bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical Reflections on Physical and Technological Test Methods in the Rubber Industry
Authors: Kainradl Primus
Published: February 2011

Surveying the development of test methods for vulcanizates since World War II and the currently used tests, we can distinguish three groups: (1) Tensile strength as well as tests for hardness and rebound, (2) Viscoelastic tests, (3) Endurance and aging tests. Along with the first group, during the war simplified tests appeared for flow and aging. Admittedly, tensile strength will continue to be employed in the future as the basic property for characterizing a vulcanizate and, still more, of a reinforcing system, even though vulcanizates of the equal tensile strength often differ in durability. For comprehensive description of vulcanizates, viscoelastic tests are advantageous and are finding ever wider use. Hardness and rebound resilience are related to viscoelastic properties and can serve as preliminary tests. Today there are numerous testing instruments, although these are mostly constructed and described by a single author. With respect to test conditions, they are very different. With increasing service requirements the necessity of endurance tests is becoming more and more recognized. These tests describe internal and external crack formation, with degradation from simultaneous heat generation. Aging from long usage, as shown by changes in properties, belongs in this group. All methods roust have a proven correlation with present product performance and, above all, be improved.
3-D Carbon Black Primary Structure Characterization via a New Electron Microscopy-Photogrammetry Technique
Authors: Mercer H. N. , Boyer A. H. , Deviney M. L.
Published: February 2011

In summary, we have presented a novel 3-D technique for image analysis of carbon black morphology. This technique involves measurements on a single aggregate while viewing this aggregate in three dimensions. The technique uses precision photogrammetry instrumentation and results in reasonable parameters characterizing carbon black. We believe this type of analysis to be useful on an individual laboratory or system basis, and not as an industry wide technique.
Analysis of Band Formation in Mill Operation
Authors: Tokita Noboru
Published: February 2011

A theoretical method has been developed to provide a rational means for preventing improper fast roll banding in drop mill operation. For a given material at a certain mill temperature, the material tends to go to the back roll with a very narrow nip distance. The material will go to the front roll at a certain nip distance as the nip is widened and will return to the back roll as the nip is again narrowed. This nip position is called the Front-Back Transition Point. A dimensionless number, the “Band Formation Index”, N0, is constant at the front-back transition point regardless of the type of mill and is a function of the friction ratio, nip distance at the transition point, and radius of the mill rolls. Applications of the N0 concept to a factory mill operation have been discussed, and practical means to avoid back roll banding and bagging have been described.
Rheology of Plastisols of Poly(Vinyl Chloride)
Authors: Collins E. A. , Hoffmann D. J. , Soni P. L.
Published: February 2011

The viscosity of PVC plastisols is seen to be affected by numerous variables. Increase in concentration of the resin causes the viscosity to rise, with the increase being more abrupt at the higher concentrations. Deviation from Newtonian behavior also increases with concentration. Decrease in the size of particles results in an increase in viscosity, the effect being more pronounced at low shear rates. Broadening the distribution of particle sizes results in a decrease in viscosity. Porous particles yield plastisols with higher viscosity as compared to nonporous compact particles. The type of plasticizer also affects the viscosity. A plasticizer which is a better solvent for PVC (low value of polymer-solvent interaction parameter, χ) results in a higher viscosity due to an increase in the amount of dissolved polymer. Additives such as alcohols and soaps affect the viscosity in an, as yet, unknown way. Fillers, heat stabilizers, and pigments also increase the viscosity. With increasing temperature, the viscosity first decreases, passes through a minimum and then increases until gelation. With further rise in temperature the viscosity again decreases and then levels out before degradation occurs. In future work, particular emphasis needs to be given to the understanding of the basic mechanism involved in the effect of additives on the flow behavior. Systematic experiments with a range of well-defined particle sizes and over a wide range of shear rates are also needed. A better understanding of the factors affecting the behavior of plastisols will go a long way in changing the art of plastisol formulation to a science.
Approximate Expressions for the Elastic Constants of Cord-Rubber Laminates
Authors: Walter J. D. , Patel H. P.
Published: February 2011

The relatively simple equations given herein for the four independent elastic constants of a single ply of cord and rubber and for the three independent elastic constants of a cord-rubber angle-ply laminate can be used to assess with sufficient accuracy for many purposes the effect of changes in constituent material properties and/or ply geometry on the stiffness characteristics of unidirectional, filamentary composites used in pneumatic tires.
Application of TMA for Rapid Evaluation of Low-Temperature Properties of Elastomer Vulcanizates
Authors: Brazier D. W. , Nickel G. H.
Published: February 2011

Static thermomechanical analysis has been investigated as a method for determining the low-temperature properties of vulcanizates. Dimensional changes of a sample in free expansion, indentation, or tension are monitored as the sample is heated at a known and reproducible rate. The first derivative of the dimensional change is simultaneously recorded. TMA/DTMA data obtained in free expansion gives the linear thermal expansion coefficient at any temperature during the experiment. The glass transition is observed as a change in slope as in dilatometric determinations. In the indentation mode, the thermogram is the result of competition between thermal expansion and indentation. For tension measurements, the thermogram records the additive sum of thermal expansion and tensional strain development. For indentation and tension, the glass transition is obtained by a standard extrapolation method. A maximum in the DTMA thermogram is also observed which represents the maximum rate of change as the sample is heated through the glass transition range. The temperature of this maximum, Tgd, is characteristic of a vulcanizate. Variation in scan rate between 2 and 20°C/min has little effect on Tgo and no effect on Tgd. At 50°C/min, thermal gradient effects predominate. For a wide range of vulcanizates in tension or indentation, Tgo or Tgd versus the Gehman rigidity modulus gives a linear relationship. Exact temperature agreement is not observed because of differences in the experimental techniques. In blends, several Tgd values are observed. Plasticizer effects can either be observed by a shift in the Tgo or by a change in the thermogram profile, the extent of indentation and temperature range over which it occurs. The extent of indentation correlates with vulcanizate hardness as expected. The indentation of a rubber sample by a flat probe has been treated mathematically in the literature, and the determination of Young's modulus by TMA/DTMA is now being investigated. In conclusion, the ease of sample preparation and the rapidity of TMA/DTMA measurements offers a quick approach to assessing the low-temperature properties of vulcanizates. At 20°C/min scan rate, runs can be completed in as little as four minutes (80°C total scan) if the sample has a single transition.
A Quantitative Study of the Carbon Black Reinforcement System for Tire Tread Compounds
Authors: Veith A. G. , Chirico V. E.
Published: February 2011

This comprehensive program clearly shows the influence of the four defined reinforcement system variables. The tread wear testing conducted over an extremely wide severity range illustrates how the influence of each variable or factor changes as the tire use of test severity is changed. The quantitative influence of the four variables is best illustrated by the index severity gradient, while the index range serves as a quick indicator. The influence of each factor of the reinforcement system increases as general test severity is increased. Carbon blacks with high structure and surface area are substantially superior to blacks with normal structure and surface area at the higher test severities. At the higher general severities, increased oil content produces higher wear rates. At any given severity level, the rate of wear passes through a minimum as carbon black level is increased. The carbon black content at this minimum wear rate shifts to higher values as general severity is raised. Test results at a series of specific cornering force levels (0.10–0.30 g range) indicate that the relative wear of typical tread compounds demonstrates crossovers of index values. Compounds that show superior wear resistance compared to a reference compound at high cornering severities often show inferior wear resistance at low cornering severities. Therefore, for maximum tread life or wear resistance, the reinforcement system with any tread rubber or rubber blend must be carefully adjusted to the anticipated level of tire use severity. The introduction of improved-technology carbon blacks with increased rubber-black interaction that is promoted by high DBP and EMA levels is a substantial advancement in rubber materials science and is most important for the production of high-performance long-treadlife tires.
A Fatigue Resistant Polychloroprene Compound for High Temperature Dynamic Applications
Authors: Tabar R. J. , Killgoar P. C. , Pett R. A.
Published: February 2011

A polychloroprene material has been developed which can replace the natural rubber materials traditionally used in dynamic, fatigue-producing applications, when these applications require high temperature stability. An optimized compound based on a mercaptan modified polychloroprene with large particle high structure carbon black, silica filler and rapeseed oil has superior compression set, improved heat aged fatigue life and comparable dynamic properties to current NR compounds. This CR compound was designed to have good fatigue life while keeping compression set to a minimum. A positive correlation between tear resistance and fatigue life has been demonstrated for a series of CR compounds.
Interlaminar Shear Strain Measurements in Cord-Rubber Composites
Authors: Lou A. Y. C. , Walter J. D.
Published: February 2011

The present work is an experimental study using an X-ray technique to measure directly the internal distribution of interlaminar shear deformations which occur during uniaxial extension of two-ply, cord-rubber, angle-ply laminates—both balanced and unbalanced. Significant interlaminar shear strains were developed between the two generally orthotropic layers of one-inch-wide specimens, which decreased almost linearly from a maximum at the edges to zero at the center line. These measurements and those as a function of cord angle were in good agreement with predictions obtained from various theories of laminated shear-flexible composites.
New Developments in a Dynamic Wire Adhesion Test
Authors: Wagner M. P. , Hewitt N. L.
Published: February 2011

The performance of the rubber-wire belt in radial tires is, of course, critical to the safety of the tire. While initial adhesion between the rubber and the steel cord is important, the only meaningful adhesion is that retained during the dynamic life of the tire. This depends on the fatigue resistance of the rubber-cord composite, as well as the resistance to deterioration from hostile environments, such as heat, oxygen, and humidity. Static pullout, even after environmental aging, bears little relation to dynamic performance in tires. No dynamic adhesion test, short of tire testing, has had widespread use. In a previous publication a dynamic test for rubber-wire adhesion was described which appeared to relate to the tire performance of the rubber skim stock. This test has been further developed and evaluated in relation to tire performance. Additionally, the test has been used as a screening method to evaluate various additives in the rubber skim formulation.
A Surface Study of Ozone Attack and Antiozonant Protection of Carbon Black Loaded Natural Rubber Compounds
Authors: Andries J. C. A. , Rhee C. K. , Smith R. W. , Ross D. B. , Diem H. E.
Published: February 2011

This work reports a direct surface analysis of ozonization of carbon black loaded NR compounds by ATR and SEM. On ozonization of raw NR or NR containing carbon black, a thick layer builds up consisting of ozonides and carbonyl compounds. It is suggested that this layer is composed principally of the reaction products of ozone with unsaturated fatty acids and unsaturated fatty acid esters found in NR. On ozonization of cured and uncured carbon black loaded NR compounds containing curatives, the NR is attacked causing a decrease of rubber on the surface and a corresponding increase in the surface concentration of carbon black. The thick ozonide/carbonyl layer did not form, probably due to the coordination of the fatty acids and esters with ZnO, which was added with the curatives. On ozonization of carbon black-loaded NR compounds containing N,N′-dioctyl-p-phenylenediamine antiozonant, a continuous film is seen by SEM which has an ATR spectrum essentially identical to ozonized antiozonant. There is no evidence of ozonized NR products, or of complex reaction products between antiozonant and ozonized NR. These results are consistent with a dual scavenger and protective layer mechanism for antiozonant protection.
High Performance Nitrile Rubber Automotive Fuel Hose
Authors: Horvath James W.
Published: February 2011

The GM-6165M specification represents a significant upgrading of the performance of nitrile rubber based automotive fuel hose. Industry acceptance of this specification could lead to consolidation of hose types, and a cost saving if it displaces epichlorohydrin rubber. Compounding to meet the GM hose specification requires a departure from traditional carbon black formulations. A specific selection of each compound ingredient for its contribution to the total performance of the hose is necessary. Bound antioxidant nitrile rubbers are recognized by those who have seriously worked with them as superior performance polymers. Their service performance is unmatched by any other nitrile rubber in the applications which have developed for them in the Automotive Industry. They have consistently performed better than suggested by laboratory testing. This report demonstrates how to compound the 28% acrylonitrile Chemigum HR-765 to meet the severe requirements of GM-6165M.
Reinforcement of Uncured and Cured Rubber Composites and Its Relationship to Dispersive Mixing—An Interpretation of Cure Meter Rheographs of Carbon Black Loaded SBR and Cis-Polybutadiene Compounds
Authors: Lee B. L.
Published: February 2011

A new approach has been proposed to characterize the state of mixing of carbon black-loaded SBR and cis-polybutadiene compounds. The basic concept is that carbon black aggregates, present when the dispersion is imperfect, affect the modulus of the uncured compound more than that of the cured compound. From cure meter curves, the torque values before and after curing can be related to moduli which can, in turn, be analyzed to give information on the state of aggregation of the carbon black. An equation is proposed which correlates the relative modulus values with volume fraction of carbon black, morphology (packing or state of aggregation) of carbon black, and polymer-carbon black interaction.
Model Compound Vulcanization—Part III. The Relationships between Sulfidic Product Yield and Stress-Strain Properties
Authors: Lautenschlaeger F. K.
Published: February 2011

Twenty accelerators were compared by model compound vulcanization, (MCV). A relationship was established between total sulfidic product yield and tensile modulus (300%) of natural rubber vulcanizates. In previous work, two types of accelerators were distinguished by MCV on the basis of their distributions of the isomeric monosulfide reaction products. Type A accelerators consists of a wide range of functional compounds such as sulfenamides and guanidines. Type B accelerators contain a thiocarbamyl or a thiophosphate group. These Types of accelerators can also be distinguished on the basis of their relationship between sulfidic product yield in MCV and tensile modulus. The difference between these two Types of accelerators can also be derived from their relationship between tensile modulus and failure properties such as tear strength and tensile strength. Type A accelerators show a somewhat higher tear and tensile strength at a given tensile modulus value. The difference is attributed to the different distribution of sulfidic crosslinks, and possibly to chain scission in vulcanizates of Type B accelerators.
Peel Mechanics for an Elastic-Plastic Adherend
Authors: Gent A. N. , Hamed G. R.
Published: February 2011

The force required to propagate a 180° bend in an elastic-plastic strip has been calculated from elementary bending theory. Measured forces for Mylar strips of various thicknesses, bent to various degrees, were in good agreement with these calculated values. The corresponding additional stripping force in a peeling experiment will depend upon the thickness of the elastic-plastic adherend, becoming zero both for infinitesimally thin adherends and for those exceeding a critical thickness tc and passing through a maximum value at intermediate thicknesses. Published data are in good agreement with these conclusions. For a strongly adhering strip, higher peel strengths are found for a peel angle of 180°, compared to 90°, and the effect is greater than can be accounted for solely by plastic yielding of the adherend. It is attributed in part to greater energy dissipation within the adhesive layer.
Inflation Pressure Loss in Tubeless Tires—Effects of Tire Size, Service, and Construction
Authors: Coddington D. M.
Published: February 2011

Maintaining proper inflation pressure in tubeless tires, particularly radials, is critical to maximum tread wear life, durability, and minimum rolling resistance for vehicle fuel economy. This paper has discussed experimental studies of tubeless tire inflation pressure loss and how it is affected by tire size, operating pressure and temperature, and innerliner construction. Inflation pressure loss rates have been measured for varied commercial production tire constructions and sizes under static, constant temperature conditions. Pilot plant built radial passenger tires with varied innerliners have been tested for inflation loss rate, both statically and dynamically. A model equation has been developed to relate inflation pressure retention (IPR) to principal parameters of tire geometry, service and innerliner construction. Correlation of predicted air retention with actual performance is promising. A tire immersion test procedure has been employed to demonstrate air loss via migration and to study its paths. These studies indicate that properly fitted tubeless tires, free of mechanical leaks, can still have significant pressure loss via permeation; that the rate of loss increases as tire size is reduced; and that an ultra-low permeability innerliner can greatly improve tire inflation retention under static and dynamic service conditions.
Crosslinking and Mechanical Properties of Liquid Rubber. I. Curative Effect of Aliphatic DIOLS
Authors: Minoura Yuji , Yamashita Shinzo , Okamoto Hiroshi , Matsuo Tadao , Izawa Michiaki , Kohmoto Shun-Ich
Published: February 2011

The structure-property relationships of polyurethane elastomers derived from a liquid hydroxyl-terminated polybutadiene/low molecular weight aliphatic diol/diisocyanate system were studied. The effects of the amount of low molecular weight diol on the mechanical properties of the elastomer were discussed on the basis of the results of stress-strain, swelling, dynamic viscoelasticity, x-ray diffraction, etc. It was found that some particular combinations of low molecular weight diol and diisocyanate specifically affect the properties of elastomers. When the mechanical properties of the elastomers were plotted against the number of methylene carbons in the low molecular weight diol, characteristic zigzag patterns were obtained. These patterns were explained by the difference in the packing and the dependence of the strength of intermolecular hydrogen bonding on whether the number of the methylene carbons was even or odd. This assumption was confirmed by x-ray diffraction.
Mechanisms of Antioxidant Action: Rubber-Bound Antioxidants Based on Nitrones—I. Non-Sulphur Vulcanizates
Authors: Scott G. , Smith K. V.
Published: February 2011

The antioxidant activities of a number of N-phenyl nitrones containing phenolic functions were compared with N-methyl nitrones and conventional antioxidants in peroxide and TMTD sulphurless vulcanizates. The N-phenyl nitrones were found to be effectively bound during vulcanization; whereas, the N-methyl nitrones were not. Unhindered phenols reacted to a higher degree and were relatively more effective than the typical hindered phenol antioxidant structures. A conventional bisphenol was effective in the sulphurless vulcanizate after solvent extraction, but this is considered to be due to the formation of an insoluble zinc salt. Synergism was observed in the TMTD sulphurless vulcanizate both before and after extraction.
Complexities of Crosslink Density in Filled Elastomers
Authors: Polmanteer K. E. , Helmer J. D.
Published: February 2011

This work was undertaken to learn more about the complicated role of fillers in reinforcing siloxane polymers and attempt to clarify why silica fillers cause the crosslink density to increase significantly more in siloxane polymers than in hydrocarbon polymers. To carry out this study it was necessary to decide upon a method for determining the effective number of crosslinks. A simple mathematical expression applicable to both filled and unfilled elastomers was developed for use with a compression modulus technique for swollen vulcanizates. The fillers studied with polydimethylsiloxane (containing a small amount of methylvinylsiloxane) were a fume silica, wet process silica, diatomaceous earth, and two ground quartz silicas. The effect of concentration of network chains on tensile strength, modulus, and dynamic mechanical properties was compared for fume silica and diatomaceous earth filled stocks. All of the types of silica studied caused the crosslink density to increase several times over that of the unfilled vulcanizate. This may be contrasted with a factor of less than 2 for a filled (carbon black or silica filler) hydrocarbon polymer. The difference in behavior of the two polymer systems was attributed to a pronounced interaction between the siloxane polymer and the silica surface. The data indicated that filler structure has a more pronounced effect on crosslink density than surface area. It was found that the log of concentration of network chains gives a straight line when plotted as a function of volume fraction filler.
High-Performance Toluene Diisocyanate-Polypropylene Glycol Castable Elastoplastics
Authors: Berger S. Edmund , Szukiewicz Waclaw
Published: February 2011

This paper deals with relatively inexpensive castable polymers based on toluene diisocyanate and polypropylene glycol and having mechanical characteristics of both elastomers and plastics. Formulation changes that increase strength and hardness have an unfavorable effect on elasticity. Generally, the described polymers have better mechanical properties than similar known materials. Polymers produced by the one-shot method seem to exhibit better heat-aging properties than prepolymer-derived analogs. A range of applications is suggested.
Reaction between Cumyl Peroxide and Butyl Rubbers
Authors: Loan L. D.
Published: February 2011

The reaction between cumyl peroxide and butyl rubbers has been followed by means of molecular weight measurements. In all cases except that of the rubber with highest unsaturation the molecular weight falls, and the scission efficiency of the peroxide is found to depend quite markedly upon the unsaturation. For the rubber of highest unsaturation a small overall crosslinking reaction was observed. The results are interpreted as showing that cumyloxy radicals react with isoprene units in the chain about 300 times as fast as with isobutylene units. The molecular weight dependence on time during the reaction has been investigated but has not been satisfactorily explained.
Vulcanization of Elastomers. 40. Vulcanization of Natural Rubber and Synthetic Rubber with Sulfur in Presence of Sulfenamides. III
Authors: Scheele W. , Helberg J.
Published: February 2011

Vulcanization of natural rubber with sulfur was studied in presence of six sulfenamides, to determine the effect of the chemical constitution of the sulfenamide on sulfur decrease and on crosslinking. The results can be condensed as follows: (1) The kinetics of sulfur disappearance is in every respect qualitatively independent of the chemical constitution of the sulfenamide. (2) For the sulfenamides investigated, the smallest and largest rate constants for sulfur decrease differed only by a factor of two. (3) Greater differences are encountered in the induction times for sulfur decrease and for crosslinking. The latter are notably longer than those for sulfur disappearance. (4) The same activation energy, 23 kcal/mole, is derived from the temperature dependence of the induction times for all the sulfenamides. (5) The dissociation of sulfenamides in solution and their reaction with mercaptobenzothiazole were investigated further. The results provide the basis for a proposed reaction mechanism, which is presented in detail and can account for a number of the features typical of sulfenamide-accelerated vulcanization. (6) The drop in sulfur concentration goes at practically the same rate, if one introduces, instead of N, N-dicyclohexyl-2-benzothiazolesulfenamide, the corresponding ammonium mercaptide in equimolar concentration.
Reactions of Accelerators of Vulcanization with Rubbers of Different Structures
Authors: Dogadkin B. A. , Feldshtein M. S. , Belyaeva E. N.
Published: February 2011

Reactivities of various rubbers (SKB, SKS-30 and NR) were studied at vulcanization temperatures, employing MBTS, CBS and sulfur as vulcanizing agents. The systems, rubber plus accelerator, and rubber plus accelerator plus sulfur were subjected to such temperatures. Reactivities of the rubbers were determined by measuring the degree of dehydrogenation indicated by formation of MBT. Reactivities were also determined by the addition of RS⋅ radicals to polymer chains, the variation in maxima of gelling and the kinetics of addition of elementary sulfur. Dehydrogenation resulting from addition of accelerator radicals to polymer chains in the rubbers assumed the following order: SKB > SKS-30 > NR. Reactivity of elementary sulfur to rubbers, in the presence of the accelerators employed, assumed the reverse order; NR > SKS-30 > SKB. The differences in the reactivities of the various rubbers is associated with the peculiarities of their structures.
Consequences and Development of an Invention
Authors: Ziegler Karl
Published: February 2011

The awarding of the Nobel Prize for Chemistry, for the year 1963, is related to the precipitous expansion of macromolecular chemistry and its industrial applications, which began precisely ten years ago at my Max-Planck-Institute for Coal Research, in Mülheim/Ruhr. The suddenness with which this began, and the rapidity with which it was propagated are comparable to an explosion. The energy sources in this case were the ingenuity, activity, creative imagination and bold concepts of the many unnamed chemists, designers and entrepreneurs in the world who have fashioned great industries from our humble beginnings. If today I stand with my colleague Natta, who has been particularly effective in promoting this explosive wave, in the limelight of distinction, and do wish to manifest, with this address, my appreciation for the honor bestowed upon me, I must begin by thanking these many anonymous persons. They, too, deserve this distinction. The extent of this “explosion” may be illustrated by two charts, in which the location of newly-established plants is indicated. The places marked by black circles refer to new production facilities which, though concerned with low molecular weight materials, nevertheless also have some connection with the address I am delivering today (Figures 1 and 2). The new development had its inception near the end of 1953, when I, together with Holzkamp, Breil and Martin observed, for several days, an almost dramatic occurrence: that ethylene gas will polymerize very rapidly with certain catalysts that are extremely easy to prepare, at 100, 20 and 5 atmospheres and, finally, even at normal pressure, to a high molecular weight plastic.
Spherulite Morphology in Thin Films of Natural Rubber
Authors: Andrews E. H.
Published: February 2011

Crystalline ‘spherulites’ grown in ultra-thin films of natural rubber at − 26° C were examined in the electron microscope. The spherulites form hollow domes, like blisters in the film, which collapse under electron irradiation producing remarkable fiber-like patterns of folds and creases. Within the spherulite, crystalline and amorphous regions coexist and the former appear to grow to a preferred thickness of a few hundred angstroms with the molecular chains oriented perpendicular to the film. The molecules are thus almost certainly folded as in polymer single crystals grown from dilute solution. Electron diffraction data suggest that relatively large regions of the spherulite correspond to single crystals. A growth mechanism for the spherulites is proposed.
From Stereospecific Polymerization to Asymmetric Autocatalytic Synthesis of Macromolecules
Authors: Natta Giulio
Published: February 2011

Macromolecular chemistry is a relatively young science. Though natural and synthetic macromolecular substances had long been known, it was only between 1920 and 1930 that Hermann Staudinger placed our knowledge of the chemical structure of several macromolecular substances on a scientific basis. In the wake of Staudinger's discoveries and hypotheses, macromolecular chemistry has made considerable progress. Very many synthetic macromolecular substances were prepared both by polymerization and by polycondensation; methods were found for the regulation of the value and distribution of molecular weights; attempts were made to clarify the relationships existing among structure, chemical regularity, molecular weight, and physical and technological properties of the macromolecular substances. It was far more difficult to obtain synthetic macromolecules having a regular structure both from the chemical and steric point of view. An early result in this field, which aroused a certain interest in relation to elastomers, was the preparation of a polybutadiene having a very high content of trans-1,4 monomeric units, in the presence of heterogeneous catalysts. A wider development of this field was made possible by the recent discovery of stereospecific polymerization. This led to the synthesis of sterically regular polymers as well as to that of new classes of crystalline polymers.
Crystalline Morphology in Thin Films of Natural Rubber: Crystallization under Strain
Authors: Andrews E. H.
Published: February 2011

The morphology of thin films of natural rubber crystallized under unidirectional strain has been examined in the electron microscope. As strain increases the spherulitic morphology of unstrained films gives way gradually to a fibrillar morphology with crystalline filaments (α filaments) measuring 60 by 250 A˚, growing perpendicular to the strain axis. The nucleation of these filaments is governed by the amount of strain but their rate of growth depends only on temperature and time. At very high strains (>300%) crystallization occurs rapidly allowing no time for filament growth, so that the resulting morphology consists of chains of nuclei (γ filaments) running in the direction of extension. The high strain transition from α to γ filaments is accompanied by no change in the electron diffraction pattern, but the earlier transition from spherulitic to filamentous growth reveals a rotation of the molecular axis into the direction of strain. This appears to correspond to a physical rotation of the α filaments about their direction of growth.
Heterogeneous Structure in Blends of Rubber Polymers
Authors: Walters M. H. , Keyte D. N.
Published: February 2011

The phase contrast microscope has been used to examine blends of rubber polymers. Mixing on a molecular scale was never observed, the more homogeneous blends consisting of a pair of interlocking “networks” with a mesh diameter of about a micron. Blending was less perfect when the polymers were of widely different viscosities, and in the worst cases consisted of lumps of the stiffer polymer embedded in the softer polymer. Blends prepared by drying mixed solutions were always exceedingly heterogeneous. Physical properties of gum stocks were not greatly affected by the size of this heterogeneity, although there was evidence from electron microscope surface replicas that rupture surfaces tend to follow the interface between the polymers. The distribution of filler, zinc oxide and protein in blends was studied using a variety of techniques. It was found that these materials (and probably many other compounding ingredients) are not always evenly distributed between the polymers, and this may be expected to affect adversely the physical properties.
Determination of Cis-1,4 and Trans-1,4 Contents of Polyisoprenes by High Resolution Nuclear Magnetic Resonance
Authors: Chen Hung Yu
Published: February 2011

A method is described for the determination of the cis-1,4 and trans-1,4 contents of 1,4-polyisoprene by nuclear magnetic resonance techniques. The error of the method is estimated to be less than 0.5%. The method can be extended to include the determination of the 1,2 and 3,4 contents of polyisoprenes. The error in these cases is estimated to be between 2 and 3%. The results obtained with three synthetic polyisoprenes are presented.
Creamed Latex Concentrate
Authors: Duckworth I. H.
Published: February 2011

Concentrated natural rubber latex accounts for nearly 10 per cent of the total Malayan rubber exports (120,000 tons in 1963). Over 90 per cent of this latex is concentrated by centrifuging. About one quarter of the remainder (2,800 tons in 1963), for which there is a steady demand particularly in America, is produced by the creaming process. In this paper a commercial process for preparation of creamed concentrate is described and the properties and uses of the product are discussed.
A Transition in Cis-1,4-Polybutadiene
Authors: Bianchi Umberto , Bianchi Estella
Published: February 2011

This paper deals with measurements of the internal pressure, Pi, carried out on cis-1,4-polybutadiene (97% cis structures). The values obtained for Pi, which represents a measure of molecular cohesive forces, show that a sharp drop in internal cohesion takes place at a temperature of about 57° C. This accounts for the behavior exhibited by this elastomer when processed on a roll mill at the same temperature.
Vulcanization with Maleimides
Authors: Tawney P. O. , Wenisch W. J. , van der Burg S. , Relyea D. I.
Published: February 2011

Mono- and bismaleimides were evaluated as curing agents to determine the effect of structure on crosslinking ability. Activity of N-phenylmaleimide derivatives (monomaleimides) as crosslinking agents is highly dependent upon the substituent on the phenyl group. Activity of bismaleimides is likewise affected by the nature of the moiety connecting the maleimide rings. Isomaleimides and itaconimides are less effective curatives. Initiators for maleimide cures include peroxides and sulfur accelerators of the thiazole type. Saturated and unsaturated hydrocarbon rubbers, except those containing a high percentage of isobutylene units, are vulcanized by a maleimide-initiator system. One of the attractive features of a maleimide curing system is that physical properties of the cured rubbers are independent of curing temperature. Further, these vulcanizates have the good aging characteristics typical of nonsulfur-cured vulcanizates. In contrast to sulfur vulcanization, the maleimide curing systems do not markedly affect the ability of elastomers to crystallize when stretched. Therefore, the T50 test cannot be used to assess the state of cure of maleimide-natural rubber vulcanizates. Maleimides containing an appropriate second functional group can be used as self-accelerating curing agents or as adhesives.
Crosslink Formation during Aging of Natural Rubber Vulcanizates
Authors: Maisey L. J. , Scanlan J.
Published: February 2011

The effect of antioxidant on the crosslinking reaction occurring during the oxidation of sulphur vulcanizates of natural rubber was investigated by using both continuous and intermittent stress relaxation measurements. Similarly, by means of continuous stress relaxation and equilibrium swelling measurements the cross-linking reaction in vacuum was followed. The presence of antioxidant or removal of air reduced considerably both continuous and intermittent relaxation and also the difference between them, which measures the crosslinking. The crosslink formation must therefore form part of the sequence of oxidative reactions.
Influence of Chemical Structures of Polyurethans on their Crystallization Capacities
Authors: Myuller B. E. , Apukhtina N. P. , Klebanskii A. L.
Published: February 2011

1. The relationship between chemical structure of urethan polymers and their crystallization capabilities has been studied. 2. It has been shown that synthetic polymers based on glycol esters; di-, tri-, and hexamethylene adipate urethans, and also polymers with side groups (methoxy-methyl- and propylethylene adipate urethans) are amorphous polymers. 3. It has been established that tetramethylene adipate urethan has the highest crystallization rate, followed by pentamethylene adepate urethan (2.2 per cent per hour), and then trimethylene- and ethylene adipate (0.11 and 0.06 per cent per hour, respectively). The half-times of crystallization for the latter three are 40, 1120, and 1060 minutes, respectively, and the degree of crystallization, 2.1, 1.7 and 1.0 per cent.
Laboratory Testing of Tread-Stock Abrasion Resistance at Constant Transmitted Power II. A New Laboratory Abrasion Instrument
Authors: Davison S. , Deisz M. A. , Meier D. J. , Reynolds R. J. , Cook R. D.
Published: February 2011

The first paper in this series described the results of laboratory measurements and road evaluation tests on a series of tread stocks over a wide range of severities, and indicated the various advantages and limitations involved in the laboratory and road measurements. It is the purpose of the present paper to describe in greater detail the abrasion instrument used in these studies. The laboratory measurement of abrasion resistance was reviewed by Buist in 1950. The paper describes 21 laboratory abraders. Developments in abrasion instruments and methods which have since appeared in the literature have been primarily concerned with modifications and refinements on these basic types. A novel type of instrument described by Newton, Grinter and Sears, uses stationary knife blades to scrape a rotating rubber disc. The research group at the Emeryville Shell Development laboratories investigating characterization of elastomeric properties some years ago decided that its requirements in laboratory abrasion testing could best be satisfied by an abrader of the Dunlop-Lambourn type because of its versatility in providing control of angular velocity, load, slip, energy transfer, and temperature. Also, in the Lambourn abrader, the motor-driven vulcanizate wheel driving a braked abrasive wheel resembles the action of a driven tire rolling on a pavement. A given section of the tire tread surface is subjected to stressing and abrasion only during the portion of the cycle when in direct contact with the abrading surface. Cooling and relaxation occur during the portion of the cycle when the section is not in contact with the surface. Viscoelastic and abrasion mechanisms can operate in the laboratory at frequency levels approximating those encountered in road tests.
Infrared and Nuclear Magnetic Resonance Studies of Microstructures of Polychloroprenes
Authors: Ferguson Raymond C.
Published: February 2011

High resolution infrared and nuclear magnetic resonance spectra confirm the structure of cis-polychloroprene prepared by a stereospecific route. Head-to-tail, head-to-head, and tail-to-tail sequence isomerism in both as- and trans-polychloroprenes has been discovered and measured quantitatively by high resolution NMR spectroscopy. The irregularity in the microstructure of neoprenes proves to be more extensive than was previously suspected.
Effect of Blending on Molecular Weight Distribution of Polymers
Authors: Haward R. N. , Wright B. , Williamson G. R. , Thackray G.
Published: February 2011

The effect of blending polymers of different molecular weight on the Q value (Q=Mw/Mn) of the blend has been considered. A mathematical expression is derived, and it shows by a simple application to monodisperse systems that blending over a wide molecular weight range is necessary to give high Q values. These principles are then applied to the ease of Ziegler and Phillips type high density polyethylenes having wide log-normal molecular weight distributions. In this way it is shown that only blending over a very wide melt index range, e.g., 1000/1, can be expected to have a measurable effect on Q. A series of physical measurements on blended and homogenized Ziegler polyethylenes shows no significant differences between blends and directly produced polymers.
Crosslinking Efficiencies of Cumyl Peroxide in Unsaturated Synthetic Rubbers
Authors: Loan L. D.
Published: February 2011

Crosslinking efficiencies of cumyl peroxide in SBR, cis-polybutadiene, acrylonitrile-butadiene rubber, and polychloroprene have been measured. For the first two rubbers approximately ten crosslinks are formed per molecule of peroxide decomposed, while for the acrylonitrile-butadiene rubber an efficiency close to unity is found. With polychloroprene approximately two molecules of peroxide are used for each crosslink formed. Analysis of the low molecular weight products of the reaction shows that ease of hydrogen abstraction by cumyloxy radicals decreases in the order given above.
Crosslinking in Low Unsaturation Rubbers
Authors: Crespi G. , Arcozzi A.
Published: February 2011

Vulcanization kinetics of low unsaturation rubbers (butyl rubber, ethylene propylene dicyclopentadiene terpolymer, and ethylene propylene cyclooctadiene terpolymer) have been studied by assuming that it involves a crosslinking reaction and a cleavage of sulfur bridges already formed. The crosslinking reaction can be explained by assuming a second order mechanism with respect to the concentration of the double bonds, whereas the cleavage reaction can be explained by assuming a first order mechanism with respect to the concentration of the sulfur crosslinks already formed. The overall vulcanization reaction has been followed through the variations of the moduli (at 200 per cent and at 300 per cent) and of the elongation at break. The crosslinking rate constant has been found to vary depending on the type of elastomer; decreasing in the order ethylene propylene cyclooctadiene terpolymer > butyl rubber > ethylene propylene dicyclopentadiene terpolymer.
Readily Curable Chlorinated Poly-α-Olefins and Ethylene-α-Olefin Copolymers
Authors: Makowski Henry S. , Cain William P. , Wei Peter E.
Published: February 2011

Chlorinated polyolefins have been prepared which are readily curable at 287° F at low chlorine contents. Their preparation depends primarily on using a chlorination solvent, generally an aromatic compound, which introduces both reactive chlorine and unsaturation. A process has been developed wherein ethylene propylene copolymers are first prepared and then chlorinated in the same aromatic solvent. Chlorinated copolymers have been cured with a variety of formulations which take advantage of the lability of chlorine atoms or of unsaturation, or of both. Properties of vulcanizates of chlorinated ethylene propylene copolymers are described.
Ethylene Propylene Dicyclopentadiene Terpolymerization
Authors: Sartori G. , Valvassori A. , Faina S.
Published: February 2011

Monomers (both monoolefinic and diolefinic) containing the bicyclo[2.2.1] heptene system copolymerize with ethylene and propylene by opening the double bond of the endo-methylenic system without rupture of the bicycloheptene system itself. Therefore, only diolefinic monomers produced unsaturated terpolymers. The rate of ethylene-propylene-dicyclopentadiene terpolymerization and the relative reactivity of ethylene and propylene are influenced by the concentration of dicyclopentadiene present in the liquid phase. The rate of vulcanization of ethylene-propylene-dicyclopentadiene terpolymers is slower than that of the other synthetic elastomers (butyl rubber, ethylene-propylene-cyclooctadiene-1,5 terpolymer).
Graft Copolymerization : On the Structure of the Graft Phase and the Mechanism of Grafting Polybutadiene Rubber
Authors: Gesner B. D.
Published: February 2011

Polybutadiene rubber undergoes grafting by direct interaction with initiator radicals rather than by transfer with growing radical chains. The insolubility of the grafted rubber is probably caused by crosslinking, which competes with grafting.
Fundamental Properties of High Structure Blacks
Authors: Voet Andries
Published: February 2011

The present study reports properties connected with physical and chemical surface reactivity of HAF and ISAF carbon blacks of a wide variation in structural characteristics. Methods used include determination of bound rubber and of crosslink in density in vulcanizates, adsorption of polar material from solution, adsorption and heat of adsorption of polar and nonpolar gases and vapors in the gas phase, retention of adsorbed vapors after temperature increase, electron micrography, chemical characteristics such as hydroquinone, quinone and oxygen contents and free radical activity. The results fail to show any direct connection between physical or chemical reactivity of the surface and structure. It appears that presumed manifestations of enhanced surface reactivity of high structure blacks either are nonexistent or can be explained from secondary effects not directly connected with reactivity of the particle surface. It could be shown that improved reinforcing characteristics of high structure carbon blacks are directly related to particle structure, either through particle fusion (persistent structure) or though van der Waals' type of attractive forces (transient structure).
Rotating Ring Crack Growth Test
Authors: Beatty J. R. , Juve A. E.
Published: February 2011

Groove cracking of tires is a continuing problem. Cracking takes place in two steps; initiation and growth. Initiation is inevitable in service from ozone cracking, cuts and nicks. This indicates that a study of groove cracking should concern itself with cut growth. A laboratory test has been developed to evaluate crack growth in vulcanizates under a variety of environmental conditions. The apparatus is compact, vibration free, and utilizes a ring-type specimen. Flexing is accomplished by running the specimen around two pulleys like a belt. Specimen preparation is simple and reproducible and a reasonable number may be tested simultaneously. Each specimen weighs approximately twenty grams and fifteen individually initiated cracks are measured on each. The large number of cracks measured makes the data amenable to statistical analysis. Strains and frequency of flexure were chosen to approximate those encountered in the service of a tire tread. Results obtained have been found to predict reasonably performance of tires on the road.