bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Mechanical Degradation on Rheological Properties of Elastomers
Authors: Folt V. L.
Published: February 2011

Several anomalies are observed in the flow of the melts of many elastomers which are not commonly observed with melts of plastics. A stress-oscillation at high rates of shear and a tendency to reach a constant level of stress at lower rates of shear are two of the more commonly encountered anomalies. Both anomalies occasionally occur in the flow of a single melt. The role of molecular weight, molecular weight distribution and branching in producing anomalous flow is demonstrated. The presence of supermolecular flow units is invoked to explain certain anomalies and supporting evidence is presented. The data strongly suggest changes in the rheological flow units take place as the conditions of shear are changed. The flow properties of many elastomers are complicated by the severe mechanical degradation taking place under these conditions of shear. Anomalous flow patterns can be either produced or removed by mechanical degradation depending upon the specific elastomer system. The extent of degradation appears to be dependent upon the flow unit governing the flow process and independent of the shearing stress or work input per unit volume of polymer sheared. The complexity and distribution of entanglements play a major role in the flow processes as well as in the mechanical degradation process of certain elastomers.
Apparatus to Measure Thermal Conductivity in Filled Rubber Stocks
Authors: Atkins J. H. , Sullivan J. E.
Published: February 2011

An instrument to measure thermal conductivity of cured rubber stocks is described. The apparatus can be used with readily available equipment or additional equipment may be purchased. The results obtained are as accurate and precise as those obtained using other instruments and can be done at a rate of three samples per hour. The apparatus is designed around a calibrated heat flux probe which measures the sample's heat flux. The heat flux, the temperature drop across the sample, and the sample thickness values permit conversion of the above data into a thermal conductivity value. Thirteen samples of Butyl rubber in a curing bladder formulation with 40-part loadings of various carbon blacks were prepared and tested. The thermal conductivity values obtained varied from 0.096 to 0.117 (Btu)/(ft2) (hr)(°F/ft) over a range of 95° F to 212° F with an overall relative standard deviation of 1.2%. The thermal conductivity of the above samples were also measured on a modified apparatus over a temperature range of 95° F to 350° F and there was no change in the thermal conductivity values. To check the above measurements, five of the samples were tested on two commercial instruments. The results agreed within 4 per cent. For reasons explained in the paper, we believe our results to be the most accurate.
The Effect of Oil and Black on the Injection Molding of EPDM Compounds. I.
Authors: DePierri William G. , Hopper J. R.
Published: February 2011

Factors affecting the flow properties of EPDM compounds have been studied and the findings of the study applied to the injection molding of these compounds. The level of oil and of black were found to change the flow properties of EPDM compounds. Higher levels of oil decreased the compound viscosity while higher levels of black increased the compound viscosity. The viscosity of the oil influenced compound viscosities. Compounds made with the more viscous (at 210° F) oil had slightly higher viscosities. However, changing from an aromatic to a naphthenic oil of similar viscosity had little effect on the compound viscosity. Compounds made from two different polymers of similar Mooney viscosity were found to have widely divergent flow behavior at high shear rates. Injection molding of EPDM compounds was studied with a molding assembly which had a capillary rheometer as barrel and plunger. Injection pressure data from the molding experiments was found to parallel closely the rheological data. An analysis of the pressure drops in passing through different parts of the mold assembly was made. The total calculated pressure drop agreed closely with the measured pressure drop. The viscous generation of heat was found to be proportional to pressure drop, and an equation is presented which relates the temperature increase to the pressure drop.
Research for a Uniform Quality Grading System for Tires. II. Wheel Speed Capability Test
Authors: Brenner F. C. , Mandel J. , Simson B. G.
Published: February 2011

The wheel speed capability of a tire is defined by a test method which determines the speed at which the tire fails on a laboratory test wheel. Data is reported on over 100 different passenger car tires of all grades and types over a range of sizes. A scaling system is devised for this property. It is found that the system produces consistent results for tires of given manufacturer's nominal grade across the size range tested and for samples produced several months apart.
Pigment Contact Potentials and Reinforcement
Authors: Havenhill R. S. , Carlson L. E.
Published: February 2011

1. A new apparatus has been described for measuring the contact potential of powdered reinforcing pigments. 2. With this apparatus, contact potentials on MPC and FT blacks, fine and coarse particle size zinc oxides, whiting, and barytes show correlation with their reinforcing properties in natural rubber and cis-1 ,4-polybutadiene rubber. 3. Contact potentials of Hi-Sil, Suprex clay, coated zinc oxides and coated calcium carbonate pigments showed no correlation with their reinforcing properties in rubber. 4. Contact potentials on the minerals, diamond, quartz, zinc oxide, calcite and barite correlated with the reinforcing properties of their pigment counterparts. 5. Contact potentials of the minerals also correlated with Mohs hardness. 6. Contact potentials on coated zinc oxide pigments correlated with their improved processing properties in rubber. 7. A new apparatus has been described for measuring the contact potentials of cured stocks in which cut surfaces, rather than molded surfaces, are used. Greater accuracy is possible due to the elimination of surface bloom and other surface contamination. 8. Contact potentials measured on the cut surface of cis-1,4-polybutadiene stocks containing various pigments showed good correlation with their reinforcing properties, thus confirming, with this new rubber, the Electrostatic Contact Potential Theory of Reinforcement.
Reaction of Deuterio Polyisoprene and Deuterio Polybutadiene with Sulfur
Authors: Shipman J. J. , Golub M. A.
Published: February 2011

Infrared absorption spectroscopy has been employed in the past in efforts to determine the nature of the chemical changes which occur in natural rubber during vulcanization. The most prominent change in the infrared spectrum of rubber accompanying vulcanization with sulfur is the appearance of a new absorption band at 10.4 µ. In the spectra of useful soft rubber vulcanizates this band is barely detectable, while in those of hard rubber (ebonite) it is moderately intense. It has not been known whether this band is related in some way to the actual crosslinking reaction or is the result of some noncrosslinking reaction between the rubber and sulfur molecules.
Law of Friction for Surfaces in Elastic Contact
Authors: Bartenev G. M. , Lavrentev V. V.
Published: February 2011

In the elastic contact of two bodies, there corresponds to each value of the normal load N a definite area of actual contact S, the magnitude of which depends on the geometry of the surfaces and the stiffness of the contacting materials. In practice, friction of solid bodies in absolute elastic contact is not observed in the strict sense of the word. With metals in general there is formed a plastic contact, the magnitude of which is determined by the yield point of the softer metal of the friction couple; with plastics there is formed a nonelastic area of contact as a result of the property of plastics of developing quasi-residual deformation with loads above the limiting forced elasticity analogous to the yield point. Along with these materials there are others which give practically complete elastic contact with solid surfaces. These include rubbery network polymers (vulcanized rubbers). With the contact of vulcanized rubbers and metals, the actual area of touching is determined mainly by the properties of the rubber as a high elastic material with a modulus of elasticity about 104 times less than that of metals. There are at present a number of facts, which confirm that the law of friction, expressing the connection between the force of friction and the normal load, is determined by the load, to the extent that the load is capable of forming an actual area of contact. This postulate, formulated for pure metals and vulcanized rubbers is expressed by the formula:
Comparison of Standard and Microtests for International Rubber Hardness
Authors: Stiehler R. D. , Roth F. L.
Published: February 2011

1. Results obtained with an electronic microtester and the standard testers for International Rubber Hardness agree within about 1 IRHD unless there is a pronounced hardening near the surface or other nonuniformity of the compound. 2. The precision of test is not quite as good with the microtester as with the standard tester, but the precision obtained with the microtester can probably be improved by using a visual indicator in place of the audio indicator for detecting the null position. 3. The values of hardness are more dependent on thickness of the specimen at low levels of hardness than at high levels. The ratio of thicknesses to be used with the standard and microtesters appears to be 4:1, rather than 6:1, in order to obtain comparable results. 4. Some compounds exhibit a pronounced hardening near the surface or other nonhomogeneity, which causes high and erratic values of hardness, particularly with the microtester. 5. The incorporation of the microtest for rubber hardness in ASTM Method D 1415 is recommended. It is particularly useful for measuring the hardness of small rubber parts, for which there is no satisfactory test at the present time in the Book of ASTM Standards.
Nuclear Magnetic Resonance Studies of Molecular Motion in Natural Rubber
Authors: Slichter W. P. , Davis D. D.
Published: February 2011

Nuclear magnetic resonance measurements have been made on natural rubber to examine how frequency, temperature, and crystallinity affect the nuclear relaxation. Moecular motions were studied by observing NMR linewidths and spin-lattice relaxation times at temperatures between −100° and 100° C, and at radio frequencies between 2 and 60 Mc. The effect of crystallinity was seen in measurements on stark rubber. The relation between frequency and temperature in the spin-lattice relaxation process is examined in terms of the Arrhenius equation and the WLF expression. The importance of using frequency as a variable in NMR studies of molecular motion is stressed.
Reinforcement of Rubber by Fillers
Authors: Andrews E. H.
Published: February 2011

The mechanical failure of a material, whether tensile failure, tear, abrasion or fatigue, always occurs by a process of rupture propagation, and this paper discusses the strength properties of reinforced rubbers in terms of this process. The effect of fillers and other reinforcing systems on rupture is illustrated and the microscopic role of filler particles discussed. The high rupture resistance of reinforced rubber is attributed to a reduction of stress at the tip of the propagating crack. Model experiments on both unfilled natural rubber and carbon loaded SBR show how such a reduction in stress can result from mechanical hysteresis in the elastomer. This new understanding of the influence of hysteresis on rupture propagation provides a firm basis for the explanation of strength-type reinforcement by fillers.
An Oscillating Disk Rheometer for Measuring Dynamic Properties during Vulcanization
Authors: Decker G. E. , Wise R. W. , Guerry D.
Published: February 2011

A forced oscillating-disk rheometer has been developed which can measure both the low and high frequency dynamic properties of a rubber specimen throughout vulcanization. It may also be used to measure the rheological properties of unvulcanized polymers. The instrument consists of a cone-shaped disk which is embedded in the rubber specimen and oscillated through a small angle while the specimen is heated under pressure. Both stress and strain in terms of torque and displacement, respectively, are measured by appropriate transducers and recorded on an oscillograph. Provisions are made for changing both frequency and strain. At low frequency, the instrument is a convenient tool for determining all of the curing parameters of a rubber specimen. At high frequencies, the change in the dynamic properties of a rubber specimen throughout vulcanization may be continuously followed. A unique feature of the rheometer is that the loss angle may be determined which permits resolution of the measured dynamic stiffness into its elastic and viscous components.
Mechanochemical Phenomena. I. Chemical Flow in Raw and Vulcanized Rubber
Authors: Slonimskii G. L. , Reztsova E. V.
Published: February 2011

1. The authors demonstrate the essential role of mechanochemical phenomena in processing. Attention is paid to the necessity of taking into account the phenomenon of chemical flow. 2. From the example of various vulcanizates there is demonstrated the possibility of mechanical processing of crosslinked polymers. Attention is paid to the significance of mechanochemical phenomena in reclaiming. 3. A demonstration is given of the influence of small additions of substances which form free radicals or which interact with them, upon the kinetics of the alteration of the properties of a polymer on prolonged milling. Attention is paid to the possibility of controlling the properties of a polymer during processing. 4. The authors show the necessity of taking into account the phenomenon of chemical flow in developing objective methods of laboratory assessment of the technological properties of polymers.
Ring-Alkylated p-Phenylenediamines as Antiozonants
Authors: Tucker Harold A. , Veith Alan G.
Published: February 2011

As part of a larger program to correlate the antiozonant activity of rubber additives with their chemical structure, we investigated a homologous series of ring-alkylated p-phenylenediamines. It seemed to us that such investigation might possibly determine whether or not a primary diamine could be an effective antiozonant. The present commercial antiozonants of greatest activity are all secondary diamines. Very little has been published on the behavior of ring-alkylated p-phenylenediamines as protective agents against ozone, probably because of the difficulties involved in preparing them. However, Cox reported on some secondary diamines of this type and said that they are “less potent than their unsubstituted analogs,” comparing them to N,N′-dialkyl-p-phenylenediamines without ring substituents. In contrast to Cox's findings, we have found that some of our primary ring-alkylated p-phenylenediamines have activities comparable with the best of commercial antiozonants.
Suppression of the Activity of Metal Ions in the Oxidation of Rubber
Authors: Kuzminskii A. S. , Zaitsev V. D. , Lezhnev N. N.
Published: February 2011

It is shown that the catalytic activity of variable valency metal ions, Cu++ and Fe+++, with respect to the oxidation of polymeric unsaturated hydrocarbons (natural and styrene-butadiene rubbers) can be completely suppressed by introducing into the polymer, materials which form strong inner complex compounds with these ions. It was established that the synthesized compounds of copper and iron with tetramethylthiuramdisulfide, diethyldithiocarbamic acid, and p-hydroxyphenyl-2-naphthylamine not only do not accelerate the oxidation of polymers, but act as inhibitors of the oxidation process. By chemical and luminescence methods the compositions of the indicated compounds were established to correspond to the following formulas: (D—deactivator) DFe and DCu (iron and copper compounds with tetramethylthiuramdisulfide); D2Fe and D2Cu (iron and copper compounds of diethyldithiocarbamic acid); DFe2 (iron compound of p-hydroxyphenyl-2-naphthylamine); DCu3 (copper compound of p-hydroxyphenyl-2-naphthylamine). These data indicate a new route for the synthesis of effective inhibitors for raw and vulcanized rubber.
Influence of Acids on Scorching and Vulcanization of Carboxylic Rubbers
Authors: Zakharov N. D. , Shadricheva T. A.
Published: February 2011

1. A study of the influence of a series of acids on the process of scorching and the process of vulcanization of mixes was made. 2. It is shown that some sufficiently strong monobasic acids, not having a noticeable influence on the decrease in scorch, do, at the same time, destroy the strengthening effect of metal oxides on vulcanizates. 3. Polybasic acids and their anhydrides lessen scorch, but at the same time slow down vulcanisation. Maleic anhydride is most interesting of the group studied. 4. Vulcanizates using magnesium stearate were tested. It was shown that its use lessened scorch, for all practical purposes, had little effect on vulcanization, and improved the properties of vulcanizates somewhat.
Water Absorption of Elastomers
Authors: Briggs G. J. , Edwards D. C. , Storey E. B.
Published: February 2011

This study considers high temperature (160° C) water absorption in the absence of oxygen. Examination of the freezing behavior of water-swollen butyl gum vulcanizates shows the water to be disposed as discrete droplets of the order of 3µ diameter, corresponding in this case with soluble residues based on zinc. Data are shown for peroxide gum vulcanizates of natural rubber, SBR, NBR, ethylene-propylene rubber, and cis-1,4 poly butadiene. Equilibrium absorption occurs, the degree being dependent on polymer impurities and state of cure. Model systems based on cis-polybutadiene show the effects of typical emulsion polymerization residues and the nature of the equilibrium balance between osmotic pressure and the retractive pressure exerted by the rubber. Classes of absorption behavior, whether low equilibrium, moderate to high equilibrium, or nonequilibrium, are discussed in terms of osmotic and rubber pressures. The temperature dependence of absorption rate is shown for the various polymers for the range 25° to 92° C. Five decades are required to accomodate the data, ranging from low rates for butyl rubber to high rates for NBR and natural rubber. Curing systems are compared, with cis-polybutadiene and butyl rubber as base polymers. Common classes of fillers and reinforcing agents are compared, particular consideration being given to the hydrophylic calcium silicate and silica fillers, which appear to facilitate leaching of electrolytes when present in sufficient loading. From the combined experience, illustrative water-resistant formulations are derived.
Solution and Diffusion in Silicone Rubber. II. Influence of Fillers
Authors: Barrer R. M. , Barrie J. A. , Raman N. K.
Published: February 2011

An investigation has been made of the effect of a high area silica filler upon the solubility and diffusion of some C4 and C5 paraffins in silicone rubbers. The membranes studied contained by weight 0, 10, 20, 30 and 40 parts of filler per 100 parts of polymer. The solubilities have been discussed in terms of two reference models: the first in which silica and rubber phases act independently as sorbents; and the second in which the filler is regarded as completely wetted by polymer and is thus a non-sorbent. Diffusion and permeation have also been considered in terms of the models, assuming with the first model an immobile sorbed layer on the porous silica. It has been found that, although some aspects of the behavior can be explained, the results are not fully in agreement with either model, and that the behavior of the heterogenous membrane is complex.
Solubility and Mobility of Sulfur in Ethylene-Propylene and Ethylene-Butene-1 Copolymers
Authors: Baldi L. , Zannetti R.
Published: February 2011

Solubility and mobility of sulfur in copolymers of ethylene/propylene and ethylene/butene-1 were determined, using S 35 according to the method developed by Auerbach and Gehman for natural rubber and certain polymers and copolymers possessing elastomeric properties. We took into consideration the effect of temperature and copolymer composition, both on the solubility and on the mobility of the sulfur. Also examined was the effect of the migration of sulfur to the surface of the vulcanized product. The results are discussed in relation to the characteristics of the vulcanization process.
Nonlinear Viscoelastic Response of Amorphous Elastomers to Constant Strain Rates
Authors: Smith Thor L.
Published: February 2011

Tensile stress-strain curves determined at constant strain rates are nonlinear because relaxation of stress generally occurs during a test and also because of inherent nonlinear effects. To develop a method for determining the conditions under which time and nonlinear effects are separable, consideration was first given to a linear viscoelastic material. It was shown that stress-strain curves determined at different strain rates superpose to yield a single curve on a plot of log σ(ε, t)/ε vs. log t, where σ(ε, t) is the stress, a function of the strain ε and the time t; by definition t equals ε/ε where ε is the strain rate. The quantity σ(ε, t)/ε was called the constant-strain rate modulus F(t) which is related exactly to the stress-relaxation modulus E(t) by the equation E(t)=F(t)(1+m) where m=d log F(t)/d log t. For amorphous elastomers tested in tensions over a wide range of strain, it was proposed that stress-strain curves determined at constant strain rates can be represented by F(t)=g(ε)σ(ε,t)/ε where g(ε) is a function only of strain and approaches unity as the strain goes to zero. To test this equation, an analysis was made of stress-strain curves of an SBR gum vulcanizate measured to rupture at numerous strain rates at 10 temperatures between −42.8 and 93.3° C. From − 34.4 to 93.3° C, g (ε) was found to be independent of both time and temperature, but at −42.8° C for strains greater than about unity, g(ε) was found to be different. The functional form of g(ε) was compared with that predicted by three different analytical expressions for representing stress-strain data. To show further the advantages of F(t) for representing stress-strain data determined at different strain rates and temperatures, previously published data on the NBS polyisobutylene were presented on a plot of log F(t)298/T vs. log t/aT. From the composite curve, E(t) was calculated and found to be in close agreement with published data.
Changes in Polybutadiene Rubber under Various Conditions of Aging
Authors: Salimov M. A.
Published: February 2011

1. The systematic relations of the oxidation of SKB under the action of heat, light, and ionizing radiation are considered and it is shown that the formation of a series of oxygen-containing products takes place (hydroperoxides, alcohols, aldehydes, ketones, acids, ethers, and esters). The general tendency for formation of these compounds was clarified for each separate case. 2. The behavior of double bonds of various configurations (1,2 and cis and trans 1,4) reveals differences in reactivity, namely: in the thermal, light, and radiation reactions, a decrease of the number of double bonds in the 1,2 position takes place, in general this is due to crosslinking and formation of volatile acids, but in the radiation reaction it is also due to hydrogenation. The increased rate of the decrease of the number of cis 1,4-bonds is in all cases interpreted as evidence of isomerization to the trans-configuration. It was shown that migration of 1,4 double bonds along the chain towards the tertiary carbon atoms and formation of conjugated double bonds (band at 1595 cm−1) takes place. 3. A decrease of the number of double bonds in the backbone (cis and trans 1,4) takes place that is mainly due to the formation of oxygen-containing compounds. Therefore, the quantitative investigation of this process can give an idea of the level of oxidative degradation. 4. The increase of the total absorption in the region 1400 to 750 cm−1 is connected with crosslinking. This, together with other existing methods (investigation of equilibrium swelling and stress relaxation) can be used for the estimation of the degree of crosslinking.
Identification of Rubber Polymers by Mass Spectrometry
Authors: Phillips J. K.
Published: February 2011

The identity of an elastomer or elastomers in a rubber compound can be determined within a few minutes by the use of a new analytical procedure described in this article. It involves high temperature pyrolysis for two seconds, in vacuo, with an arc imaging furnace and subsequent analysis of the gaseous pyrolyzate with a mass spectrometer. Numerical values derived from the mass spectra of standards permit semi-quantitative analyses of some mixtures of elastomers in cured products. Qualitative analyses have also been made on most of the common textile polymers and a small number of miscellaneous polymers.
Mechanochemical Modification of Polybutadiene (SKB) by Maleic Anhydride
Authors: Baramboim N. K. , Popov V. I.
Published: February 2011

In recent years there have been a number of papers devoted to the special features of mechanochemical copolymerization of a number of natural and synthetic polymers with some special comonomer such as maleic anhydride. As a result of this mechanochemical copolymerization there are formed linear and branched products, containing isolated units of maleic anhydride. The anhydride rings of maleic anhydride are easily opened in the presence of moisture, and each unit of maleic anhydride in the copolymeric product forms the group (see PDF for diagram) Thus mechanochemical binding of the maleic anhydride makes it possible to “carboxylate” the polymers, modifying the properties of the original polymers according to the nature and amount of the carboxyl units added. In general mechanochemical modification by maleic anhydride leads to an increase in the stiffness, strength, adhesion to metals, hydrophilic nature and the possibility of carboxyl crosslinking. Thus the properties of modified natural rubber and SKS (butadiene-styrene rubber) approximate to those of carboxylated rubbers. This method of modification offers particular interest as a result of the simplicity and general availability of the mechanical apparatus (mills and internal mixers) required for the process.
Vulcanizate Structure, Relaxation, and Tensile Strength of Polyisoprenes
Authors: Hoffmann M. , Unbehend M.
Published: February 2011

The tensile strength of lightly-filled sulfur vulcanizates of 1,4-cis polyisoprene is lower the more the specimen has undergone deformation after removal of a definite stress. With equal tensile strength, this deformation multiplied by the modulus is proportional to the square of the filler concentration. Along with this deformation the volume of the elongated specimen increases through the formation of internal stress cracks. Rupture originates even at lower stresses in the neighborhood of the filler particles. It is affected by the size of the filler particles as well as by the chemical nature of the filler and by the structure of the network. Encouraged by these results we checked the network structure. We examined the stresses at high elongations, the photoelaetic homogeneity and the turbidities and viscosities of solutions of the degraded vulcanizates, and found small local variations in crosslink density and differences in the number of elastically-ineffective chain ends. The number of these chain ends and the local variations of crosslink density may increase greatly during vulcanization, and substantially reduce the tensile strength.
A Study of Sulfenamide Acceleration
Authors: Morita E. , Young E. J.
Published: February 2011

Sulfenamide—sulfur curing systems containing zinc oxide and stearic acid respond to both ionic and radical reaction conditions. Scorch delay and rate of the vulcanization are determined by the basicity and steric structure of the amine forming the amide, and by the accelerator-sulfur ratio. Sulfenamides derived from heterocyclic amines which form stable sulfides showed progressive improvement in scorch delay as the concentration of the sulfenamides was increased at constant sulfur level. In contrast to this group, the acceleration rates of sterically hindered sulfenamides were slow and their scorch delay decreased with increased accelerator concentration. The assumption that the initial step in sulfenamide acceleration is the dissociation of the sulfenamide into benzothiazolyl sulfenamide and amine radicals does not satisfy these experimental results. Consideration of the rate of sulfenamide-sulfur reaction and the stability of these intermediates has been suggested as an alternate explanation. Higher concentrations of accelerators in general resulted in vulcanizates with higher modulus and a larger number of effective sulfur crosslinks. About 1.5–2 atoms of sulfur per effective crosslink were found for vulcanizates where one mole of sulfenamide was used per atom of sulfur. It was also found that at this high concentration of sulfenamide a considerable fraction of the benzothiazolyl sulfenyl groups was initially bound to the rubber molecule and later released as extractable 2-mercaptobenzothiazole derivatives. Part of these groups which remained bound to rubber were reducible to form 2-mercaptobenzothiazole. Part of the true combined sulfur is released as ZnS in later stages of cure.
Intermolecular Forces and Chain Flexibilities. IV. Internal Pressures of Polyethylene Glycol in the Region of Its Melting Point
Authors: Allen G. , Sims D.
Published: February 2011

Experimental support for the suggestion (Part III), that the freezing-in of chain conformations is a major factor contributing to the low values of internal pressure found in polymeric glasses compared with the glass transition regions for corresponding rubbers, is advanced as a result of tests on a commercial sample of polyethylene glycol. The reliability of the results is considered.
The Cyclization of Natural Rubber
Authors: Lee D. F. , Scanlan J. , Watson W. F.
Published: February 2011

The resinification of natural rubber by acid catalysts has been investigated since the beginnings in 1937 of interest in the chemical reactivity of rubber. During the reaction there is a partial loss in unsaturation but no change in the empirical formula of the rubber, C5H8. No general agreement exists on the decrease in unsaturation, values from 40 to 90% of the original having been quoted. (see PDF for diagram) The reduction in the number of double bonds has been attributed to an intramolecular bond formation leading to formation of cyclic structures. D'Ianni, Naples, Marsh, and Zarney have suggested the generally favored structure I, formed by reaction between pairs of adjacent isoprene units of the rubber chain. Van Veersen on the other hand, has proposed the more highly condensed polycyclic structure II. with the cyclization proceeding along the chain to involve a number of adjacent isoprene groups.
Reaction of Chloral with 1,4-Polyisoprene
Authors: Pinazzi Christian , Pautrat Rene , Cheritat Roland
Published: February 2011

The cis-1,4-polyisoprenes are composed of 2-methyl-2-butene units, the double bonds of which must be favorable to the addition of strongly electrophylic reagents such as certain aldehydes. Chloral is of this type and its ionic reactions with various simple olefins has been described. We found it worth while to transpose these results to polyisoprenic macromolecules, either natural or synthetic. The ionic reactions generally create less modifications of the chain, such as fission or crosslinking, than would result from free radical reactions. Also, if the formation of free radicals is avoided, the possible fixation of chloral on the halogen carrying carbon (group —CCl2—CHO) becomes very unlikely. Pure anhydrous chloral is used as the reagent. A solution of 2% cis-1,4-polyisoprene (natural) in cyclohexane or decalin (free of peroxides) is heated under a nitrogen atmosphere with the reagent and in presence of a catalyst such as AlCl3 or BF3 at a concentration of 1–3% relative to the polyisoprene. The macromolecular product obtained is then subjected to a fractionation by the chloroform-methanol combination. After purification and desolvation of the main fraction an elemental analysis is made and the level of fixation n calculated based on the chlorine content. Table 1 relates some of the results obtained by using AlCl3 or BF3. In the absence of catalyst (Figure 1, A) the level of fixation is low: n=4 and therefore the nature of the reaction remains uncertain. In the presence of AlCl3 or of BF3, n increases rapidly in function of the temperature and of the relative molar concentration of the reagents, as shown by the curves B and C of Figure 1. The highest level of fixation obtained in these experiments is n=22. Figure 2 demonstrates this limit which is reached beyond the molar ratio of m=4, in the presence of AlCl3 (3%). Table 2 shows the particular action of AlCl3 which among all the catalysts tested proves to be as effective as BF3 without yielding any notable crosslinking of the macromolecular substance.
The Indenter Hysteresimeter for Testing Dynamic Properties
Authors: Tangorra G.
Published: February 2011

The results obtained up until now with the indenter hysteresimeter confirm that it is a fast and useful instrument for the technologist. A theoretical analysis, supported by experimental data, suggests a broadening of its field of application by the attainment of specific dynamic mechanical parameters of the tested materials. The instrument can be easily calibrated. Its adaptability permits its advantageous use where a remote control, as for instance inside a thermostat, is required, and allows its combination with electronic units, simply and easily available, for automatic operation when this is necessary.
Identification of Elastomers by Infrared Spectrophotometry
Authors: Fiorenza Aldo , Bonomi Giuseppe
Published: February 2011

The use of infrared spectrophotometry for the identification of elastomers is discussed, after having reviewed the general principles on which spectrophotometry is based and after having considered the principal types of atomic vibration. There follows a description of the principal methods of analysis for solution and pyrolysis, the presentation of the spectra obtained from 14 different elastomers and their mixtures, and finally the assignment of the fundamental bands in the spectra themselves.
Behavior of Sulfenamide Accelerators under Adverse Processing Conditions
Authors: Dibbo A. , Lloyd D. G. , Payne J.
Published: February 2011

The technological target of this work has been to show how the best use can be made of available sulfenamides under the most adverse processing conditions. The overall conclusions are given in Table 5. On balance, therefore, the best recommendation for an accelerator system for use under adverse conditions is one based on a blend of 2-(4-morpholinyl mercapto) benzthiazole plus a nitroso retarder where the accelerator is used at normal concentrations. Because of the linear relationship between additional processing safety and Curetard concentration, the amount of Curetard added can be easily adjusted to meet individual circumstances. The use of higher concentrations of 2-(4-morpholinyl mercapto) benzthiazole can be recommended for those cases where it is possible to reformulate the stock and where a faster cure is essential.
The Determination of Cure Time with the Curometer
Authors: Payne A. R.
Published: February 2011

The vulcanization of rubber is a complex process but its main feature is the introduction of crosslinks between the otherwise independent linear molecules of the raw rubber. It is logical, therefore, to relate cure measurement to this process. The Curometer measurement can be regarded as measuring the introduction of crosslinks but, as initially conceived, determination of the cure time by mere imspection of the trace, allowed too much play for personal judgment and ignored all but one piece of the data provided by the continuous trace. The possibility of measuring the introduction of crosslinks as the reaction proceeds has encouraged consideration of what is meant by adequate cure and has suggested the use of crosslinking cure with a number attached, say 90 to 95% as giving more precision to this concept than is possible in continuing to use the term “optimum”. Optimum can then be used when a specific property is required such as the time to reach the maximum tensile strength. It will be appreciated that scorch can in principle be similarly treated though, as the shape of the commencement of the log/linear plots show, the reaction is less simple, and cannot be regarded even approximately as of the first order. However, extrapolation of the straight line backwards in time does give a reproducible time where the line crosses the abscissa corresponding to zero crosslinking. The use of scorch values is very much a matter of experience and rather arbitrary relative grading of stocks. Obviously further work in association with factory processing would be necessary before the Curometer could serve completely the dual purpose of more exact scorch as well as cure determination. Meanwhile, cure determination is now more firmly based.
Crosslinking Chlorosulfonated Polyethylenes
Authors: Maynard J. T. , Johnson P. R.
Published: February 2011

The broadening practical use of chlorosulfonated polyethylene elastomers for applications where good resistance to heat, oil, light, oxygen, and ozone is needed has been accelerated by the development of several chemically distinct curing systems. Optimum use of these saturated elastomers requires a knowledge of the chemistry of these curing reactions and the effect of the resulting crosslink structures on vulcanizate properties. The high reactivity of the sulfonyl chloride crosslinking sites allows wide latitude in choice of curing chemistry, and crosslink type can be controlled to give a preponderance of ionic salt bonds or to give a mixture of covalent and ionic bonds. The role of water, alcohols, sulfur accelerators and free radical stabilizers in the various practical curing systems is discussed. The development of wholly organic curing systems for chlorosulfonated polyethylenes is reviewed. The properties of vulcanizates of chlorosulfonated polyethylenes are also significantly controlled by the base polyethylene, by chlorine content, and by chlorine distribution. The effects of these variables on vulcanizate properties is briefly reviewed.
The Relation of Transition Temperatures to Chemical Structure in High Polymers
Authors: Boyer Raymond F.
Published: February 2011

The primary purpose of this paper is to summarize some of the general relationships between chemical structure and transition temperatures for polymers. In addition to the two primary transitions, the melting point Tm, and the glass transition TG, other transitions occurring either below TG or between TG and Tm are discussed. A secondary purpose of this paper is to make a preliminary attempt at some rational nomenclature and classification scheme for polymer transitions, especially in the case of polymers having multiple transitions. This article is not intended to be a complete review of the literature on transitions in polymers. Our paper was inspired by a comprehensive lecture on multiple transitions presented by Dr. Karl Wolf in Midland, Michigan, during the summer of 1960. The substance of this lecture has recently been published. Willbourn has also been concerned with the classification of multiple transitions. A recent comprehensive report by Saito, Okano, Iwayanagi and Hideshima called “Molecular Motion in Solid State Polymers” also considers in elaborate detail many of these same problems.
Antioxidants and Antiozonants for General Purpose Elastomers
Authors: Ambelang J. C. , Kline R. H. , Lorenz O. M. , Parks C. R. , Wadelin Coe , Shelton J. Reid
Published: February 2011

The purpose of this article is to review the developments in antioxidants for rubber over the past 25 years since the publication of Davis and Blake's “Chemistry and Technology of Rubber”. The intent is to provide a guide for rational use and further development. Accordingly, the organization of the material is as follows: a) Outline of the mechanism of oxidative attack and antioxidant action. b) Critical review of methods of evaluation. c) Survey of antioxidants in the literature. Numerous reviews of antioxidants in one or more aspects have been published. These have been duplicated only so far as necessary to form a complete outline. Patent references are included only when the specification cites experimental data in support of the claims of antioxidant action. Usage divides rubber antioxidants into four categories: 1) Polymer stabilizers, which are added in the polymerization plant to repress the action of oxygen during drying and storage of the uncured rubber. 2) Antioxidants, which are added in compounding to prolong the useful life of the vulcanizate by retarding the oxidative changes that occur over a long period of service. 3) Flex-crack inhibitors, antioxidants which retard crack initiation or crack growth under conditions of cyclic deformation. 4) Antiozonants, substances which by chemical action (or by a combination of physical and chemical processes) delay the onset or growth of cracks resulting from ozone attack. (This definition is written to exclude waxes, which protect from ozone by forming a chemically nonreactive surface film.) There is a closer fundamental connection between polymer stabilizers and vulcanizate antioxidants than among other classes. The discussion of mechanisms of oxidation and antioxidant action will introduce the first two. Evaluation of the two classes of materials are operationally different and will be discussed separately. The present discussion is limited to “general purpose” elastomers of the present time; namely, NR, IR, SBR and BR.
Resins Used in Rubber
Authors: Powers Paul O.
Published: February 2011

Resinous materials have long been used to aid in the processing of rubber and to impart special properties to the vulcanized product. Resins have been described as various solid or semisolid organic substances. Originally, naturally occurring resins such as rosin were employed but with the advent of synthetic resins, many of these have been used with natural and synthetic rubber. In general the resins considered here are readily fusible and relatively low in molecular weight, the average value often being less than one thousand. However, thermosetting resins are also employed, usually being introduced into the rubber at a low stage of condensation. Resins are frequently added to assist in processing and often are considered as softeners although they are higher in molecular weight than most softeners and their efficiency as softeners is somewhat less. However, they do not soften the resulting vulcanizate and may even increase the hardness.
Effect of Carbon Black Structure Aggregate Size Distribution on Properties of Reinforced Rubber
Authors: Stacy C. J. , Johnson P. H. , Kraus G.
Published: February 2011

1. Broadening of the aggregate size distribution of carbon black leads to significant changes in optical properties, such as lower tinting strength and greater dissymmetry of light scattering. 2. Effects on vulcanizate properties are generally small, the most significant effect being lower hysteresis for blacks of broad distribution. 3. In moderately severe service, treadwear is unaffected by differences in breadth of aggregate size distribution sufficient to cause large changes in tinting strength. 4. Tinting strength is not a reliable criterion of treadwear quality unless carbon blacks of equal structure and breadth of ASD are compared. 5. The results of this study do not contradict earlier results on carbon black blends which show significant losses in treadwear resistance as a result of severely broadened nodule (“particle”) size and, incidentally, also aggregate size distributions.
Capillary Rheometry of Carbon-Black-Filled Butadiene—Acrylonitrile Copolymers
Authors: Nakajima N. , Collins E. A.
Published: February 2011

Capillary rheometry of carbon-black-filled butadiene—acrylonitrile copolymers at 125°C was performed over a wide shear rate range. The data were corrected for pressure loss in the barrel and at the capillary entrance, and for the non-Newtonian velocity profile (Rabinowitsch correction). No appreciable effect of pressure on viscosity was observed. The die swell values were very small, 1.1–1.4. This fact and the shape of the plots of shear stress vs. shear rate imply the presence of a particulate structure, which is probably built by carbon black surrounded with bound rubber. Unlike the behavior of raw amorphous elastomers, the steady-shear viscosity, the dynamic complex viscosity, and the viscosity calculated from tensile stress-strain behavior were significantly different from each other. That is, the capillary flow data indicated an alteration of the structure towards strain softening, and the tensile stress-strain behavior showed strain hardening, indicating retention of the structure up to the yield point. In the dynamic measurement, being conducted at very small strain, the structure is least disturbed. With unfilled elastomers essentially the same deformational mechanism was believed to be responsible in these three measurements, because the results can be expressed by a single master curve.
Identification of Elastomers in Tire Sections by Total Thermal Analysis. II. White Sidewall Compounds of EPDM and Blends
Authors: Sircar A. K. , Lamond T. G.
Published: February 2011

Total thermal analysis curves can identify all polymers in the blends of EPDM and other elastomers that are used for white side walls. DSC and DTG curves in nitrogen are most promising, while those in oxygen can be used as corroborative evidence. There is close correspondence between DSC and DTG peak temperatures for the elastomers that degrade by endothermic reaction (EPDM, CIIR). The difference in glass transition temperature of the many combinations is not big enough, but this also provides corroborative evidence. The method has been tried in analyzing white sidewalls from commercial tires and was found to give results in good agreement with infrared analysis in most cases.