bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relation between Glass Transition Temperature and Composition of Ethylene Propylene Copolymers
Authors: Maurer J. J. 
Published: February 2011

Abstract
Vulcanizate properties and processability of ethylene propylene copolymers (EPR) are known to be sensitive to variations in polymer microstructure. A basic understanding of the practical performance of EPR requires a knowledge of this microstructure and means for evaluating it. This study was concerned with determining the utility of a previously proposed method for quantitative analysis of microstructure in EPR. The influence of crystallinity effects on the glass transition temperature (Tg) of this polymer was also examined. A major objective of this work was to determine whether, as suggested by literature data, a minimum can exist in the relation between Tg and composition of EPR. If so, it would seriously impair the proposed method for quantitative microstructure analysis. Data relating Tg and composition were obtained by differential thermal analysis (DTA) and infrared analysis (IR) of EPR fractions obtained by gradient elution fractionation. An apparent minimum was observed in the curve defined by this data. Analysis of this minimum suggests that it is due to nonrandom microstructure. In the samples examined, it was evident in the 25 to 40 mole per cent propylene range. Low temperature annealing studies indicate that the minimum is not from crystallinity although there is some indication that small amounts of crystallinity can be induced in these systems by annealing. Analysis of the main Tg interval in a variety of EPR samples showed that three types can be distinguished. These appear to correspond to random, stereoblock, and random-block polymers. Further, a main Tg near −58° C. was observed over the 20 to 74 mole per cent propylene range in some nonrandom systems. Because of this, it is concluded that the proposed system for quantitative microstructure analysis in EPR is generally inapplicable to nonrandom systems. However, the data indicate that useful information about EPR microstructure can be obtained by the techniques described.
Viscoelastic Properties of SBR Containing Particles of Crosslinked Polystyrene
Authors: Nakajima N. , Collins E. A. 
Published: February 2011

Abstract
It has been shown that methods are available for fundamental characterization of viscoelastic behavior of elastomers containing crosslinked particles. With the Rheometrics mechanical spectrometer and the Mooney rheometer operated at slow speeds, the elastic modulus and loss modulus were obtained at 100°C in the frequency range of 2.5×10−4−2.5×102 rad·s−1. In this frequency range, both the rubbery response of the SBR matrix and the response of polystyrene copolymer particles were observed. The former was in the higher frequencies and the latter in the lower frequencies, with a considerable overlap of both responses. From the magnitude of the temperature-time shift, it was learned that the deformations of both SBR matrix and polystyrene copolymer particles were involved. The steady-shear viscosities were measured with the Instron capillary rheometer. At extrusion temperatures of 85 and 100°C, the extrudates were distorted at the high shear rates. Calculations show that the polystyrene copolymer phase attains the glassy state, because pressure and frequency raise the glass transition from 51°C to the extrusion temperature.
Effect of Carbon Black Particle Size Distribution on Electrical Conductivity
Authors: Sircar A. K. , Lamond T. G. 
Published: February 2011

Abstract
Wide particle size distribution (PSD) of carbon black increases electrical conductivity, consistent with the industrial practice of manufacturing conductive grades. An explanation has been offered based on the lower linear average diameter of wider-distribution blacks. Consequently, for the same weight, there is a larger number of particles in the broad-PSD black. The resulting agglomerates are therefore more numerous, although somewhat reduced in dimension because of higher packing density. The larger number of agglomerates results in lower average gap width, which accounts for the increased electrical conductivity.
Die Swell and Normal Stresses: An Explanation
Authors: Vlachopoulos J. 
Published: February 2011

Abstract
Newtonian fluids show a small increase (about 10%) in cross-section diameter on emerging from a capillary at low Reynolds numbers (Re≪1). Highly viscous elastic fluids, such as polymer melts, exhibit a far greater increase, sometimes between 200 and 300%. This phenomenon is often referred to as “Barus effect” or “die swell” and is usually described quantitatively in terms of the swelling ratio (d/D), which is the ratio of extrudate diameter to capillary die diameter. The swelling of polymer extrudates is generally attributed to normal stresses which are released when the extrudate emerges from a capillary die. The exact mechanism of this swelling process is far from being fully understood, even for the simpler case of Newtonian fluids. Because so many plastics processes involve extrusion through dies, prediction and control of die swell are of great technological importance. Several expressions have been proposed for the prediction of die swell, centered on the concept of the elastic recovery of the swelling process. These expressions relate the swelling ratio (d/D) to the recoverable shear (σ), which is defined as half the ratio of first normal stress difference to shear stress. The papers of Nakajima, Graessley, and Bagley discuss the solidlike response of the extrudate on emerging from the die. They apply the concepts of rubber elasticity to predict a swelling ratio (d/D) asymptotically proportional, for large values of swelling, to the square root of the recoverable shear. Tanner's expression is based on the elastic recovery of a “BKZ” fluid and predicts a swelling ratio asymptotically proportional to the cube root of the recoverable shear. Experimental evaluations of the above expressions have been carried out by a number of investigators. However, no definite conclusions can be drawn because of the highly questionable determination of normal stresses at the shear rates involved in die swell (10−103s−1). Despite the many investigations on die swell, there is very little known of how the polymer structure influences the swelling ratio. The existing expressions for predicting die swell can incorporate the polymer structure effects through the definition of shear modulus, which is related by Hooke's law to the recoverable shear. The shear modulus, however, is unambiguously defined only at small deformations. Consequently, for the large deformations involved in die swell, a new theory is definitely needed. In this paper a new expression for die swell is developed based on non-Gaussian chain statistics as applied to a molecular network.
The Oxidative Aging of a Compounded Natural Rubber Vulcanizate
Authors: Pett R. A. , Tabar R. J. 
Published: February 2011

Abstract
For the type of natural rubber compound used in the impact absorbing bumper system, it has been shown that an apparent zero order reaction rate is valid for the degradation of tensile strength, elongation at break and tear strength during oven aging. The zero order rate applies to aging times beyond an induction period and prior to the onset of hardening. Since the rates follow the Arrhenius equation for rate-temperature dependence, accelerated aging can be readily applied to the prediction of long term changes in properties (within the temperature range of 82–171°C). The magnitude of the activation energy determined from losses in mechanical properties indicates the dominance of oxidative degradation as the mechanism of the losses in properties.
Use of ESR to Investigate Formation of Free Radicals on Compounding Rubbers with Carbon Blacks
Authors: Jamroz˙ M. , Kozłowski K. , Sieniakowski M. , Jachym B. 
Published: February 2011

Abstract
The problem of rubber reinforcement is of great importance in rubber technology. Free radicals formed during mastication play an important role in the reinforcement of the rubber-filler system. The reinforcement of rubber systems is usually explained in terms of chemical interactions between rubber and filler; however, there are also opinions that the interactions are physical in nature. So far, the mechanism of reinforcement is an open question. Undoubtedly, reinforcement is influenced by free radicals formed during mastication and the physicochemical state of the surface of active fillers. The formation of free radicals during plasticization of rubbers has been already reported. Investigations by an ESR technique of free-radical formation during compounding of rubbers with various carbon blacks are described in the present paper.
Influence of Carbon Black Surface Properties and Morphology on Hysteresis of Rubber Vulcanizates
Authors: Medalia A. I. , Laube S. G. 
Published: February 2011

Abstract
A linear relation is found between tan δ and a loading-interfacial-area parameter, ϕψ, for NR vulcanisates with six untreated carbon blacks at several loadings. In IIR, a better linear relation is found between tan δ and a modified parameter ( ϕ1.5ψ0.5), indicating that the dependence on loading is relatively stronger than on interfacial area. In both polymers, a graphitized black gives high tan δ and an oxidized black gives low tan δ (at the appropriate value of the loading-interfacial-area parameter). The data suggest a slight effect of aggregate morphology, in that carbon blacks of more compact, less open aggregate structure tend to give lower tan δ; however, the results are on the borderline of experimental error. The value of tan δ at high amplitude is a linear function of ΔE′, where ΔE′ is the difference between the elastic modulus at low and high amplitudes. This indicates that tan δ depends on the number and strength of interaggregate interactions, as proposed by Payne. Reduced rubber-black interaction, as with the graphitized black, gives more interaggregate interaction, leading to higher ΔE′ and tan δ; and conversely with the oxidized black. With the graphitized black in IIR, tan δ is even higher than expected from the value of ΔE′; thus it appears that in the virtual absence of polymer-filler interaction, molecular slippage may make an additional contribution to hysteresis.
Young's Modulus and Dynamic Mechanical Properties of San Resins Modified with Ethylene-Propylene Rubber
Authors: Brancaccio A. , Gargani L. , Giuliani G. P. 
Published: February 2011

Abstract
The dependence of Young's modulus and dynamic mechanical properties of a new high impact resin, ATS (acrylonitrile-styrene copolymer polymerized in the presence of ethylene-propylene-triene terpolymer), on the composition and morphology of the dispersed phase is examined and compared to that of ABS resins (acrylonitrile-styrene copolymer polymerized in presence of polybutadiene). The relationship between modulus and composition is different for the two resins because of the different morphology of the rubbery phases. The experimental results are compared to the predictions of several mathematical models. This analysis is extended to the dynamic moduli E′ and E″, measured over a wide range of temperatures covering the main transition of the rubbery phases.
Interpretation of Deviations from NEO-Hookean Elasticity by a Two-Network Model with Crosslinks and Trapped Entanglements
Authors: Ferry John D. , Kan Hsin-Chia 
Published: February 2011

Abstract
Deviations from neo-Hookean elasticity in crosslinked rubbers, as measured by the ratio ψ=C2/(C1+C2) where C1 and C2 are the Mooney-Rivlin coefficients, have been found to be represented by a single function of fN, which is the ratio of network strands terminated by trapped entanglements to the total number of strands terminated by either trapped entanglements or crosslinks. It is assumed that the structure can be represented by a two-network model in which the crosslink network is neo-Hookean and the network of trapped entanglements is Mooney-Rivlin. The ratio fN is calculated from literature data for C1 and C2 and entanglement spacing derived from data on the uncrosslinked rubbers together with the Langley theory for the probability of entanglement trapping. Results are obtained for five polymers with different entanglement spacings over considerable ranges of degree of crosslinking and molecular weight before crosslinking, both of which influence the extent of entanglement trapping. The calculation is also applied to poly (dimethylsiloxane) networks crosslinked in the presence of diluent. The results show why, in various different investigations, C2 has been observed to increase, decrease, or remain approximately constant with increasing C1 or degree of crosslinking.
Structure and Properties of Microcomposites and Macrocomposites from Block Polymers
Authors: Aggarwal S. L. , Livigni R. A. 
Published: February 2011

Abstract
The incorporation of a rubber phase in glassy polymers, as is well known in the case of high impact polystyrene, leads to an increase in their impact strength. Block polymers offer three principal approaches for obtaining multiphase glassy polymers in which an elastomer phase is present in the matrix of the glassy polymer. They are: (1) control of block polymer composition, (2) blending of block polymer with homopolymers, and (3) polymerization of a solution of a block polymer in the monomer corresponding to one of the blocks. The observed properties, such as impact strength, modulus, and heat distortion temperature, desired in rubber-modified glassy polymers are discussed for block polymer systems prepared using the above approaches.
Work Input Control of Production Batch Mixing
Authors: O'Connor G. E. , Putman J. B. 
Published: February 2011

Abstract
Mixing control has been discussed in terms of equipment, rotor speed, compound uniformity, and mixing efficiency. It is desirable to have a minimum number of control parameters to describe the effect of mixing on equipment and material properties. This paper has specifically compared work input to time-temperature control specification. The first criterion was that work input give a prediction of Mooney viscosity fter mixing. The results of mixing on two different size Banburys verified that work input per kilogram of rubber is independent of mixer size. Further, mixing at different speeds, but to the same work input level, does not affect the Mooney viscosity of the final mix. Work input, therefore, appears to be a practical measure of mixing and is independent of mixer sizes and mixing speeds. Representative production mixing was carried out using both time-temperature and work input controls. Significant improvements in Mooney viscosity and scorch, oscillating disk rheometer and die swell uniformity result from work input control. The degree of improvement varies, however, and is dependent on the compound, mixing equipment, and mixing cycle. The improvement in uniformity with work input control, therefore, cannot be generalized but must be looked at with consideration to these three parameters. The final objective was to improve efficiency in terms of power and mixing time. Work input control improves efficiency by decreasing cycle time. Savings are dependent on the compound, mixing equipment and cycle; they will vary, depending on these factors.
Uniaxial Extension and Compression in Stress-Strain Relations of Rubber
Authors: Wood Lawrence A. 
Published: February 2011

Abstract
A comprehensive literature survey shows the general applicability of the generalized normalized Martin, Roth and Stiehler equation to uniaxial stress-strain data in extension and compression on rubber vulcanizates. The equation can be expressed as F/M=(L−1−L−2) expA (L−L−1) where F is the stress on the undeformed section and L the ratio of stressed to unstressed length. The equation contains two constants—M, Young's Modulus, the slope of the stress-strain curve at L=1, and A an empirical constant. The conformity of stress-strain data to the equation can readily be determined by a plot of logF/(L−1−L−2) against (L−L−1). In almost every case a straight line is obtained, from the slope and intercept of which both the constants can be determined. The range of validity of the equation usually begins near L=0.5 (in the compression region) and continuing through the region of low deformations often extends to the region of rupture in extension. If uniaxial compression data are available the modulus can thus be obtained by interpolation through the region of low deformations, where experimental data are often somewhat unreliable. The value of the modulus M varies with the nature of the rubber, the extent of vulcanization, and the time and temperature of creep or stress relaxation. The value of the constant A is near 0.4 for pure-gum vulcanizates, increasing to values near 1.0 with increasing filler content, and showing an abrupt increase when crystallization occurs. Direct experimental observations where the deformation of a single specimen is varied continuously from compressive to tensile deformation, are cited to show that M, defined as the limit of the ratio of stress to strain, is independent of the direction of approach to the limit at L=0.5. The normalized Mooney-Rivlin plots show F/[2M (L−L−2)] against L−1. These graphs have only limited regions of linearity corresponding to constant values of the coefficients C1 and C2. Since these regions do not include the undeformed state the Mooney-Rivlin equation cannot be used at low elongations or in compression. The values of C1 and C2 show very wide fluctuations for the Mooney-Rivlin plots of experimental data, which are themselves usually well represented by the Martin, Roth, and Stiehler equation with different values of the constant A. In view of all these considerations the conclusion of the present study confirms that of Treloar in his recent publications in failing to find much utility in making Mooney-Rivlin plots. The failure to represent the experimental data at low elongations and the inability to correlate the constants with theoretical predictions based on strain energy or statistical theory considerations are the most serious objections.
Green Strength in Emulsion SBR
Authors: Buckler E. J. , Briggs G. J. , Dunn J. R. , Lasis E. , Wei Y. K. 
Published: February 2011

Abstract
The present study and that published previously show that crosslinks based on quaternary ammonium halide salts introduced into emulsion SBR-type polymers confer green strength on blends with other compatible rubbers. The crosslink density employed did not exceed 1 link per 3000 combined monomer groups, equivalent to two links per weight-average polymer chain. Judging by the positive slopes of stress-strain curves, green strength obtained in this manner will persist up to at least 50°C. The crosslinks can be broken by mechanical shear and will re-form under resting conditions during times ranging from days at room temperature to minutes at 150°C. Prolonged mechanical shear in laboratory mixing equipment causes progressive loss of modulus and reduction in the slope of the stress-strain curves of compounds containing these labile crosslinks. Similar effects are observed in corresponding control compounds containing no labile crosslinks, but the initial advantage of the crosslinked compounds is progressively reduced and may be lost if shearing is sufficiently prolonged. Available evidence suggests that the principal cause of loss of modulus through shear is selective breakdown of the high molecular weight fraction of the base polymer. The breakdown of the longer chains, which are those most likely initially to carry three or more crosslinks, eliminates most of the network structure responsible for enhanced modulus. Whether chemical effects contribute to loss of modulus remains to be determined, but the evidence suggests that any such effects will be of lesser importance. Because the shear encountered in small laboratory mixing devices differs from that in full-scale factory equipment and stress-strain curves may not reliably predict green-stock behavior, the significance of the present findings can only be determined by factory trials. It is evident, however, that for the most efficient utilization of high green-strength SBR, exposure of the crosslinked SBR component to mechanical shear during mixing should be held to a minimum. On the other hand, to achieve smooth sheets or profiles at the forming stage, the final compound should be subjected briefly to a high degree of shear at as low a temperature as practicable, to break the labile crosslinks in the stock. Green strength will be recovered during subsequent rest periods. The present study suggests that these conditions should be readily achieved in a calendering operation, such as normally used for preparing carcass plies. However, to a greater extent than in most polymer developments, the final proving ground for applications for this new modification of SBR must be full-scale factory trials.
Crystallizable Trans-Butadiene-Piperylene Elastomers
Authors: Bruzzone M. , Carbonaro A. , Gargani L. 
Published: February 2011

Abstract
The synthesis of a crystallizable synthetic rubber based on butadiene and piperylene in the presence of active vanadium-based catalysts is described. This outlet for piperylene (a cocomponent with isoprene of the C5 cut of naphtha crackers) would allow a rational utilization of both monomers present in the same cut and draw the best advantage from the complementary properties of the copolymer described in this work and cis-1,4-polyisoprene. The butadiene units in the copolymer are in the trans-1,4-configuration. The piperylene content giving a good compromise between crystallization at low temperature (temperature sensitivity) and crystallization upon stretching (strain sensitivity) is 30 ± 5 mol%. The copolymer shows outstanding green strength and tack, and it is less prone than high-cis-polybutadiene and trans-polypentenamer to crystallization at low temperature, because of a particular combination of thermodynamic parameters. Among these, melting point and glass transition are somewhat adjustable by controlling the piperylene content in the range specified. The properties of this crystallizable rubber suggest its use as a general-purpose rubber, possibly in combination with other conventional elastomers.