bluuebunny/crossref_metadata_2025 huggingface dataset:
An Improved Flexing Machine. I. Description and Application to Studies of Cut Growth
Authors: Wu R. T. , Sapper D. I.
Published: February 2011

A new flex testing machine has been developed which yields accurate information on cut growth of vulcanizates. Its unique features are accurate temperature control of the test chamber (25°–200° ± 1° C), adjustable work input upon the test specimen by varying both the frequency of flexing (100–600 ± 1 rpm) and flex angle, and accomodation of a large number of test specimens (90–120). Furthermore, provision is made to test with a specific testing atmosphere, either oxidative or inert, depending on the required severity of conditions. Advantages of the test machine are: a) simple operation, once the test conditions are established: b) rapidity of testing, since a large number of specimens can be tested at the same time; and c) excellent reproducibility in preparing test specimens, varying and maintaining test conditions, and measuring cut growth. The maximum standard error for the test is about 12%. A further advantage is that compounds of varying degrees of hardness, for example, tire treads, shoe soles, and belt compounds, can be tested on the same machine by adjusting the severity of the test conditions. Effects of polymer and compounding variables on cut growth are discussed using data obtained with this new flexing machine.
Vulcameter Determination of Best Cure
Authors: Gehman S. D. , Maxey F. S. , Ogilby S. R.
Published: February 2011

Using a continuous cure curve to select a minimum number of stepped cures, it should be possible to vulcanize and test fewer sheets to determine best cure. This procedure is attractive for its potential of expediting the output of physical testing laboratories and especially for reducing the work load of stress-strain testing. Cure curves recorded with the Vulcameter approximated first-order reactions. Equations were derived to calculate the final force and rate constant from recorded force values without carrying the reaction to completion. A chart is suggested to assist in calculating the rate constant. Time for a given fractional rise in force depends only on the rate constant so that a chart for obtaining it is relatively simple. Experience and correlation with service performance in selecting best cures is emphasized. 95% rise times from Vulcameter curves were compared with conventionally selected best cures for a wide variety of compounds. Indications are that experience with the method might reduce the number of test-sheet cures to determine optimum stress-strain properties to one, two, or three depending upon the compound and the exactness required.
Liquid-Metal-Bath Stress-Strain Apparatus
Authors: Hall G. L. , Rigby J. D. , Liska J. W.
Published: February 2011

A simple, reliable apparatus for measuring stress-strain properties of vulcanizates at temperatures up to at least 800° F has been developed. The heating medium is a molten metal bath which provides uniform temperature distribution and rapid heat transfer while excluding atmospheric oxygen. Ultimate tensile strengths are in excellent agreement with those obtained in conventional air-oven tests. Stress relaxation tests show the effects of excluding atmospheric oxygen from the specimens. Somewhat higher ultimate elongations are obtained in the liquid-bath than in air-oven apparatus, for which possible reasons are suggested. Results on vulcanizates of heat-resistant polymers demonstrate that retention of physical properties at 500° F or 600° F cannot be safely predicted from data obtained at 400° F. The curing system, as well as the base polymer, is very important to high temperature resistance. In both Diene and butyl rubber compounds, for example, resin cures were superior in this respect to more conventional curing systems.
Diaphragm Vulcanized Adhesion Test Method
Authors: Taylor C. E.
Published: February 2011

By using a rubber diaphragm as pressure transmitting medium, a cured adhesion test method has been developed which permits controllable curing pressures to be employed. The quest for a new adhesion test method was occasioned by lack of confidence in existing test methods with respect to reproducibility and correlation between testing sites. The diaphragm cures “hi place” with a minimum of rubber movement as compared to excessive press pressures which induce flow. Controllable vulcanizing pressures and temperatures permit accurate adhesion evaluation of individual components in the laboratory under conditions which closely approximate manufacturing methods. A prime goal has been evaluation of true chemical bonding and elimination of all possible mechanical adhesion contributions inherent in most rubber-product fabrications. The diaphragm pressure adhesion test can be used by Quality Control, Development, or Research Department as an accurate tool to evaluate the chemical adhesion potential of rubber and common reinforcing components. Since adhesion values are machine recorded, all laboratory time and error in tabulations and calculations are eliminated. Basic principles of the technique permit evaluation of chemical bonding of rubber to yarns, fibers, and cords with equal effectiveness.
Rheological Properties of Polybutadienes Prepared by n-Butyllithium Initiation
Authors: Gruver J. T. , Kraus Gerard
Published: February 2011

The flow behavior of n-butyllithium-polymerized polybutadienes was investigated as a function of molecular weight, temperature, and shear rate. At low shear rates these polymers exhibit Newtonian flow up to molecular weights of several hundred thousand so that “zero shear” Newtonian viscosities can readily be determined without the risk of long extrapolation. Above 10,000 molecular weight the Newtonian viscosities obey the well-known 3.4 power dependence on weight-average molecular weight. The entanglement spacing molecular weight is estimated at 5600. The temperature dependence of viscosity is substantially independent of molecular weight and shear stress and can be represented analytically by functions proposed in the literature. The apparent activation energy for viscous flow is not constant, but decreases with rising temperature. The flow of the polymers becomes increasingly non-Newtonian with the product of shear rate, molecular weight and Newtonian viscosity. However, the departure from Newtonian behavior is apparently less than for any polymer system whose flow behavior has been described in the literature. The indications are, therefore, that sharp molecular weight distribution and freedom from long chain branching favor Newtonian flow and that the n-butyllithium initiated polybutadienes represent some of the most perfectly linear, narrow distribution polymers known.
Swelling of Filled Rubber Vulcanizates
Authors: Boonstra B. B. , Taylor G. L.
Published: February 2011

A detailed study has been made of the swelling of vulcanizates containing “adhering” and “non-adhering” fillers. The restriction of the swelling of vulcanizates containing “adhering” fillers compared to the swelling of the corresponding pure gum vulcanizate does not take place in solvents with solvent power below a critical value. The solvent power is indicated by the volume fraction of rubber (vr0) in the swollen pure gum vulcanizate. It appears that the critical value, vrc, is not very dependent on the type of black and slightly dependent on the crosslink density. Graphitized (2700° C) blacks differ from all other fillers in that they cause no restriction in swelling for any solvent, nor do they increase the swelling of the apparent matrix as is the case with non-adhering fillers. A semi-quantitative explanation for the observed phenomena is proposed.
Relation between Glass Transition Temperature and Composition of Ethylene Propylene Copolymers
Authors: Maurer J. J.
Published: February 2011

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Field Desorption Mass Spectra of Polymer Chemicals
Authors: Lattimer R. P. , Welch K. R.
Published: February 2011

From the results presented here, it is clear that FD-MS is a very effective analytical method for determining molecular weights of polymer chemicals. Molecular ions were the only prominent ions produced in the FD mode of analysis for the series of representative polymer chemicals discussed in this paper. Good molecular ion spectra were obtained even from compounds that are quite unstable, both structurally and thermally. It is also evident, on the other hand, that FD-MS by itself provides only limited chemical structure information. The molecular weight is provided and often nothing else. Fortunately the molecular weight and “chemical intuition” regarding the history of the sample in question are often enough to deduce the structure. If not, then other techniques are available to provide complementary information. Electron impact (EI) mass spectra can be run on the same samples to obtain fragmentation patterns, and other spectro-scopic techniques (infrared and magnetic resonance) can be used to provide detailed structural information. Several application areas can be identified in which FD-MS can play an important role in the characterization of nolymer chemicals in industry. These include chemical identification (molecular weight and structure determination), direct detection of components in mixtures, identification of liquid chromatographic (LC) effluents, characterization of polymer blooms and extracts, identification of vapors from polymer processing, and identification of polymer chemical degradation products. For many of these applications the samples to be analyzed are very complex mixtures of chemical compounds. Electron impact mass spectroscopy is quite limited in its ability to analyze such complex mixtures due to the extensive fragmentation (and perhaps decomposition) that takes place in the ion source. Since molecular ions are normally the only prominent ions formed in the FD mode of analysis, FD-MS can be a very powerful tool for the characterization of polymer chemical mixtures. In summary, field desorption mass spectroscopy can in many cases provide molecular weight and structural data for polymer chemicals heretofore not obtainable by any analytical technique. In addition this information complements well the structural data obtained by magnetic resonance, infrared, and electron impact mass spectroscopy. We therefore feel confident that FD-MS will become increasingly important in the characterization of polymer chemicals in the future.
Finite Deformation Behavior of Elastomers: Dependence of Strain Energy Density on Degree of Crosslinking for SBR
Authors: Tsuge K. , Arenz R. J. , Landel R. F.
Published: February 2011

The non-linear mechanical behavior of styrene-butadiene rubbers (SBR) having five different crosslink densities (νe) has been determined in large deformation biaxial stress-relaxation tests of thin-sheet specimens. A significant experimental development was the use of individual strain gages at the specimen support points to determine directly the stress distribution in the web. The tests indicated the separability of strain and time effects for extension ratios up to 3.0 for the most lightly crosslinked SBR. Long-time data showed the equilibrium shear modulus Ge to be directly proportional to νe. The ratio W/Ge was independent of crosslinking so that the strain energy density W has the same functional strain dependence for all SBR systems.
Ozonolysis of Polyisoprene Popcorn Polymer
Authors: Miller G. H. , Tobias R. H.
Published: February 2011

Ozonolysis of polyisoprene popcorn polymer gave the volatile products: water, formic acid, acetic acid, levulinaldehyde, 2,5-hexanedione, and propionic acid. The rates of formation of levulinaldehyde and 2,5-hexanedione varied during the 96-hour ozonolysis period; more levulinaldehyde was formed during the early stages, and more 2,5-hexanedione during the later stages. The molar yields of formic and acetic acid were approximately 20 and 10 times larger, respectively, than the average hexanedione or levulinaldehyde yield. A chain unzipping mechanism is postulated for the production of most of the formic and acetic acids, and it is believed that most of the 2,5-hexanedione is formed in secondary reactions initiated by alkoxy or peroxy radicals. A large amount of oxygen remained on the polymer which still had a high degree of unsaturation following the ozonolysis. Ozonolysis of bulk PIP is not a satisfactory way for the determination of head-to-head and tail-to-tail structural sequences. The evidence obtained, however, indicates that the polymer is composed primarily of head-to-tail structural units.
The Mechanical Stability of Natural Rubber Latexes
Authors: Pendle T. D. , Gorton A. D. T.
Published: February 2011

From the information presented in this paper and from the cited literature, it is clear that the mechanical stability of natural latex can be influenced by a large number of factors. The arguments presented here suggest that the effects of most of these factors are explicable in terms of classical colloidal stability theory. It is suggested that the ionic strength of the aqueous phase of natural latex is a key feature in determining stability because of its effects on the electrical double layers around the latex particles. Increases in ionic strength reduce stability because of compression of the electrical double layer, such compression permitting closer approach of adjacent particles, and consequently, an increase in the attractive forces between them. Other phenomena are explained by postulating adsorption of anions at the particle surface where they have the effect of increasing the potential of the surface and therefore the repulsive force between adjacent particles—the attractive force being presumed to remain constant. It is believed that not all of the possible factors influencing the mechanical stability of natural latex concentrates have yet been discovered and, more generally, that the specific effects of anions on colloidal stability remain to be evaluated. In this context further investigation of the nonvolatile acid anions present in natural latex could be worthwhile. The way in which the mechanical stability of natural latex concentrates is affected by both internal and external factors and the means which latex producers use to control this characteristic have been shown. The results presented here illustrate the sensitivity of the mechanical stability test as a measure of the stability of the latex particle to mechanical influences and thereby indicate its value both to the producer and consumer of natural latex.
Factors Which Influence Autohesion of Elastomers
Authors: Rhee C. K. , Andries J. C.
Published: February 2011

The following conclusions can be drawn from our studies: (1) An optimum molecular weight (Mn=2095) exists for t-octylphenol-formaldehyde resin to give maximum autohesion to rubber compounds. A critical level of the phenolic resin is required in a given rubber compound to make the tackifying action effective. In addition, the presence of polar groups in a resin molecule is a structural requirement in order for the resin to provide tackiness to rubber compounds. (2) The autohesion of a rubber compound decreases as the loading of processing oil increases from 5 phr to 25 phr. This behavior is independent of the type of oil. (3) The autohesion of a rubber compound decreases with increasing carbon black level, surface area, and structure. (4) Autohesion maximizes at an optimum molecular weight of rubber. (5) Humidity has a pronounced effect on the autohesion of aged SBR compounds, whereas very little effect on that of aged NR compounds. (6) A dual diffusion-adsorption mechanism is operative in autohesion.
Investigation of the Structure-Property Relationships of Improved Low Compression Set Nitrile Rubbers
Authors: Chang D. M.
Published: February 2011

The effect of polymer structures on the rubber processing and physical properties of the improved Hycar 1090 low compression set nitrile rubbers was investigated. The molecular weight and acrylonitrile content of a polymer are important variables in determining the compound processing and vulcanizate physical properties. Within the range of 21 to 88 Mooney, a blend of high and low Mooney polymers has approximately the same properties as those from a single polymer of the same Mooney viscosity. The molecular weight distribution was not significantly broadened to become an important factor affecting the polymer properties. All polymers with Mooney viscosities from 21 to 88 showed good properties. An understanding of the structure and properties of this new type of NBR, will help in choosing the right kind of polymer for particular applications.
Photo-Oxidation of an IR Vulcanizate
Authors: Yano Shoichiro
Published: February 2011

On irradiation with uv light, changes in uv and ir spectra were observed. In the uv spectrum, a minimum at 290 nm due to sulfur, dibenzothiazyl disulfide, and double bonds in the main chains disappeared initially by the consumption of them; but the minimum reappeared on further irradiation reflecting the formation of carbonyl groups. On the other hand, in the ir spectrum two absorption bands appeared at 1720 cm−1 (due to carbonyl groups) and 3450 cm−1 (due to hydroxyl groups). The latter band faded out suggesting the decomposition of hydroperoxides when the vulcanizate was kept in the dark after irradiation. From the findings of the wavelength dependence of photo-oxidation on uv and ir spectra, it was found that the degradation occurred below about 430 nm. However, investigation of the wavelength dependence of photo-oxidation by the measurement of the crosslink density gave the results that crosslinking reactions occurred below about 340 nm, scissions of C-C and polysulfide crosslinks between 340 and about 400 nm, and scissions of polysulfide crosslinks between 400 and 600 nm. These were confirmed by measurements of the dynamic modulus during irradiation. The relative modulus E′(t)/E′(0) increased on irradiation with light at 253.7 nm in a longer time region reflecting a crosslinking reaction. On the other hand, on irradiation with light above 330 nm, E′(t)/E′(0) decreased with time. Change in E′(t)/E′(0) could be represented by the equation of the first order reaction containing an exponential term and the rate constant was determined. The activation energy was calculated as 18.6 kcal/mole from the temperature dependence of the rate constant and agreed with that for scission of polysulfide crosslinks. The photodegradation of the IR vulcanizate occurred also on irradiation with visible light (> 430 nm), and the modulus decreased.
Testing Submergible Power Cables for Oil Well Applications
Authors: Martin Jon W.
Published: February 2011

A downhole simulator can be used to test oil well power cable, providing results more quickly and economically than can be obtained from field testing. Electrical properties of the cable can be monitored durng the test. Thermal limits can be established. Field degradation mechanisms can be reproduced. TRW uses the facility to evaluate oil well cable designs and to test new cable insulation and protection materials. From this experience, submergible cables have been improved to meet the most severe downhole conditions being encountered throughout the world.
Migration and Blooming of Waxes to the Surface of Rubber Vulcanizates
Authors: Nah S. H. , Thomas A. G.
Published: February 2011

The model proposed in this paper appears to give an adequate explanation for the magnitude of the blooming rates observed. The driving force is due to elastic stresses set up around the precipitated wax particles and thus the blooming rate is influenced quite strongly by the modulus of the rubber. On the basis of this mechanism it would be expected that unvulcanized rubber would show little blooming, and this is in accord with general observations on such materials. The solubility of the wax is an important parameter and, because of its sensitivity to temperature, the ambient temperature and the melting point of the wax will be important factors influencing the blooming in practical applications. The precipitation of the wax has been assumed to occur at imperfections in the material. The source of these is not yet clear, although impurities could clearly be important. The values that have to be assumed for the volume fraction of these seeding sites, about 10−3, is not unreasonable in general magnitude for impurity concentrations.
Extrusion-Shaping of Curved Hose Reinforced with Short Cellulose Fibers
Authors: Goettler L. A. , Lambright A. J. , Leib R. I. , DiMauro P. J.
Published: February 2011

A new development in hose technology, the direct shaping of curved hose reinforced with short fibers at the extrusion die, is described. By moving the inner and outer portions of the tube die out of concentricity in a programmed sequence, the extrusion direction can be made to deviate from the machine axis and thus to produce bends in the hose. This process has been demonstrated on planar S-bends of a 38 mm hose. Bend radii as tight as 13 mm to the inside of the bend are feasible. Such a hose might find various industrial applications. Performance characteristics are similar to cord reinforced coolant hoses. The reproducibility of the die motions and timing sequences to produce the hose shapes are maintained by a digitally controlled hydraulic cylinder that is driven through a stepper motor. The driver for the stepper motor could involve hard-wired or microprocessor circuitry. All of the components for this system are commercially available with the exception of a customized extrusion head to accomodate the mounting and connection of the hydraulic cylinder. This unique process for producing curved hose is contingent upon the use of short fiber reinforcement for several reasons: (a) The reinforcement must be present in the stock before it is extruded. (b) The dispersed short fibers give the hot extruded hose structural integrity to minimize shape distortion before cure. (c) The hoop-wise fiber orientation pattern produced in the novel conically expanding die is augmented by additional reinforcement in the thinner hose wall that occurs on the inside of the bend. An important consequence of the third item above is that the curved hose sections display practically the same burst strength as a straight section, despite the wall thinning that occurs as a result of offsetting the die and pin. The production and performance of these short-fiber reinforced curved hoses can be rationalized in terms of the fluid and mechanical behavior of short fiber composites.
Upgrading of Scrap Rubber Powder by Vulcanization without New Rubber
Authors: Acetta A. , Vergnaud J. M.
Published: February 2011

Rubber powder recovered from old tires can be converted to materials with interesting, useful physical properties. Rubber powder is recognized as a valuable raw material which may be processed into several useful products. In the cure cycles described, using only rubber powder and vulcanizing agent without virgin parent-compound, rubber powder can be converted to a plastic or elastomeric material, according to the percentage vulcanizing agent. As in the case of classical rubber vulcanization, the physical properties of the vulcanizates from rubber powder are found to be largely dependent on the conditions of cure. The effect of vulcanizing parameters on the vulcanizate properties were particularly studied.
Laboratory Vulcanization as an Aid to Factory Air Analysis
Authors: Willoughby B. G. , Lawson G.
Published: February 2011

The pollution problems of the rubber industry are complex and the pollutants arise from a variety of sources. Prior knowledge of the nature of these pollutants is invaluable to the successful execution of a factory monitoring program. Such a knowledge enables the most appropriate monitoring equipment to be preselected and provides for cost effective analysis. The collection and analysis of hitherto unidentified compounds requires a degree of control which is most easily achieved with a laboratory vulcanization. The results presented here show that this control enables a wide range of volatile species to be captured and permits yields to be optimized for the purposes of identification. Examples of the control that may be achieved in a laboratory vulcanization include the ability to handle samples without loss and to carry out this work with ready access to the most sophisticated analytical equipment. A knowledge of the chemical nature of the fumes from a vulcanizing rubber is not only of value to the industrial hygienist but also provides an insight into the chemical processes of vulcanization. For example, evidence for the free radical contribution to a sulfenamide cure can be obtained. Of special note is the fact that these data can be obtained from fully compounded rubber stocks.