bluuebunny/crossref_metadata_2025 huggingface dataset:
Tires for Modern Roads
Authors: Tompkins E. S.
Published: February 2011

The following notes summarize a lecture which has been given to a number of sections of the Institution of the Rubber Industry and to Engineering Societies and other bodies over the past ten years. It has been revised and brought up to date from season to season. For the 1964–65 session it has a new title, emphasizing the recent closer understanding of the mechanism of tire grip in the wet. The lecture is divided into four sections :-(a) basic work the tire has to do; (b) components of the tire and the parts they play; (c) influence of the road; (d) examples of tires for modern roads.
Elastomers Based on Polycyclic Bisphenol Polycarbonates
Authors: Perry K. P. , Jackson W. J. , Caldwell J. R.
Published: February 2011

Polycarbonate elastomers were prepared by the addition of phosgene to a pyridine solution of poly (tetramethylene ether) glycol and bisphenols containing norbornane-type groups. These elastomers do not contain the classical “tie-down” points—crosslinks, hydrogen bonding, or crystallinity—which, heretofore, have been considered necessary for good elastomer properties. This work introduces a new concept in elastomer chemistry : bulky, three-dimensional groups are effective tie-down points. Most of the elastomers were prepared with 4,4′- (2-norbornylidene) bis(2,6-dichlorophenol). For comparison, several elastomers with bisphenol-A were also prepared. A statistically designed experiment was carried out to determine the effect of composition variables on the properties of these elastomers. The properties were determined on films cast from methylene chloride and, in many cases, on wet-spun fibers. These elastomers have elongations of 400–600 per cent and instantaneous elastic recoveries up to 100.
Effect of Certain Crystalline Substances on Physical Properties of Elastomers I. Stress-Strain behavior
Authors: Linnig Frederic J. , Parks Edwin J. , Stiehler Robert D.
Published: February 2011

Crystalline organic compounds containing a β-naphthyl group cause pronounced stiffening of rubber vulcanizates under certain conditions. When these materials are removed by extraction, the reinforcing effect vanishes. Reversibility of this effect indicates that the forces involved are not those associated with primary bonds. Reinforcement by at least one of these materials, PBNA, is obtained with vulcanizates made from various elastomers and vulcanizing agents, and is essentially independent of the state of cure. In some instances about five per cent of PBNA, the most effective of these, produces the same stiffness on first extension as 40 phr carbon black. Any PBNA dissolved in the rubber has no effect on stiffness. Thus, less than three per cent crystalline PBNA may produce an isotropic Young's modulus of about 20 kg/cm2 at room temperature. At higher concentrations of PBNA, strain continues to decrease but hardness does not change proportionally. The temperature coefficient of Young's modulus for PBNA reinforced rubber is negative, like that for vulcanizates containing carbon black. However, the increased solubility of PBNA with rising temperature makes quantitative determination of the temperature coefficient difficult. The PBNA-rubber structure is partly destroyed by repeated extensions to twice the original length. However after 5 extensions a substantial enhancement of modulus remains. Addition of PBNA to a rubber vulcanizate does not affect significantly the glass transition temperature. Though the reversible nature of reinforcement with PBNA strongly suggests a physical mechanism, the stiffening cannot be explained by existing theories of physical reinforcement.
Role of Ozone in Dynamic Cut Growth of Rubber
Authors: Lake G. J. , Lindley P. B.
Published: February 2011

The effect of ozone on the growth of cuts in rubber strips subjected to repeated tensile deformations has been investigated. At tearing energies below a critical value ozone accounts for all the cut growth, and in this region the rate of growth is substantially independent of tearing energy. At higher tearing energies, cut growth also occurs due to mechanico-oxidative rupture, the rate of this type of growth increasing rapidly with increasing tearing energy so that the effects of ozone are normally slight. For vulcanizates of natural rubber and SBR unprotected by anti-ozonant, the characteristics of dynamic ozone cut growth can be deduced from static measurements. If a natural rubber test piece is not allowed to relax to zero strain on each cycle, the effects of ozone are important over a wider range of tearing energy.
Reduced Variables and Integral Equations in Design of Plastics and Rubber Structures
Authors: Hopkins I. L. , Wentz R. P.
Published: February 2011

The long-time creep behavior of a hard rubber storage battery jar is analyzed by means of (a) reduced variables applied to stress relaxation in torsion, and (b) numerical solution of the integral equation connecting stress relaxation and creep. The validity of the integral relation is shown by calculation of creep in compression (ASTM D-621) from stress relaxation in torsion.
Relation of Modulus of Urethan Rubber to Molecular Weight of Polyester
Authors: Little Julian R. , Gregg Robert A.
Published: February 2011

The modulus of polyurethan rubber prepared from poly(ethylene propylene) (70–30) adipate and diphenylmethane diisocyanate by chain extension and cross-linking with water is proportional to the reciprocal molecular weight of the polyester diisocyanate. The modulus at a given molecular weight is lowered by chain extension of the polyester with diisocyanate. The modulus is increased 40 per cent by change of the diisocyanate to 1,5-naphthalene diisocyanate and reduced 60 per cent by change to 2,4-toluene diisocyanate.
New Vulcanizing Agents for Ethylene Propylene Elastomers. III
Authors: Wei P. E. , Serniuk G. E. , Rehner John
Published: February 2011

Perhalogenated bicycloalkenes, such as the Diels—Alder dimer of hexachloro-cyclopentadiene and perchloro-1, 1′-bis(2,2′-eyclopentene), can vulcanize saturated hydrocarbon elastomers like EPR when used in combination with sulfur. The activity is enhanced by the presence of certain metal compounds. In the vulcanization of EPR by means of the system octachlorocyclopentene/sulfur/metal compound, it is disadvantageous to replace the sulfur with conventional “sulfur donor” compounds or with conventional vulcanization accelerators. However, the vulcanizing activity of the system is enhanced by the presence of the dihydrochlorides of dithiodiformamidine, phenylenediamine, diaminotoluene, and diaminophenol, and also dichlorodimethylhydantoin and trichloroisocyanuric acid. The mechanism of vulcanization of saturated hydrocarbon elastomers by the system octachlorocyclopentene/sulfur/ferric oxide (or chloride) has been studied by chemical investigation of a model system. The experiments indicate that the perhalogenated compound is a chlorine donor. The chlorine reacts with ferric oxide and with sulfur to form a complex of ferric chloride and sulfur tetrachloride which is proposed as the primary vulcanizing species, serving to activate the hydrocarbon molecule by hydrogen abstraction. Supporting evidence was obtained by independent synthesis of the complex, and by demonstration that, in the presence of sulfur, it can crosslink polyethylene. This mechanism also provides a plausible explanation for the observed effects of amine hydrochlorides, and of “sulfur donors” or conventional accelerators when used in place of elemental sulfur, and for the fact that oxides of bivalent metals, in contrast to those of trivalent metals, fail to activate vulcanization by octachlorocyclopentene. Combinations of certain organic peroxides and perhalogenated compounds also can vulcanize EPR in the presence of sulfur and ferric oxide. When the stoichiometry of the components is favorable, one obtains synergistic effects between the two classes of agents on tensile strength. However, synergism is not observed with all members of these two classes.
New Vulcanizing Agents for Ethylene Propylene Elastomers. IV
Authors: Serniuk G. E. , Wei P. E. , Rehner John
Published: February 2011

Di(trichloromethyl) sulfone and dichloromethylene-bis(trichloromethyl sulfone) can vulcanize saturated hydrocarbon elastomers like EPR when used in combination with sulfur. The activity is enhanced by the presence of certain metal oxides. These agents are also effective in some other elastomers, and in their blends with EPR. They are also effective in combinations with octachlorocyclopentene, and with cumyl peroxide. Synergistic effects are observed in the tensile properties of such systems. Dichloromethylene-bis(trichloromethyl sulfone) is so active in EPR that it gives rise to scorch. Efforts to alleviate this drawback by the use of sulfur donor compounds or retarders, and by other means, have not yet proved to be successful. Di (trichloromethyl) sulfone appears to be quite tolerable as far as scorch is concerned, but its lachrymatory nature might be a disadvantage in large-scale non-vented processing operations. Chemical studies carried out with model systems indicate that perchloromethyl sulfones do not all follow the same mechanism in the vulcanization of saturated hydrocarbon elastomers. Reaction schemes are proposed for the behavior of some of the sulfones investigated.
High Temperature Elastomers for Extreme Aerospace Environments
Authors: Sieron J. K.
Published: February 2011

To meet the ever increasing environmental requirements imposed on sub-system components of advanced aerospace weapons systems, a comprehensive project to develop high strength, high temperature resistant elastomeric materials has been pursued. To attain this goal, research on reinforcement, stabilization, and crosslinking systems for butyl, ethylene propylene terpolymer, and fluoroelastomers was carried out. Results obtained in earlier work with the hydrocarbon elastomers disclosed that fine-particle-size, high-structure carbon black provided excellent tensile properties at high temperatures. Further work on stabilization systems resulted in the discovery that stannous oxide was effective for phenolic-resin-cured butyl at temperatures up to 500° F. For EPT, vulcanization-stabilization systems which provided a threefold improvement in useful life of this elastomer at temperatures in the range 300° F to 500° F were elucidated. Preliminary studies on fluoroelastomer reinforcement led to the finding that properly dispersed carbon fiber imparted not only better high temperature tensile strength, but also improved life at temperatures up to 600° F. In the present work, fibrous magnesium silicate, a material which normally would be used for dusting uncured rubber or as a paint filler, was found to be an effective reinforcing material for fluoroelastomers. Vulcanizates prepared with an acicular-platy form of this material have tensile strength at 400° F which is 80% greater than that with commonly used medium thermal carbon black. Hot tear strengths with even greater improvements were also realized, and as an added bonus, resistance to deterioration over a temperature range of 600° F to 700° F was also noteworthy. Primary implication of this work lies in renewed awareness that elastomeric vulcanizates are composite materials. Reinforcing materials as well as other additives are very influential in determining the engineering properties and performance of elastomers.
Controlled Instability of Polymers for Grid-Type Satellites
Authors: Snyder C. E. , Weir D. S. , Cross W. B.
Published: February 2011

A novel fabrication concept for passive communication satellite construction based on a wire grid reflective surface and a gas holding bladder that acts to deploy the structure is reported. Disappearance of this bladder or film web is advantageous for orbital stability. Likely polymer structures that permit formation of volatile fragments with no crosslinking are surveyed and from the disubstituted vinyl monomer family the n-butyl methacrylate ester is chosen. Physical demands on the bladder are met by this selection, and data are shown that demonstrate the feasibility of photolysis of monomer under conditions obtainable in orbit.
A Synthesis of Poly(2,4-Perfluoroalkylene-6-Perfluoroalkyltriazine)S
Authors: Dorfman Edwin , Emerson William E. , Cakr Russell L. K. , Bean C. Thomas
Published: February 2011

By thermal cyclodeamination reactions, perfluoroalkyleneimidines and perfluoroalkylamidines have been polymerized to give crosslinked triazine compositions. This reaction involves condensation of the reactants with elimination of ammonia and is illustrated in the formation of I. The amidines and imidines were prepared by the facile addition of ammonia to perfluoroalkane nitriles. Where the mono- and difunctional reactants were of comparable reactivity, essentially random condensations occurred so that gelled polymers were obtained. Properties of these gels varied, depending upon the reactant ratios used, from rather weak, gummy material to tougher inelastic polymers. Tensile strengths observed with these polymers generally ranged from 100 to 500 psi at about 100 per cent elongation. The triazine gels exhibited interesting thermal stability, showing no rapid decomposition up to 420° C; it was thought that with the discovery of a synthesis which would give linear, ungelled, triazine polymer that polymers having improved physical properties might be obtained.
Triazine Elastomers
Authors: Griffin W. R.
Published: February 2011

Three technically feasible routes have now been established for preparation of linear perfluoroalkylene triazine polymers. The most advanced route is based on addition polymerization of long chain fluorocarbon dinitriles and diamidines, followed by acylation and cyclodehydration to triazine polymer. Large research samples have been made, but crosslinking to thermally stable vulcanizates is still a problem. An alternate method, active halogen elimination from a difunctional fluorotriazine monomer, has been, demonstrated. High molecular weight polymer has been formed, but it is not elastomeric at room temperature. The low temperature flexibility is a function of structure and not of the method of polymerization, therefore other monomers with longer fluoroalkyl groups hold promise of elastomeric products. The route has attractive economics, but elastomeric products with crosslinking capability must be demonstrated. Coupling of diiodofluoroalkyl triazine monomers employing ultraviolet radiation has been demonstrated. This route is not being pursued because of research required and the predicted high cost of monomer preparation, when compared to the previous two routes. Evaluations of compounded vulcanized triazine elastomer show excellent resistance to hydrocarbon fuels and hydraulic fluids at 370° C and to long term air aging at 300° C. Tensile strength is in the 500 psi range, but is expected to improve with closer control of molecular weight and branching of the polymer. Excellent prospects are in view for fuel tank sealants, wire insulation and elastomer components for hydraulic systems useful in the 300° to 400° C range.
Poly-m-Carboranesiloxanes as Thermoresistant Elastomers
Authors: Scheoeder Hansjuergen , Schaffung Otto G. , Larchar Trescott B. , Frulla Floro F. , Heying Theodore L.
Published: February 2011

Selected members of the SiB polymer family were developed as elastomers for high temperature applications. To this end, polymerization procedures, processing technology, and testing techniques were extensively established. Progress of this work was judged from basic measurements, such as tensile strength, elongation, and hardness which were regularly performed at temperatures ranging from —80° F to 800° F, altogether on more than 300 molded test panels. With proper selection and concentration of reinforcing fillers and antioxidants, vulcanizates of SiB-2 and SiB-4 rubber exhibit outstanding heat-aging resistance. They show tensile strengths of 400–450 psi and elongations of 100–150% at ambient temperature, and withstand temperatures of 800° to 900° F in air, demonstrating a useful life of 24 hours and 2 hours, respectively. In addition, they were still found to be flexible at −40° to −80° F, thus indicating a wide range of elasticity. Certain specialty applications where thermal-oxidative stability is required are already being considered.
Hydrofluorocarbon High-Temperature Integral Fuel Tank Sealants
Authors: Anspach W. F.
Published: February 2011

Supersonic aircraft in the Mach 3 range have increased temperature requirements for many materials of construction. One of the most critical problem areas is the integral fuel tank where state-of-the-art elastomeric sealants no longer meet those requirements. New sealants resistant to hydrocarbon fuels at temperatures in excess of 500° F are urgently needed. A high temperature integral fuel tank filleting sealant has been developed based on a mixture of high and low molecular weight hydrofluoroearbon polymers. This sealant has a solids content of 85 per cent and cures at modest temperatures. It is a one component system stable for several weeks at ambient temperatures and for longer periods if refrigerated. The sealant exhibits good room temperature and high temperature mechanical properties both before and after aging in hydrocarbon fuel and fuel vapor at temperatures up to 500° F. A typical formulation showed an increase in tensile strength and better than 50 per cent retention of elongation after 1000 continuous hours exposure to fuel vapor at 500° F. Adhesion to metal substrates is good and samples have resisted rupture and loss of adhesion when pressurized at 500° F for 1000 hours. This is only an interim solution to the critical fuel tank sealant problem in Mach 3 aircraft. Research is continuing to improve its useable life and to eliminate a possibly serious corrosion problem with titanium substrates. It must be emphasized, however, that sealants based on hydrofluorocarbons, fluorosilicones, and other available elastomers can at best provide interim solutions to the high temperature sealant problems and that new base polymers, such as the triazine and polyether elastomers currently being developed by the Air Force Materials Laboratory, are needed to provide sealants which completely meet requirements.
Effect of Liquid Rocket Fuels and Oxidizers on Elastomeric O-Ring Seals
Authors: Bellanca C. L. , Salyer I. O.
Published: February 2011

O-ring seals of selected elastomeric and compliant materials were evaluated for resistance to liquid rocket fuels and oxidizers in a simulated end-use test. Oxidizers were nitrogen tetroxide, chlorine trifluoride, and 90 per cent hydrogen peroxide; fuels were mixed hydrazines, pentaborane, and Hybaline A-5. Tests were made at 73° F with all fluids; further, the effect of elevated temperature (160° F) on seals was evaluated in nitrogen tetroxide, hydrogen peroxide, and mixed hydrazines. At 73° F only polytetrafluoroethylene was resistant to all of the fluids; however, elastomeric materials were found which were satisfactory for specific fuel or oxidizer systems. Butyl and ethylene propylene rubber appear satisfactory for long term storage in the presence of mixed hydrazines and Hybaline A-5. The fluorocarbons appeared best of the elastomeric materials for use with pentaborane and hydrogen peroxide.
Elastomers for Use in Heart Valves
Authors: Raible D. A. , Keller D. P. , Pierie W. R. , Koorajian S. , Partridge E. G.
Published: February 2011

Approximately 0.1 per cent of silicone rubber balls from the estimated 18,000 implanted Starr-Edwards heart valve prostheses have been found to be variant. This material variation has initiated investigations of present material and accelerated the search for new and improved elastomers. Descriptions of various types of artificial heart valve prostheses, environmental conditions, design requirements and test apparatus are presented. Variant balls exhibit external physical damage by surface grooves and splits. Internal changes and discolorations from absorbed lipid materials have also been observed. Variant silicone rubber balls have poor physical properties compared with nonvariant or non-implanted balls. This reduction lowers the resistance to damage. The engineering laboratory evaluation program of elastomeric materials includes the compilation of test data on balls molded from silicone, butyl, ethylene propylene, polybutadiene and chlorohydrin rubbers. Butyl and polybutadiene rubbers were selected to demonstrate the extremes of the resilience spectrum with respect to the hydraulic performance of the ball type prosthesis. Compounds with low resilience for less ball rebound appear to be advantageous in this application To date, butyl rubber has exhibited excellent wear resistance in laboratory durability testers.
Elastomers in the Human Body
Authors: Falb R. D. , Grode G. A. , Leininger R. I.
Published: February 2011

Several problems arise when polymeric materials are placed in the body: (1) damage to the body such as blood coagulation, hemolysis, and protein denaturation, and (2) degradation of the polymers caused by exposure to the body's enzyme system. Several methods are presented in this paper to produce elastomeric materials that do not cause clotting of blood. This is accomplished by chemically binding a mucopolysaccharide (heparin) to their surfaces. The materials that have been treated in the work are silicone rubber, polyester polyurethan rubber, natural rubber, and butadiene pyridine rubber.
Resistance of Silicone Rubbers to Body Fluids
Authors: Boone J. L. , Braley S. A.
Published: February 2011

Certain medical grades of silicone rubber have been found to be very useful for implantation in the extremely demanding environments encountered inside man's body. These materials are used in plastic surgery as replacement for soft tissue and cartilage. They are also useful as prostheses, tubes or devices that are used in contact with various body fluids, such as bile, stomach acids, urine and blood. Fairly recently there have been a few instances of failures of artificial heart valves prostheses, which have been caused by an absorption of fatty materials into silicone rubber components of these prostheses. These failures are a matter of great concern, and efforts are being made to study this problem with the hope of finding some solution.
Hydrolytic Stability of Urethan Elastomers
Authors: Ossefort Z. T. , Testroet P. B.
Published: February 2011

Data have been presented bearing on the hydrolytic stability of a wide variety of urethan elastomers (Table III). It has boon shown that polyester based elastomers are considerably more susceptible to hydrolytic attack than polyether elastomers up to 158° F. The nature of the attack and results obtained are profoundly influenced by the temperature. At temperatures of 120° F and above the attack appears to be a “simple” hydrolysis consisting of scission of main chain ester groups resulting in reversion of the rubber. In this case aging over water and in water are similar. At temperatures below 120° F the attack cannot be rationally treated without considering the part played by fungi. In this case exposure over water yields drastically different results from immersion— the former being more severe by several orders of magnitude. Typically the attack over water involves a short term (two to three weeks) cracking of stressed or unstressed specimens and a gradual softening which takes place over a period of many months. The cracking seems to be connected with fungus attack. Resistance of polyesters to hydrolytic attack can be improved by the use of additives such as diisocyanates, fungicides, and carbodiimides. The latter are most useful and apparently scavenge the carboxylic acid resulting from hydrolytic breakdown of the polyesters thereby preventing autocatalysis. Their ability to react with carboxylic acids under these mild conditions has been reported. Differences among polyesters not only in inherent resistance to hydrolysis but also in response to inhibition are found. As has been seen the early cracking can be eliminated by use of sulfur cures, or inclusion of a fungicide but only at the expense of reduced resistance at 158° F. Accelerated tests have been shown to correlate reasonably well with outdoor exposures. Results on unstressed specimens correlate with the 158° F test while the stressed specimens yield results similar to exposure at 95 per cent R.H. and 100° F. Not all linear polyesters are susceptible to hydrolysis such as is poly (ethylene propylene adipate). The terephthalate polyesters, poly (ethylene terephthalate) and poly(1,4 cyclohexane diearbinyl terephthalate), have been exposed in the form of thin films over water at 158° F for 14 months and over water at 95 per cent R.H. and 100° F for 23 months without visible signs of deterioration. They are apparently stabilized by the presence of the aromatic rings or steric factors or a combination of these. In conclusion it must be said that although some progress has been made in protecting polyester urethan elastomers from hydrolytic failure under tropical and high humidity conditions, the problem has only partially been solved.
Abrasion Resistance and High Speed Tensile Strength of Elastomers
Authors: Ecker Ruprecht
Published: February 2011

In earlier communications, we defined abrasion, especially of tires, as a thermal-oxidative process caused at high velocity of mechanical rupture. Other authors (e.g., Schallamach, Boggs, Zapp etc.), with theoretical and experimental tests, prove the importance of viscoelastic behavior as a characteristic property for abrasion. The results of experiments on six elastomers (NR, IR, BR, SBR, IIR, and EPT) compared in tire tread compounds are communicated and discussed in the present work. Tensile strength was determined over a temperature range of 20° to 140° C at deformation speeds of 10 to 20,000 % elongation per second. Forced, non-resonant vibrations were used to determine viscoelastic properties, e.g., resilience, storage modulus, and loss modulus. As abrasion is a consequence of frictional processes, coefficients of friction, dependent on temperature, were measured on dry, wet, and frosty asphalt/fine concrete track. The apparatus is briefly described. From these test results, an empirical relation established between abrasion, friction, viscoelastic properties, tensile strength at high speed and temperature allows one to predetermine the abrasion behavior of a vulcanizate in the laboratory.
Model Interpretation of Thermal Conductivity of High Polymers II. Stretched Amorphous High Polymers
Authors: Eiermann K.
Published: February 2011

Thermal conductivity phenomena in stretched amorphous high polymers are explained qualitatively and quantitatively using model concepts. Among other things, a relation is derived between anisotropy of thermal conductivity and linear coefficient of expansion.
Dynamic Mechanical Properties of Cross-Linked Rubbers. I. Effects of Crosslink Spacing in Natural Rubber
Authors: Ferry John D. , Mancke Ralph G. , Maekawa Etsuji , Oyanagi Yasuji , Dickie Ray A.
Published: February 2011

Complex shear compliances of five samples of natural rubber crosslinked by cumyl peroxide and three samples crosslinked by sulfur, covering a broad range of average crosslink spacing, have been measured over a frequency range of 0.1 to 1000 cps and a temperature range from −18 to 55° C. The data were all reduced to 25° C by shift factors calculated from an equation of the WLF type. In the transition zone of frequencies, the viscoelastic functions were closely similar; the loss tangents of the cumyl peroxide vulcanizates were identical within experimental error, and those of the sulfur vulcanizates were shifted somewhat to the left on the logarithmic frequency scale with increasing degree of vulcanization. In the rubbery zone, the losses persisted to much lower frequencies than could be expected from configurational rearrangements within individual strands on the basis of current molecular theories, reflecting slow relaxation mechanisms whose presence has also been deduced from other measurements. The magnitude of the loss tangent at a given frequency in this zone (e.g., 1.6 cps) increases substantially with the average spacing between crosslinks in both cumyl peroxide and sulfur vulcanizates. The possible role of trapped coupling entanglements as a source of the slow relaxation mechanisms is discussed.
Note on Conductivity and Modulus of Carbon-Black-Loaded Rubbers
Authors: Payne A. R.
Published: February 2011

Electrical conductivity and dynamic shear modulus measurements were made simultaneously on carbon black-filled natural rubbers. G′, the in-phase shear modulus, and the electrical conductivity, G, were shown to vary in an approximately similar way as the amplitude of dynamic oscillation was increased. Both G′ and C altered sigmoidally from a high value at low amplitudes of oscillation to very much reduced values at high amplitudes of oscillation. Recovery curves for conductivity were shown to be parallel with respect to the logarithm of the time, even though the initial deforming amplitudes varied widely.
Structure of Ethylene Propylene Dicyclopentadiene Terpolymers
Authors: Cooper W. , Eaves D. E. , Tunnicloffe M. E. , Vaughan G.
Published: February 2011

Terpolymers of ethylene, propylenc and C14-dicyclopentadiene have been compared with model compounds to determine the structure of combined termonomer units. Reactions with iodine monochloride, bromine and the infrared spectra of the terpolymers indicate that dicyclopentadiene polymerizes at the 9,10 double bond without ring-opening or disproportionation.
Cohesive Energy Density and Internal Pressure of High Polymers
Authors: Voeks John F.
Published: February 2011

A method for estimating the intermolecular pair potential in high polymers from density data alone is illustrated. The cohesive energy density and internal pressure of several polymers are calculated in this way. The results agree satisfactorily with various other estimates.
Accelerated Oxidations of Polyisoprene. II. Effects of Hydrazines, Sulfur Compounds, and Phenyl-β-Napthylamine in Solution
Authors: Mayo Frank R. , Heller J. , Walrath R. L. , Irwin Katherine C.
Published: February 2011

At concentrations of 0.1 to 1 mM, phenylhydrazine causes marked decrease in viscosity of polyisoprene solutions in a few minutes at 50° C (see section II). This effect requires the presence of oxygen but no preoxidation of the rubber. Two molecules of oxygen are absorbed and about one fifth to one tenth of a chain is cleaved per molecule of phenylhydrazine added. The reaction is essentially complete within 20 min. This fast reaction is not much affected by the presence of antioxidants but results in the formation of some material (possibly phenolic) which reduces the effectiveness of other prooxidants. 1,1 -Dimethylhydrazine and 1,2-diphenylhydrazine, unlike phenylhydrazine, have slow but sustained effects. Hydrazine monohydrate is intermediate in its action. Investigation of the effects of several sulfur compounds on polyisoprene solutions brought out some striking effects and a need for further work. p-Thiocresol is a strong prooxidant for our polyisoprene solutions at concentrations below 0.2 mM. At higher concentrations, induction periods occurred with some, but not all, samples and could be shortened by the addition of t-butyl hydroperoxide. Di-p-tolyl disulfide was somewhat less active, but its effect increased regularly with its concentration. Other aryl thiols and disulfides had similar activity but benzyl derivatives did not. At low concentrations, benzene sulfinic acid and p-toluene sulfinic acid are as strong prooxidants as the aryl thiols; at high concentrations they are more active but short lived. A few other sulfur compounds or combinations had no interesting prooxidant properties. In contrast to results on polyisoprene, aryl thiols and sulfinic acids had little effect in preliminary tests in promoting the oxidation of cyclopentene and methyl-cyclohexene. The effects of a common rubber antioxidant, phenyl-β-naphthylamine, alone and in combination with various prooxidants, were followed by oxygen absorption and viscosity changes. The effects are complex; there are indications of both catalytic and anticatalytic effects, and of both scission and crosslinking. The results are most useful in showing the potential of the method for future work on understanding and comparing effects of antioxidants.
Accelerated Oxidations of Polyisoprene. IV. Effects of Sulfinic Acids on Bulk Natural Rubber
Authors: Mayo Frank R. , Parkinson D. B.
Published: February 2011

This paper shows that benzene and toluene sulfinic acids cause rapid disintegration of a cured tread stock in the presence of air at 30° C, a slower reaction in the absence of oxygen. The sulfinic acids also cause rapid solution of smoked sheet in o-dichlorobenzene at 30° C in the absence of oxygen to give mobile solutions.
Vulcanization of an Ethylene Propylene Diene Rubber
Authors: Frensdorff H. K.
Published: February 2011

This study concerns the sulfur vulcanization of EPT with dithiocarbamate accelerators. The reactions undergone by the accelerators are equivalent to those found during natural rubber or SBR vulcanization; TMTM and TMTD are almost completely converted to ZDMC. During vulcanization about 50% of the double bonds are saturated, and approximately one crosslink is formed for each two double bonds initially present. Equilibrium swelling measurements before and after mercaptan cleavage were used to determine the concentration of all crosslinks and that of monosulfide ones as functions of vulcanization conditions. Vulcanization kinetic were followed by Monsanto rheometer measurements. The process takes place in two stages: an initial fast reaction representing vulcanization by the primary accelerator, followed by a slower first order reaction due to acceleration by ZDMC. Accelerator, sulfur, and zinc oxide concentrations have little effect on the rate constants which, however, are nearly proportional to polymer unsaturation. The rate constants approximately double with each temperature rise of 10° C.
Radiotracer Studies of Carbon Black Surface Interactions with Organic Systems. I. Experimental Approach and Initial Results from Chemisorption and Vinyl Polymerization Studies
Authors: Deviney Marvin L. , Whittington Lawrence E.
Published: February 2011

Radiotracer techniques have been applied to the study of interactions of carbon black surface functional groups with two chosen organic systems. The basic reaction mechanisms demonstrated in this study may have implications in elastomer reinforcement. Direct radiochemical evidence supports the conclusions of Hallum and Drushel (based on less direct polarographic data) that surface quinonic groups exhibit hydrogen abstraction activity toward tertiary hydrogens in paraffinic hydrocarbons. Studies on the system carbon black and styrene using tritium radiotracer have provided direct evidence that phenolic hydrogens participate in the polymerization acceleration and graft polymer formation reaction and are transferred to the growing polystyrene chains as postulated by Donnet. Several methods have been developed for specifically labelling certain oxygenated functional groups on the carbon surface with tritium and for tritium labelling carbon black in aromatic hydrogen positions. The techniques developed in this work and the basic reaction mechanisms derived will permit this investigation to be extended into a radiochemical study of carbon black surface interactions with elastomer related systems of interest to the rubber industry.
Radiochemical Determination of Low Unsaturations in Polyisobutene
Authors: McGuchan R. , McNeill I. C.
Published: February 2011

A radiochemical technique involving the use of 36C1 has been described previously for the measurement of butyl rubber unsaturations. This method has now been applied to the estimation of the much lower concentration of double bonds present in polyisobutene prepared by the cationic polymerization of isobutene at a low temperature. The nature of the reaction of polyisobutene with radiochlorine in the absence of air is examined, and the experimental results are discussed in relation to present theories of the mechanisms of chain termination in cationic polymerization.
Pyrolysis Gas Chromatography of Natural Rubber and Synthetic Polyisoprene
Authors: Jernejčič M. , Premru L.
Published: February 2011

Pyrolysis gas Chromatographic isothermal and temperature programed separation of volatile components of unvulcanized natural rubber and synthetic polyisoprene was made on P-E columns Q and U. Besides identifications, relative quantitative differences between pyrolysis degradations of natural rubber and synthetic polyisoprene in pyrolysis temperature range 550°–750° C were established. It was found that the method was not suitable for an analogous study of vulcanized samples.
Determination of 1,4 and 3,4 Addition in Polyisoprenes by Rapid Pyrolysis and Vapor Phase Chromatography
Authors: Vacherot Monique , Marchal Jean
Published: February 2011

These results indicate that, after calibration, this technique can be used to determine the ratio of 1,4 and 3,4 addition in polyisoprenes where the arrangement of monomer units is the same as the polymers used here. This limitation depends on study of other specimens which will show whether sequence distribution has any effect on the results of pyrolysis.
Method for Structural Characterization of High Polymeric Networks by an Osmotic Pressure Technique
Authors: Seeley R. D. , Rand P. B.
Published: February 2011

An apparatus was designed to measure the osmotic pressure of solvent-polymer systems. The method is unique in that semirigid polymers may be incorporated as the solute component without specimen fissures occurring from excessive solvent dilative action. The advantages of this technique are: high polymeric materials both elastomeric and plastic can be structurally characterized by the same technique; the calculated effective molecular weight of the polymer network will reflect a value consistent with the polymer's performance characteristics; and the method is only restricted to lyophilic polymer—solvent systems.
Aspects of Friction and Wear of Tires Arising from Deformation, Slip, and Stresses at Ground Contact
Authors: Savkoor A. R.
Published: February 2011

The role of tread patterns in adhesion on wet roads is emphasized. Tread patterns cause the stress distribution in the area of contact to be wavy and variable both in time and space. Deformation of an inflated tire against a hard flat surface induces a symmetrical and inwardly directed shear stress distribution at the ground contact. Shear stresses have been calculated with certain simplifying assumptions. Apart from the importance of cornering and stability of automobiles, study of a tire set at a slip angle is also important to wear, because high temperatures prevail at the tread surface. Forces developed on wet road surfaces are very low; this leads to use of a high hysteresis tread rubber to give additional friction on such surfaces. Tests carried out elsewhere at high speeds on roads sprayed with water have been of limited value in evaluating the hysteresis component of friction resulting from deformations since change in tread properties resulting from unknown contact temperatures due to surface heating was not considered. Measurements of cornering force on two tires with glass plate apparatus at a speed of only 4.5 cm/sec on dry and lubricated surfaces indicate that the contribution due to hysteresis can be appreciable. Finally, theories explaining the mechanism of wear occurring at the contact between rubber and a hard surface are discussed.
Friction and Viscoelastic Properties of Polymeric Solids
Authors: Ludema K. C. , Tabor D.
Published: February 2011

When a hard slider slides over a rubber surface, there is a close relation between sliding friction at various speeds and temperatures and viscoelastic properties of the rubber. If friction is due to an adhesion mechanism this may be explained in terms of the way in which area of contact A and shear strength s vary with speed and temperature. Area of contact is determined by the elastic modu us of the rubber; during sliding the deformation process is a relatively low frequency one. In contrast, shear strength s involves very high strain rates in a thin surface layer; this corresponds to a very high frequency process. By combining these two effects the observed friction behavior may be explained. Behavior of polymers below their glass transition temperature is very different. Correlation between sliding friction and various viscoelastic peaks is not at all strong. On the other hand, conventional viscoelastic data correlates well with rolling friction. This shows that high local pressures at the contact regions do not substantially change the viscoelastic characteristics. In sliding, however, there are very high shear strains in the surface and appreciable tearing and transfer of polymer; presumably these violent deformations, although in themselves speed and temperature dependent, bear little relation to deformation processes involved in conventional low strain viscoelastic studies. The good correlation with rubber suggests that, even at the high strains involved in sliding, slip of chain segments over one another still remains the basic mechanism of shear. With PTFE, sliding friction shows a dependence on speed and temperature which resembles a viscoelastic peak. However, it is probable that this refers to gliding of crystallites of PTFE over one another where the effective strains are enormous and not to conventional viscoelastic peaks determined under conditions where strains are very small. Apart from its bearing on friction studies the work described in this paper suggests that more information is needed on viscoelastic properties of polymers at high pressure and at large strains.
Thermodynamic Aspects of the Glass-Rubber Transition
Authors: Staverman A. J.
Published: February 2011

In 1933 Ehrenfest defined transitions in which not only the thermodynamic potential but also the specific volume and entropy of the two states are equal. For these transitions he derived three relations, between the differences of the coefficients of dilatation and of compressibility and the specific heat on one hand and the slope of the transition curve in p-T-space on the other hand. Although it is beyond any doubt that the glass-rubber transition in polymers is not a second order transition as defined by Ehrenfest, yet the term “second order transition” is often applied to it. The confusion arising from this abuse of a physically well defined concept is enhanced by the fact that some of Ehrenfest's relations are under certain circumstances valid for the glass-rubber transition, although in those cases the physical background of these relations is quite different from that of a second order transition in Ehrenfest's sense. In fact, the essence of the glass transition was formulated clearly and correctly by Simon in 1931 and consists in the assumption that in a glass one or more internal parameters are not in equilibrium but are frozen in. Conditions required for the validity of each of Ehrenfest's relations are inspected. The equality of two functions of the dilatation and the compressibility coefficients and the specific heats of the two states depends on the condition that there is only one frozen parameter in the glass state. If there is more than one frozen parmeter, then the equality turns into an inequality and the physical meaning of the difference between the two sides is derived. Similar relations as those derived between the quantities mentioned, can be derived between specific heat, modulus of elasticity and temperature coefficient of that modulus. These new relations are more interesting for practical purposes and less subject to experimental errors than the older ones. Finally expressions for the slope of the transition curve are investigated. Validity of any one of the expressions depends on the physical condition required for a material to become a glass. Inversely from the validity of any of the possible expressions insight in the glass transformation can be derived. The scarce available data give the impression that a material turns into a glass whenever its excess entropy decreases below a critical value.
Applicability of Free Volume Concept to Relaxation Phenomena in the Glass Transition Range
Authors: Kovacs A. J.
Published: February 2011

Except for discrepancies mentioned with respect to pressure investigations, which need future clarification, we can conclude in a general way, as follows. As far as only average parameters of macroscopic specimens are considered (complex moduli, or dielectric constants, volume or heat content etc...), the free volume concept can relate variations of molecular mobility to changes of an average free volume in a semiquantitative way. This average free volume can no longer fully characterize the wide variety of molecular motions involved in the kinetics of redistribution of holes in the liquid during recovery experiments. These kinetic processes involve a wide distribution of retardation times, which may be associated with local distribution of holes, or with that of cooperating groups of molecules, or molecular segments. On the other hand, free volume is not necessarily the fundamental molecular parameter which controls rate of configurational changes, characterized by variation of entropy of the liquid. Even if this is the case, most of the above discussion may be applied to any other average excess parameter, as far as the Doolittle equation is formally adopted, in which f/b is expressed in terms of the new parameter, rather than that of free volume. However, since relaxational free volume, as determined from the WLF equation, and independently measured volume changes are often in close agreement, this means that variations of excess entropy, or those of configurational free energy, and changes in volume are closely related. This conclusion is in agreement with that of Eisenberg and Saito, who found that the Gibbs—Dimarzio theory, based on configurational entropy, is practically equivalent with the free-volume approach. Thus, the free volume concept remains still a valuable tool for unifying different kinds of rate processes from both a theoretical and an experimental point of view, especially in the glass transition range.
Thermoelasticity and the Temperature Coefficient of Unperturbed Polymer Dimensions
Authors: Puett D.
Published: February 2011

The strain dependence of fe/f (ratio of the internal energy component of the force to the total retractive force) for a crosslinked, amorphous network is analyzed in terms of the C2 factor which appears in the semiempirical relation for rubber elasticity. Appropriate equations are derived and applied to literature data for several polymers and copolymers. The temperature coefficients of the mean square end to end distances thus obtained are often quite different from the values determined by averaging ƒe/ƒT at several extensions.
Thermodynamic Examination of the Polymorphic Transition of Trans-1,4-Polybutadiene. I. Theoretical Premises
Authors: Natta G. , Pegoraro M. , Sziálgyi L.
Published: February 2011

It is known that oriented fibers of trans-1,4-polybutadiene shrink when heated, in correspondence with the solid-solid state transition. In ideal fibers this occurs at a temperature which is solely a function of applied stress. The possibility of converting thermal energy into mechanical work by a cyclic process is examined, for an ideal fiber, on the basis of the contraction taking place under a predetermined axial stress at the corresponding temperature, and a subsequent elongation occurring at lower temperatures, under an axial stress which is either zero or lower than the previous one. A theoretical study is made of a possible thermodynamic cycle, and the resulting efficiency is calculated.