcanized rubbers made from low-molecular fractions (45,000) to a lower degree than of those made from high molecular weight fractions (above 133,000). 4. The value of the maximum elasticity of vulcanized rubbers obtained from rubbers of the same molecular weight is not dependent on the type of accelerator used.
The Plastic Flow and Elasticity of Raw Rubber and Raw Rubber Mixes
Authors: Gengrinovich B. I. , Slonimskii G. L.
Published: February 2011

Data have been obtained on the mechanical properties of rubber, two-component rubber-carbon black systems, and loaded raw rubber mixes at various temperatures and under different stresses. The true viscosity and the elasticity modulus of a raw rubber mix depend on the time, temperature, and the magnitude of the applied force ; it is suggested that this is a consequence of the variability of the structure of the mix under stress and on heating.
The Influence of Temperature on The Kinetics of Cut Growth in Vulcanizates
Authors: Gul V. E. , Vilnits S. A.
Published: February 2011

Recently published research has conclusively demonstrated that rupture in vulcanizates represents a process which increases with time. Slow and fast stages of rupture were discerned. Through the use of high speed photography it was found that, in the usual testing of tensile strength, the rate of rupture growth is initially very small but then quickly although intermittently increases. This behavior occurred both in the rupture of specimens which were not cut and in testing specimens that had been previously cut. The effect of a cut has been thoroughly investigated. Studies conducted on the mechanism of rupture in elastomers indicate that the rupture of vulcanizates has much in common with that of brittle solids. Nevertheless there is a significant difference in the mechanism of rupture in elastomeric materials and brittle solids. It was natural, therefore, to expect a significant change in the kinetics of rupture growth in the region of the glass transition temperature. The aim of the present investigation was to follow the change in the kinetics of rupture of vulcanizates through the transition from the rubbery to the glassy state.
Crosslink Density in Polybutadiene
Authors: Howland L. H. , Nisonoff A. , Dannals L. E. , Chambers V. S.
Published: February 2011

1. A method has been developed for the measurement of crosslink density of diene polymers. This method, which involves the use of radioactive chain transfer agents, is applicable to ungelled polymer prepared under a wide variety of conditions so that any polymerization variable can be studied independently. 2. The crosslink density in polybutadiene decreases with decreasing polymerization temperature. At low molecular weight of polymers, the amount of crosslinking varies linearly with the polymerization temperature. 3. The crosslink density of polybutadiene increases with increasing number-average polymer molecular weight. The rate of increase is less for polymer prepared at −18° C than for that polymerized at 5° to 50° C. This means that, in a polymerization, as the average molecular weight increases with conversion the crosslink density increases. However, when the molecular weight is kept constant, by changes in the modifier loading, the crosslink density of polybutadiene appears to be independent of the degree of conversion attained within the range of 0.12–0.48. 4. The crosslink density of a high molecular weight fraction of polybutadiene was not significantly different from that of the whole polymer (from which about 3% of low molecular weight material had been removed). 5. The kind of initiator system does not affect the crosslink density of polybutadiene, providing the initiator loading is not too high. However, if large amounts of initiator are used in the polymerization, 10% or more of the polymer molecules may not contain mercaptan modifier. 6. Tertiary alkyl mercaptans are necessary for the crosslinking studies because they do not appear to give side reactions. Primary dodecylmercaptan and diisopropyl xanthogen disulfide are unsatisfactory for determinations because they appear to add to the double bonds of the polymer molecule in addition to the usual chain transfer reactions. 7. Incomplete emulsification of monomers in some 5° C recipes apparently increased the crosslink density of polybutadiene by retarding the diffusion of monomer into the monomer-polymer particles.
Cis to Trans Isomerization of Polyisoprene
Authors: Golub M. A.
Published: February 2011

Although polybutadiene readily undergoes photochemical or radiation chemical cis to trans isomerization in solution sensitized by bromine atoms or thiyl radicals, no such isomerization has been achieved with polyisoprene. Moreover, although polyisoprene has been isomerized to a variety of resins, no evidence for any cis to trans change in this polymer has been heretofore described. This communication reports the cis to trans isomerization of polyisoprene in solution catalyzed by elemental selenium at temperatures of around 180–200° C. A common structure was obtained having a cis/trans ratio estimated to lie somewhere between 50/50 and 60/40, starting with either the essentially all-cis polyisoprene (Hevea) or all-trans polyisoprene (balata). The mechanism presumably involves π complexing of the polymer double bonds with selenium in the manner depicted for the selenium-catalyzed isomerization of oleic acid and stilbene. A 2–3% solution of Hevea or balata in a suitable high-boiling solvent such as o-dichlorobenzene or tetralin, containing 0.5 g/l powdered selenium, was refluxed under nitrogen for 2–5 hours. Subsequently the solution was cooled, and filtered to remove the selenium which separated out. Methanol was added to the filtered solution to coagulate the polymer, which was washed with alcohol, airdried and its structure analyzed by infrared absorption procedures. The recovered polymers were lower in molecular weight than originally, dropping in a typical case (e.g., Hevea) from a viscosity average molecular weight of about 550,000 to 300,000.
Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates
Authors: Dunn J. R. , Scanlan J.
Published: February 2011

The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.
Thermal Degradation of Polyacrylonitrile, Polybutadiene, and Copolymers of Butadiene with Acrylonitrile and Styrene
Authors: Straus Sidney , Madorsky Samuel L.
Published: February 2011

Polybutadiene and a copolymer consisting of 76.5 per cent butadiene and 23.5 per cent of styrene were investigated as to the rate of their thermal degradation. The rates for polybutadiene indicated an activation energy of 62 kilocalories per mole. The copolymer had very high initial rates of degradation followed by a rapid drop, so that it was not possible to obtain a reliable activation energy. Polyacrylonitrile and a copolymer consisting of 31 per cent of acrylonitrile and 69 per cent of butadiene were investigated with regard to the nature and distribution of volatile products, as well as to the rates of their thermal degradation. The rates were very high initially, but dropped rapidly so that it was not possible to determine accurately the activation energy. The acrylo-nitrile-butadiene copolymer showed a decomposition pattern similar to that of polybutadiene. Here, too, the activation energy could not be deduced accurately from the rate curves. Comparative thermal stability in terms of temperature, at which half of the polymer sample is evaporated in 35 minutes of heating, is as follows: 407° C for polybutadiene, 374° C for SBR, 364° C for polystyrene, 360° C for NBR, and 316° C for polyacrylonitrile.
The Swelling Behavior of Natural Rubber Latex
Authors: Allen P. W.
Published: February 2011

The distribution of a swelling agent (methyl methacrylate) among the particles of natural rubber latex has been shown to be nonuniform. Large particles absorb more swelling agent than do small particles. The data are analyzed by means of the thermodynamic treatment of Morton, Kaizerman, and Altier.
Bond Strength of Tread and Breaker Stocks under Repeated Deformations
Authors: Levitin I. A. , Korablev Yu G. , Kornev A. E. , Babitskiĭ B. L.
Published: February 2011

As the tire industry changed over to production from synthetic rubber a new form of service failure was encountered—stripping of the tread from the breaker. This phenomenon is most noticeable where SBR rubbers are used, and also at the boundary layer of pliedup rubbers differing in composition, having different moduli and different degree of cure in the zone of contact with each other. In recent times there have been carried out a considerable number of investigations of the dynamic strength of a system of pliedup rubbers. The results show that an important influence is exerted upon the bond strength of pliedup rubbers by their flow, which governs the increase in contact area in the boundary layers, by the diffusion of the separate links of the chain molecules of one pliedup layer into the other by the degree of the pliedup rubbers, and the bonding layers between the layers of rubber. The compounding ingredients also affect the bond strength. As a result a number of technological measures were taken to increase bond strength between the components of tires on the adoption of SBR in the industry. These were directed towards increasing the surface contact between the layers, and towards improving the surface of the semifinished products before plyingup. An important effect upon the improvement of the surface properties of tires was evidenced by increased pressure in the building process, roughening of the tread and breaker, pressing of the uncured casings after building, and introducing into tire formulas accelerator groups which ensure increase in the time spent by the stocks in the viscous flow state in the initial period of vulcanization. One method of attaining higher dynamic strength in the tread-breaker system was some increase in the modulus of the breaker rubber by increaisng the amount of channel black. A recently developed formula for tread rubber with increased elasticity and for a stiff breaker noticeably reduced the failures of tires from stripping of the tread from the breaker. Nevertheless this problem still occupies the center of attention in the industry.
Thermal Expansion Measurements and Transition Temperatures, First and Second Order
Authors: Dannis Mark L.
Published: February 2011

When any pure material goes through a change in state, its physical properties change greatly. In each phase the physical properties are relatively constant or change slowly enough with temperature that the rate of change of a property such as volume is a constant. This rate of change of volume is the thermal expansion coefficient, (∂V/V)/∂T. The thermal expansion coefficient is almost constant, experimentally, as long as the temperature range over which measurements are made does not include a phase transition. At the transition temperature, abrupt changes in volume are found as illustrated in Figure 1. Polymeric materials often show changes in physical properties not necessarily accompanied by abrupt changes in volume, even though the expansion coefficient does change. Since the expansion coefficient changes, some change in internal structure is suspected, and the name second-order transition (Tg) has been adopted. This kind of change is roughly diagrammed in Figure 2. This latter change at the second-order transition temperature can be found in every known polymer, even though many polymers possess clear, first-order, crystalline transitions as well. Hevea rubber, for example, has a crystalline melting point of 28° C, compared to its Tg about −70°. These data are shown, copied from Boyer and Spencer, as Figure 3.
Thermoelastic Phenomena in Natural Rubber Compounds during Cyclic Deformation
Authors: Votinov M. P. , Sulzhenko L. L. , Kuvshinskiĭ E. V.
Published: February 2011

1. The initial stages of stretching of natural rubber gum compounds ((λ≦4.5)) and of filled compounds ((λ=1.8−4)) are characterized by liberation of heat equivalent to the work of deformation according to Equation (lb). Further deformation takes place with liberation of surplus heat caused by- crystallization of the rubber. The relation between the work of deformation and the heat effect is given by Equation (1a) 2. The beginning of crystallization and its degree at a given elongation depend on the degree of vulcanization and on the nature of the dispersed fillers. The rubbers with the highest modulus crystallize the poorest. Active fillers such as channel black promote crystallization to a greater degree than silica gel and chalk. 3. A rate of deformation of 100% per second assures adiabatic conditions without taking special measures. 4. It was determined that errors in the quantitative analysis of the process of adiabatic stretching of rubbers result from lack of knowledge of the true heat capacity of the compound and especially from inaccuracy of measurement of elongation during the relaxation cycle.
The Importance of Rheology in the Processing of Rubber. 1. Rheological Investigations of Rubber Solutions
Authors: Edelmann K. , Kolbe G.
Published: February 2011

Using the mastication of rubber as an example, it is shown how rheology can be utilized, even in the industrial processing of macromolecular substances, to obtain, from an easily and quickly determined flow curve, a value dependent on the weight average molecular weight, and a numerical value for the polymolecularity. Solutions of chain macromolecules with a sort of Gaussian molecular weight distribution give a symmetrical flow curve with an inflection point which, as the velocity gradient which is independent of the concentration, is a function of the average molecular weight. At the same time the slope of the linearized flow curve provides a numerical value for the polymolecularity of the material in question. In this way, even those changes in a macromolecular substance which occur during factory processing can be measured, as is the case here with masticated rubber.
The Reaction of Ozone with SBR Rubbers
Authors: Erickson E. R. , Berntsen R. A. , Hill E. L. , Kusy Paul
Published: February 2011

All SBR vulcanizates, when tested in a relaxed state, reacted with ozone of low concentrations to form a film of oxidized products which provided an effective barrier against further attack by gaseous ozone. SBR vulcanizates that were under stress, but which contained no effective antiozonant in their formulation, were readily attacked by ozone. The absorption of ozone appeared to begin with an initial rate of zero which was followed by rapidly increasing rates until a maximum had been reached, when ozone cracks were visible on the surface of the rubber. SBR vulcanizates that were under stress, but which contained an antiozonant, were protected from an attack by ozone to a degree that ranged from poor to excellent. The degree of protection depended (a) on the differential in the rates of reaction of the antiozonant and the rubber hydrocarbon with ozone, (b) on the initial concentration of the antiozonant on the surface of the vulcanizate which reacted with ozone to form a barrier of oxidized residues, and (c) on the rate of effusion of fresh antiozonant from within the rubber to the outer surface of the barrier. SBR vulcanizates containing a naphthenic processing oil as an extender were not so resistant to ozone as standard SBR vulcanizates. It is probable that the effectiveness of the antiozonants tested in these vulcanizates was reduced by their high solubility in the oil phase. SBR vulcanizates containing trioctyl phosphate as a plasticizer were vigorously attacked by ozone. It is possible that the gaseous ozone dissolved to some extent into the plasticizer phase, increasing the concentration of ozone in the area causing a more severe oxidation of the rubber. SBR vulcanizates that had been coated with an antiozonant by dipping the specimen several times into a solution of the antiozonant in a solvent were found to contain a higher concentration of the antioxonant directly on the surface of the vulcanizate than in the case where three parts of the antiozonant were added during vulcanization. A mechanism for the ozonization of SBR vulcanizates has been proposed which includes a possible mechanism for the protective action of antiozonants. A rate equation has been derived from this mechanism which was consistent with the experimental rate data.
Chemical Inhibition of Ozone Degradation of SBR
Authors: Kilbourne H. W. , Wilder G. R. , Van Verth J. E. , Harris J. O. , Tung C. C.
Published: February 2011

The standard rubber antioxidant types which are capable of imparting ozone resistance to SBR vulcanizates are summarized. The 6-ethoxy-l,2-dihydro-2,2,4-trimethylquinoline and para phenylenediamines are shown to represent the most active structures. Steric, mesomeric, and resonance effects are shown to be important in imparting high levels of antiozone activity. When electronegative groups are substituted in an active structure, antiozone effectiveness is greatly reduced. Antiozonant activity is attributed to efficient stopping of ozone-induced free radical chain reactions in the polymeric structure.
Basic Problems in the Theory of Bond Strength between the Plies of a Rubber Article
Authors: Patrikeev G. A.
Published: February 2011

The problem of ensuring adequate bonding strength between uniform and nonuniform layers in composite vulcanized rubber articles is particularly vital in the production of high grade multi-ply articles for heavy duty (high speeds, high dynamic loading and considerable heat build-up) and also in the production of multi-ply articles from dissimilar compounds based on synthetic rubbers of different structural type. In works practice various methods are known for the production of two-ply and multi-ply composite vulcanized rubber articles, based on plying-up in the hot state (sometimes combined with buffing of the unvulcanized parts and the use of special materials to increase the tackiness of the stocks) and also on the use of solvents and the cementing of the stocks by a cement, sometimes of several types applied in sequence. Difficult technological tasks arise in the production of composite articles with dissimilar plies based on rubbers of different chemical composition, for instance of natural and sodium butadiene (or chloroprene) or of natural (or butadiene) and butyl rubber. In spite of considerable practical successes, many of the tasks enumerated above remain unsolved, and there is hardly any great hope of success without a previous examination of a number of basic theoretical questions. A theory of strength has not been worked out even for the most simple case—the stretching of a strip of unloaded vulcanized rubber. There are many questions unstudied, the examination of which must precede the development of a theory of the strength of dissimilar plies in a multi-ply composite rubber article. Before considering the separate questions we regard it as worthwhile to formulate the general tasks of a theory, keeping within the bounds of the problem under discussion, i.e., bond strength. According to the minimum requirements, theoretical investigations ought to enable the selection of correct basic (determinant) scientific lines and to facilitate the development of rational methods of investigation, reflecting the essential aspects of the phenomenon being studied. Of course, major failures and unplanned and wasted labor are often caused by the choice of mistaken lines of investigation or are the outcome of the use of mistaken methods of testing.
Choice of Resilient Materials for Anti-Vibration Mountings
Authors: Snowdon J. C.
Published: February 2011

This article attempts to determine, solely from the aspect of vibration reduction, the criteria which define a good antivibration mount material. It concludes firstly that such a material should possess a high damping factor which does not increase greatly with frequency, and secondly, that it should be free from any major increase in dynamic modulus with frequency. Results of transmissibility measurements on a variety of resilient materials indicate that high damping synthetic rubbers normally possess a dynamic modulus which increases rapidly with frequency. It is shown that this modulus increase is responsible for the poor isolation afforded by these rubbers at frequencies above the resonant frequency of the mounting system, and not their inherent high damping as commonly supposed. Filled butyl rubber is an exception, affording an isolation at high frequencies not greatly inferior to that of natural rubber, yet at the same time possessing much higher damping.
Constitution and Variability of Rubber from Individual Trees
Authors: Kemp A. R.
Published: February 2011

A special procedure of collecting rubber latex directly from the tree by dropping it directly into alcohol to coagulate and preserve it has been described. The color, hardness, solubility in benzene or chloroform and viscosity of the soluble portion of this alcohol-coagulated rubber has been found to vary widely in the case of rubber from 24 individual trees in a Costa Rica rubber estate. While it is shown that rubber from individual trees show wide variations, the results from bulked latex and crepe are close to the average results found for the 24 trees. The results from the present investigation show that rubber direct from the tree contains soluble and insoluble fractions like those found in crepe and smoked sheet. Lower polymers in crepe and smoked sheet are also present in the latex as it emerges from the tree. It was found that some trees yielded a rubber almost completely soluble in benzene or chloroform, while in others, the soluble portion was as low as 61 per cent, with the average being 80 per cent. High viscosity of the sol and insoluble gel both lead to hard tough rubber. The alcohol coagulums varied widely in color from almost white in the ease of some trees to various shades of cream in most of the others. A new and unexpected finding was that four of the 24 trees yielded a distinctly grey mottled coagulum. This grey color apparently comes from the presence of clotted grey lutoids not apparent in the latex itself. The constitution of sol and gel rubber is discussed and data are presented on the solubility and viscosity of the solutions obtained from the gel fraction. From these data it is concluded that the difficultly soluble gel is a three dimensional network structure with either oxygen or carbon-to-carbon linkages between the polyisoprene chains.
Fine Particle Reinforcing Silicas and Silicates in Elastomers
Authors: Bachmann John H. , Sellers John W. , Wagner Melvin P. , Wolf Ralph F.
Published: February 2011

Reinforcement has been described as “the enhancement of one or more properties of an elastomer by the incorporation of some ingredient thus making it more suitable for a given application”. This definition gives an excellent qualitative description of the reinforcement of an elastomer, but lacks the quantitative aspects necessary to prescribe specifications for materials to be included in the present review on reinforcing siliceous fillers. The scope of the present review will therefore be defined in terms of the properties of the siliceous fillers rather than in terms of the degree of enhancement of one or many elastomer properties. Experience has shown that substantial improvement in the physical properties of vulcanizates generally cannot be expected from siliceous fillers greater than 50 millimicrons in number average particle size, or less than 50 square meters per gram in specific surface area. These specifications will be used to delineate the silicas and silicates included in the present review, a general outline of which is presented in the following paragraphs: Description of the silica and silicate fillers is made difficult by lack of established categories for these materials. To aid in their classification, a brief discussion of manufacturing methods is presented. Then, lists of commercially available products are introduced. Physical and chemical properties of commercially available reinforcing silicas and silicates are presented, based on information in current brochures obtained from manufacturers. Failure by the manufacturer to specify his methods has occasionally diminished the usefulness of published data. for example, the term average particle size is not specific as it does not state which statistical average value is intended. The lengthy treatment given testing methods constitutes a plea to define or specify test methods. The three properties of primary interest in reinforcing silicas and silicates are the particle size, the chemical nature of the surface, and the state of aggregation. A comprehensive discussion of the chemical nature of the surface is prohibitive because of the wide scope of the topic. Nevertheless, a quick survey was made of this subject with the objective of presenting adequate information to allow an interpretation of the behavior of the fillers in elastomers. The groups encountered are principally siloxane (Si—O—Si), silanol (SiOH), and reaction products of the latter with various hydrous oxides. Attention is focused on silanol groups. Their dehydration and rehydration, their chemical reactivity, and their propensity for hydrogen bonding are considered briefly to aid in understanding interactions of the fillers with elastomers and with curatives.
Elastomeric Properties of Butyl Rubber
Authors: Buckley D. J.
Published: February 2011

On first thought, the properties controlling the behavior of high molecular weight substances would appear to be so overwhelmingly numerous as to defy consolidation and simplification. However, upon analysis, it can be seen clearly that they all reduce to areas of consideration which make up a relatively small group. For elastomers, such a grouping might be as follows. Size Shape Order and Disorder Composition Crosslinked Network Response to Deformation Degradative Reactions This reviewer does not intend to imply that each area can be considered mutually exclusive of any of the others. There is ample evidence of considerable interaction between these areas. Moreover, it is not intended to imply that the approach to elastomeric problems is utterly simple. The complexity within any one of the areas mentioned is well known from the literature on polymers. However, it is suggested that a grouping or classification such as given here can assure a greater clarity of concept and objectivity of analysis and experiment in approaching otherwise obtuse and complicated polymer problems. As each new polymer material comes under research scrutiny in this sense, the general “laws” governing polymer behavior are clarified and extended. This is a result of the fact that each new material usually provides features which invite and encourage research, particularly where uncertainty exists. The ease of butyl type polymers will be reviewed in this sense with two purposes in mind: (1) to define and correlate the knowledge derived from butyl research which has contributed to a better understanding of the principles of polymers, and (2) to suggest (often by inference) areas where potentially fruitful research in the same direction is still possible. This review will consider butyl polymers beyond the polymerization stage. Except where necessary to develop the proposed objectives, the chemistry of polymerization will not be considered. A number of references are recommended to the reader interested in the polymerization aspects. No attempt will be made in this review to consider butyl end uses or the compounding and technological information associated therewith. Some exception to this restriction will be made when the particular property under consideration warrants it. Rather, this review will attempt to show how a development of the basic knowledge of polymer behavior can be put to use in the solution of technological problems.