bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastomer Blends. Compatibility and Relative Response to Fillers
Authors: Callan J. E. , Hess W. M. , Scott C. E.
Published: February 2011

The relative compatibility of eight different commercially available elastomers, blended in two-way combinations in three different proportions, was measured as a function of zone size on phase contrast optical micrographs using the Quantimet Image Analyzing Computer. Average cross sectional areas of the disperse phase in different blends were measured utilizing micrographs of the relatively noise-free QTM meter images which were characterized by greatly enhanced contrast. A study of the commercially important blends of polybutadiene with SBR was completed using both Differential Thermal Analysis and Electron Microscopy. Blends of several types of polybutadiene with SBR ordinarily exhibited only one glass transition temperature when examined in the vulcanized state. However, the same blends, uncured, showed the Tg's typical of each individual polymer. Moreover, electron micrographs of SBR blends with three different polybutadienes (Butyllithium, Ziegler, and Emulsion types) showed the existence of discrete polymer zones. Blends of BR/SBR, though more compatible than most polymer systems (e.g., NR/BR), were not homogeneous at the molecular level. A comprehensive study of carbon black distribution between 50/50 blends of several commercially important elastomers was completed. A high structure HAF carbon was added to elastomer preblends to give a 40 phr loading. Filler distribution was then assessed from the frequency of aggregates in the separate polymer zones. The studies indicated that BR and SBR have the highest affinity for a standard type carbon black. Polychlorobutadiene and Nitrile rubbers showed a somewhat lower affinity, though appreciably higher than that of natural rubber. EPDM and Butyl showed the lowest carbon black reactivity. Finally, carbon black transfer was investigated in a variety of polymer systems using Electron Microscopy and Pyrolytic Gas-Chromatography. The extent of carbon black transfer from Butyl to BR, NR and SBR was quite significant. In summary, transfer can occur when the adsorptive capacity of the filler has not been fully utilized. This situation can exist if the masterbatch has minimum heat or mechanical history, or involves low molecular weight or low unsaturation elastomers.
Crosslinking, Filler, or Transition Constraint of Polymer Networks. I
Authors: Blanchard A. F.
Published: February 2011

For a polymer network at equilibrium in solvent, Flory and Rehner related the polymer fraction νr of the swollen volume to the molecular weight Mc of the chains between crosslinks. Their equation is represented below by the function F(νr) with [Mc] denoting the effective mesh weight, i.e., that obtained by physical measurements. Hence the effective crosslinking 1/[Mc]g from swelling measurements νr is given by 1/F(νr).
Polymers from Cycloolefins
Authors: Scott Kenneth W. , Calderon Nissim , Ofstead E. A. , Judy W. A. , Ward J. P.
Published: February 2011

Ring-opening polymerization of cycloolefins has led to a variety of new plastics and elastomers with a great range in physical properties. Ring-opening polymerization of cycloolefins, employing organoaluminum-tungsten salt catalysts, is a special case of olefin metathesis, a new reaction. The ring-opening reaction occurs at the double bond and allows making either large ring macro-cyclics or high molecular weight linear chains. Under certain conditions ringchain equilibrium can be established in these systems.
Inflation and Compression of Rubber Tubes between Parallel Plates
Authors: Charrier J. M. , Gent A. N.
Published: February 2011

When a thin-walled rubber tube containing an incompressible fluid is compressed between two parallel plates the internal pressure rise depends on the restraints in the contact regions. When there is no friction in the contact zone the pressure rise is lower than when slip is prevented, so that the tube, regarded as a spring, has a compression stiffness which depends on the frictional conditions. The same considerations apply to the inflation of a tube between fixed parallel plates. In this case unstable inflation sets in at a critical pressure when the interfaces are frictionless; the tube develops a pronounced bulge when this pressure is approached. Simple theoretical relations are derived for the internal pressure and compressive force for both these deformations, and for both boundary conditions, assuming that the rubber is neo-Hookean in elastic behavior. Experimental measurements on tubes of different dimensions are shown to be in reasonably good quantitative agreement with these theoretical predictions in all cases.
Volume Change Accompanying Rubber Extension
Authors: Goebel J. C. , Tobolsky A. V.
Published: February 2011

A new equation for the volume dilation accompanying rubber extension is obtained from a reinterpretation of the kinetic theory equation for rubber elasticity. This equation is shown to describe published volume-extension data better than either that derived from simple kinetic theory or that derived from the Mooney-Rivlin equation.
Identification and Determination of Polymers in Compounded Cured Rubber Stocks by Pyrolysis and Two-Channel Gas Chromatography
Authors: Cole H. M. , Petterson D. L. , Sljaka V. A. , Smith D. S.
Published: February 2011

Methods for analysis of carbon-black-loaded vulcanizates are of considerable interest to the rubber industry and to those supplying its raw materials. Identification of polymers or copolymers present in such stocks is an important step in this analysis. Often it becomes desirable also to determine the composition of a blend of two or more elastomers. In recent years gas chromatographic analysis of volatile pyrolysis products has been increasingly applied to these intractable materials. A wide variety of polymers and experimental techniques for pyrolysis and subsequent chromatographic analysis have been used. A complete resume of this work is beyond the scope of this report, but recent papers dealing with the use of these methods in elastomer analysis include those of Groten, Hulot and Lebel, Blenkin, Lebel, Fiorenza and Bonomi, and an excellent review of pyrolytic techniques by Brauer. This study was an evaluation of the applicability of simultaneous flame ionization and electron capture (dual-channel) chromatography, with or without temperature programming to polymer identification and to quantitative analysis of elastomer blends.
Relation between Abrasion and Strength of Rubber
Authors: Grosch K. A. , Schallamach A.
Published: February 2011

The temperature dependence of abrasion of various gum and black-filled rubbers on silicon carbide paper is closely similar to the temperature dependence of their energy density at break determined at a high rate of extension. The conclusion is drawn that this type of abrasion is predominantly due to tensile failure, as had been envisaged in earlier work. The effective rate of extension during abrasion at a sliding velocity of 1 cm/sec is about 10,000 per cent/sec. The volume of abraded rubber is approximately proportional to the ratio between frictional energy dissipation and energy density at break. The proportionality constant is greater for black-filled than for gum rubbers. The effects of temperature and velocity on the abrasion of non-crystallizing gums are interrelated by means of the Ferry transform, indicating the viscoelastic nature of the abrasion process operating on these compounds.
Friction of Rubber
Authors: Savkoor A. R.
Published: February 2011

A theory of the adhesional friction of rubber is developed by considering adhesion as a time-dependent process in which a tangential force helps to overcome an energy barrier of the work of adhesion. The frictional phenomenon, as a consequence of such adhesion, would arise primarily from deformation of the rubber aggregates in contact with a smooth, hard surface constituting the “top layer”. The existence and importance of such a highly-deformed layer has been shown by Schallamach in his studies on surface conditions. The true area of contact is considered to increase with time of adhesion as is generally observed in quasi-static behavior of viscoelastic materials. Deformation characteristics describing the time-temperature dependence of mechanical properties would then be reflected in the friction behavior. A simple phenomenological approach is taken here instead of a complicated one with the theory of rate processes applied to basic molecular activity. Variation of the friction force with viscoelastic properties is in fair agreement with the experimentally-obtained results of Grosch. The static coefficient of friction equals the dynamic coefficient at extremely low speeds. The analysis is confined to steady-state conditions and the influence of frictional heating is considered negligible.
A Theory of Dynamic Rubber Friction
Authors: Schallamach A.
Published: February 2011

Assuming dynamic friction to arise from the shearing and subsequent breaking of distinct bonds between the rubbing members, a general equation is derived for the frictional force which involves the number and average life of the bonds as well as the average time lag between breaking and re-making of a bond at a given site. In the case of friction between rubber and smooth, hard surfaces, the bonds are attributed to local molecular adhesion between rubber and track, both formation and breaking of the bonds being thermally activated rate processes. A theory developed on this basis reproduces the experimental results obtained by Grosch in that the coefficient of friction as function of the velocity has a pronounced maximum. The height of the maximum and the velocity at which it occurs are in semi-quantitative agreement with Grosch's findings.
Distribution of Tensile Strength Data
Authors: Heap R. D.
Published: February 2011

The problems of tensile strength estimation are outlined, with particular reference to Ease's work showing that tensile data for rubbers are distributed doubly exponentially. Efficient estimators are given as weighted means for samples of up to six observations, and efficient but simple, easily calculated approximations to these are given. Large or incomplete samples are also considered. A suggested scheme for treatment of experimental data is given, including experimental results comparing the recommended estimators with the mean and median, and showing a doubly exponential distribution of observations.
Relaxation Response of Polyurethan Elastomers
Authors: Theocaris P. S.
Published: February 2011

The transient extension relaxation modulus E(t) and the lateral contraction ratio vr(t) for a polyurcthan elastomer have been measured simultaneously in the transition region from glass to rubber. The differential moiré method was used in these measurements and yielded simultaneous values of the longitudinal extension and the lateral contraction principal strains of the tension specimen. Composite curves of E(t) and vr(t) reduced to a standard temperature were obtained by applying the method of reduced variables. The time factors KT in both curves coincided, and followed the WLF equation. The shear and bulk modulus characteristic functions were determined from the extension modulus and lateral contraction ratio functions. The values of the lateral contraction ratio in relaxation were determined by using data of the extension relaxation modulus along the whole viscoelastic range and the initial value of the lateral contraction ratio at the rubbery state and applying an indirect method. The results obtained by the indirect method coincided with the experimental values. The shear modulus function was evaluated from the extension relaxation modulus and the lateral contraction ratio functions and compared with the shear dynamic compliance determined by Landel. The experimental data indicated that a linear relationship holds between the lateral contraction ratio in relaxation and the bulk modulus along the whole response spectrum. The same relationship was previously shown to hold for a series of various polymeric substances.
Viscoelastic Behavior of Open Cell Foams
Authors: Gent A. N. , Rusch K. C.
Published: February 2011

Open-cell foams show abnormally large mechanical damping due to the energy dissipated in forcing air in and out of the foam during a deformation cycle. This pneumatic damping has recently been treated theoretically and experimentally. The dependence upon the test-piece dimensions, the frequency of deformation and the viscosity of the fluid has been shown to be in good agreement with the theoretical predictions. The dominant property of the foam structure is its permeability to fluids. This has also been measured for a number of different foams and related to their structural features by means of a simple model. A review is given of these developments.
Compliance-Time-Temperature Relationships from Indentation Measurements on a Pure-Gum Rubber Vulcanizate
Authors: Roth Frank L. , Bullman George W. , Wood Lawrence A.
Published: February 2011

Previous work on the calculation of shear compliance J (limit of the ratio of strain to stress at zero deformation) from observations of the indentation of a flat natural rubber surface by a rigid sphere has been extended over greater ranges of time, temperature, and state of vulcanization. The extreme ranges of time were 5 sec to 23.5 hr and of temperature −67 to +100° C. The curves of JT against log t−60 (where t−60 is the equivalent time at −60° C and T is in °K) were sigmoid with a region of maximum slope and continuing through a region of minimum slope extending over about 7 decades. In contrast with predictions of the Williams, Landel, and Ferry equation, the empirically determined shift of abscissa necessary to give a single JT curve was found to be a linear function of T−1 with a slope corresponding to an “apparent activation energy” of 36.9 kcal (°K)− (mole)−1 (154.5 k.J (°K)−(mole)−1).
Pressures and Flow Rates in Extruders with Axially-Variable Geometry
Authors: Tangorra G.
Published: February 2011

The problem of predicting pressures and flow rates for extruders, with geometrical parameters arbitrarily variable along the axis is considered for isothermal, Newtonian conditions. A graphical method is applied to an actual case of a truncated, cone-shaped extruder. Experimental results are reported. The same general procedure, but with further simplified formulas, is applied subsequently to cases of extruders having diameter, pitch, and thread depth linearly variable along the axis.
Butadiene and Isoprene Rubber in Giant Tire Treads
Authors: Krol L. H.
Published: February 2011

The lower abrasion found for IR in comparison with NR in an identical formulation could well be counterbalanced by proper modification of the formulation. In spite of the increased black level the heat build-up can still be kept within the limits set by the NR reference. Also, for ternary blends the reduced abrasion resistance of IR can be offset by increasing the black content, without sacrificing loss properties.
Stereoregular Polymerization of Butadiene with Alkylaluminum Chlorides and Cobalt Octoate
Authors: Gippin Morris
Published: February 2011

The requirement of water or oxygen to activate the diethylaluminum chloride co-catalyst used with a cobalt compound to produce 98 per cent cis-1,4 poly-butadiene was reported previously. Activation is considered to form two alkylaluminum compounds differing in Lewis acidity. Several reactions presumed to lead to the formation of the higher acid were carried out with a minor proportion of the diethylaluminum chloride by partial dealkylation with organic hydroperoxide, halogen, tertiary alcohol, organic halide or aluminum. Water is neither necessary nor desirable in the ethylaluminum sesquichloride-cobalt octoate catalyst system. Polar solvents do not appreciably alter the cis-1,4 catalysis with diethylaluminum chloride/water/cobalt octoate, but do decrease the rate or extent of polymerization with increasing dielectric constant of the solvent. A mechanism of cobalt catalysis of butadiene polymerization is proposed.
Relaxation of Disulfide and Tetrasulfide Polymers
Authors: Tobolsky A. V. , MacKnight W. J. , Takahashi M.
Published: February 2011

The chemorheology of crosslinked polyethylene disulfide, polyethylene tetrasulfide, and mixtures of these polymers with elemental sulfur is investigated. It is shown that stress decay in the disulfide polymer occurs by scission of the small quantities of higher polysulfide linkages present in the network. It is also shown that elemental sulfur decreases the chemical relaxation time in crosslinked polyethylene disulfide in a predictable manner.
Oxidative Scission of Natural Polyisoprenes in Solution
Authors: Bell C. L. M.
Published: February 2011

Polyisoprenes are oxidized by a chain reaction in which a large number of oxygen molecules are absorbed for each reaction chain started. During the oxidation, scission of the polymer backbone takes place. Using solutions of natural rubber and gutta percha, measurements of the relative amounts of oxygen absorbed and scission produced indicate that most scission occurs during propagation of the oxidation chain. However, more detailed analysis of the data indicates that scission also occurs nearly every time an oxidation chain is terminated.
Solution Masterbatching Studies
Authors: Scott C. E. , Eckert F. J.
Published: February 2011

Hydrosolution masterbatching (HSMB) imparts excellent dispersion and improved pigment-to-polymer adhesion to carbon and oil masterbatches of poly-butadiene, SBR and blends of these rubbers. Tire tests show HSMB stocks to resist wear slightly better than like stocks mixed in a conventional manner. The HSMB process can be used to produce fully compounded vulcanizable tread stocks in which the stock is discharged continuously from a drying extruder. The dispersion and adhesion advantages of HSMB stocks are also noted in complete masterbatches. HSMB oil, black, and polymer masterbatches usually have higher viscosity, tensile strength, hardness, and dynamic modulus but lower resilience and reduced scorch safety, in comparison with conventionally mixed stock. Carbon black dispersion as revealed by light and electron microscope analysis is excellent. Experiments characterizing carbon gel and development of carbon black dispersion on HSMB stocks (vacuum dried), indicate the total effective molecular contact between elastomer and pigment to be increased, so that, in effect, surface area is increased.
Statistical Variability of Ultimate Properties of SBR Gum Vulcanizates
Authors: Fedors R. F. , Landel R. F.
Published: February 2011

The statistical variability of ultimate properties for 8 samples of SBR-sulfur gum vulcanizates differing in crosslink density by a factor of about 25 was studied. It is shown that these variability data, determined at one rate and one temperature, can be correlated when plotted as a reduced failure envelope. The envelope obtained in this manner agrees reasonably well with the reduced envelope previously reported which was constructed from break data obtained by testing (a) single specimens of constant crosslink density at varying rate and temperature and (b) single specimens at constant rate and temperature but varying crosslink density. It is also shown that the statistical variability data for all samples, including a benzene-soluble one, can be represented by a double exponential cumulative distribution function. It is also shown, in agreement with previous work, that the most probable values of σb when plotted as a function of νe exhibit a maximum in σb at a low value of νe.
Relation of Water Vapor Permeability of Elastomers to Molecular Structure
Authors: Iyengar Y.
Published: February 2011

This communication is a quantitative correlation of water vapor permeability of nonpolar elastomers with molecular structure. Permeability of physical blends and of composite layers of elastomers are also discussed. Permeability—Elastomer Structure.—Steric hindrance and unsaturation influence water vapor permeability of elastomers. The low permeability of isobutylene—isoprene (butyl) rubber is attributed to the presence of bulky methyl groups in its isobutylene component. The high unsaturation in isoprene and butadiene is blamed for the high permeability of natural rubber and styrene butadiene rubber. Hence, permeability should be correlated quantitatively with a factor which can evaluate and combine these two structural parameters. Defining the factors A and B to express the relative molar concentrations of unsaturated and steric groups in the average monomer unit of elastomers as (unsaturation) A=1+x/X (steric groups) B=1+y/Y
High Quality Foams from NIR Latex
Authors: Angove S. N. , Graham E. S. , Hilditch G. , Stewart R. A. , White F. L.
Published: February 2011

Foam rubber properties have been measured for NIR latexes as a function of acrylonitrile content of the copolymer and as a function of ratio of NIR latex to NR latex and high modulus SBR latex. Foam rubber made from NIR latex had good aging and oil resistance, combined with the desirable high tensile strength and elongation characteristic of natural rubber foam. Resilience and low temperature flexibility of NIR foams were found to be lower than that achieved with foams of either SBR or NR latexes. Although compression modulus of NIR foam was lower than that of a high modulus SBR foam and approximately equivalent to that of NR foam, it was effectively increased by the addition of either such SBR latex or a high-styrene resin latex.
Studies of the Compounding of Nitrile Rubber with Shellac
Authors: Jose K. A. , Baneejee S.
Published: February 2011

Shellac is highly compatible with nitrile rubber and can be incorporated in this rubber on a roll mill up to 50 phr without any difficulty. It acts as an antiscorching agent and plasticizer at processing temperatures. To a small extent, it retards cure increasing the cure time from 30 to 40 minutes at higher concentrations of shellac. This is not harmful in industrial applications. Shellac improves physical properties like modulus, tensile strength, tear resistance, hardness, swelling in hydrocarbon oils to a considerable extent. Resilience remains the same. Abrasion resistance is reduced. Heat generation is more with higher percentage of shellac. It can be seen that the optimum concentration of shellac for the best physical properties is 20 to 30 phr.
Thermal Degradation of Aged Chloroprene Rubber Studied by Thermogravimetric Analysis
Authors: Denardin Elton L. G. , Samios Dimitrios , Janissek Paulo R. , de Souza Gabriel P.
Published: February 2011

The thermal degradation of original and aged chloroprene rubber was studied using thermogravimetric analysis. Thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTG) techniques were used to detect the mass loss during the temperature elevation. By the analysis of the mass loss curves through usual kinetic methods, it was possible to evaluate the different degradation processes present in the overall degradation. The activation energies of the degradation processes were obtained using the dynamic, non-isothermal Kissinger and Osawa methods and the half-width at half-high technique (HWHH). The results obtained demonstrate clearly the differences between original and aged chloroprene rubber as well as the influence of the air and N2 in TGA.
New Generation Carbon-Silica Dual Phase Filler Part I. Characterization and Application to Passenger Tire
Authors: Wang Meng-Jiao , Kutsovsky Yakov , Zhang Ping , Murphy Lawrence J. , Laube Steven , Mahmud Khaled
Published: February 2011

A new carbon-silica dual phase filler (CSDPF) 4000 has been developed for passenger tire application. Analytically, this filler is featured by higher levels of silica at the surface of the aggregate and higher silanol contents compared with the CSDPF 2000 family of products introduced previously. From the compounding point of view, this new dual phase filler shows higher polymer-filler interaction on the carbon domains and lower filler-filler interaction relative to the conventional fillers used in tire tread compounds. The new filler shows significant improvement in wet skid resistance over the earlier products. When this filler is employed in passenger tire tread compounds, the tradeoff among rolling resistance, wear resistance and wet skid resistance of the tire can be significantly improved compared with conventional fillers.
Emulsion Rubbers Copolymerized with Monomeric Antioxidants
Authors: Meyer G. E. , Kavchok R. W. , Naples F. J.
Published: February 2011

It has been shown that dual functional compounds bearing antioxidant and polymerizable functions can be copolymerized with numerous monomers in emulsion systems. Somewhat higher initiator levels and/or increased temperature appear to be required for normal polymerization rates in the presence of these monomers. The only incompatible initiator—monomer combinations found are those of persulfate and benzoyl peroxide with amine antioxidants. The dual functional monomers retain their normal antioxidant characteristics in the copolymerized form and are not removed by solvent extraction nor volatilization except under conditions that destroy the polymer. The amine antioxidants, in the copolymerized state, cause comparatively little discoloration on aging and cause no migratory stain while providing antioxidant protection equivalent to high-quality, conventional amine antioxidants.
Liquid Carboxyl-Terminated Poly(Butadiene)
Authors: Hoffman R. F. , Gobran R. H.
Published: February 2011

In general HC-434 is a relatively homogeneous, difunctional polymer that can be readily chain extended through a variety of cure reactions. To date most of the work has been done with epoxide and aziridinyl curing agents, and a moderate amount of work has been done to improve the rates of cure by means of catalysts. Both aromatic amines and chromium salt complexes have proven to be effective catalysts. The physical properties of the chain-extended polymer with reinforcing fillers approach those of SBR vulcanizates, but improvement is still needed to achieve the properties required for tire formulations. The liquid polymer systems are suitable for belting, hose, and molding applications. However, additional work is required to develop the optimum cure systems for physical properties, faster catalysts, and alternative chain-extension reactions with other reactive curing agents.
Processing and Properties of Liquid Rubbers
Authors: Humpidge R. T. , Matthews D. , Morrell S. H. , Pyne J. R.
Published: February 2011

Difficulties of compounding liquid rubbers are discussed and detailed descriptions are given of mixers for the adequate continuous dispersion of carbon black and of light-weight injection molding machines suitable for the pastes which result; some of the problems of injection molding are outlined and suggested solutions given. The reinforcement of liquid rubbers with textile fibers is discussed and suggestions proposed for the layout of a factory suitable for the processing of liquid rubbers.
Specific Shape Characterization of Carbon Black Primary Units
Authors: Hess W. M. , McDonald G. C. , Urban E.
Published: February 2011

A full field feature specific image analysis system has been developed for direct morphological characterization of carbon black in the electron microscope. The system provides quantitative size and non-dimensional shape information, as well as qualitative classification into specific shape categories using pattern recognition programming methods. Data on samplings of 500–1000 primary black units can be recorded on magnetic tape in less than 10 minutes. Although not yet tested on a full range of rubber grade blacks, the new system has demonstrated good sensitivity in resolving morphological differences among a series of four HAF blacks of varied DBP absorption. The blacks exhibited large frequency variations across nine specific shape categories which range from spheroidal to fibrous types. Within each category, the unit size and non-dimensional shape factors were similar for all four blacks. On a composite average basis, however, large differences in unit size (longest dimension or projected area), anisometry (length/width ratio), and irregularity (perimeter/area ratio) were observed. The new image analysis system also has the capability of volume measurements based on microdensitometry. Although data is limited at this time, such measurements should provide more three-dimensional approximations of carbon black unit size. It is also anticipated that microdensitometry will aid in the determination of domain (particle) size.
Chlorobutyl Covulcanization Chemistry and Interfacial Elastomer Bonding
Authors: Zapp R. L.
Published: February 2011

A new analytical and diagnostic technique has been developed and applied to covulcanized Chlorobutyl—polydiene rubber blends that indicates the existence or absence of interfacial bonds. This technique of differential solvent swelling is based upon solvent—elastomer interaction parameters and draws upon the analogy to filler-adhesion analysis of vulcanized networks. Interfacial bonds between dispersed Chlorobutyl and polydiene rubber phases are first obtained with very active thiuram and thiuram tetrasulfide curative systems. Subsequently less active curatives utilizing bis-alkylphenol polysulfides as sulfur donors were also found to promote interfacial bonds. By means of mercaptan probes it was established that strong evidence of interfacial bonds in covulcanized networks was associated with a preponderance of monosulfidic crosslinks. Prolonged heating, which matures polysulfidic links to more thermally stable monosulfidic links, did not produce strong interfacial bonds where none existed after the initial vulcanization cycle. Thus, interfacial bonds must be formed with more thermally stable monosulfide links during the initial stages of vulcanization. Reinforcing carbon black has a minimal effect upon the acquisition of interfacial bonds or the sulfur-bond chemistry. The curative formulation remains the factor which governs production of the monosulfidic links required for strong interfacial bonding. A definite correlation was found between interfacial bonding and physical strength of fully compounded Chlorobutyl—SBR covulcanized blends. Carbon-black reinforced systems covulcanized with a sulfur donor, such as bis-alkylphenol polysulfide, as the sole source of sulfur, displayed tensile strengths and rupture energies considerably greater than the equivalent systems containing elemental sulfur.
The Compression Set Behavior of Nitrile Rubber
Authors: Jahn H-J. , Bertram H-H.
Published: February 2011

The compression set (C.S.) of a vulcanizate depends on the formulation, processing, and conditions of cure. The following factors are the most important: (a) the type of elastomer, (b) the curing system, (c) the type and amount of filler, (d) the type and amount of plasticizer, (e) the type and amount of antioxidant, (f) the type of cure (press, steam, or hot air), and (g) the cure time and temperature. The present paper is intended, as far as possible, to describe these relationships quantitatively. Most tests will refer to nitrile rubber. We have modified the C.S. method described in ASTM D-395. The deviations are as follows : (1) When C.S. is plotted as a function of the duration of compression, the resulting curves rise steeply for roughly the first seven days, afterwards becoming flatter. The higher the test temperature, the steeper the curve. The ordinary compression times of 22 and 70 h still correspond to the steep part of the C.S. curve; here relatively small inaccuracies in the compression time and test temperature bring large errors in the C.S. readings. Therefore, to improve the correlation between C.S. readings and field behavior the test was extended to seven days in most cases. Longer test times would have been experimentally impractical. (2) As a rule, only C.S. figures relating to 20°, 70°, and 100° C are found in the literature, so test temperatures were extended to include practical conditions. Generally, therefore, C.S. readings were taken at twelve different temperatures ranging from −60° C to +160° C. (3) According to the standards the test pieces should be cooled to room temperature after removal of the load and before the recovery measurement is carried out. Only ASTM D-1229-62 requires the remeasurement to be taken at the load temperature. This ensures accurate measurements of the C.S. at low temperatures. In our tests this was done in every case because at high temperature the C.S. readings are lower since (1) many elastomers recover better at elevated temperatures than at room temperature and (2) the thermal expansion of the test piece can be measured in addition to the recovery. Nevertheless, the differences between remeasurements taken at room temperature and the test temperature are small if the test temperature is fairly high. Where lower test temperatures are used, the remeasurement should always be taken at test temperature if useful results are to be obtained. In all the tests the time allowed for recovery between removal of the load and the remeasurement was thirty min.
The Relationship of Properties of Synthetic Poly(Isoprene) and Natural Rubber in The Factory. The Effect of Non-Rubber Constituents of Natural Rubber
Authors: Gregg E. C. , Macey J. H.
Published: February 2011

The causes of some of the differences in properties between compounded natural rubber and compounded synthetic poly (isoprene) have been traced to the insoluble non-rubber material in natural rubber. This material is mostly denatured proteins and is responsible for the higher modulus, faster scorch time, higher heat buildup, and higher hot tear strength of natural rubber. These properties may be related to the pigment effect of the denatured protein to act as a reinforcing filler at low concentrations (3–4 per cent by wt) as well as a curing activator. The greater green strength of compounded natural rubber has been related to its more perfect configurational regularity which contributes to faster crystallization. The crystallite concentration increases with increasing stress and the crystallites act like a reversible reinforcing pigment which disappears when the stress is released. The faster plastication rate has been related to the synthetic stabilizers used. Natural rubber hydrocarbon has been shown to be a high molecular lactone arranged in a six membered ring. We speculate natural rubber forms as a prosthetic group connected through a lactone linkage (or the δ-hydroxy acid precursor to the lactone) to a protein molecule in the cell of hevea brasiliensis. It is this structure of a high molecular weight hydrocarbon (natural rubber) attached to a (denatured) protein molecule that accounts for the remarkable dispersability of the insoluble fraction of natural rubber in rubber solvents : the rubber end of the structure tends to dissolve in the rubber solvent while the highly polar, insoluble protein end prevents solution. This structure is the reverse of a micelle in water in principle.
Rubber Chemicals from Cyclic Amines. VII. Cycloalkylthioamines as Accelerators and Prevulcanization Inhibitors
Authors: Morita E. , Boustany K. , D'Amico J. J. , Sullivan A. B.
Published: February 2011

Cycloalkylthioamines per se are moderately active accelerators. When used in conjunction with the benzothiazole accelerators, these thioamines act as prevulcanization inhibitors with cure activating properties, and generally, increase the crosslink density of the vulcanizates. The inhibition action of the cycloalkylthioamine may be due to its activity as a BtSH scavenger and also to its ability to reduce the number of the labile sulfur atoms, thereby the reactivity, of the more active polythiobenzothiazole intermediates. In addition to these capabilities the inhibition action of PVI in a benzothiazole sulfenamide-accelerated stock may be due to its ability to react with the free amine liberated during vulcanization. The relation of the curing properties of the cyclohexylthioamines to the structure of the amine moiety is analogous to the cases of dithiodiamines and 2-(imino)dithiobenzothiazoles as vulcanizing agents, or N-substituted-2-benzothiazole sulfenamides as accelerators. The relative curing properties either as accelerators or prevulcanization inhibitors can be attributed to the relative stability of the S-N bond based on the steric and electronic nature of the amine moiety. The cyclohexylthioamines derived from pyrrolidine and hexamethyleneimine are the most active as accelerators. The cyclohexylthioamine derived from the equally basic piperidine is slightly less active and gives significantly longer scorch delay. As a prevulcanization inhibitor the less basic morpholino and 2,6-dimethyimorpholino derivatives give much longer delayed action. The piperazine derivative is the most effective as a prevulcanization inhibitor.
Study of Crystallinity in Polymers by the Use of “Molecular Probes”
Authors: Guillet J. E. , Stein A. N.
Published: February 2011

Recent experiments in our laboratories have shown that the technique of gas chromatography can be utilized to obtain information about polymer structure and interactions in the solid phase. Although it might appear reasonable to apply the name “gas chromatography of polymers” to such experiments, the terminology is misleading in that the polymer is obviously not in the gas phase, nor is it undergoing a Chromatographic separation. The terms glpc (gas—liquid partition chromatography) and gspc (gas—solid partition chromatography) appear to be equally inapplicable. In fact the nature of the experiment has more in common with the molecular beam technique for gas reactions and we prefer therefore to refer to these as studies on polymers using “molecular probes.”
Gas—Liquid Chromatography on Polymers. II. Temperature Coefficients for Polyisobutylene—Hydrocarbons
Authors: Leung Yu-Kwan , Eichinger B. E.
Published: February 2011

Studies of the thermodynamics of polymer solutions by conventional static methods at very high concentrations of polymer are relatively few. Therefore, comparisons between enthalpy parameters obtained by the methods of glc and vapor sorption are limited to only a few cases. One other system for which comparable data are available is natural rubber and benzene. In this case, the glc value of κs is +0.18, while κs = 0.01 ± 0.1 has been obtained by vapor sorption. It appears from the somewhat sparse data collected to date that estimates of the residual enthalpy obtained by glc methods are as reliable as those obtained by static methods. Corrections for gas phase imperfection must be very carefully applied.
Some Novel Systems for Crosslinking Polychloroprene
Authors: Kato H. , Fujita H.
Published: February 2011

During the past three decades polychloroprene (CR), one of the earliest synthetic elastomers, has been widely used in many and varied technological applications. The established curing technique generally involves metal oxides as curing agents. The combination of ZnO and MgO with 2-mercaptoimidazoline (NA-22) as an organic accelerator is commonly used. Notwithstanding much work, the essential mechanism of the curing reaction is so complicated that many details remain to be resolved. An effective substitute for NA-22 has become desirable in Japan, mainly because of environmental pollution. Our search for novel organic accelerators has been stimulated by these circumstances and has resulted in the discovery of some promising candidates. This paper is concerned with these new accelerators for the vulcanization of CR and with certain chemicals which stabilize CR vulcanizates cured by them.
Strain-Dependent Dynamic Properties of Carbon-Black Reinforced Vulcanizates. I. Individual Elastomers
Authors: Sircar A. K. , Lamond T. G.
Published: February 2011

The degree of carbon—black particle aggregation (transient structure) in conventional vulcanizates varies with the nature of the elastomers. This is revealed by the variation of (Gm′−G∞ƒ′), which is a measure of the transient structure. The relationship between Gm″ and (Gm′−G∞ƒ′) as well as that between strain work and normalized modulus show similarity to earlier work in which the polymer type was not varied. This suggests that carbon-black structural elements act as energy storage units and are of the same type in all these polymers. While the decrease of in-phase modulus is primarily caused by carbon-black particle units, tan δ reflects also the effect of the polymeric matrix.
Quantitative Determination of the Polymeric Constituents in Compounded Cured Stocks by Curie-Point Pyrolysis—Gas Chromatography
Authors: Krishen Anoop , Tucker Ralph G.
Published: February 2011

Pyrolysis—gas chromatography has been shown to be an excellent technique for quantitative estimation of polymers. Its acceptance is apparent from the large number of publications reported in the past year. The increasing complexity of the constituents used in various applications has necessitated the use of more precise and sophisticated control over the experimental variables. The Curie-point pyrolysis technique has been able to provide a degree of control which has not been possible with any of the other pyrolysis techniques used. In this technique, the sample is heated in a helium stream to a precisely duplicable temperature which is dependent on the composition of the alloy used for the pyrolysis wire, the maximum temperature being the Curie-point when the ferromagnetic wire becomes paramagnetic and is thus incapable of absorbing any energy from the high frequency induction current source. The fast temperature rise results in more specific products on pyrolysis, and any contamination from previous samples can be avoided by using a new wire each time. Application of this technique to complex polymeric mixtures containing a large number of monomeric species is of considerable importance in establishing the composition of these mixtures. The ability to handle cured samples without any elaborate pretreatment makes this technique much more useful.
Structural Change Accompanied by Plastic-to-Rubber Transition of SBS Block Copolymers
Authors: Fujimura M. , Hashimoto T. , Kawai H.
Published: February 2011

It was shown that some block copolymers and their blends with corresponding homopolymers exhibit stress softening. When the specimens are stretched beyond the yield point, they become rubbery and exhibit high elasticity and large recoverable deformation, as a result of a breakup of their original rigid structure. Moreover, the deformed specimens heal, in that the properties of the original undeformed specimens are recovered upon removal of applied stress. This effect was attributed to the reformation of the original microdomain structure. In this work, we investigated an SBS block copolymer and a blend of the copolymer with homopolystyrene in regard to the structural change accompaning the plastic-to-rubber transition and the healing process. Electron microscopy and small angle X-ray scattering (SAXS) were used.
Strength of Elastomers. A Perspective
Authors: Smith Thor L.
Published: February 2011

The strength and extensibility of an elastomer depend on its overall viscoelastic properties, as reflected in the time and temperature dependence of stress-strain curves, and also on those discrete processes, including crack formation and growth, that culminate in high-speed crack propagation. The discrete processes determine the lifetime of a specimen; the viscoelastic characteristics affect the dependence of stress on deformation. The interplay between these effects causes strength and extensibility to depend strongly on test conditions. An elastomeric network composed solely of highly mobile chains is very weak indeed and fractures at a low elongation. This characteristic differs diametrically from that expected of an idealized network of mobile chains. If such a network were stretched, stress concentrations and unbalanced forces at the molecular level, which can result from short chains, entanglements, and network imperfections, would be vitiated rapidly by stress-biased segmental diffusion, especially at the elevated temperature. Therefore the network should be able to withstand a high elongation and thus a high stress. Hence, the low strength always exhibited by a single-phase non-crystallizable elastomer at elevated temperatures is incompatible with the characteristics ascribed to a network in the molecular theory of rubber elasticity. A network of mobile chains is weak for two reasons. First, microcracks develop readily in a stretched specimen. Their formation is usually attributed to stress concentrations near heterogeneties either within or on the surface of a specimen. Second, and most importantly, a microcrack—once it forms—encounters little resistance to growth because the chains are highly mobile. High strength results not because microcracks do not develop but because their growth is impeded. Unless processes that impede growth come into play, a microcrack enlarges rapidly and catastrophic propagation soon follows. When chain mobility is relatively low, the dissipation of energy through viscoelastic processes near the tip of a slowly growing crack retards its progressive growth. But this source of strength is rather ineffective except within narrow ranges of temperature and extension rate, or time scale more generally. Thus, high strength and toughness result from other mechanisms that impede crack growth. Effective mechanisms usually come into play and impart toughness if colloidal particulate fillers or plastic domains are present, except at low concentration.
Polyester in Reinforced EPDM—Factors Affecting Thermal Degradation
Authors: Shinada Y. , Hazelton D. R. , Esso Kagaku K. K.
Published: February 2011

Polyester cord strength loss in EPDM depends on three factors: the presence of moisture, the nature of the cure system, and the aging environment. Of these factors, moisture is most critical. Cord degradation is caused by hydrolysis and is catalyzed by amine or amine-like compounds formed from the curvatives. High temperature also accelerates the deterioration. Knowledge of the service environment is required to decide whether PET may be used to reinforce EPDM. Moisture has a very harmful effect on PET degradation, and a dry environment increases service life substantially. The most feasible method of controlling PET cord strength loss is via curative choice to minimize or avoid nitrogen-containing curatives. Use of desiccant to remove moisture gives no improvement under normal service conditions. “Amino Nitrogen Index” is shown to be useful in formulating EPDM cure systems which have least effect on PET. Systems with an ANI of less than 6 give satisfactory performance. Curatives and accelerators commonly used in EPDM can be ranked according to this concept to aid future compound development. The peroxide system is suggested for maximum heat and compression set resistance. Based on the laboratory performance level of commercial EPDM/cord systems, PET can be used in properly-compounded EPDM at temperatures to 125°C in combined glycol/air and to 150°C in hot air. The cord strength loss of rayon, nylon, and aramid is independent of cure system amino nitrogen content. When the proper cure system is used, the durability of PET is comparable to aramid in hot air. PET is equivalent in performance to rayon and nylon up to 125°C in glycol/air, but far below aramid. Aramid, nylon, and rayon appear suitable for continuous exposure to 150°C glycol. However, in practical applications of these cords other factors such as intermittent environmental changes, dimensional stability, etc. must be considered.