bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic Properties and Polymer Solvent Interaction Parameters for Silicone Rubber Networks
Authors: Seeley R. D.
Published: February 2011

The relationships of the volume fraction of rubber (silica reinforced silicone rubber vulcanizates) at equilibrium swelling to a corresponding solvent-rubber interaction parameter have been found to agree quite well with theory throughout the entire range of volume fractions investigated. Composite sigmoidal curves were constructed from the ϕrs versus μ data for the different vulcanizates. Temperature and solvent effects were found to merely shift the plotting points along the curves for the respective vulcanizates. Contrary to other work linear relationships between ϕrs and μ were found in this investigation only in the range of moderate dilations. Such relationships could lead to serious misinterpretations if the investigations involved ϕrs versus μ data near an inflection point. Thus, the value of μ relative to a corresponding ϕrs not only depend upon solvent (s) and temperature, but also upon the level of vulcanization at moderate to high dilations. The entropy, enthalpy, and free energy changes associated with the configurational changes occurring in the network structure of the rubber were calculated. The thermodynamic properties were found to be consistent and uniform throughout the dilation range. Limiting osmotic pressures were determined to obtain effective number average molecular weights of the crosslinked chains. The molecular weight values were found to average slightly less than three times those obtainable from ve/Vr data. Finally, this investigation has shown that reinforced silicone rubber vulcanizates at equilibrium swelling in a variety of solvents exhibit the swelling behavior predicted by theory. However, swelling behavior at moderate to high swelling was found to be unrelated to the rubber in general, but related more specifically to the network structure of the vulcanizate. At low dilations, the characteristics of the silicone rubber species control the swelling behavior.
Identification of Antioxidants, Accelerators and Plasticizers in Rubber Compounds by Column Chromatography and Ultraviolet and Infrared Spectrophotometry
Authors: Fiorenza A. , Bonomi G. , Saredi A.
Published: February 2011

This paper deals with separation of antioxidants, accelerators, and plasticizers in rubber compounds by column chromatography. The chromatographic diagrams obtained by a special ultraviolet detector and the spectra of the various fractions obtained from the extracts of eleven compounds are reported. With suitable reference samples, many other antioxidants and some other accelerators can be identified in addition to those tested in the present work. The identification of the components of the extract is improved examining the fractions also by IR spectrophotometry, employing either the technique of NaCl plates or, better, that of KBr pellets. Other very useful auxiliary techniques are paper and thin layer chromatography and gas chromatography.
Effect of Sulfur Crosslinks on Radical Recombination in Irradiated Elastomers
Authors: Kvashenko Yu Yu , Kuzminskii A. S. , Fedoseeva T. S.
Published: February 2011

It was found that sulfur crosslinks intensified radical decay in glassy polymers. The process follows a migration mechanism, free valency being transmitted both along and between molecular chains.
Rapid Method for Studying Molecular Weight Distribution of Isoprene Polymers
Authors: Polyakova G. R. , Pravikova N. A.
Published: February 2011

A nomogram was plotted for low molecular weight isoprene polymers of 1,4-cis- and 3,4-structures, which made it possible to obtain MWD curves of the polymers from titration curves. A study was made by turbidimetric titration of the MWD of isoprene polymers having 3,4-structure obtained in tetrahydrofuran at low temperatures, and 1,4-cis-isoprene polymers, obtained in a hydrocarbon solution with LiC2H5. It was found that MWD of isoprene polymers with 3,4-structure was considerably wider than that of 1,4-cis-polymers; this is in satisfactory agreement with kinetic views on the molecular distribution of such polymers.
Rubber Chemicals from Cyclic Amines. II Dithioamines and Sulfenamides as Accelerators and Curing Agents
Authors: Morita Eiichi , D'Amico John J. , Young Evan J.
Published: February 2011

Dithioamines and sulfenamides derived from various cyclic amines were evaluated as accelerators and vulcanizing agents. Structural variations of these compounds are correlated with their scorch delaying properties, accelerating activity and vulcanization efficiency, employing the Mooney Viscometer and the Monsanto Oscillating Disk Rheometer. The relative cure characteristics differed with changes in the basic structure of the compounds, and with the size and type of the cyclic amine moiety. However, the piperidine derivatives consistently showed longer scorch delay and slower mean cure rate than the corresponding derivatives of pyrrolidine, hexamethylenimine or heptamethylenimine. In the case of the thiazolyl sulfenamides, the type of substitution in the thiazolyl group also influenced scorch delay. An empirical relation was observed between the effect of concentration of the thiazolyl sulfenamides on scorch delay and the results of differential thermal analyses of sulfenamide and sulfur blends.
Reinforcement and Abrasion
Authors: Westlinning H.
Published: February 2011

Physical properties, and also abrasion resistance of vulcanizates are determined essentially by: the polymer, the network (crosslink density), and the molecular superstructure of the crosslinked network (reinforcement) introduced by the amount and type of filler. To establish the relation between reinforcement and abrasion one must first elucidate effects of polymer crosslink density. EXPERIMENTAL Measurement techniques.—Difficulties in determining the laboratory abrasion of rubber are well known. For the problem at hand, a method should be used which will give reproducible results with minimum effort. In addition, abrasion measurements should be possible for compounds ranging from unfilled to highly filled vulcanizates. Two basic principles had to be observed in developing an apparatus to fulfill these requirements: (1) surface velocity of the test specimens was selected to be commensurate with the rolling speed of tires, e.g. approximately 80 km/hr; (2) a relatively large amount of rubber should be worn off, to increase the accuracy of the determinations.
Advances in Tire Technology Introduction to Symposium. (Cleveland, Ohio, April 24, 1968)
Authors: Sjothun Irvin J.
Published: February 2011

The current interest in tires, transportation, and passenger safety in highway vehicles, prompted this symposium on advances in tire technology. Everyone is familiar with tires, at least to the degree that he recognizes them on his car. It seems the average layman thinks a tire is something that is somehow put together and thrown into a mold where it is given shape, but he has little conception of the compound, construction, or design engineering required. We are also hearing new as well as old names. Of tire types there are such names as bias, bias belted, and radial; of cord types such names as rayon, Tyrex, nylon, polyester, glass, and wire. You hear other terms such as wide oval, wide tread, aspect ratio, rim diameter, white wall, red ring, high performance, and many more. The tire carries the load, absorbs shocks, withstands impacts, goes through mud, ice and snow, and gives the consumer a minimum concern and minimum cost in spite of the ever increasing requirements placed on it.
Demographic Study of Tire Hazard Failures
Authors: Dobie W. J.
Published: February 2011

We have shown through the results of a detailed in-depth, nation-wide survey of tire road hazard damage a number of significant factors: (1) Tire cutting by glass is the most frequent cause of road hazard damage in all types of service and for all types of tires. (2) Road hazard damage due to rupture occurs more frequently on high speed highways than in any other type of service. Rupture damage is a more frequent occurrence in 4 ply nylon tires than in 2 ply rayon. (3) The relative incidence of road hazard damage is a function of both population density and precipitation.
Skid Resistance of Passenger Car Tires on Wet Surfaces
Authors: Maycock G.
Published: February 2011

This paper reports investigations into the effect of tread pattern, pattern modifications, tread material, and tire casing construction, on skid resistance of passenger-car tires at speeds between 25 and 80 mph on a range of wet road surfaces. The technique was to brake the front wheels of a car until they locked, and to record deceleration of the vehicle. From the deceleration record, both peak and locked-wheel values of braking force coefficients were obtained. The method is described and an assessment of the errors is given. The experiments showed the importance of adequate drainage of the region of contact between tire and road, particularly at higher speeds, in order to remove the lubricating film of water. Such drainage can be provided either by a tread pattern or a coarse road surface. The results indicate the importance of each and their inter-relation. Results of various modifications to a standard tread pattern are given; these show that on smooth surfaces worthwhile increases in wet road adhesion at high speeds can be obtained by suitable design of tire tread patterns. Magnitude of increases in friction due to changes in tread material are given for both peak and locked-wheel coefficients. Ratios of peak to locked-wheel coefficients have been calculated over a wide range of surface and tire combinations. They show the potential value of devices enabling a vehicle to make use of these high coefficients.
Lubricated Friction of Rubber. IV. Characteristics of Roads
Authors: Percarpio E. P. , Bevilacqua E. M.
Published: February 2011

We have described evidence showing that wet friction of rubber on hard surfaces is affected by two components in the hard surface—one deformation, the other abrasion. In this report we relate this to the properties of road surfaces and show that with appropriate simple measurements it is possible to estimate the relative importance of these two contributions in roads. SLIPPERINESS OF ROADS Data on slipperiness of roads taken under controlled conditions with a standard reference are rather limited, the most extensive material available applying. to European roads. We have therefore made a survey, which is continuing, in which we measure the properties of roads in use. Results reported here give us considerable confidence that roads are so similar in character that our sample is representative and that quantitative analysis of their surface characteristics can be made. It is well established that roads become slippery by polishing in use; the methods described here make it possible to estimate that extent of polishing in a quantitative way.
Kinetics of Alkyllithium Initiated Polymerizations
Authors: Hsieh H. L. , Glaze W. H.
Published: February 2011

The kinetics of alkyllithium initiated polymerizations is reviewed for publication in Rubber Reviews for 1970. It contains nine sections: introduction, the structure of organolithium compounds, rate of polymerization, rate of propagation, rate of initiation, molecular weight and molecular weight distribution, polymerization of diene and vinyl monomers in polar solvents, copolymerizations, and polymerizations of polar monomers. A total of 205 references are cited.
Mechanism of Emulsion Polymerization
Authors: Gardon J. L.
Published: February 2011

Emulsion polymerization is one of the most important processes for the manufacture of polymers for rubbers, plastics, coatings, finishes, and adhesives. By the correct choice of comonomers, initiators, surfactants, and reaction conditions, a great variety of latex products are manufactured which meet many specific requirements in their applications. However, there is a great gap between this mostly empirically developed and sophisticated technology and our scientific understanding of it. The present paper presents a theory based on a single internally consistent model which predicts several experimentally available data of emulsion polymerization: the particle size, the conversion—time relationship, the dependence of particle size and molecular weight on conversion, and the influence of surfactant, of initiator and of monomer. This theory is based on extension of the assumptions first proposed by Smith and Ewart and Haward, and later modified by Stockmayer and O'Toole. It differs from these earlier theories in that the derived relationships are quantitative and contain no adjustable parameters. Also, the validity limits of the predictions are defined. The present form of the theory does not apply to all monomers, initiators, surfactants and reaction conditions commonly used in the practice of emulsion polymerization although its predictions are in good accord with experimental results obtained with model systems complying with the assumed conditions.
Glass Transitions in Polymers
Authors: Shen M. C. , Eisenberg A.
Published: February 2011

We hope that the preceding presentation has made it clear that the glass transition is not a simple phenomenon, but a very complicated process which is still not understood in all of its ramifications. The nature of the glass transition temperature (Tg), to begin with, has been the source cf considerable controversy for many years. The observation of its rate effects, on the other hand, and its similarity to second-order transition, on the other, has caused much confusion. It is not until recently that there is promise for reconciliation. It appears at present that Tg is what one experimentally observes when the material is on its “slow boat” to T2 In other words, Tg is a kinetic manifestation of a thermodynamic process (T2). There is, in fact, no inherent controversy between these two views, since each explains one aspect of the “many-faced” transition. The solution of this problem was actually alluded to in the classical paper of Kauzmann, although it was not recognized as such. The credit of explicit clarification goes to Gibbs and DiMarzio, who first argued the case in quantitative terms.
Polychloroalicyclic Ketones as Promoters for Crosslinking Polymers
Authors: Morita E.
Published: February 2011

Polychloroalicyclic ketones are chlorine liberating compounds which in combination with activators and coagents promote crosslinking of saturated and unsaturated polymers. One of the most active ketone is octachloro-3-cyclohexen-l-one (OCTA). During the curing process the alicyclic ketones transform into phenols and probably some phenates. The most effective activators are magnesium and calcium hydroxides and oxides. These curing systems are also activated by acidic and basic fillers. Active coagents are sulfur, p-benzoquinones and maleimides. EPM of superior thermal stability is obtained with the chlorinated p-benzoquinones as the coagent. The apparent order of crosslink formation in EPM using these curing systems is pseudo first order. In case of OCTA/MgO/coagent system, the specific rate of crosslink formation is directly proportional to (MgO)1/2/(OCTA) and the maximum crosslinks formed vary linearly with (MgO)1/2/(OCTA). The OCTA system is most suitable for curing saturated polymers or their blends, and not for black stocks of high unsaturation polymers because of its high reactivity. Saturated polymers may be heated with OCTA and MgO and modified to unsaturated polymers which are curable by the conventional sulfur-accelerator system.
Tensile Rupture of Rubber
Authors: Thomas A. G. , Whittle J. M.
Published: February 2011

The dependence of tensile strength of a number of vulcanizates on temperature has heen studied. A critical temperature θc is found for natural rubber at which an abrupt change in strength occurs. This temperature depends on degree of crosslinking and also on the nature of the vulcanizing system. The presence of carbon black filler increases the strength above θc but has little influence on the value of θc or the strength at temperatures below it. The behavior can be explained qualitatively in terms of a change in mechanism of rupture from essentially a tear process above θc to a crack growth process below it. The influence of vulcanizing system is mainly due to changes in the nature of the crosslink rather than changes in regularity of the main chain as shown by the rate of low temperature crystallization.
Physics of the Slipping Wheel. II. Slip under both Tractive and Lateral Forces
Authors: Livingston D. I. , Brown J. E.
Published: February 2011

The mechanics of the slipping wheel has been investigated further with respect to the general problem of slip in any direction under the action of any combination of lateral and tractive force exerted by the road. The tire was considered to have two main directions of anisotropy in the contact surface, and a theory was proposed connecting the resultant force vector with the resultant slip vector regardless of their orientation. The connection was established through the use of a quantity called the slip-modulus which contains the lateral and longitudinal stiffness moduli and the slip components. The behavior of a tire may then be described by a characteristic relationship between the force and the slip-modulus, as has been found for pure lateral or longitudinal slip. Experimental measurements from three literature sources on the effects of tractive on lateral force were used to deduce the characteristic relationships, which represented a considerable condensation of the data. Thus, the theory was confirmed. The pressure distributions underlying these relationships were also calculated by a method given in this work and their distortions attributed to an artifact of variation of the ratio of the coefficient of friction to stiffness modulus with slip.
Research for a Uniform Quality Grading System for Tires. III. Breaking Energy
Authors: Simon B. G. , Mandel J. , Brenner F. C.
Published: February 2011

A test procedure designed to classify tires according to their average breaking energy has been applied to a sample of passenger car tires. Data are reported on 127 different tires of all grades and types over a range of sizes. A scaling system is devised and applied to the data. It is found that the system leads to conclusions similar to those derived from the original data.
Micrography of a Triblend
Authors: Marsh P. A. , Mullens T. J. , Price L. D.
Published: February 2011

A micrographic study has been made of a banbury-mixed triblend consisting of natural rubber, neoprene and ethylene-propylene terpolymer, of the composition 50 NR/30 CR/20 EPDM, in a pure gum blend as well as loaded with 35 phr N-330 black. A combination of techniques was used, including phase microscopy and electron microscopy of frozen as well as of embedded sections. Each of the above techniques contributed to the final interpretation of the observed complex phenomena. In the pure gum blend natural rubber forms a continuous phase. Neoprene rubber shows a three dimensional network of large strands of an average width of about three microns. The EPDM is dispersed in small globules throughout the matrix, generally of less than one micron diameter. Three different blends were made in which the carbon black was added to one single elastomer and then cut back with the remaining elastomers. The fourth blend was made by incorporating black in a preblend of the elastomers. A systematic approach to the evaluation of the carbon black distribution in triblends is described and its importance to reinforcement discussed. Problems in measurement of zone sizes are explained. The affinity of the black for the various elastomers is indicated. A major conclusion is that carbon black does not transfer from one elastomer phase to another during mixing. Most of the findings are applicable to all blend systems.
Effects of Termonomers on Crosslinking Rate and Crosslink Structure of Ethylene Propylene Terpolymers
Authors: Kujimoto K. , Nakade S.
Published: February 2011

A study was made concerning both the rate of crosslinking and the structure of crosslinks of terpolymers that have dicyclopentadiene, 1,4-hexadiene, methylene norbornene, and ethylidene norbornene for termonomers so as to look into the role of termonomers during crosslinking of ethylene propylene terpolymers. In the study, activation energy and frequency factor were determined by the rate constant of crosslinking. And differences in crosslinks were analyzed by both chemical and physical methods. Infrared analysis to follow the consumption of double bonds was adopted to examine the manner of crosslinking. With respect to the magnitude of the rate constant, ethylidene norbornene was first, followed by 1,4-hexadiene, methylene norbornene, and dicyclopentadiene. The structure of termonomers affected the apparent activation energy and the apparent frequency factor was subject to the influences of said structure and others including the variation in the degree of unsaturation. During the early stage of crosslinking, the formation of the polysulfide crosslink was paramount to all others and the speed of conversion therefrom either to disulfide-type or to monosulfide varied with the kind of terpolymers and was in proportion to the rate constant of crosslinking.
Relationships between Chemical Structures of Crosslink Sites and Physical Properties of Vulcanized Rubbers. Part V. Analysis of Chemical Structures of Combined Sulfur in Crosslink Sites for Various EPDM Vulcanizates
Authors: Imoto M. , Minoura Y. , Goto K. , Harada H. , Nishihira K. , Fujita H. , Fujimoto K. , Izuta T. , Kono K. , Fujioka K. , Shiota A. , Oba M. , Oshita H. , Usamoto T.
Published: February 2011

Various EPDM vulcanizates with different chemical structures of crosslink sites, such as C—C, C—R—C and C—Sz—C linkage, were obtained by using a variety of curing agents. C—Sz—C linkage was separated into polysulfide linkage and monosulfide linkage by using the LiAlH4 method which was confirmed beforehand with model compounds. The relationships between the chemical structure of combined sulfur in the crosslink sites and the type of curing agents used were clarified. For example, the mole ratios of polysulfide linkage to all the combined sulfurs in the vulcanizates by using DCP—S8, TMTD, S8—TMTD and S8-zinc dimethyldithiocarbamate curing system were respectively 0.35, 0.25, 0.53 and 0.82 at 160° C for 45 minutes. But in DCP—S8 curing system considerable C—C linkages seemed to be formed in addition to the C—Sz—C linkage.
Relationships between Chemical Structures of Crosslink Sites and Physical Properties of Vulcanized Rubbers. Part VI. Oxidative Degradation of EPDM Vulcanizates
Authors: Imoto M. , Minoura Y. , Goto K. , Harada H. , Nishihira K. , Fujita H. , Fujimoto K. , Izuta T. , Kono K. , Fujioka K. , Shiota A. , Oba M. , Oshita H. , Usamoto T.
Published: February 2011

Relationship between the chemical structures of crosslinks and the degree of oxidative degradation of EPDM vulcanizates was studied by stress relaxation and oxygen absorption measurements. It was found that the vulcanizates having C—Sx—C crosslink showed slower stress relaxation than the vulcanizate having other crosslink structures, i.e., C—S—C, C—C, and C—R—C. It was thought that C—Sx—C bond would reduce the scission of the network in oxidative degradation, since some polysulfide compounds had the same effect of protecting scission as antioxidant. The similar results were obtained in oxygen absorption measurements. In the case of heat aging, the vulcanizate having C—Sx—C linkage increased in crosslinks during aging and the rate of crosslinking was equal to the rate of scission of the network in the early stages, but the vulcanizates having other types of crosslinks did not show such behavior.
An Infrared Analysis for Ethylidenenorbor-Nene in Ethylene—Propylene—Ethylidenenor-Bornene Rubber
Authors: Levine I. J. , Haines R. G.
Published: February 2011

An infrared method based on the 5.88 μ absorption was developed for the analysis of ethylidenenorbornene in EPDM. The method was calibrated using a VPC analysis for unreacted monomer and by the addition of dichlorocarbene followed by an elemental analysis for chlorine. A check by NMR on a selected sample showed good agreement with the other methods.
Accessibility of the Carbon Black Particle Surface to Elastomers
Authors: Aboytes P. , Voet A.
Published: February 2011

Experimental carbon blacks were prepared with the generally encountered slit-shaped pores of discrete dimensions of 9,12.5, and 16 A˚ width in greatly differing size distribution. Equilibrium adsorption in the saturation range was determined in n-hexane for butadiene—styrene elastomers of the SBR type of average molecular weights of 1500; 2000; 15,000; and 300,000. In attempting to correlate the saturation adsorption values with carbon black surface areas, it was found that a simple linear relation in the range investigated could only be obtained by assuming that pores of 9 A˚ width were inaccessible to SBR of 1500 and 2000 MW; that pores of 9 and 12.5 A˚ width were inaccessible to SBR of 15,000 MW; and that all pores smaller than 20 A˚ width were inaccessible to SBR of 300,000 MW. The data indicated that there are no differences between high, regular and low structure blacks in saturation elastomer adsorption under conditions of equivalent dispersion. Equally, upon breaking the persistent carbon chain structure by dry ball milling in an inert atmosphere and equalizing the chemical surface properties by removal of surface oxides, no difference in elastomer adsorption from solution was observed. It must be concluded that commonly used high molecular elastomers do not have any access to smaller carbon black pores. Since access to the surface is a prerequisite for reinforcement, it is obvious that the surface in the pores of carbon black generally does not participate in reinforcing elastomers. The elastomer adsorbed per unit external black surface area appears to be independent of the carbon chain structure, indicating that the so called surface activity of the carbon black is independent of the chain length.
EPDM and Chlorobutyl Blends for Tire Sidewalls
Authors: Speranzini A. H. , Drost S. J.
Published: February 2011

Laboratory data have shown that the performance of tire sidewall components can be significantly improved by substituting EPDM and halogenated elastomers, either alone or in combination, for a portion of the highly unsaturated polymers now in use. Blends of EPDM and general purpose polymers provide improved weathering resistance, especially static ozone resistance. Blends of EPDM, chlorinated polymers and highly unsaturated elastomers offer a further improvement in weathering resistance and markedly better resistance to flex cracking. Chlorobutyl has been found to be more effective than polychloroprene in enhancing the dynamic properties of these blends. The level of performance achievable by these blends is a function of the chlorinated elastomer concentration. Current Los Angeles outdoor tire test results indicate that 25% RHC EPDM blends with general purpose elastomers perform adequately as sidewall components in the bias ply construction. The more severe dynamic sidewall flexing of the bias-belted and radial constructions, however, appears to require a higher level of sidewall performance. For these constructions, the tire test results indicate that select blends of EPDM, chlorinated butyl and highly unsaturated rubbers should provide satisfactory performance.
New Reactions for the Vulcanization of Natural Rubber
Authors: Baker C. S. L. , Barnard D. , Porter M.
Published: February 2011

One objective of a new crosslinking system for NR is a vulcanizate possessing good strength and fatigue properties and a high resistance to reversion; a second is a vulcanizate with reversibly thermolabile crosslinks. The reaction of amine-chloroboranes with NR was expected to give carbon-boron-carbon crosslinks possessing some measure of lability at high temperatures. In practice, the proportion of covalent crosslinks formed is very low and this is attributed to intramolecular additions and cyclizations. The majority of the effective crosslinks are stress-labile at ambient temperatures and the vulcanizates, therefore, have extremely high rates of creep and stress-relaxation. The nature of these crosslinks is still unknown. In all other aspects the physical properties of the vulcanizates are acceptable, reversion and aging resistance being particularly good. Surprisingly, the presence of the stress-labile crosslinks either in large preponderance or in various proportions with covalent crosslinks introduced by the compatible vulcanizing agents, dicumyl peroxide or TMTD-zinc oxide, did not impart the expected, very high tensile strengths. The amine-chloroborane vulcanizates are resistant to ozone cracking because of the rapid relaxation of surface strains. The second novel vulcanization system examined utilizes the attachment of hydroxyl or amino groups to the rubber chain by the thermal reaction of the appropriately substituted nitrosobenzene. Crosslinking is induced by means of difunctional isocyanates. This can be achieved in a one-step process, mixing and vulcanization being carried out under conventional conditions. A preferred variation, which overcomes the handling problems of free nitroso compounds, makes use of novel urethanes formed by the prereaction of p-nitrosophenol and diisocyanates. The efficiency of crosslinking and physical properties of the vulcanizates are much improved by the use of extra diisocyanate and by small additions of zinc dimethyldithiocarbamate which appears to act catalytically. Gum and black-filled vulcanizates have excellent reversion and aging resistance and, even before serious attempts at optimization, physical properties similar to those of a good sulfur vulcanizate.
The Influence of Residual Olefin Structure on EPDM Vulcanization
Authors: Baldwin F. P. , Borzel P. , Cohen C. A. , Makowski H. S. , Van de Castle J. F.
Published: February 2011

While the results of our study leave many questions regarding vulcanization still open, it is concluded that: 1. Effective, practical vulcanization of polymers containing simple monoolefinic residues by sulfur/accelerator, sulfur donor/accelerator, p-quinone dioxime (or dinitroso benzene), and halogenated alkyl-phenol/formaldehyde resins demands that there be present hydrogen on carbon alpha to the double bond (allylic hydrogen). 2. Peroxide curing is most efficient when the olefinic moiety presents a vinyl or vinylidene group. In the case of the latter, reactivity is enhanced when the doubly-substituted, double-bonded carbon atom is part of a strained ring system. while allylic hydrogen is not necessary, its presence is advantageous in these low unsaturation elastomers. 3. The presence of sulfur in a peroxide cure generally decreases vulcanization efficiency, the more so the more active the olefinic residue in the unmodified vulcanization reaction. However, when main chain scissioning is a highly significant part of the overall reaction, the presence of sulfur can actually enhance vulcanization efficiency. 4. Conventional sulfur/accelerator vulcanization is quite sensitive to the nature of the olefinic residue present. Vulcanization rate, efficiency, and crosslink distribution can be affected. Hence, no far-reaching generalizations can be drawn regarding “best” structures beyond that made in Conclusion 1 though internal olefins appear most active. 5. Effective, practical vulcanization with halogenated alkylphenol/formaldehyde resins in an initially uncatalyzed system demands not only allylic hydrogen but also a 1,1-disubstituted or 1,1,3-trisubstituted ethylene moiety.
Vulcanization of 1, 5-Polyenes with Sulfur as a Consecutive Reaction
Authors: Scheele Walter
Published: February 2011

The preceding treatise describes the vulcanization of 1,5-polyenes as a consecutive reaction based on kinetic investigations. Two ways of quantitative treatment of vulcanization processes are developed: one empirical and the other based on the kinetics of consecutive reactions. The results possibly give information about the sulfur content of the crosslinks, how to calculate their number, and, in certain circumstances, check the sulfur balance. The conditions are discussed which enable the kinetic results to be applied to such applications.
Mechanism of Rubber Coagent Peroxide Cure System
Authors: Cornell J. A. , Winters A. J. , Halterman L.
Published: February 2011

Peroxide vulcanization mechanisms of curing natural and synthetic rubbers have been extensively investigated. Little work has been reported on the use of polyfunctional monomers as coagents. Utilizing a model hydrocarbon, decane, with dicumyl peroxide and a methacrylate ester monomer, the mechanism for vulcanization in polyethylene is postulated. In the absence of the monomer, the dicumyl peroxide has been shown to abstract a hydrogen from the backbone —CH2— to form a radical. This radical terminates with another radical similarly formed to produce a crosslink. With n-decane, C20 dimers are formed. On the addition of a methacrylate ester, the hydrogen abstraction appears to still take place, but the methacrylate is added to the radical. This is not a typical polymerization initiation since the chain length of the methacrylate side chain is extremely short. Depending on the concentration, it may be limited to a single addition product. Using methyl methacrylate, infrared and nuclear magnetic resolution spectra confirm this addition product under experimental conditions. A similar product was also obtained when ethylene dimethacrylate was reacted, hydrolyzed, and re-esterified to the methyl ester. Comparative products using branched hydrocarbons indicated that tertiary hydrogens were also abstracted. Comparison of IR spectra obtained in a peroxide coagent vulcanization of polyethylene indicated the lack of polymethacrylate absorption. This curve is similar to that obtained with the decane, but quite different from that obtained with a mixed polymer of polyethylene and polymethyl methacrylate or polyethylene dimethacrylate.
Lithium Aluminum Hydride Analysis of Sulfur-Cured Vulcanizates
Authors: Studebaker M. L.
Published: February 2011

Since 1955 we have used lithium aluminum hydride for qualitative and quantitative analysis of the polysulfide content of various types of rubber vulcanizates. The first results were of qualitative or semiquantitative value, but by 1959 we felt that the method was revealing quantitative information. This work was presented at the International Meeting of the Division of Rubber Chemistry, A.C.S. and subsequently published. Since that time we have analyzed many thousands of rubber vulcanizates, and the method appears to provide useful data which are generally consistent with the results obtained with other probes. During this period several other laboratories have worked with lithium aluminum hydride with varying success. Other probes have been applied to the analysis of crosslink type. Among them are triphenylphosphine, sodium di-n-butyl phosphite, mercaptan-amine combinations, phenyllithium, and methyl iodide. The method of analysis with lithium aluminum hydride, including sample treatment prior to reduction and the titrations subsequent to reduction, has been investigated almost continuously in our laboratory since 1955. Some of the conclusions from this work are presented in this paper. We have also endeavored to study vulcanizates by combinations of probes which, taken together, tend to substantiate the simple stoichiometric relationships which are the basis of this method of analysis. Some examples will be presented. In reviewing the large mass of data which has been accumulated over a decade, it is impossible and undesirable to list all of the experimental results. Instead we will attempt to touch various topics in an overall survey. Actually, the majority of the results on method improvement are not suitable for this presentation, since virtually any factor which adversely affects the results gives nonreproducibility and scatter when plotting the measured quantities against the variables such as time, temperature, etc. Therefore, the results leading to an improvement in technique increase reproducibility; whereas undesirable practices have the opposite effect. This situation should be familiar to those who have studied oxidative phenomena, for instance.
Effect of Crosslink Structure on Properties of Natural Rubber
Authors: Lal Joginder
Published: February 2011

Natural rubber-sulfur-diphenylguanidine vulcanizates were allowed to react with triphenylphosphine under nitrogen to convert polysulfidic crosslinks principally to di- and monosulfidic crosslinks and to assess the effect of this change in the chemical nature of the crosslinks on tensile strength, flex life, and oxygen absorption characteristics. The vulcanizates were analyzed for organically combined sulfur and polysulfidic sulfur. Data obtained by this approach were treated statistically and showed that polysulfidic crosslinks are not essential for attaining high tensile strength or superior flex life. In another approach, polysulfidic crosslinks were introduced into dicumyl peroxide-cured vulcanizates containing carbon-carbon crosslinks to yield two-stage vulcanizates. Data for these vulcanizates fitted the curve of tensile strength as a function of 300% modulus for the precursor samples. It was further shown that the reduced failure envelope for natural rubber gum vulcanizates is independent of the type and relative concentration of chemical crosslinks. An interesting observation was made that the tensile strengths of dicumyl peroxide-cured samples were enhanced on extraction with acetone. Vulcanizates which had lost 95–99 per cent of their polysulfidic sulfur due to reaction with triphenylphosphine exhibited significantly lower rates of oxygen absorption at 100° C as compared to the untreated vulcanizates. This suggests that polysulfidic structures in the original vulcanizates act as oxidation initiators.
A New Approach to Rubber Reinforcement
Authors: Harwood J. A. C. , Payne A. R. , Smith J. F.
Published: February 2011

Hysteresis is an important factor in determining the strength of rubber vulcanizates, and the presence of small particle fillers in a rubber increases the hysteresis in at least two ways, (a) hydrodynamically and (b) viscoelastically. The two contributions are additive, the first remaining substantially constant with strain rate and temperature and the second increasing with decreasing temperature. The viscoelastic contribution is attributed to the region of immobile rubber chains close to the surface of the filler particles and has the effect of changing the viscoelastic response of the rubber network. It plausibly accounts for the observation that the strength behavior of a filler-loaded rubber at one temperature is similar to that of a gum rubber at a lower temperature. This change of viscoelastic behavior in the interphase between the polymer and the filler surface leads to a high level of creep even at low strains when filler or other solid particles are present. In the case of a strain-crystallizing rubber such as gum NR, only regions of high strain contain the necessary particulate inclusions. In this circumstance strength is obtained without serious creep in the bulk phase. Thus well-compounded natural rubber gum vulcanizates meet the requirements of a strong rubber with low creep and good resilience to a remarkable degree.
The Load Dependence of Laboratory Abrasion and Tire Wear
Authors: Grosch K. A. , Schallamach A.
Published: February 2011

The first outcome of this investigation is that non-proportionality between sliding abrasion and load has relatively little effect on the load dependence of tire wear, which is almost entirely governed by the load dependence of the contact length, unless the inflation pressure is very low. The modified theory on the wear of slipping wheels predicts near proportionality at constant slip between wear in crab walk and side force. This relation is useful for test procedures and has been qualitatively confirmed by experiment. The theory suggests, furthermore, the existence of a severity effect on tire wear ratings which is independent of ambient or tire temperature and is expected to affect the wear rating of different tires if road tests are carried out on test routes with radically different surface topology.
Effect of Finite Extensibility on the Viscoelastic Properties of a Styrene-Butadiene Rubber Vulcanizate in Simple Tensile Deformations up to Rupture
Authors: Smith T. L. , Dickie R. A.
Published: February 2011

Stress-strain and rupture data were determined on an unfilled styrene-butadiene vulcanizate at temperatures from −45 to 35° C and at extension rates from 0.0096 to 9.6 min−1. The data were represented by four functions: (1) the well-known temperature function (shift factor) aT; (2) the constant-strain-rate modulus, F (t, T) reduced to temperature T0 and time t/aT, i.e., T0F (t/aT)/T (3) the time-dependent maximum extensibility λm (t/aT); and (4) a function Ω(χ) where χ=(λ−1)λm0/λm, in which λ is the extension ratio and λm0 is the maximum extensibility under equilibrium conditions. The constant-strain-rate modulus characterizes the stress-time response to a constant extension rate at small strains, within the range of linear response; λm is a material parameter needed to represent the response at large λ; and Ω(χ) represents the stress-strain curve of the material in a reference state of unit modulus and λm=λm0. The shift factor aT was found to be sensibly independent of extension. At all values of t/aT for which the maximum extensibility is time-independent, the relaxation rate was also found to be independent of λ. These observations indicate that the monomeric friction coefficient is strain-independent over the ranges of T and λ covered in the present study. It was found that λm0=8.6 and that the largest extension ratio at break (λb)max is 7.3. Thus, rupture always occurs before the network is fully extended.
Stiffness of Molecular Chain of Synthetic Rubber
Authors: Furukawa J. , Yamashita S. , Kotani T. , Kawashima M.
Published: February 2011

The principal polarizabilities of rubber molecules, including copolymers, were evaluated by the arithmetic sum of the polarizabilities of the components. The mean polarizabilities thus calculated are in good accordance with those from the refractive indices. The anisotropic polarizabilities of polymeric units for several kinds of rubbers were calculated and compared with those estimated from stress-optical coefficients. Length or molecular weight of a statistical link thus estimated is used as a measure of stiffness of rubber molecules. There is a good accordance in statistical links between anisotropy and viscosity measurements in a theta solvent. The molecular weight or length of a statistical link thus obtained is found to be compatible with the value calculated from the end-to-end distance in a theta solvent. The ultimate elongation of rubber is correlated with the stiffness and can be estimated from the measure of stiffness of the chain.
The Study of Polymers by High-Temperature ATR Spectroscopy
Authors: Fujimoto K. , Wataya K.
Published: February 2011

A new high-temperature attenuated total reflectance apparatus (HATR) was constructed and used at different temperatures for making infrared measurements on the same liquid or solid sample. It was found that this method was applicable to the continuous quantitative analysis of changes occurring during chemical reactions such as polymerization, isomerization, and crosslinking. In the bulk polymerization of styrene, the process of monomer consumption could be followed progressively. In the crosslinking reaction of high cis-polybutadiene by sulfur-accelerator or peroxide crosslinking systems, the decrease of cis content and its partial isomerization to trans structure was measured. Furthermore, in the cross-linking reaction of ethylene-propylene terpolymers (EPDM), the consumption of double bonds was observed over the course of the reaction with both sulfur-accelerator and peroxide crosslinking systems. The effect was greatest in the case of methylenenorbornene-type EPDM.
Dependence of Relative Volume on Strain for an SBR Vulcanizate
Authors: Fedors R. F. , Landel R. F.
Published: February 2011

Volume-extension data for an SBR-peroxide vulcanizate are presented. It is shown that Gee's expression, in conjunction with the experimental stress-strain response for the vulcanizate, leads to a volume-extension expression which describes the experimental data.
Multicomponent Polymerization. I. Integration of the Rate Equations
Authors: O'Driscoll K. F. , Knorr R.
Published: February 2011

The equation describing instantaneous copolymer composition in free radical vinyl copolymerization has been known and verified for many years. Although this equation has been integrated to give composition as a function of conversion, no analytical expression has been presented which gives conversion as a simple function of time. In this paper a derivation and experimental verification of such an equation is presented. Applications to problems in copolymerization kinetics are also considered. Extension of the equation to systems of more than two monomers is postulated.
The Control of Copolymer Distributions in Batch and Tubular Reactors
Authors: Ray W. H. , Gall C. E.
Published: February 2011

In this paper, the problem of maintaining a specified copolymer composition distribution in a batch reactor is considered. The advantages of temperature control, rather than monomer addition are discussed, and the necessary and sufficient conditions for temperature control in the face of monomer depletion are derived. Examples are worked to illustrate the results for a practical range of temperatures.
Application of Viscoelasticity to the Processibility of Elastomers
Authors: Kontos E. G.
Published: February 2011

The processibility of elastomers can be studied systematically by splitting up the process into component unit operations. By applying the theories of applied mechanics and taking into consideration the viscoelastic nature of raw rubbers modest theoretical progress has been made in predicting and correcting processing deficiencies. Important viscoelastic properties affecting the rheological behavior of rubbers have been identified. The existing relationships between macromolecular structure and the important viscoelastic properties have been presented for several synthetic rubbers. The dependence of some unit operations such as milling, calendering, and building on maximum relaxation time and viscosity has been demonstrated.
A Digital Computer Program for Compound Optimization
Authors: Beaumont R. A. , Hartmann N. E. , Chamberlain C. M.
Published: February 2011

In recent years the advent of computers has allowed the analysis of result of far more sophisticated experiments than was possible by manual methods and this has encouraged rubber compounders to investigate the effect on properties of changing many compound variables simultaneously. By using appropriate experimental designs, then fitting property response equations to the data by regression techniques, it is possible to predict the properties of any compound within the experimental range considered. Given a set of response equations describing all the properties of interest in terms of the levels of compound variables, optimization of the compound becomes the problem of “—the determination of the ‘best’ set of factor combinations or design variables consistent with specified constraints”.