bluuebunny/crossref_metadata_2025 huggingface dataset:
Important Mechanical and Chemical Factors in the Failure Behavior of Polybutadiene Rubber Undergoing Oxidative Aging at Ambient Temperature
Authors: Kim C. S.
Published: February 2011

Zhurkov's molecular kinetic concept of failure for hard solid materials was extended for application to rubber systems which undergo oxidative degradation during long-term atmospheric exposure. In an effort to analyze the chemical and mechanical effects separately, the dependency of the life-time of the uniaxially stressed rubber was expressed in terms of (1) chemical effects involving the primary chemical bonds in the effective chains, and (2) mechanical effects involving the network structure of the rubber.
The Contribution of Deformation Losses to Rubber Friction
Authors: Hegmon R. R.
Published: February 2011

Bulk friction of rubber is defined as the friction due to deformation losses. Analytical and experimental investigation of bulk friction showed excellent agreement. The coefficient of bulk friction depends on the geometry of the rough surface and increases linearly with the mean pressure. Friction depends on two dynamic rubber properties, it decreases with increasing dynamic modulus and increases with increasing damping factor.
Sulfur Crosslinks in Polybutadiene Vulcanizates
Authors: Gregg Earl C.
Published: February 2011

For the first time the crosslink terminus structure of monosulfide crosslinks and the amount of that structure in an elastomer vulcanizate has been determined directly from a sample of the vulcanizate. By measuring the rate of swelling of vulcanizates, immersed in either methyl iodide or methyl bromide, the rate of crosslink cleavage was measured. Comparison of this cleavage rate with the cleavage rate of model monosulfide compounds permits a measure of the terminus structure of the monosulfide crosslinks. The fraction of each monosulfide structure was determined from the cleavage rate equation for the vulcanizate. The monosulfide crosslink terminus structure in a particular polybutadiene vulcanizate was found to be saturated, having secondary carbon atoms on both sides of the sulfur atom, i.e., it was a saturated, tetrafunctional crosslink equal to 38% of the total crosslinks.
Nuclear Magnetic Resonance Study of the Interaction of SBR with Carbon Black
Authors: Waldrop M. A. , Kraus G.
Published: February 2011

The nuclear magnetic resonance relaxation characteristics of an amorphous styrene—butadiene copolymer (SBR-1500) containing HAF and ISAF carbon black and an HAF carbon black containing SBR-1500 adsorbed on it from solution have been investigated at 30 Mc/sec over a temperature range of −100° to 100° C. The spin-lattice relaxation time (T1) passes through a single, broad minimum at about 30° C. The precise location of this minimum which is ascribed to the onset of segmental motion in the copolymer is not strongly dependent on the presence of carbon black. The nuclear magnetic resonance results reported suggest that the spectrum of correlation times of the elastomer strongly associated with the carbon black particles, i.e., the “bound rubber” is not significantly different from that of the bulk elastomer containing no carbon black—at least for the frequencies sampled by the NMR technique used. The results thus fail to confirm recent proposals in the literature suggesting that filler particles in elastomers are covered with a layer of polymer in which segmental motion is severely restricted and which constitutes a significant, if not the major portion of the rubber.
Heterogeneity and Crosslinking of Elastomer Blends. Investigations of Chlorobutyl with Highly Unsaturated Elastomers
Authors: Rehner John , Wei Peter E.
Published: February 2011

Literature on the fundamental physios and chemistry of elastomers blends is limited, even though blends are employed commercially. Past research on individual elastomers is inadequate for a good understanding of blends. Properties of elastomers blends, unlike those of plastic blends, depend on vulcanization chemistry. The general problem is therefore one of understanding the nature and properties of elastomer blends in which complex chemical reactions have been superimposed on a complex physical state. The present paper is a preliminary examination of both of these aspects.
Elastically Effective Strand Density in Polymer Networks
Authors: Langley N. R.
Published: February 2011

A new expression is derived which relates the density of elastically effective strands in a polymer network to the densities of random cross-links, main-chain scissions, and entanglements and to the molecular weight distribution of the initial linear polymer. Methods are recommended for characterizing the cross-link and scission densities from measurable sol fractions and for determining the entanglement density empirically. The strand density can be evaluated quite easily for the random and uniform initial molecular weight distributions. The new expression differs appreciably from that of Mullins and Bueche, owing principally to a new criterion for effectively trapping network entanglements. The statistical approach used to derive the strand density is also used in a new derivation of an existing implicit expression for the gel fraction.
Kinetics of Accelerated Vulcanization—III N-Cyclohexyl-Benzothiazole-2-Sulfenamide Accelerated Sulfur Vulcanization of Rubbers
Authors: Bhatnagar S. K. , Banerjee S.
Published: February 2011

Sulfenamide type of accelerators are well known for their outstanding processing safety combined with ultra-strong accelerating activity resulting in superior quality vulcanizates. Sulfenamides derived from different amines afford varying degrees of scorch delay and accelerating activity. Since there is no unanimity on the chemistry involved in this type of accelerated vulcanization, a preliminary study has been carried out to gain some insight into the mechanistic scheme. The present paper contains reports on the effects of varying concentrations of N-cyclohexyl-benzothiazole-2-sulfenamide (CBS) on the rate of free sulfur decrease and cross-link formation as well as zinc sulfide formation—whenever it occurs—both in the absence and presence of zinc oxide and of zinc oxide and stearic acid. The influence of temperature has also been investigated.
Thermodynamics of Mixing of n-Alkanes with Polyisobutylene
Authors: Flory P. J. , Ellenson J. L. , Eichinger B. E.
Published: February 2011

The volume changes on mixing polyisobutylene (PIB) with n-pentane, n-hexane, n-heptane, n-octane, n-decane, and n-hexadecane have been determined by direct measurements at 45°, and for n-heptane at 0 and 50° as well. They are negative in every case; the magnitude of the excess volume decreases with chain length, and increases with temperature. These results on volume changes, which are beyond the scope of conventional theories of polymer solutions, are rationally taken into account by the recent statistical mechanical theory of solutions which relates properties of the mixture to characteristics of the pure liquids manifested in their equation-of-state parameters. The negative enthalpies of mixing found by Delmas, Patterson, and Somcynsky for all of these systems with the exception of PIB-n-hexadecane are similarly shown to arise from negative equation-of-state contributions to the enthalpy which reflect differences between the liquid characteristics of n-alkane and PIB. The energy contributed by interchange of neighbor species in contact is shown to be small but positive, as should be expected for the nonpolar molecules involved. It diminishes with chain length of the alkane, becoming little greater than zero in the limit of an infinite alkane chain (polymethylene). Osmotic pressures of concentrated solutions (∼ 15–50%) of PIB in n-octane at 25° yield values of the residual chemical potential, expressed in terms of the conventional parameter χ, which are well reproduced by the theory without arbitrary parameters. The partial molar enthalpy and entropy of dilution are dominated by equation-of-state contributions rendering both of them negative, despite the large positive combinatory entropy. The appearance of critical miscibility at higher temperatures is thus predicted by the theory without resort to special explanations.
Determination of the Equation of State of Polyisobutylene
Authors: Eichinger B. E. , Flory P. J.
Published: February 2011

The density, thermal expansion coefficient, and thermal pressure coefficient for polyisobutylene of mol wt 40,000 have been accurately determined from 0 to 150°. Results are compared with the reduced equation of state employed in the theory of solutions. The characteristic parameters v*, T*, and p* required for the treatment of polyisobutylene solutions are obtained from the experimental results.
Cuts and Cut Growth in Tires
Authors: Brenner F. C. , Barton F. W.
Published: February 2011

Forty tires were subjected to severe road use on a course (approximately 3500 miles) that included Belgian block, over highways at turnpike speeds while overloaded. The course was repeated until the tires were worn smooth. At the end of each course, the number of new cuts and the length of all cuts in grooves was determined. Ten miles of Caliche (sharp stones) road was included between the first and second measuring period. The tires experienced a total of 169 cuts. Forty seven of these grew, 34 of which grew less than 0.11 inch. No cut grew continuously throughout the test. The cuts grew but not enough to cause tire failure except in one case where the cut exposed the fabric.
Intercalated Montmorillonites as Fillers for Acrylonitrile-Butadiene Rubber
Authors: Zaborski Marian , Kunert Anna , Pietrasik Joanna , Szynkowska Malgorzata Iwona , Lesniewska Ewa
Published: February 2011

Modified montmorillonite was used as filler for NBR. The effect of the montmorillonite structure and its concentration was studied. The composites were prepared with the use of a laboratory two-roll mill. Unmodified montmorillonite (MM_Na) agglomerated in NBR rubber resulting only in small enhancement of mechanical properties. The most effective exfoliation of the montmorillonite was observed for the modifier with two long chains (dihydrotallowdimethylammonium chloride (2M2HT)) and at its higher concentration (C1). The modified filler did not agglomerate in NBR. The montmorillonite (MM_2M2HT(C1)) formed a secondary filler network. This very well dispersed network demonstrated the strong reinforcement. Increasing the content of MM_2M2HT(C1) to 20 parts by wt. improved significantly the tensile strength of NBR vulcanizates (tensile strength > 25 MPa). Montmorillonite intercalated with hydrotallowdimethylbenzylammonium chloride (MM_2MBHT) did not improve the properties of the studied materials.
Oil Distribution in iPP/EPDM Thermoplastic Vulcanizates
Authors: Abraham Tonson , Barber Norman G. , Mallamaci Michael P.
Published: February 2011

Scanning Probe Microscopy (SPM) was used to determine the volume fraction of oil-swollen particulate rubber and oil-swollen plastic in thermoplastic vulcanizates (TPVs) produced from iPP and EPDM rubber. Sample preparation and SPM imaging conditions allowed the ratio of the rubber and plastic area imaged for a TPV sample to be equated to the phase volume ratio. The hydrosilylation cured TPVs contained no filler or inorganic components (other than about 1 ppm of platinum catalyst, based on dry rubber) that would decrease the accuracy of the SPM analysis. The accuracy of the SPM method used for TPV phase volume determination was established by analysis of an oil-free TPV of known composition. The densities of the individual TPV components (rubber, oil, crystalline and amorphous plastic phase), which were assumed to be additive in the composite, were used to calculate the oil distribution between the TPV rubber and plastic phase, since the volumes of the individual components (the extent of plastic crystallinity was measured by differential scanning calorimetry) were known. Thus, the amount of oil in the oil-swollen TPV rubber and plastic phase could be quantified. This information, coupled with the Tg of the oil-swollen amorphous plastic phase, indicated that a substantial amount of oil was present as a separate oil phase that is surrounded by the oil-swollen amorphous plastic phase. To date, it has been assumed that the oil in a TPV partitions between the rubber and amorphous plastic phase, with the plastic crystallites being oil free. This work is the first demonstration of the presence of a separate oil phase in TPVs, and the first accurate determination of the oil content in the oil-swollen rubber, miscible oil in the oil-swollen amorphous plastic, and the free oil in TPVs.
Mechanical and Swelling Behavior of Double Networked Natural Rubber Cured Using a New Binary Accelerator System
Authors: Marykutty C. V. , Mathew G. , Thomas Sabu
Published: February 2011

The concept of double networks, which impart chain orientation to elastomers, is a rather new idea. Double networks were induced in natural rubber vulcanizates cured with different accelerator systems. Double networked natural rubber with different extensions cured with N-cyclohexyl benzothiazyl sulphenamide (CBS) and 1-phenyl 5-ortho -tolyl 2,4 dithiobiuret was studied and the effect of extension on the mechanical properties and swelling was analyzed. The extent of chain orientation was analyzed through anisotropic swelling studies. The modulus, tensile strength and tear strength showed an increase with increased residual extension ratio. The effect was more predominant in the longitudinal direction than in the transverse direction. The ultimate tensile elongation showed a slight deterioration. It was revealed that the formation of double networks with higher residual extension ratios restricted the entry of the solvent. Based on the studies it was concluded that residual extension has a profound effect in determining the final properties of vulcanizates.
T-Peel Tearing of a Model Black-Filled Natural Rubber Tread Ply Vulcanizate
Authors: Adamu B. , Hamed G. R.
Published: February 2011

T-peel tearing of a model black-filled natural rubber tread ply vulcanizate has been carried out. Tearing alternates between slow (“stick”) and fast growth stages (“slip”). “Stick” fracture involves sideways cracking into the loading direction. This blunts the peel front, slows forward tearing, and results in rough fracture surfaces. “Slip” fracture is the sudden forward growth of a crack, leaving relatively smooth fracture surfaces. “Stick-slip” fracture is characteristic of highly reinforced rubbers; it is also seen in edge-cut tensile specimens and trouser tear specimens of black-filled NR.
Reinforcement of Polyisobutylene with Anisodiametric Filler Particles of Poly(Ethylene Terephthalate)
Authors: Kargin V. A. , Sogolova T. I. , Metelskaya T. K.
Published: February 2011

The addition of particles of anisodiametric shape to a polymer, in the absence of chemical reaction, has a considerable influence on the mechanical properties of the polymer even with comparatively low concentration of the filler. It may be safely stated that the increase in strength, in 50% modulus, and in the flow temperature of filled systems is connected with the shape and dimensions of the particles which have been added. The conditions under which the experiment was carried out made it possible to observe the influence of the shape of the particles of the filler upon the physical and mechanical properties of the polymer in the pure form. It is suggested that the reduction in the temperature of flow which was observed with the addition of comparatively low concentrations of the filler with lengths not exceeding 100 µ, is due to the action of such fillers upon the secondary structures in the amorphous polymer.
Carbon Black Structure in Rubber
Authors: Payne A. R. , Watson W. F.
Published: February 2011

Some of the properties of carbon blacks in rubber are ascribed to its “structure”. This paper presents results on the sinusoidal dynamic straining of rubber/carbon black vulcanizates over an amplitude range including strains less than 0.1% and suggests that an elucidation of structure effects and the nature of the structure underlying them is forthcoming from these results. The dynamic properties are profoundly modified by special processing. Heat treatment of stocks containing structural carbon blacks and particularly the use of N-methyl-N,4-dinitrosoaniline can greatly reduce structure effects. They are absent with attrited blacks. Similar results have been obtained with silica fillers, for which certain metal soaps virtually eliminate structure effects. Structure effects are shown to be not essentially related to the rubber network, including the type of rubber, but to be due to a physical, three-dimensional structure of the filler itself within the rubber; the rubber acts merely as a dispersing medium and a matrix to allow the filler structure to re-form after breakdown. These changes of the filler structure are often the major cause of hysteresis at low extensions. Mixtures of carbon black and organic liquids demonstrate the existence and properties of the physical carbon black structure in absence of rubber. The properties of the rubber have the structural effects of the filler superimposed upon them.
Mechanism of Antiozonant Action. I. Consumption of p-Phenylenediamines in Rubber Vulcanizates during Ozonization
Authors: Lorenz Otto , Parks Carl R.
Published: February 2011

The consumption of N,N′-bis(1-methylheptyl)- and N-isopropyl-N′-phenyl-p- phenylenediamine in cis-polybutadiene vulcanizates was measured as a function of the ozonization time and the initial diamine concentration. The results are consistent with a rapid reaction of the antiozonants with ozone and the formation of a protective layer on the surface of the rubber. Film formation was confirmed by microscopic studies. Besides direct reaction with ozone and film formation, chemical reactions between the p-phenylenediamines and ozonized rubber took place since a certain amount of the consumed diamine (up to 45 %) became attached to the rubber network.
Tensile Strength of Amorphous Gum Rubbers
Authors: Bueche F. , Dudek T. J.
Published: February 2011

A new molecular theory of tensile strength has been formulated for amorphous gum vulcanizates at temperatures well above the glass temperature and found to be in agreement with recent experimental data. It is shown that the stress on the rubber at break will consist of two parts, the normal kinetic theory stress on the network and the highly rate dependent stress held by the fully extended chains. The fraction of the chains in the fully extended state at the instant of break is greater for a lightly crosslinked rubber than for a highly vulcanized rubber under nonequilibrium test conditions. The theory allows the molecular weight of the freely orienting unit to be calculated. Reasonable values are obtained for EPR and SBR which lend support to the validity of the ideas involved. The kinetic-theory stress contributes the major portion of the stress at break in highly crosslinked amorphous gum rubbers. However, the stress at break for low degrees of crosslinking is largely the result of stresses in the most highly elongated chains.
Mechanism of Antiozonant Action. II. Effect of Antiozonants on the Ozonization of 2,6-Dimethyl-2,6-Octadiene and 2-Butene
Authors: Lorenz Otto , Parks Carl R.
Published: February 2011

The ozonolysis of 2,6-dimethyl-2,6-octadiene and 2-butene as model compounds for polyisoprene and polybutadiene was investigated using gas chromatography to follow the reaction. Ozonolysis led to mixtures containing mainly the corresponding carbonyl compounds and peroxy compounds, such as ozonides and polymeric peroxides. Ozonization of the model compounds in the presence of antiozonants or addition of antiozonants to the ozonized model compounds indicated that antiozonants react at least in three different ways: (a) All effective antiozonants reacted rapidy with ozone. (b) All antiozonants reacted readily with ozonides and slowly with polymeric peroxides, whereby the corresponding carbonyl compounds were formed. (c) Difunctional secondary amines, such as p-phenylenediamines, reacted readily with the formed aldehydes leading to polymeric compounds. In ozonized polydiene vulcanizates, a relinking of severed chain ends is achieved by this reaction, whereby the diamine becomes attached to the rubber network. Relatively basic amines effect aldol condensation of aldehydes.
Vulcanization of Rubber by Means of Resins
Authors: Thelamon Claude
Published: February 2011

Vulcanization has been the subject of much careful research since its discovery by Goodyear in 1840. Originally “vulcanization” meant a treatment of rubber with sulfur and heat, but now the word has a much broader connotation, since it has been discovered that numerous substances can produce the same effect as sulfur. Vulcanization is the process by which rubber passes from the predominantly plastic state to a predominantly elastic state by means of an irreversible transformation. This phenomenon is due to the formation of intermolecular bridges, leading to a more or less dense steric structure. Materials capable of vulcanizing rubber can be classified in three large categories: 1. Compounds which liberate sulfur during vulcanization, e.g., sulfur chloride and tetramethylthiuram disulfide. It is thought that nascent sulfur is particularly active, giving rise to the formation of crosslinks. 2. Compounds inducing vulcanization by means of radical reactions, such as peroxides. 3. Bifunctional compounds, among which phenol/formaldhyde derivatives seem to be the most interesting. Materials in the third group will be the object of this study.
Addition of Unsaturated Monomers to Rubber and Similar Polymers
Authors: Pinazzi C. , Danjard J-C. , Pautrat R.
Published: February 2011

The addition of different ethylene monomers to polyisoprene was studied in order to throw a light on reaction mechanisms and structures of reagents. It was attempted, during the planned transformations, to maintain as best as possible the shapes and sizes of initial macromolecules, upon which rests the property of high elasticity. For this purpose, it was decided to avoid grafting reactions, as well as any reactions affecting the nature of the polyisoprenic chain, e.g., scission, cross-linking, and cyclization. After the completion of the work carried out by one of the authors on the addition of maleic anhydride, the existence of two mechanisms was brought to light: the one is of a radical type, produced by adding an unsaturated reagent on a methylene close to a double bond of chain; the other is of a thermal nature, triggered by the action not of a catalyst, but of a rather high temperature. It is clear that the latter process does involve isomerization of a part of chain double bonds. The model to which maleic anhydride is connected has been deduced by examining the reaction aptitudes of a series of monomers. The major part of highly polymerizable materials, with the exception of acrylonitrile, were eliminated a priori, in order to avoid both homopolymerization reactions and graftings. The monomers in which double bonds are depleted in π electrons are more apt to give the desired reactions. The more favorable effect is obtained with α carbonyl (maleic anhydride and γ crotonolactone). Other factors were also taken into account. The work reviewed here enabled us to assess the way in which reactions evolve according to the considered mechanisms and produce new macromolecular materials. The resulting compounds have a high rubberlike elasticity and show a high chemical reactivity, due to anhydride or lactone side groups.
Stress-Strain Testing of Rubber at High Rates of Elongation
Authors: Dannis Mark L.
Published: February 2011

It is well known that the properties of rubbery materials depend upon the speed or rate at which they are tested or used. A considerable body of work has shown that the dynamic properties of rubber change with the time scale of the test and, in particular, at very short times or at very fast rates, the properties approach those of plastics, i.e., high modulus and low elongation. These dynamic properties are measured by oscillation methods, usually at small strains. In contrast to this class of information, where the material is rarely strained to failure, one can also strain rubbers unidirectionally to failure at strain rates that correspond to the high frequencies of dynamic measurements. In linear extension experiments, as the rate of stretching increases tensile strength rises, elongation drops, apparent modulus increases, and relaxation losses may go up or down depending upon the particular rubber and the time scale of the phenomenon that is being investigated. Extrapolating the change in tensile strength with rate of testing suggests that tensile strength as we know it should change drastically when measured at very high rates of speed. That is, since the viscoelastic properties of rubber are time dependent, and also dependent upon the speed at which they are tested, the tensile properties of rubbers measured at room conditions with the ordinary Scott or Instron machines probably do not have the same values as at the speeds and frequencies that might be encountered in such situations as tire wear. Hence, we should like to measure the properties of rubbers at very high rates of speed, presumably comparable to those encountered in tire tread wear, in order to find out how much properties do change as the speed of test is increased. In order to measure stress-strain properties at rates of elongation comparable to those we believe exist in tire tread usage, we had to develop a small high speed tensile machine. The purpose of this paper is to describe that machine and some results obtained with it.
Determination of Tetramethylthiuram Disulfide
Authors: A˚kerström Stig , Lindahl P. E. Björn
Published: February 2011

A method for the determination of small amounts of TMTD is described. The method is applicable to other tetrasubstituted thiuram disulfides. The reproducibility of the determination of TMTD is ±2%.
Liquid Chromatographic Separations Using Rubber as the Stationary Phase
Authors: Brewer P. I.
Published: February 2011

In a previous communication it was reported that certain polymers could be separated from mineral oil by a liquid chromatographic method. n-Heptane was used as the mobile phase and small pieces of thin vulcanized natural latex as the stationary phase. It has now been found that compounds of lower molecular weight can also be separated by this method. The use of rubber for the separation of compounds of low molecular weight was first described by Boldingh; he found it advantageous first to swell the rubber with a different solvent from that used as the mobile phase. The use of a crosslinked dextran (“Sephadex”) for separating compounds in aqueous solution has been described by Gelotte. Vaughan has mentioned the possibility of using crosslinked polystyrene beads for this purpose.
Properties of Resilin, a Rubberlike Protein
Authors: Weis-Fogh Torkel
Published: February 2011

There is much circumstantial evidence in favor of the belief that elastin and some other structural proteins exist in the rubberlike state of matter (see reviews by Wöhlisch, 1939; Astbury, 1940; Meyer, 1950; Kendrew, 1954), but it will be shown that the crucial evidence from thermodynamic experiments is ambiguous. The discovery of a new type of highly elastic structural protein, resilin ( Weis-Fogh, 1960; Bailey and Weis-Fogh, 1961), made it possible to re-investigate the problem by using more suitable samples. Since the thermodynamic experiments reported here gave a clear-cut answer, it was legitimate to interpret in detail the mechanical and optical properties of resilin according to the kinetic theories of rubber elasticity and so to obtain valuable information about the molecular structure of at least one rubberlike protein (Weis-Fogh, in preparation). Resilin is the essential elastic component in certain mechanical springs in the cuticle of arthropods (cf. the Latin resilire, to spring back) and it has a number of properties which make it ideally suited for this type of investigation (Weis-Fogh, 1959; 1960). When swollen with water, it exhibits typical long-range elasticity, it is heat-stable up to 140° C, crosslinked by very stable covalent bonds and insoluble in all solvents that do not break the peptide backbone but it is easily digested by all kinds of proteolytic enzymes. Moreover, it is secreted as thick continuous layers by the epidermis in a pure form unmixed with other proteins, lipids or polysaccharides and spatially separated from chitin, the only other structural component of the rubberlike cuticle (Weis-Fogh, 1960; Bailey and Weis-Fogh, 1961). It is thus possible to obtain native resilin in the form of relatively large, homogeneous samples, 0.1 mm thick and 1 mm long. Such samples are hyaline, devoid of color, and mechanically as well as optically isotropic in all directions and at all degrees of swelling. They are also devoid of structure (light and electron microscopy), and no trace of crystallinity has been found (X-ray diffraction) even in samples that were stretched near to the breaking point and then slowly dried (Elliott, Huxley, and Weis-Fogh, in preparation). The amino acid composition is unique and different from that of elastin, elastoidin, silk fibroin and collagen, and about one third of the side chains carry polar groups (Bailey and Weis-Fogh, 1961). The rubberiness of elastin is generally thought to be intimately connected with the scarcity of polar groups (5%; cf. Lloyd and Garrod, 1946). This paper will deal with experiments that show that the elastic force of resilin is connected with entropy changes caused by deformation, as in true rubbers, rather than with changes in internal energy, as in most solids.
Beta Ray Absorption in Polymers and Determination of First and Second-Order Transition Temperatures
Authors: Zannetti R. , Manaresi P. , Baldi L.
Published: February 2011

It is possible to determine the first- and second-order transition temperatures of polymers, copolymers, and other organic and inorganic substances with good accuracy and reproducibility by measuring their absorption of beta radiation. Variations in the measured absorptions are in essence related to variations in the product of the density and thickness of the sample, so that the method can be employed, in practice, when seeking information concerning variations in density, with the temperature or the time. The technique was used to investigate a number of polymers, e.g., polyethylene terephthalate, polystyrene, polyethylene, 1,4-cis polybutadiene, natural rubber, polyisobutylene, polybutene-1, polypropylene, and certain copolymers of ethylene/propylene and ethylene/butene-1. Finally, data pertaining to phase transitions in organic and inorganic substances are presented. The results are discussed., and compared with those obtained by other methods.
Mechanochemical Phenomena in Polymers. II. The Effects of Initiators and Inhibitors of Chain Processes
Authors: Reztsova E. V. , Kipkina B. T. , Slonimskii G. L.
Published: February 2011

1. The substantial effect of inhibitors and initiators of chain radical processes on the change in the properties of rubbers in milling, as well as on the resistance of vulcanizates to fatigue, has been shown. This indicates a mechanochemical mechanism for processing of polymers and in the fatigue of elastomers. The act of mechanical scission of chemical bonds, with the formation of free radicals which initiate the secondary chain processes, rests on these processes. 2. The possibility has been shown of regulating the properties of polymers during processing, and also of increasing the dynamic fatigue resistance of vulcanizates by incorporating small quantities of additives active in regard to free radicals.
Solution Properties of Polybutadiene and trans-Polyisoprene Fractions
Authors: Cooper W. , Eaves D. E. , Vaughan G.
Published: February 2011

Linear polybutadienes, prepared with butyl lithium as catalyst, and polybutadienes branched by exposure to γ-radiation have been fractionated and the fractions examined by osmometry and light scattering. Turbidimetric second virial coefficients (A2τ) of mixed polymer fractions are virtually the same as those of the higher molecular weight components of the mixtures for most compositions. This is true both for mixtures of linear with linear and linear with branched polymer. The higher the molecular weight of the fraction, the greater the effect; the addition of 1 per cent microgel to a linear polymer reduced A2τ by a factor of three. The presence of microgel or high molecular weight branched polymer has been shown to be responsible for the very high molecular weights previously reported for polybutadienes from light scattering measurements. It is conveniently removed by shaking the solutions with calcium sulfate. Second virial coefficients obtained either by light scattering or osmometry are, within the limits of experimental error, uninfluenced by branching in the polymer. In general those factors which lead to increased branching also result in increased polydispersity, and it is the latter which results in the decrease in A2τ. The fall of the osmotic second virial coefficient (A2τ) with molecular weight is much smaller than would be calculated theoretically, and the fall in A2τ is greater than would be expected, notwithstanding the fact that for some of the fractions Mw/Mn<1.1. This indicates that A2τ is sensitive to the low molecular weight species present in the fractions, whereas the reverse must apply to A2τ. Natural or synthetic trans-polyisoprene showed analogous behavior to polybutadiene, although, owing to experimental difficulties, sharp branched fractions could not be obtained. The following viscosity-molecular weight relationships were obtained in benzene solution: [η]=1.45×10−4M0.76 for butyl lithium-catalyzed polybutadienes, and [η]=4.37×10−4M0.65 for natural and synthetic trans-polyisoprenes.
An Oscillating Blade Microtome for Rubber
Authors: Southern E. , Thomas A. G.
Published: February 2011

In a study of the equilibrium swelling of rubber in thick oils, thin samples, about 0.1 mm thick, were required so that equilibrium could be reached within a reasonable time. Thin sheets can be molded, but they are frequently very anisotropic and therefore undesirable. Although it is possible to microtome very thin samples of rubber at sufficiently low temperatures where it is relatively stiff, only small areas are obtainable, and it is a difficult and inconvenient process if several square centimeters are required. An oscillating blade microtome of simple design was therefore constructed, capable of cutting sufficiently thin slices, about 2 cm square, at room temperature. Because of the sawing action of the blade the cutting force is greatly reduced and deformation of the sample is minimized.
Formation and Decomposition of Hydroperoxides of Atactic Polypropylene
Authors: Manasek Z. , Berek D. , Micko M. , Lazar M. , Pavlinec J.
Published: February 2011

1. The authors study the kinetics of formation and decomposition of peroxides in the oxidation of atactic polypropylene in air in the temperature range from 20° to 120°. 2. The effective energy of activation of accumulation of peroxide (24 to 25 kcal/mole) and of decomposition of peroxides (27 kcal/mole) are determined. 3. It is found that the reduction in the molecular weight is a function of the concentration of peroxides in the polymer.
The Structure of Angular Polycycloisoprene
Authors: Wallenberger F. T.
Published: February 2011

Lewis and Brö nsted acids, heat, silent electric discharge and cathode rays cause progressing isomerization of synthetic and natural cis-1,4-polyisoprene to yield a polymeric product which has the empirical formula, (C5H8)n identical with that of the initial rubber hydrocarbon. The reaction, commonly carried out in benzene with stannic chloride as catalyst, is accompanied by an increase in specific gravity, refractive index and polymer melt temperature and a decrease in unsaturation, intrinsic viscosity and molecular weight of the material. The resulting polymer, readily soluble in a variety of solvents, is known as cyclized rubber, cyclo-caoutchouc, or “Pliolite-NR”, manufactured by the Goodyear Tire and Rubber Company. Staudinger recognized as early as 1926 that the reaction proceeds by isomerization and intramolecular cyclization. D'lanni postulated formation of cyclohexane rings within the polymer chain, while Veersen extended D'lanni's proposal and suggested random protonation of bonds leading to intralinear, mono-, di-, and polycyclic ring polymers. Ideally, complete and stereoselective cyclization would lead to angular polycycloisoprene. Comprehensive reviews concerning the chemistry of the cyclization have been published by Reese and by Bloomfield. This communication provides the first chemical structure proof of the cyclized product. It is based on the cyclization of cis-1,4- and of trans-1,4-polyisoprene. The resulting products were identical and their properties in agreement with literature data. Hence cyclization must have proceeded through a common intermediate.
Mechanics of Foamed Elastic Materials
Authors: Gent A. N. , Thomas A. G.
Published: February 2011

The deformation of a foamed elastic material, both in tension and compression, and its resistance to tearing and to tensile rupture, have recently been derived on the basis of a model consisting of a large number of thin threads joined at their ends to form a three-dimensional network. A general account of this theoretical treatment, and the evidence for it, is presented. The theory is extended to deal with small deformations of closed-cell foams; relations for Young's modulus and Poisson's ratio are derived. The viscous damping of open-cell foams due to air flow through the network of threads is also discussed.
Creep of Pure-Gum Rubber Vulcanizates from Indentation-Time Measurements
Authors: Wood L. A. , Roth F. L.
Published: February 2011

The compliance J (limit of the ratio of strain to stress at zero deformation) has been determined from measurements of the indentation of a flat rubber surface by a rigid sphere, as a function of time t and temperature T. The results are subjected to two successive operations: (1) Jis multiplied by the absolute temperature T and (2) an empirically-determined number is added to the logarithm of the time at each temperature to make the values of JT agree as well as possible. For natural rubber from 25° to −40° C the shift required appears to correspond to a constant “activation energy” of 38kcal/mole; from −40° to − 60° C the shift is in quite good agreement with that predicted by the equation of Williams, Landel, and Ferry. Butyl rubber yields an “activation energy” of 20 kcal/mole while styrene-butadiene rubber gives a value of 22 kcal/mole. The resulting curve of JT against log t shows a sigmoid form with an increase of slope over 2 to 3 decades and a decrease at higher values. There is usually an extended region of nearly constant slope corresponding to the conditions of normal use of rubber products. For natural rubber this slope is 1 to 2% per decade; for the synthetics it is appreciably higher, reaching a value of 15% per decade for nitrile rubber. This behavior differs from that of a classical idealized polymer network, for which the compliance would approach an equilibrium value at long times.
Solution and Diffusion in Silicone Rubber. I. A Comparison with Natural Rubber
Authors: Barrer R. M. , Barrie J. A. , Raman N. K.
Published: February 2011

The diffusion and solubility of n- and isobutane and of n- and neopentane has been studied in the range 30° to 70° C, in polydimethylsiloxane rubbers. The solubilities are very similar to those in natural rubbers and show comparable agreement with the statistical theory of polymer penetrant mixtures. Diffusion coefficients are at least an order of magnitude greater in silicone than in natural rubbers. The very low energy of activation, ED, of about 4 kcal/mole is almost invariant among the hydrocarbons studied and is the same as for self-diffusion and viscous flow in this rubber. The low value of ED means that permeabilities of the hydrocarbons increase as the temperature falls. Because diffusion in silicones is less dependent upon molecular size and shape of penetrant than in natural rubber, the silicones are less selective though much more permeable separation barriers.
Effect of Compression on the Shear Modulus of Rubber
Authors: Payne A. R.
Published: February 2011

When a cylinder of small diameter-height ratio is compressed, it buckles. A theory has been developed by Haringx to describe this, based on the Euler theory of struts. This paper shows how Haringx's theory is applicable to the compression of rubber and to cylinders of moderate shape factor, which do not visibly buckle, and relates the changes in the shear modulus of a rubber which is compressed, to the degree of compression and the shape factor of the cylinder.
Temperature and Frequency Dependence of the Dynamic Deformation and Losses of Elastomers
Authors: Bartenev G. M. , Zelenev Yu V.
Published: February 2011

The results of this investigation of the temperature and frequency dependence of the deformation and mechanical loss of elastomeric network polymers in the temperature range from −90 to +120° C may be understood on the basis of the conceptions of three types of relaxation processes in these materials: orientation of the units of the chain molecules, overcoming of the secondary crosslinks (entanglements) in the movement of the segments, and the process of destruction of the polysulfide bonds, which comprise quite a small part of the total number of the chemical crosslinks. The first process is connected with the glass-transition and leads to the occurrence of a low-temperature maximum of mechanical losses, while the third leads to a high-temperature maximum. The first and third relaxation processes are apparently characterized by narrow spectra of relaxation times, which may be substituted for approximately by the corresponding averaged relaxation times. For the second process the spectrum of relaxation times is probably very wide and it is not possible to make the analogous substitution; this also explains the absence of a third mechanical loss maximum and the occurrence of a well marked frequency dependence of the deformation amplitude in the high-elastic range. The models of a network polymer considered for low and high temperatures give a qualitative description of all the main mechanical properties of these materials.
Use of Lithium Aluminum Hydride in the Study of Surface Chemistry of Carbon Black
Authors: Rivin D.
Published: February 2011

Considerable interest has been focused in recent years on the effects of carbon black surface chemistry on its properties in rubber and other polymer systems. Methods have been developed in our laboratory for the quantitative characterization and description of the surface chemistry of carbon blacks. The total surface acidity as given by the active (acidic) hydrogen is determined by reaction with strongly basic lithium aluminum hydride in diethyl carbitol, or by equilibration with aqueous alkali under nitrogen. Exclusion of oxygen is essential since carbon blacks readily undergo base catalyzed oxidation. Selective neutralization techniques are employed to further differentiate between strong and weak surface acids. For example, using aqueous sodium bicarbonate solution, only those acids stronger than carbonic acid will be neutralized. Strong acids, as determined by bicarbonate neutralization, are shown to be aromatic carboxyl groups, while weak acids determined by difference between total acidity and strong acid content are phenols and hydroquinone derivatives. Neutral quinone and lactone surface groups are quantitatively determined by chemical reduction with lithium aluminum hydride, or alternatively by analysis of their thermal decomposition products (carbon monoxide and dioxide, hydrogen, and water) obtained on vacuum pyrolysis of carbon black. The distribution of neutral and acidic surface groups on representative channel, furnace, and thermal black is discussed in terms of the state of oxidation of the individual carbons.
Internal Field Emission in Carbon Black-Loaded Natural Rubber Vulcanizates
Authors: van Beek L. K. H. , van Pul B. I. C. F.
Published: February 2011

The nonohmic behavior of carbon black-loaded natural rubber vulcanizates was studied. Three samples contained high-abrasion furnace black (HAF) in good, moderate, and poor dispersion. Another sample contained a good dispersion of medium thermal black (MT). The nonohmic behavior of the poor HAF dispersion and that of the MT dispersion could be interpreted as due to internal field emission across insulating gap widths of 2 and 2.5 µ. The existence of such gaps was confirmed by electron micrographs. No clear evidence of internal field emission could be obtained for the good and moderate HAF dispersions where, according to electron micrographs, the gaps are much narrower. There is some indication that the degree of dispersion can be correlated with field emission characteristics.
Reagglomeration as a Cause of Tread Groove Cracking
Authors: Hess W. M. , Burgess K. A.
Published: February 2011

A tendency for zinc and sulfur to reagglomerate, along with wax, has been observed in oil extended SBR and natural rubber tires. In high concentrations these relatively brittle reagglomeration areas are associated with poor resistance to groove cracking. The pigment-polymer environment has a significant effect on the occurrence of non-carbon reagglomeration. An increase in reagglomeration in oil extended SBR treads is favored by: 1. Poor initial dispersion of the non-carbon components. 2. Fine particle size and low structure carbon blacks. 3. Excessive zinc and wax. Conversely, reagglomeration can be reduced or eliminated by good dispersion of all compound ingredients, the use of higher structure or larger particle size carbon blacks, and through blending with polybutadiene.
State of Branching in Regular Polyisoprene
Authors: Poddubnyi I. Ya , Erenburg E. G.
Published: February 2011

Fundamental data about the intrinsic viscosity in an ideal solvent of a fraction of polyisoprene with a cis unit content of approximately 85% comes from branching. Such polyisoprenes were obtained by the action of complex catalysts or by the action of lithium. We have established that the macromolecules of rubber which were obtained with a complex catalyst under the usual conditions appear on the whole to be linear. At the same time, in the samples investigated approximately 10% consists of colloidal strongly to crosslinked polymer. It can be seen that disturbance of the rate of polymerization during preparation of polyisoprene in the presence of complex catalyst brings about the formations of strongly branched polymer. Such polymer contain one branch per approximately 250 monomeric units. Knowledge of the features of the hydrodynamic behavior of macromolecules allows one to express the assumption that the trans units in the polyisoprene macromolecule obtained with a complex catalyst is not disposed in a random manner along the chain but forms a comparatively linear block of trans units. For the polymers investigated an equation for the dependence of the intrinsic viscosity in benzene on the molecular weight was obtained. For polymers which were obtained under action of a complex catalyst this was [η]=1.12×10−4×M0.78 or ln M=5.063+1.28 ln [η] or for isoprene polymers from lithium [η]=1.33×10−4M0.78 ln  or M=4.967+1.28 ln [η].
Benzothiazyl Disulfide-Accelerated Vulcanization of Carbon Black Loaded Natural Rubber
Authors: Studebaker M. L. , Nabors L. G.
Published: February 2011

Sulfur group analyses of reinforced MBTS accelerated vulcanizates reveal chemical differences which can be related to the surface chemistry of the carbon blacks. The analytical procedure is based on the treatment of the vulcanizate with lithium aluminum hydride followed by potentiometric titration of sulfide and mercaptan sulfur. The polysulfide crosslink density and the values of x in the R—S—Sx—S—R polysulfides are dependent upon the quinone content of the carbon black. Both the quinone content and the surface area of a carbon black appear to determine its influence on the disappearance of free sulfur and the apparent crosslinking of the vulcanizate.