bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of Random and Block Copolymers of Butadiene and Styrene. I. Dynamic Properties and Glassy Transition Temperatures
Authors: Kraus G. , Childers C. W. , Gruver J. T.
Published: February 2011

The effect of monomer sequence on physical properties was investigated for butadiene—styrene solution copolymers made by organolithium initiation. The polymers varied from random copolymers of uniform composition along the polymer chain to ideal block polymers of specific block sequence arrangement and included rubbers of intermediate degrees of randomness. Uniform composition random copolymers exhibit a single glass transition temperature and a very narrow dynamic loss peak corresponding to this transition. The glass transition can be predicted from the styrene content and the microstructure of the butadiene portion of the rubber. Random copolymers in which composition varies along the polymer chain, and to some extent between molecules, exhibit a single glass transition, but the dynamic loss peak is broadened. The extent of this broadening is shown to be compatible with the sequence distribution, polymer segments of various compositions losing mobility at different temperatures. This indicates a tendency for association between segments of different chains which are similar in composition. Block copolymers display two transitions, corresponding to Tg for each type of block. The position and width of the dynamic loss peaks are related to block length and compositional purity of the blocks.
Strain-Wave Propagation in Strips of Natural Rubber Subjected to High-Velocity Transverse Impact
Authors: Smith Jack C. , Fenstermaker Carl A.
Published: February 2011

If a flexible filament marked at intervals along its length is struck transversely by a flying projectile, high-speed photography reveals a shifting of the marks caused by passage of a strain wave. Analysis of these shifts provides data on the strain and average strain velocity in the wave. Tests were performed on strips of lightly vulcanized natural rubber at transverse impact velocities up to 65 m/sec, and the resulting strain-velocity distributions analyzed for viscoelastic effects. Analysis showed that although creep effects were small in the observation time interval of 1–8 msec after impact, significant creep must have occurred at the point of impact within the first millisecond, and additional significant creep occurred at times greater than 8 msec. Strain-wave-front velocity calculated from the quasistatic stress—strain curve was 35.2 m/sec, but a value of approximately 60 m/sec was observed. Strain at the wave front, however, tended to attenuate as the wave propagated causing progressive decrease in the strain-wave-front velocity.
Stress-Strain Behavior of Swollen Polymeric Networks
Authors: Rijke A. M. , Taylor G. L.
Published: February 2011

The network parameters of swollen, solution-crosslinked polymer filaments can be collected from deswelling measurements in solutions of nonpermeating polymer or, as shown in this paper, from the stress—strain relation when in equilibrium with the surrounding solvent. The degree of swelling, at which the partial molar free energy of elasticity equals zero, is found to vary with solvent power in agreement with earlier findings on other systems. Comparison with results of studies on rubber networks crosslinked in the absence of diluent, show that previously observed discrepancies between theory and experiment can be attributed to the deficiency of the single term involving the one-third power of the volume fraction of polymer in the swollen network to describe the contribution of the partial elastic free energy.
Micromethod for Estimation of the Degree of Crosslinking in Elastomers from Compression Modulus of Swollen Vulcanizates
Authors: Smith Derek A.
Published: February 2011

The method uses small specimens (of volume less than 0.1 cc) which swell to diffusion equilibrium in hydrocarbon solvents within 8 hr. Measurements of deflection to better than one μ are made with a modified Wallace microhardness tester, which is described. The name “reticulometer” is proposed for this instrument. Using peroxide-crosslinked natural rubbers swollen to equilibrium νr values of about 0.23 in n-decane or in benzene, values for the concentration of physically active network chains determined by the present method were not greatly different from those determined by conventional “equilibrium” stress—strain measurements in tension on the same samples. Detailed differences are discussed. The chief advantages of the microcompression method are: (a) the use of small samples of shape and size convenient for carrying out other conventional measurements of network chain density; (b) the rapid attainment of diffusion equilibrium encouraging the use of fully swollen specimens and minimizing the risk of inhomogeneous distribution of swelling agent; and (c) the rapidity of testing compared with tension measurements.
A Universal Calibration for Gel Permeation Chromatography
Authors: Grubisic Z. , Rempp P. , Benoit H.
Published: February 2011

Gel permeation chromatography is one of the most powerful techniques for characterizing the polydispersity of polymeric materials. A versatile commercial apparatus has been used successfully in numerous laboratories on various problems of molecular weight distributions. But one of the difficulties still unsolved is the problem of calibration, i.e., the relation between elution volume and molecular weight. Some authors have assumed that retention time depends on the contour length of the molecular chain. Others think that it is more reasonable to use the radius of gyration or some average volume of the polymer molecule as the calibration parameter. In a recent paper we have reported GPC retention times of a series of polystyrenes exhibiting different molecular structures: linear, star-shaped, and comb-like. All were of known molecular weight and of low polydispersity. Obviously the conventional calibration method, where the logarithm of molecular weight is plotted against elution volume, does not yield a universal curve for all the samples. Retention times for branched samples were always larger than those for the linear homologs of the same molecular weight. We therefore tried using the hydrodynamic volume as the calibration parameter.
Techniques for Examination of High Impact Polystyrene by Electron Microscopy
Authors: Williams R. J. , Hudson R. W. A.
Published: February 2011

Techniques are described that make visible internal structure of individual rubber particles in a high impact polystyrene matrix, including replication of fractured surfaces and ultramicrotomy, and a novel method of hardening the material by irradiation.
Thermal Stability of Polyester vs. Polyether-Based Urethans
Authors: Singh A. , Weissbein L. , Mollica J. C.
Published: February 2011

It has been shown, by means of continuous and intermittent stress relaxation measurements and oven aging studies, that polyester-based urethans are more resistant to thermal degradation than the corresponding polyether-based urethans at temperatures in the range of 50° to 150° C. It has also been shown that this difference in thermal stability is due to irreversible, oxidative cleavage of polyether chain segments. Addition of representative antioxidants of the hindered phenolic and amine types to the polyether-based prepolymers prior to curing was found to be ineffective in improving the thermal stability of the resultant polyurethan elastomer. And, finally, the practical significance of these thermal stability studies has been demonstrated through heat buildup measurements.
Network Chain Distribution and Strength of Vulcanizates
Authors: Gehman S. D.
Published: February 2011

Physical characteristics of rubber network structures usually enumerated and discussed are network chain density, crosslink functionality, average chain length between crosslinks, entanglements which act somewhat like crosslinks, and free chain ends which are network defects. Chemical factors include structure of the chain molecules, type of crosslinks, whether monosulfide, disulfide or polysulfide, or direct carbon-to-carbon bonds. Side effects of vulcanization reactions such as chain scission or combination of minor quantities of chemical fragments from the vulcanizing system are also recognized. One might think that these variables would be adequate to account for physical properties of elastomers but explanations of strength aspects of vulcanizates are still unsatisfactory. Something is missing in these considerations, that is, the distribution of crosslinks along a main chain or the length sequences of monomer units in network chains. Usually a random distribution is implicitly assumed. If the distribution is always random and nothing can be done about it and it cannot be measured anyway, there may seem to be little point in writing about it. However, an ideally random distribution for all crosslinking systems and polymers seems very improbable. The importance of network chain length distribution for physical properties has been, of course, well recognized in theory. Bueche's calculations showed that viscoelastic resistance to deformation increased markedly with increased crosslink functionality, that is, as more chains are involved in the displacement of a crosslink. His molecular theory of tensile strength was based on the concept of short, overloaded network chains which snapped and transferred their loads to neighboring chains. An alternate point of view is that short chains are detrimental because they do not stress orient as well as longer chains.
Extrusion of Polymer Melts and Melt Flow Instabilities. II. Site of Initiation and Mechanism of Melt Flow Instability
Authors: Bialas Gene A. , White James L.
Published: February 2011

In the second part of this paper we will make a critical survey of experimental studies on the site of initiation, the structure of the unstable flow regime, criteria for the inception of the instability and mechanisms for initiation of the unstable flow regime. Some new experimental data will be cited in the discussion of criteria.
Performance of SBR and BR Tread Compounds as a Function of Carbon Black Dispersion, Surface Chemistry, and Structure
Authors: Scott C. E. , Chirico V.
Published: February 2011

A study has been made of the effect of carbon black dispersion, oxygen volatile, and extremes in chain structure development on vulcanizate properties and treadwear. The effect of poorly dispersed carbon black is to reduce wear resistance, tensile strength, strain energy, and groove cracking resistance. Other vulcanizate properties are not as noticeably affected. The role of oxygen functionality in reinforcement was investigated in a series of oxidation and devolatilization experiments. Added oxygen functionality of a critical amount reduces modulus, strain energy and treadwear resistance. Attempts to raise these properties through added acceleration results in greatly reduced treadwear. Carbon black-elastomer adhesion is indicated once again as the sine qua non of wear resistance. Carbon blacks possessing an unusually high level of reticulate chain structure require a lower level of chemical crosslinking than carbons of normal structure level for maximum treadwear resistance. This finding is consistent with a reinforcement theory involving stress dissipation by transfer to the carbon-elastomer interface, where relief occurs by slippage over the friction surface.
Studies on Dicumylperoxide Vulcanization of Natural Rubber in Presence of Sulfur and Accelerators
Authors: Manik S. P. , Banerjee S.
Published: February 2011

The effect of sulfur, MBT, zinc oxide and stearic acid, either singly or in mixtures, on the DCP vulcanization of NR has been studied. In all cases DCP decomposes by a first order law, but the rate constant is higher in presence of MBT. Sulfur and MBT, separately or together reduce the crosslink density, each mole of Sx or MBT destroying one mole of DCP. In mixes containing DCP together with sulfur, MBT, zinc oxide and stearic acid the crosslink density is initially additive. The mechanical properties and the aging characteristics of the vulcanizates have also been reported.
Studies on Blended Polymers. VIII. Blending of Carboxy SBR and Vinylpyridine SBR
Authors: Iino H. , Tsukasa M. , Nagafune T. , Sekaicho K. K. , Minoura Y.
Published: February 2011

Blends of carboxy-SBR and vinylpyridine-SBR, in which interactions were expected to occur between the two types of polymer molecules, were prepared by different blending methods and with different vulcanizing systems, and the variation of their properties with varying mixing ratio was studied. Latex blending was compared with blending on the mill. Investigations were carried out for each blend type with (1) a common curing agent for both polymers, (2) curing agents that affect only one of the polymers, and (3) a combination of curing agents, each of which affects one of the polymers. To examine the state of mixing, the blends were dyed and observed under the microscope. It was found that latex blending gave sufficiently good mixing to enable the interactions between the two polymers to influence the properties strongly, the blending being better than that achieved on the mill. However, when a combination of curing agents that affected the polymers singly was used, the effects of the interactions was no longer observed.
Rheological Behavior of Elastomers. I. Melt Viscosity Characteristics of Uncured Epichlorohydrin Rubber
Authors: Collins Edward A. , Oetzel John T.
Published: February 2011

The data presented indicates that: Mooney viscosity does not give an accurate indication of the viscosity or heat build-up for the polymers under the shear rates and temperatures experienced in factory operations. A new ane more reliable test is needed. The Brabender plasticorder as well as the Instron have the potential of filling this need. Hydrin 200, a 100 Mooney polymer, has a viscosity similar to Neoprene W and lower than or equal to Hycar 1052 under the conditions of shear and temperature found in usual elastomer processing operations. Hydrin 100, a 56 Mooney polymer, has a viscosity which is lower than either Hycar 1052 or Neoprene W. Both Hydrin 100 and Hydrin 200 exhibit lower heat build-up due to shear induced heating than either Hycar 1052 or Neoprene W. This lower shear heat build-up reduces the danger of scorching during processing. Basic rheological data has been presented for four elastomers: Hycar 1052, Hydrin 100, Hydrin 200 and Neoprene W. This data can be used to obtain a better understanding of the processing characteristics of elastomers.
The Viscosity of Carboxy-Terminated Polybutadienes
Authors: Kraus Gerard , Gruver J. T.
Published: February 2011

Newtonian viscosities have been determined for carboxy-terminated polybutadienes varying in microstructure, molecular weight and degree of carboxy-functionality. The latter was varied by total or partial methylation of initially di- or mono-functional polymers. The viscosity of non-functional (methylated) polybutadienes is shown to be proportional to the 3.4 power of the weight average chain length, irrespective of microstructure, provided the comparison is made at equal (T−Tg). The temperature dependence of viscosity is well represented by the Vogel equation, with constants given by Berry and Fox for polybutadiene of 8% vinyl unsaturation, again independent of microstructure. The presence of carboxy end groups increases the viscosity as a result of an association equilibrium with raises the effective molecular weight of the polymer. The absolute magnitude of the temperature coefficient of viscosity increases with carboxy-functionality, as required by the postulated association equilibrium. Theoretical calculations show that the viscosities of mono-carboxy polybutadiene and α,ω-dicarboxypolybutadiene cannot be reconciled unless some of the carboxy-associations in the latter are intramolecular. In the molecular weight range considered the glass temperature is substantially independent of carboxy-functionality.
Some Aspects of the Relationship between Molecular Structure and Flow Behavior of Polymer Melts
Authors: Blyler L. L.
Published: February 2011

The shear dependent viscosity and related properties of a number of ethylene polymers of differing molecular structure have been characterized using a capillary extrusion rheometer. The structural aspects of interest were average molecular weight, branching, and the presence of strong intermolecular secondary forces. It was found that average molecular weight influences the degree of shear dependence of the viscosity, branching affects both flow activation energy and the nature of the observed “melt fracture” phenomenon, and intermolecular hydrogen bonding enhances viscosity and activation energy and leads to increased shear dependence of flow behavior. The results are interpreted in terms of specific molecular mechanisms.
Thermoelastic Behavior of Natural Rubber
Authors: Shen Mitchel C. , McQuarrie Donald A. , Jackson Julius L.
Published: February 2011

Stress—temperature measurements of natural rubber were carried out up to the elongation ratio, α, of 2.0. An automatic stress relaxometer was constructed for this purpose which can be completely enclosed in a controlled environment. Experiments were so conducted as to minimnze possible chemical effects and nonequilibrium conditions. Relative internal energy contribution to stress, fe/f, is calculated as a function of α in terms of statistical and thermodynamic theories. Both of these yield similar results. It is shown that in the region of low strains (1.0<α<1.5),fe/f decreases rapidly with increasing α, but appears to remain constant at 1.5<α<2.0. This observation is not in agreement with the prediction of the current statistical theory of rubber elasticity, which stipulates that the energy effects are intramolecular and independent of deformation. Implications of these findings are discussed. It is suggested that perhaps at low strains the intermolecular interactions are large in comparison with intramolecular energies, but become relatively insignificant at higher elongation ratios. The temperature coefficient of unperturbed chain dimensions is also calculated from thermoelastic data. It is constant only in the region 1.5<α<2.0. Finally, a new, more exact derivation of the Elliott—Lippmann anisotropy factor in terms of the statistical theory is given in the Appendix.
Evidence for Chemical Interaction in Carbon and Polymer Associations. Butyl and Acidic Oxy Blacks. The Possible Role of Carboxylic Acid Groups on the Black
Authors: Gessler A. M.
Published: February 2011

Assuming that the enhanced reinforcement capacity of oxidized black in butyl is related specifically to acidity provided by carboxyl groups on the surface of the black, the black was neutralized by esterification and saponification, respectively. The reduced carbon-polymer bonding activity resulting from these neutralizations is discussed in the light of the cationic interaction mechanism which it is proposed is involved.
Thermal Analysis of Butadiene Styrene Block Copolymers
Authors: Anderson J. N. , Weissert F. C. , Hunter C. J.
Published: February 2011

The Gordon—Taylor—Wood relationship between composition and glass temperature has been used as the basis of a DTA method for block styrene analysis in butadiene styrene copolymers having the same microstructure and a similar compositional distribution. The determined K value of the Gordon—Taylor—Wood equation for these polymers prepared with a butyllithium catalyst is in fair agreement with values previously determined for emulsion butadiene styrene copolymers. The total styrene content of the copolymer was determined using the refractive index method, and the composition of the “non-block” segment of the copolymer was obtained from DTA measurement using a Tg as a function of composition graph The amount of block styrene can then be obtained by difference. Evidence is presented supporting the validity of the method, and the results are compared with those obtained by a chemical method which involved polymer degradation by a hydroperoxide in the presence of osmium tetroxide. The thermal analysis requires approximately one-half hour. All measurements are made on the dry polymer eliminating the necessity of redissolving the polymer as required by most other methods of analysis.
A New Improved Tirecord Fatigue Tester
Authors: Forster M. J. , Prettyman I. B.
Published: February 2011

Based on the illustrations presented, it is suggested that the SCEF fatigue tester has given realistic results, consistent with general principles established in tire dynamics analysis and performance. It has done this with a simple test specimen, yet one which locates the test cord in an environment similar to that found in service. Testing results have been reproducible and obtained in a reasonable time. It is felt that it will make a unique and meaningful contribution to the laboratory evaluation of fatigue performance characteristics of a tirecord.
A Peroxide Curing Butyl Rubber
Authors: Oxley C. E. , Wilson G. J.
Published: February 2011

The reactions of peroxides with polymers have been studied for some time. They form an extensive part of vulcanization technology. Two types of reactions are generally recognized, those leading to crosslinking between polymer chains and those leading to scission of the chains. Natural rubber, polybutadiene and ethylene-propylene rubber are examples of polymers in which crosslinking reactions take place to a greater extent than reactions leading to chain scission and these polymer reactions with peroxides form a useful method of vulcanization. On the other hand, polyisobutene is an example of a polymer which degrades extensively and for polyisobutene and butyl rubber, peroxides have not found use as cross-linking agents.
The Correlation between Entanglement and Chemical Crosslinks in EPDM Vulcanizates
Authors: Baldwin F. P. , Borzel P. , Makowski H. S.
Published: February 2011

Using peroxide cured specimens prepared from a selected EPDM terpolymer containing olefinic residues derived from ethylidene norbornene, and Young's modulus measurements taken in compression on n-heptanc swollen vulcanizates, a correlation between the apparent total, effective network chain density and the chemical network chain density has been derived. The type of correlation equation used may be generally useful.
The Engineering of Polymers for Mechanical Behavior
Authors: Kelley F. N. , Williams M. L.
Published: February 2011

The broad subject matter in this paper is treated in only cursory fashion. Our intent was to present an approach to the systematic analysis of the relationships between engineering properties and molecular variables for viscoelastic materials. Literature omissions will undoubtedly be numerous, but the basic concept of the Interaction Matrix allows for continual upgrading and refinement. The examples chosen were based on the stress relaxation modulus which provided an ideal starting point due to the wide use of this property in viscoelastic stress analysis and fracture mechanics. Other important engineering parameters which might be selected for similar examination include bulk compressibility and dilation for example; and, of course, the rupture properties under various imposed stress fields.
Transfer of Labeled Hydrogen between Elastomers and Carbon Black
Authors: Papireb E. , Voet A. , Given P. H.
Published: February 2011

Radioactive hydrogen exchange was studied between tritium labeled carbon blacks and elastomers as well as between tritium labeled elastomers and carbon blacks, after solvent mixing and after milling. A substantial exchange was observed upon solvent mixing of an unsaturated elastomer (SBR) and a reinforcing black (HAF), with commercial blacks as well as in carbon black samples from which surface oxide groups were removed by calcination. Milling did not significantly increase the hydrogen exchange. Nonreinforcing blacks did not show any exchange. Saturated elastomers, such as butyl rubber, which bond predominantly to the carbon black particles by means of surface oxide complexes, did not show any significant hydrogen exchange, not even with channel blacks. The phenomena could be adequately explained by assuming as the material basis of reinforcement of unsaturated elastomers a process of chemisorption through abstraction of reactive hydrogen from the elastomer to a reactive site on the carbon black surface, followed by a chemical reaction of the resulting elastomer free radical chain with another reactive carbon black site. Thus, active sites on the carbon black surface and reacting hydrogen in the unsaturated elastomer are the determining factors in reinforcement.
Low-Frequency Losses in Rubbers Cross-Linked in the Presence of Diluent
Authors: Langley N. R. , Dickie R. A. , Wong Chiu-ping , Ferry J. D. , Chasset R. , Thirion P.
Published: February 2011

Measurements of the complex shear compliance have been made from 0.1 to 7 cycles/sec and from − 5° to 45° C on several samples of natural rubber cross-linked by dicumyl peroxide in the presence of a diluent oil (volume fraction of rubber, v2=0.63 and 0.76) which was subsequently extracted. The properties of the extracted vulcanizates were compared with those having the oil still present and with those of conventional undiluted vulcanizates. Measurements of the diffusion coefficient of radioactively tagged n-hexadecane in trace amounts through the polymer structure were also made both before and after extraction of the oil. The diffusion coefficient was higher in the presence of the oil by an amount consistent with the Fujita theory for concentration dependence of diffusion rate based on free volume considerations. The low-frequency mechanical losses (reduced to 25° C by the method of reduced variables), as measured by the loss tangent, were shifted to higher frequencies by the presence of oil to a much larger degree than would be expected from the difference in local mobility gauged by the diffusion coefficient. The equilibrium modulus, derived by extrapolation to zero frequency, was diminished by the presence of oil to a greater extent than the factor of v21/3 expected from the simple theory of rubberlike elasticity. The low-frequency losses in the extracted vulcanizates were smaller than those in conventional vulcanizates with comparable degrees of cross-linking; the differences are attributed to differences in network topology.
Effect of Oil and Black on the Injection Molding of EPDM Compounds, II, Molding Studies
Authors: DePierri W. G.
Published: February 2011

The results which we discussed in this paper show that the demands made on the compound in an injection molding operation are more severe than those made by compression molding. The flow properties of the compound are much more critical in injection molding because of the high flow rates which are encountered. Compounds must have viscosities which are low enough to allow the mold to fill completely in the injection step. The level of oil and black in the compound are very important factors in controlling compound viscosity. The cure system is more critical, for it must give good physical properties at the elevated temperatures used in injection molding. The ability to attain good physical properties at low cure temperatures does not necessarily mean that good properties will be achieved at elevated cure temperatures as was shown by the comparison of physical properties of specimens prepared by high temperature injection and low temperature compression molding. The physical properties of injection molded specimens made from some compounds cured at high temperatures indicated a lower state of cure at optimum cure than compression molded specimens cured at lower temperature. Much of this effect can be explained by changes in state of cure caused by the increased temperature. The oil type used in the compound did not appear to be especially important in determining the physical properties of molded items. Oil level, however, is an important factor in determining both the processability of a compound and the physical properties of the finished product. Some of the problems associated with injection molding of EPDM compounds encountered in this work may result from the experimental injection molding equipment used in the study and may not be evident when commercial equipment is employed. Other of the problems could be solved by compounding, especially by changes in the cure system.
Analysis of Tire Tread Rubbers by Gas Chromatography
Authors: Ney E. A. , Heath A. B.
Published: February 2011

A method is presented which allows the simultaneous quantitative determination of natural rubber, polybutadiene and SBR in tire components. The method consists in pyrolyzing samples of cured and filled ternary rubber mixtures at 450°–550° C and subjecting the decomposition products to programmed gas chromatography. The quantities of dipentene, vinyl cyclohexene, and styrene formed during pyrolysis are then used to determine the percentage ratio of natural rubber, polybutadiene and SBR in the vulcanizate.
Skeletal Deformation Vibrations and Rotational Isomerism of Methylbutenes and Methylpentenes as Model Compounds of 1,4-Polyisoprene
Authors: Shimanouchi T. , Abe Y.
Published: February 2011

Infrared spectra of methylbutene and methylpentenes in the skeletal deformation region have been measured. The force constants for the skeletal deformation vibrations are determined from the frequencies of isobutylene, isobutylene-d6, and methylbutenes. The frequencies of methylpentenes are calculated for the various conformations, and the stable rotational isomere determined. The energy differences between the isomers are determined from the temperature dependence of the spectra. These results are correlated with the conformations of cis- and trans-1,4-polyisoprene chains, and possible conformations are suggested.
The Effect of Crosslink Structure on the Tensile Strength and Oxygen Absorption Characteristics of Natural Rubber Vulcanizates
Authors: Lal J.
Published: February 2011

The chemical nature of crosslinks in natural rubber—sulfur—diphenylguanidine vulcanizates was modified by reaction with triphenylphosphine under nitrogen to determine the effect of this change on tensile strength and oxygen absorption characteristics of the vulcanizates. The vulcanizates were characterized by organically combined sulfur and polysulfidic sulfur. Polysulfidic crosslinks, i.e., crosslinks containing three or more sulfur atoms in the crosslink, were found not to be essential for the attainment of high tensile strength in these vulcanizates. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted the tensile strength versus 300% modulus curve for the control samples. Vulcanizates which had been reacted with triphenylphosphine for 16 days at 80° C, had lost 95–99.6% of their polysulfidic sulfur. These triphenylphosphine-reacted vulcanizates exhibited significantly lower rates of oxygen absorption at 100° C as compared to the untreated vulcanizates. This suggests that polysulfidic structures in the original vulcanizates act as oxidation initiators.
Rapid Stress-Induced Crystallization in Natural Rubber
Authors: Mitchell J. C. , Meier D. J.
Published: February 2011

Stress-induced crystallization in a rapidly stretched natural rubber gum vulcanizate has been studied using thermal techniques to follow the development of crystallinity. A special-purpose analog computer has been assembled and used online to process the thermal and mechanical data obtained in high speed tensile testing. Roughly first-order room temperature crystallization kinetics curves were obtained having time constants of 50–60 msec in the range of 400–540% extension. While the rate of this rapid, presumably primary crystallization appears rather insensitive to elongation in this limited range, the extent of crystallization at 400 msec increases smoothly from zero at 340% elongation to around 18% at 540% elongation. It is shown that our high-speed tensile tester can stretch this vulcanizate fast enough that most of the crystallization takes place after extension has been completed. Stress—strain curves obtained at this high rate are compared with those obtained at lower rates where crystallization takes place during the stretching.
Friction and Frictional Rise of Wedge Sliders on Rubber
Authors: Schallamach A.
Published: February 2011

The friction of wedge sliders on rubber depends surprisingly little on the angle between their leading faces and the rubber surface. Friction remains moderate even when this angle is 90°. A simple theory is put forward which accounts qualitatively for the observed limitation of the frictional force and which also predicts an experimentally verified lift of the sliders. In agreement with these findings, a photoelastic investigation of the stress distribution around the sliders reveals that no ramming pressure precedes them in the rubber. The absence of a ramming pressure is attributed to a forward tilt of the rubber which originates from the couple of the frictional force with respect to the undeformed rubber underneath.
Research for a Uniform Quality Grading System for Tires
Authors: Brenner F. C.
Published: February 2011

The National Traffic and Motor Vehicle Safety Act of 1966 requires the establishment of a uniform quality grading system. This paper discusses the needs for the system and the complexity of the problem. The system proposed here will depend on five properties; tread wear, traction, impact resistance, endurance, and wheel speed capability.
Mastication of Elastomers II. Cold Mastication of Natural Rubber
Authors: Bristow G. M.
Published: February 2011

The cold mastication of natural rubber in oxygen is shown to proceed rather more rapidly than that in air. Reasons for this difference are considered. Mastication under these conditions is considered as a low temperature oxidative process and consistent with this the subsequent reactions of RO2 radicals produced by mechanical shear are shown to lead to some additional chain scission. The thermal oxidation of rubber masticated in oxygen is rather more rapid than that of rubber masticated in nitrogen in the presence of a radical acceptor.
Effect of Carbon Black Dispersion on the Mechanical Properties of Rubber Vulcanizates
Authors: Boonstra B. B. , Medalia A. I.
Published: February 2011

A study has been made of the mechanics of mixing of carbon black in rubber by determining the influence of agglomerates in the mix on the final properties of the vulcanizate. It is suggested that the mixing starts with the forming of soft agglomerates which contain polymer and black in about the proportion of the void ratio aa determined by oil absorption. In subsequent stages these agglomerates are torn apart— to smaller and smaller sizes and finally dispersed. When the agglomerates that are first formed in the mix are left intact as is the case in a very short mixing cycle, a noticeable deteriorating effect is found on the mechanical properties relating to rupture (tensile, abrasion). On the other hand, viscosities and moduli for short mixing cycles can be higher by a factor of 2 or more than the final viscosity and modulus after all the black is apparently well dispersed. This has been shown both experimentally and theoretically. Hard particles have also been added intentionally to assess the effect of their size, frequency and chemical nature. It appears that hard particles in an amount of 10–20% of the total black become very harmful at an average diameter of about 1 µ. At the 0.5 µ size, particles of medium thermal black are almost without influence on service properties of the vulcanizate such as tensile and tear strength, abrasion resistance, etc. Above the critical size, the size of the particle has little influence on the reduction in mechanical properties. This reduction is determined by the amount (by weight) of the coarse particles present. The effect of these hard particles on tensile and abrasion is much greater than that of the soft agglomerates formed in short mixing cycles.
Theory for the Meridian Section of Inflated Cord Tires
Authors: Day R. B. , Gehman S. D.
Published: February 2011

The general equation for the equilibrium shape of an ideally thin, flexible, inflated, undeflected cord tire is derived from the equilibrium conditions for an individual cord. Various special cases are discussed and equations are derived for the cord tension, bead tension, and shearing stress between plies.
Adsorption Modification of Fillers and Structure Formation in Solutions of Polymers
Authors: Taubman A. B. , Tolstaya S. N. , Borodina V. N. , Mikhaĭlova S. S.
Published: February 2011

On addition of a solid disperse phase to a polymer one requisite for its effectiveness as an active filler is close similarity of the molecular properties of the surface of the particles and the polymer. This along with high “dispersity” (specific surface area) is mainly responsible for the high effectiveness of various types of carbon black—a hydrophobic filler of organic origin. For the same reason the majority of mineral fillers, which are usually of hydrophilic character, have relatively low capacity for the active filling of polymers, which is made evident in improvement in the mechanical and other properties of the filled material. As a consequence particular importance attaches to processes of adsorption modification, i.e., the alteration of the molecular properties of the surface of particles of hydrophilic fillers by orientated adsorption of surface-active substances (SAS). The hydrophobicization of the surface of the particles of filler which takes place here increases their “wettability” by the polymer phase and enhances the strength of its bond to the polymer, as has been investigated in detail in the work of P. A. Rebinder et al.. In this case modification leads to activation of the filler; in a number of cases however activation does not take place. As models for filled systems we may take concentrated suspensions of particles of the fillers in solutions of polymers containing additions of surface-active substances, which depending upon the concentration in the solution and proportionally to its increase, at first peptize the particles, lyophilizing them, and then stabilize them as a result of lyophobicization. This causes in sequence coagulation structure-formation in the system and then destruction of the resulting structures. A number of investigations have been devoted to the influence of fillers and pigments on the properties of polymers in the presence of surface active substances —in rubbers, and in lacquers and paints based on drying oils, but the laws of adsorption modification of mineral disperse phases and its influence on the filling effect in connection with the composition and molecular properties of the complex system: polymer-solvent/filler (or pigment)/surface-active substance have not been systematically studied. The present paper aims to investigate this question.
Reinforcement of Rubber in Latex. III. Electron Microscope Investigation
Authors: Pechkovskaya K. A. , Senatorskaya L. G. , Berman B. Z. , Dogadkin B. A.
Published: February 2011

Electron-microscope photographs show that with the addition to the latex of substances bringing about the effect of reinforcement of the rubber by fillers, there is observed a coalescence of the globules with the formation of a continuous rubber phase, as a result of which direct contact of the rubber is brought about with the particles of filler. This confirms the conceptions previously developed1 of the conditions of reinforcement of rubber in latex.
Use of White Pigments in the Rubber Industry
Authors: Vohwinkel K.
Published: February 2011

Anatase is recommended for all pure-white rubber products, on which no particular demands are made with respect to chalking and yellowing. For pure-white compounds with less chalking tendency, either post-treated anatase or zinc sulfide is useful. (These statements are based upon the studies made on the white pigments given in Table 6). White, pale creamy tints, with especially high resistance to chalking and yellowing, and very good resistance to static cracking, may be obtained with post-treated rutile. These rutile types are also recommended for the whitening in color adjustments, when blue tints are undesirable. Untreated rutile (Bayer titanium dioxide Rutile U was tested) is very well suited for increasing the heat stability of silicone rubber vulcanizates. Lithopone is well adapted for whitening cheap compounds. It must be mentioned that anatase, because of its bluish tint, is especially popular in the rubber industry and is at this time more widely used than the post-treated rutile types.
Vulcanization of Elastomers. 38. the Reactivity of Synthetic Rubbers. I
Authors: Scheele W. , Schulze W. , Hillmer K-H.
Published: February 2011

Investigations relating to the development of other than conventional procedures for vulcanizing synthetic rubbers, especially cis-1,4-polybutadiene, are reported. The results were as follows: 1. cis-Polybutadiene and trans-polybutadiene containing 2% and more of 1,2 addition can be crosslinked to a certain extent by means of dibenzothiazolyl- or dibenzimidazolyldisulfide. 2. cis-1,4-Polyisoprene undergoes a much lower degree of crosslinking with the above disulfides. 3. The physical properties of vulcanizates are considerably improved if the molecules of the added disulfides contain groups which react with isocyanates. When diisocyanates are incorporated, supplementary crosslinking sites are formed. 4. The crosslinking of cis- and trans-polybutadiene via DBIS and Desmodur 15, in the absence and presence of black is described in more detail. The usual physical properties are determined and compared with those obtained when sulfur is used as the vulcanizing agent.
Effect of Sulfur during Radiation Curing of Poly(Vinyl Ethyl Ether) and Ethylene-Propylene Rubber
Authors: Lal Joginder , McGrath James E.
Published: February 2011

A study was made of the effect of sulfur, during radiation curing, on the physical properties of poly(vinyl ethyl ether) and an ethylene/propylene copolymer containing HAF carbon black. The presence of sulfur enabled the attainment of higher maximum tensile strength and generally higher crosslink density than when sulfur was omitted. Furthermore, the maximum tensile strength of the sulfur-containing samples was obtained at a lower radiation dose than in the corresponding control experiments. For a given swelling ratio, a higher tensile strength was generally obtained for samples irradiated in the presence of sulfur. For a given dose of radiation, the per cent elongation-at-break values of poly(vinyl ethyl ether) samples decreased as the amount of sulfur in the recipe was increased. In contrast, in the ethylene/propylene rubber the presence of sulfur resulted in an increase in the elongation values. The per cent sol values were also quite high for the ethylene/propylene vulcanizates as compared to the corresponding values in poly(vinyl ethyl ether) samples. In both rubbers, lower sol values were obtained in the presence of sulfur. Chemically bound sulfur was found in poly(vinyl ethyl ether) samples irradiated in the presence of elemental sulfur or dicyclopentamethylene thiuram tetrasulfide. The ability of the network to lose a portion of the combined sulfur by reaction with triphenyl phosphine may indicate that some of the crosslinks contain disulfide and/or polysulfide groups.
Aldehyde-Amine Accelerators. The Structure of Some Substituted Dihydropyridines
Authors: Westfahl J. C. , Craig David
Published: February 2011

This paper reports unequivocally the structures of the main components in “butyraldehyde-aniline” and “heptaldehyde-aniline” which are commercial vulcanization accelerators and “propionaldehyde-aniline” which is not commercial. All three components are dihydropyridines.
New Elastomers Derived from Copolymers of Tetrahydrofuran and Propylene Oxide
Authors: Dickinson L. A.
Published: February 2011

The homopolymers of tetrahydrofuran, polytetramethylene glycols, may be chain-extended to form polyurethane elastomers. These materials, while possessing a low glass point temperature, suffer from cold hardening, and it was decided to investigate copolymers of tetrahydrofuran and propylene oxide as elastomer ingredients. The preparation of these copolymers has been achieved by use of a boron trifluoride etherate polymerization catalyst. Details are given of the properties of both the copolymer and derived elastomers at nominal compositions in the range 50–85 weight per cent of tetrahydrofuran. The copolymers described were synthesized as ingredients for castable elastomers, and in consequence viscosity effects are important. It has been found that no significant increase in viscosity occurs until the tetrahydrofuran content exceeds 75 weight per cent. This indicates that each side methyl group exerts a screening effect over an average of 13 atoms of the polymer backbones. The mechanical testing of the derived elastomers indicates that the copolymerization of tetrahydrofuran and propylene oxide leads to material possessing a low glass point temperature and much better physical properties than the homopolymer of propylene oxide. The elastic properties of a chain-extended diol are dependent on the degree of crosslinking and on the incidence of network deficiencies. Network deficiencies are caused by the presence of monofunctional species in the copolymeric diols, and a novel technique for determining diol monofunctionality based on analysis of physical test data was evolved for these studies.
Relative Contributions of Viscoelasticity and Aging to the Relaxation of Rubber Vulcanizates
Authors: Thirion P. , Chasset R.
Published: February 2011

Relaxation in relatively stable, gum natural rubber vulcanizates has been studied to determine the effects of viscoelasticity and aging, respectively, using a dark, air-oven. A quantitative analysis of experimental results shows that, in the case of a dicumyl peroxide vulcanizate at 100° C, relaxation is caused by aging, except in its initial stages. Stress decreases as a linear function of time, in agreement with theoretical assumptions. Conversely, at 30° C, the effect of aging is negligible. At this temperature the difference between actual stress and stress extrapolated to infinite time, is proportional to a negative power of time. At intermediate temperatures, both phenomena occur simultaneously over a time interval ranging from. 3 minutes to 150 hours.
Law of Deformation of Cured Rubber
Authors: Bartenev G. M. , Vishnitskaya L. A.
Published: February 2011

Consideration is made in this article of the uniaxial stress and compression deformation of vulcanized rubber, for which there exists a sufficient amount of accurate experimental data. One of the present authors established a considerable while back that for lattice polymers (vulcanized rubbers) in the coordinates σ (true stress) and ε (deformation) , the equilibrium curves for stress in the range 100 to 200% are expressed by practically straight lines. Furthermore, this behavior was confirmed in a number of our investigations based on more accurate methods of measurement (cf. Reference 2), and also in a number of foreign papers. (Note 1. The stress is regarded in relation to the actual cross-section of the specimen of deformed rubber, the deformation in relation to the initial length of the specimen. Note 2. For comparison of single-parameter formulas with experience the experimental data are presented each time in coordinates such that a straight line corresponded to the formula in these coordinates. For these coordinates we selected the stress σ and the “generalized coordinate” of deformation ε0, which is a different function of the multiple of stress A in the various single-parameter equations.) Within the limits of scatter of the experimental data the equilibrium curves for uniaxial deformation below the limit of proportionality (100–200% with stress and 20–30% for compression) are expressed by the following single-parameter law: