bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms Involved in the Recycling of NR and EPDM
Authors: Verbruggen M. A. L. , van der Does L. , Noordermeer J. W. M. , van Duin M. , Manuel H. J.
Published: February 2011

The thermochemical recycling of natural rubber (NR) and ethylene-propylene-diene rubber (EPDM) vulcanizates with disulfides was studied. NR sulfur vulcanizates were completely plasticized when heated with diphenyldisulfide at 200 °C. It could be concluded that both main chain scission and crosslink scission caused the network breakdown. NR peroxide vulcanizates were less reactive towards disulfide at 200 °C, and only reacted through main chain scission. For EPDM a temperature range of 200–275 °C was studied. In the presence of diphenyldisulfide at 200 °C there was almost no devulcanization of EPDM sulfur vulcanizates, and at 225 and 250 °C there was only slightly more devulcanization. A decrease in crosslink density of 90% was found when 2×10−4 mol diphenyldisulfide/cm3 vulcanizate was added and the EPDM sulfur vulcanizates were heated to 275 °C. EPDM peroxide vulcanizates showed a decrease in crosslink density of ca. 40% under the same conditions. The lower reactivity of EPDM towards disulfide compared with NR is the result of higher crosslink densities, the presence of a higher percentage of more stable monosulfidic crosslinks and the fact that EPDM is less apt to main chain scission relative to NR.
Ozone Detection by Crack-Induced Opacity in Rubber
Authors: Mott P. H. , Roland C. M.
Published: February 2011

Initially transparent polybutadiene develops micron-sized surface cracks when stretched and exposed to ozone. The consequent reduction in the transparency of the rubber provides a facile method for quantifying the ambient ozone concentration. The rate at which opacity develops is linearly dependent on the amount of ozone, and increases with increasing strain. This method of detecting atmospheric ozone has high sensitivity (1 ppb), a broad dynamic range, and is unaffected by the presence of other chemicals. The surface morphology of exposed material can be interpreted in terms of crack nucleation and growth.
A Novel Method for 13C-NMR Spectroscopy of Polymer in Emulsion: Quantitative Analysis of Microstructure of Crosslinked Polybutadiene in Latex
Authors: Kawahara Seiichi , Bushimata Saori , Sugiyama Takashi , Hashimoto Chihiro , Tanaka Yasuyuki
Published: February 2011

A novel analytical method using high resolution 13C-NMR spectroscopy to study polymer latex, which is a heterogeneous system comprising polymer dispersoid and water, is described. The appropriate concentrations of surfactant and dried rubber content of a polybutadiene latex, which give the best spectrum, were found to be 1 w/v % and 10%, respectively. The half-widths of resonance peaks for the latex sample were almost identical to the half-widths obtained in solution, which were about one-third the width of those obtained using a solid sample of either a crosslinked or soluble polybutadiene. Nevertheless, the signal to noise ratio for the latex sample was slightly smaller than that for the solution sample. The values of spin-lattice relaxation time, T1, for the latex sample were similar to those for the solid sample. These demonstrate that the latex state C-NMR spectroscopy will be a powerful technique for structural characterization of crosslinked gels in the dispersoid because it gives a high resolution spectrum comparable to solution state spectroscopy, showing short T1 values corresponding to those for solid state C-NMR spectroscopy. High resolution latex state 13C-NMR spectroscopy was used to determine the concentrations of the various isomers of the polybutadiene in the dispersoid.
Atomic Force Microscopy of Elastomers: Morphology, Distribution of Filler Particles, and Adhesion Using Chemically Modified Tips
Authors: Haeringen D. Trifonova-Van , Schönherr H. , Vancso G. J. , van der Does L. , Noordermeer J. W. M. , Janssen P. J. P.
Published: February 2011

The microdispersion of silica and carbon black-based filler particles in unvulcanized and vulcanized ethylene-propylene-diene terpolymer (EPDM) rubbers was investigated by atomic force microscopy (AFM). Tapping mode phase imaging was found to be particularly useful for imaging of the filler aggregates and for the visualization of single primary filler particles. It was demonstrated that the use of silane coupling agents significantly improves the microdispersion of silica filler in the rubber matrix, as compared to (a) silica without coupling agent, and (b) to carbon black. These results correlate very well with the observed mechanical properties of the materials. In addition, adhesion imaging and the analysis of measured pull-off forces allowed us to differentiate between the filler particles and the rubber matrix, as well as between different types of filler particles. The application of chemically modified AFM tips in pull-off force measurements allowed us to monitor the increase of the hydrophilicity as a result of plasma treatment of the surface of crosslinked poly(dimethylsiloxane), and as a result of chlorination of butyl rubber.
Indentation Tests on Elastomer Blocks
Authors: Busfield J. J. C. , Thomas A. G.
Published: February 2011

The problem of indentation hardness for elastomer blocks has been examined at two levels. Initially an examination of the geometric non-linearity was undertaken. It was observed that the empirical equations adopted by the various standards organizations to predict the stiffness relationships were not always applicable. It appears that the classical Hertz solution to the problem gives a better representation of the general behavior. A finite element approach was also adopted here to tackle the large displacement problem and the limitations of this approach have been discussed. This geometric problem is further complicated in practice by the effect of the finite thickness of the elastomer sheet. This problem has also been analyzed and a suitable general relationship proposed to account for the finite thickness effects. The second problem examined is how the effects of the non-linear elasticity of the material can be tackled. It is shown that the form of the elastic stored energy function at small strains influences the indentation behavior.
Cut Growth in Vulcanizates of Natural Rubber, cis-Polybutadiene, and a 50/50 Blend: Part II. Cracking Patterns in the Strained State
Authors: Hamed G. R. , Kim H. J.
Published: February 2011

The tensile strengths, σb, and apparent fracture energies, G, of edge-cut strip specimens (28 mm wide) of carbon black-filled vulcanizates of natural rubber (NR), cis-butadiene rubber (cis-BR), and a 50/50 blend have been determined. The BR vulcanizate exhibited a rather steady decrease in σb with increasing cut size, c, and fractured by simple growth of the original cut tip. NR and the NR/BR blend exhibited much higher strengths as well as a drop in σb at a critical cut size, ccr≈2.2 mm. High strengths are attributed, at least in part, to substantial longitudinal cracking prior to catastrophic fracture, especially when cccr. Below ccr, normalized strengths of the NR and NR/BR were comparable and exceeded those of BR. For all three vulcanizates, calculated fracture energies depended on cut size. Photographs of a deformed NR/BR specimen, which had developed the auxiliary cracking, revealed that longitudinal crack tips appear as "corners" propagating along the loading direction. As a longitudinal crack progresses, strain energy is released by the retraction of (sheared) material into the unstressed zone at the extremity of crack opening.
Science and Technology of Reclaimed Rubber
Authors: le Beau D. S.
Published: February 2011

Developments in the rubber reclaiming industry are closely related to those in the rubber industry in general. The vulcanized rubber produced by the latter becomes in time the raw material used by the former. Although not superficially obvious, there has been considerable change in the reclaiming industry in the past two decades, required by the introduction of large proportions of synthetic rubber. Since this occurs both alone and in blends with natural rubber, reclaiming of SBR had to be studied in detail so that processes could be adjusted to give approximately the same viscosity from synthetic rubber and from natural, retaining existing procedures for fiber removal and mechanical handling as much as possible. It would have been economically impossible for reclaimers to use any process which required segregation and separate disposal of a substantial part of their raw material. The machinery used in the production of reclaim, and the reclaiming processes used today, are for the major part still the same as used before. The object of reclaiming vulcanized scrap is still the same, i.e., the breakdown (depolymerization) of the scrap to a plastic state which will permit reuse of it in the current rubber processing machinery for the manufacture of new goods. This breakdown is achieved by the application of energy. The type of energy is fundamentally irrelevant, but economics today dictate that it be heat, with partial exclusion of the oxidizing atmosphere, and therefore most of today's reclaim production is carried out in steam. One new continuous reclaiming process was developed during the last fifteen years which relies on electric energy to provide the necessary heat and working of the vulcanized scrap. A fundamental change in requirements of reclaim was also brought about once the synthetic rubber production had proceeded to the point where it was commercially possible to assign more detailed specifications which described the polymer processing behavior limits—a feat not previously achieved for commercial natural rubber. This type of specification was carred over to a considerable extent into the production and sale of today's reclaim. All in all, the extensive research and polymer knowledge which were acquired for the successful production of synthetic rubber have resulted in a much greater control in the production of reclaim and a much greater understanding of the reactions occurring in polymers during reclaiming. Because vulcanized scrap usually contains extraneous material (fiber) which must be removed during reclaiming the process conditions have in the past been selected primarily to accomplish this removal and were not those best suited for the actual reclaiming reaction. Progress has been made during these last years in removing the fibrous materials before reclamation, thereby permitting conditions in the devulcanization cycle to be determined by the actual needs of the vulcanized scrap.
Fundamental Studies of Rubber Blends
Authors: Corish P. J.
Published: February 2011

To sum up our findings on the requirements for rubber blends with vulcanizate properties arithmetically interpolated between those of the constituent rubbers one needs: (a) Rubbers which have similar values of solubility parameter and which also yield blends whose vulcanizates exhibit a single glass transition temperature. (b) Rubbers of similar viscosity. (c) Mixing methods capable of giving good disaggregation of compounding ingredients and satisfactory distribution between the constituent rubbers. (d) Rubbers of similar curative requirement and cure rate and curative systems capable of giving interlocked networks. (e) Suitable choice of plasticizer, which may offset slight deficiencies in (a) and (b). There still remain many unanswered questions, which it is hoped will be answered in future research.
Electron Microscopy of Heterogeneous Elastomer Blends
Authors: Marsh Peter A. , Voet Andries , Price L. D.
Published: February 2011

Microheterogeneity has been observed in several elastomer blends on thin frozen sections, microtomed in a nitrogen atmosphere to eliminate all surface oxidation and cracking, in both phase and electron microscopes. Phase photomicrographs and electron micrographs showing identical detail were obtained on sections swollen in a solvent. During sample preparation the swollen sections are stretched. Samples are examined, after solvent evaporation, in the stretched state. Stereomicrographs of palladium shadowed carbon replicas of the sections indicated that the contrast in electron microscopy corresponds to thickness differences in the sections. These thickness differences were shown to be directly related to the differences in swelling characteristics of the individual elastomer microphases. By using a nonswelling liquid, no phase differences could be observed. By allowing the stretched sections to retract, phase differences diminished to almost complete disappearance. Heterogeneity exists in many elastomer blends. In SBR blends with polybutadiene, however, heterogeneity was observed only in the initial mixing stage, but complete compatibility was found to exist upon continued mixing. The interpretation of electron micrographs of blends loaded with carbon blacks is more complex, since swelling characteristics of the elastomer phases are altered by the presence of a reinforcing filler. No evidence was found for large scale phase transfer of carbon black.
Carbon Black Distribution in Elastomer Blends
Authors: Hess W. M. , Scott C. E. , Callan J. E.
Published: February 2011

A new electron microscope technique permits study of the heterogeneity of elastomer blends and filler distribution therein. Vulcanizates are embedded with a specific monomer system which is subsequently polymerized. Specimens are then sectioned with an ultramicrotome and examined in the electron microscope. Excellent contrast between polymers was obtained in examination of blends of natural rubber with several other elastomers. The homogeneity of these blends is shown to be influenced by mixing procedure and polymer characteristics such as viscosity and various interaction effects. Differences in filler location in elastomer blends can also be detected readily. Carbon black (ISAF) will usually locate preferentially in the polybutadiene in a 50/50 preblend with natural rubber. This affinity is shown to depend on polymer viscosity and can be varied. Investigations with precipitated silica and chemically oxidized ISAF suggest that polarity factors can supersede viscosity considerations and determine filler locations in the blend system. The carbon black content of polybutadiene in 50/50 blends with natural rubber was systematically varied from 7 to 95 per cent. Road wear and tensile strength were highest with most of the carbon black in the polybutadiene. Hysteresis and tear strength were optimized with about 60 per cent of the black in the polybutadiene.
NMR Study of Polypropylenes of Different Structure and Steric Order
Authors: Natta G. , Lombardi E. , Segre A. L. , Zambelli A. , Marinangeli A.
Published: February 2011

In agreement with results previously published by other workers, the reported data indicate the usefulness of NMR spectra of polymers for configurational analysis and clearly show the increased possibility of investigation offered at frequencies of 100 Mc/s. The problem of quantitative determination of the number of inversions and retentions and of the percentage of heterotactic methyl groups either by the use of the index of alternation and retention at 60 Mc/s or by examination of the methyl spectrum at 100 Mc/s requires a more detailed study to determine the precision of the analytical method and its accuracy. Generally, as regards the interpretation of the ratio between the numbers of alternations and of retentions, we deem it of interest to report that this ratio, in contrast to the hypothesis of other workers, is not in itself sufficient to determine the average length of the sterically ordered segments in stereoblock polymers. In fact, the hypothesis that inversions of steric configuration are randomly distributed is generally not valid, as clearly demonstrated by the fact that it is possible, by the use of suitable catalysts24, to obtain stereoblock polymers not separable by physical methods and which simultaneously have syndiotactic and isotactic crystallinity as determined by x-ray analysis. This fact indicates at least the presence of stereoblocks of considerable length and is incompatible with a random distribution of the retentions and inversions of steric configuration in the macromolecule. On the other hand, even when it becomes possible to determine exactly the content of heterotactic methyls and to calculate the average length of the regular segments, x-ray or infrared analysis will still be required because the presence of isotactic or syndiotactic crystallinity in a polymer requires only that at least a considerable part of the stereoregular segments be sufficiently long.
Sequence Distribution in Copolymers Physical Property Studies
Authors: Harwood H. James
Published: February 2011

The physical properties of copolymers are determined by their compositions and by the distribution of monomeric sequences in their chains. In some cases, sequence distributions can be determined from or correlated with physical properties observed for copolymers. Such determinations or correlations are relatively simple when calculations are based on run numbers.
Influence of Environmental Variables on Characterization of Polymer Decomposition by Thermogravimetry
Authors: Dudley M. A. , Smith Derek A.
Published: February 2011

The influence of balance design, dynamic atmosphere, buoyancy and convection, shape and material of sample support, sample mass and degree of comminution, heating rate, heat of reaction, and composition of sample atmosphere on polymer TGA are briefly reviewed and some new data are presented.
Molecular Weight Dependence of Relaxation Spectra of Amorphous Polymers in the Rubbery Region. VIII. Comparisons of Experimental Relaxation Spectra of Commercial Synthetic Rubbers with those Estimated from Molecular Weight Distributions
Authors: Yasuda Genichi
Published: February 2011

Synthetic rubber of different species, types, and degrees of mastication were used to examine the general validity of the proposed relationship between mechanical relaxation spectra in the rubbery region and molecular weight distribution. Results show that the proposed relationship can be well used to discuss quantitatively the role of molecular weight distribution in the theoretical behavior of a raw rubber while being processed.
Structural Characteristics of Alkyllithium Catalyzed Polymers Derived from Butadiene and Styrene
Authors: Weissert F. C. , Johnson B. L.
Published: February 2011

More than a million miles of tire testing is generally required to prove the utility of a new elastomer. For example, such a program has recently demonstrated that an alkyllithium solution polymerized butadiene styrene copolymer (Duradene rubber) has improved abrasion resistance over that of emulsion SBR1. It is, thus, extremely important to find meaningful relationships between the structure of an elastomer and its commercial importance to further guide the polymer chemist toward the development of new general purpose or specific application elastomers from laboratory sample through to final tire evaluation. Butadiene homopolymers and butadiene styrene copolymers prepared by alkyllithium catalysis in hydrocarbon solution offer unique opportunities to relate basic polymer structure parameters to tire compound performance. Their mixed micro-structure (cis-1, 4, trans-1, 4, and vinyl) preclude crystalline transitions which would otherwise complicate the interpretation of structural behavior. Furthermore, this polymerization system permits the production of controlled and specific variations in molecular weight distribution and degree of branching. n-Butyllithium catalyzed 1, 4-polybutadiene with its mixed microstructure and high cis-1, 4-polybutadiene have both shown outstanding abrasion resistance, especially under conditions of severe tire service. There is as yet no generally clear molecular interpretation for the outstanding abrasion resistance of the 1, 4-polybutadienes. For reasons of both improved processing and increased wet traction, these 1, 4-polybutadienes are seldom used alone but are blended with either natural rubber or SBR plus large amounts of extending oils. As a start, using as few fundamental concepts as possible, attempts were made to relate the industrial processing, heat build up, traction, and abrasion resistance characteristics of amorphous elastomers to two features measurable in terms of molecular parameters. The macrostructure (molecular weight distribution and branching) of the polymer is especially related to processing behavior. The glass temperature, Tg, of a polymer characterizes both the temperature and rate of deformation conditions in which the polymer exhibits rubbery behavior. Hence, the polymer Tg is directly related to both heat build-up and failure characteristics of an elastomer. Thus we shall be mostly discussing polymer structure in just two terms (i) macrostructure and (ii) Tg.
Cleavage Reactions in Crosslinked Urethan Elastomers
Authors: Tobolsky A. V. , Johnson V. , MacKnight W. J.
Published: February 2011

A study of network cleavage in a crosslinked polyurethan elastomer was made using the technique of stress relaxation. The data could be well represented by a sum of two exponential decay terms, and a theoretical explanation for this is presented. Stress relaxation in the polyurethan sample is discussed in terms of the reversible cleavage of linkages formed by isocyanate reactions. It is possible to identify two different decay processes and to obtain activation energies for them. These are identified with cleavage of two different linkages. It is not possible, at present, to give a certain chemical identification of the linkages responsible for stress decay.
Network Scission Processes in Peroxide Cured Methylvinyl Silicone Rubber
Authors: Thomas D. K.
Published: February 2011

In what appeared to be a complex system it transpires that network scission in methylvinyl silicone rubbers at temperatures below 250° C is due largely to hydrolytic reactions in the main chain polymer. At temperatures of 250° C and above there are indications that a significant amount of scission arises from oxidative reactions in the crosslinks, and that this reaction is catalyzed by acidic residues in the rubber. There is no indication that acidic byproducts of the vulcanization reaction catalyze the hydrolysis of siloxane bonds in the polymer. In conventional heat aging tests in which the rubber remains in an unstrained condition the effects of hydrolysis will only be observed if the concentration of water in the system is allowed to rise. Under these circumstances softening will occur because of a shift in the position of equilibrium in the reaction ∼Si—O—Si—O∼ + H2O→∼Si—OH+ HO—Si—O∼ On aging the material in a well ventilated situation the effects of hydrolysis are not seen and the silicone rubber becomes brittle after long exposure at high temperature. This embrittlement must result from additional crosslinking caused by oxidative reactions in the methyl groups of the main chain polymer. When the rubber is used in compression or tension, hydrolytic scission will affect performance, and in applications of this sort it is important to dry the rubber before use and prevent access of moisture to the component during use. With filled rubber the silica filler is a further source of moisture and drying needs to be carried out at elevated temperatures immediately before use. In order to improve the confined heat aging performance of silicone rubber an alternative filler to fine silica is needed which does not have the same affinity for water. It may be, however, that ability to reinforce silicone rubber and affinity for water are inseparable.
Simultaneous Measurements of Stress and Infrared Dichroism on Polymers I. Stress Relaxation of Vulcanized Natural Rubber
Authors: Gotoh Rempei , Takenaka Tohru , Hayama Naomi
Published: February 2011

A method for simultaneous measurements of stress and infrared dichroism as time-dependent behavior of polymer films was devised using a double beam infrared spectrometer. The film sample held between clamps of a stretching device was placed just in front of the entrance slit of the spectrometer where the sample and reference beams came alternately. Two polarizers were used, one in the sample beam and the other in the reference beam. Thus the sample and reference beams were polarized to have the electric vectors parallel and perpendicular to the stretching direction of the sample, respectively. With this arrangement the spectrometer responded only to the difference in the transmittance of the two beams. Setting the spectrometer at one of the wavenumbers of the absorption band maxima, we could record continuously the change in its dichroism during mechanical treatments which gave rise to molecular orientation in the sample. The stress was recorded automatically by means of a pair of strain gauges pasted on the cantilever beam of the stretching device. By theoretical considerations, a simple relationship was found to exist between the quantity recorded on the spectrometer by this method and the orientation function of transition moment of a vibrational absorption band with respect to the stretching direction. The method was applied to the stress relaxation experiments of vulcanized natural rubber carried out at different elongations less than 600 per cent and at room temperature. Changes of infrared dichroism were measured for five absorption bands at 1664, 1380, 1361, 1129, and 844 cm−1, of which the last one is a crystalline band. From the results of this study, the stress relaxation observed was ascribed mainly to the amorphous orientation rather than to the crystalline orientation, which was completed almost immediately after elongation.
Ultimate Tensile Properties of Elastomers. IV. Dependence of the Failure Envelope, Maximum Extensibility, and Equilibrium Stress Strain Curve on Network Characteristics
Authors: Smith Thor L. , Frederick J. E.
Published: February 2011

Uniaxial tensile data from tests at different rates of extension over a wide temperature range are considered for butyl, silicone, Viton B, SBR, and natural rubber vulcanizates (series A) and for six Viton A-HV vulcanizates (series B) of differing crosslink densities. For series A and for A-6 in series B, equilibrium stress-strain data were obtained at large deformations by an indirect method. The ultimate tensile properties of all vulcanizates were previously characterized by a time- and temperature-independent failure envelope. The failure envelope's maximum extension ratio, (λb)max, to be equal to or less than (λ∞)max, the maximum extension ratio (hypothetical) in the absence of rupture and also the maximum extension ratio of network models. Failure and equilibrium data for series A vulcanizates are represented by a specific function of the equilibrium modulus and the maximum extensibility; except for SBR and possibly Viton B, equilibrium and failure data are sensibly identical; thus, (λb)max≅ (λ∞)max. For series B vulcanizates, qualitative considerations indicate that (λ∞)max/(λb)max is greater than unity and possibly dependent on crosslink density. Consideration of network models suggests that (λ∞)max should be directly proportional to Mc1/2 and inversely proportional to (〈r2〉0/M)1/2. For series A, no correlation between (λb)max and (〈r2〉0/M)1/2 was found. For series B, it that (λb)max ∝ Mcβ, where β is a constant in the neighborhood of 0.7. For all vulcanizates, (σb)max≅ 104 (λb)max−1, where (σb)max is the stress in psi (based on the undeformed cross section) at (λb)max.
Failure of Polymeric Materials under Biaxial Stress Fields
Authors: Sharma M. G.
Published: February 2011

Failure behavior of polymeric materials depends considerably on which of the three material states (glassy, transition, and rubbery states) occurs. Failure behavior of polymeric materials can be described by the concept of failure surfaces in principal stress or principal strain space. For a Hycar elastomer, octahedral shear stress criterion described failure very well for stress states corresponding to the first quadrant of the stress space. For cellulose acetate butyrate, maximum shear stress criterion characterized failure reasonably well for stress states corresponding to the first and the fourth quadrants of stress space. It appears that it is possible to predict triaxial failure behavior from known biaxial failure properties.
Streaming Birefringence as a Rheological Research Tool
Authors: Wayland Harold
Published: February 2011

This paper reviews theoretical and experimental evidence currently available to establish criteria “to aid the experimenter who wishes to use streaming birefringence as a tool for studying fluid flow. Instrumental techniques are reviewed, and the possibilities for both qualitative and quantitative flow visualization by streaming birefringence in pure Newtonian liquids, colloidal suspensions, and dilute and concentrated polymer solutions are discussed. Methods of reconstruction of the velocity and stress fields from birefringence data are outlined.
Verification of the Flory Theory of Random Reorganization of Molecular Weight Distribution. Kinetics of Methylsiloxane Polymerization
Authors: Carmichael Jack B. , Heffel James
Published: February 2011

Distributions of linear and cyclic methylsiloxanes were determined by gas liquid chromatography during acid clay catalyzed reactions of equal molar amounts of D4[D= (CH3)2SiO] and MM[M= (CH3)3SiO1/2 at 80° C. Theoretical and experimental distributions of the linear siloxanes are compared as a function of time. The relatively large amounts of MD4M and MD8M present after 0.5 h indicate that D4 initially enters the linear chains as a unit. Sufficient reorganization has occurred after 0.5 h that the distribution of MD10M through MD13M is approximately random. The distribution of shorter chains becomes increasingly random as the reaction proceeds toward equilibrium. A corollary to the above conclusions is that the rate constant for propagation of dimethylsiloxanes appears to be approximately independent of molecular size.
Orientation Induced Nucleation in Polymer Crystallization
Authors: Binsbergen F. L.
Published: February 2011

Crystallization kinetics of polymers crystallizing from the melt are influenced by the mechanical history of the sample. Strain free samples show a larger crystallization half time than samples in which the strain has not been completely removed by relaxation at a suitable temperature. A larger number of nuclei has been assumed to be present in strained samples than in strain free ones. This has been called “orientation induced” or “stress induced” nucleation. This communication presents a morphological description of the phenomenon and of the underlying type of nucleation. My observations were made with a microscope (Reichert ‘Zetopan-Pol’) equipped with a hot stage and 24-mm camera, and mainly with the polarizers crossed. For most of my experiments I used polypropylene, but similar phenomena were also observed with several other polymers.
Breaking Energy of Rubbers
Authors: Grosch K. , Harwood J. A. C. , Payne A. R.
Published: February 2011

Recent investigations of failure of rubbers and plastics have indicated that hysteresial losses in a polymer are an important factor in fracture. This communication reports experimental evidence that the energy density at break of a polymer is amply related to the hysteresis loss in the polymer. A previously unstrained sample is stressed at a constant extension rate to rupture and the mean value of the rupture load is determined from a number of these measurements. A fresh rubber test piece is then extended under the same conditions until just before rupture, and then retracted at the same rate as was used for extending the rubber. The energy at or near break is determined by measuring the area under the load extension curve, and the hysteresis loss determined from the area between the extension and the retraction curves.
Structural Characterization of Filled Vulcanizates Part 1. Determination of the Concentration of Chemical Crosslinks in Natural Rubber Vulcanizates Containing High Abrasion Furnace Black
Authors: Porter M.
Published: February 2011

The degree to which HAF black restricts the swelling of natural rubber vulcanizates in n-decane has been determined using a vulcanizing system in which the stoichiometry of crosslinking is unaffected by the carbon black. The dependence of the degree of restriction, as measured by the ratio of the volume fractions of rubber in the filled and unfilled vulcanizates swollen to equilibrium, on the concentration of carbon black follows an exponential relationship previously proposed by Lorenz and Parks. This is found to be equivalent to a simple linear relationship between the apparent and actual crosslink concentrations: napparent/nactual=1+Kϕ, where K is a constant characteristic of the filler and φ is its volume fraction in the vulcanizate. The relation has been used to determine actual crosslink concentrations in filled natural rubber vulcanizates. HAF black is found to cause increases of up to 25 per cent in the yield of polymer to polymer crosslinks in conventional sulfur vulcanizing systems, accompanied by changes in rate of cure and of crosslink reversion. All these are small compared with the effect of the filler on many physical properties.
Cis-trans Isomerization in Polyisoprenes. Part VII. Double Bond Movement During Isomerization of Natural Rubber and Related Olefins
Authors: Cunneen J. I. , Higgins G. M. C. , Wilkes R. A.
Published: February 2011

When trans-3-methyl-2-pentene or trans-3-methyl-3-hexene is treated with butadiene sulfone, thiolbenzoic acid, and dibenzoyl disulfide under anaerobic conditions, the olefin undergoes only cis-trans isomerization. However, similar reactions in the presence of oxygen or peroxides also cause changes in the position of the double bond. The latter structural modification is probably caused by acidic compounds formed by oxidation of the isomerization reagents. With natural rubber the nonrubber substances prevent movement of the double bond, and cis-trans isomerization is the sole change, even when the reaction with sulfur dioxide is carried out under aerobic conditions.
Silicone Rubber: A New Diffusion Property Useful for General Anesthesia
Authors: Folkman Judah , Long David M. , Rosenbaum Richard
Published: February 2011

Ether, nitrous oxide, halothane, and cyclopropane diffuse through silicone rubber. General anesthesia can be produced in dogs by passing the vapors of any of these anesthetic agents through a coil of silicone rubber tubing, each end of which is placed in an artery and vein. Potential applications include a new method for general anesthesia and a simple accurate vaporizer for halothane.
Organized Amorphous Copolymers. Polystyrene and Polyisoprene System
Authors: Gallot Bernard , Mayer Roger , Sadron Charles
Published: February 2011

We have described a systematic study of block copolymers of the type AB in which one component is crystalline polyoxyethylene, following an observation in these laboratories that block copolymers adopt a regular structure in the presence of a preferential solvent for one block component of the system at appropriate concentrations. We have recently extended this study to the case of amorphous block copolymers of polyisoprene (block A) and polystyrene (block B) in the presence of a preferential solvent S for one or the other. The systems studied have been principally of the kind AB/S (two-block copolymers) and less thoroughly of the type BAB/S (three-block copolymers).
Two Network Model for Vulcanizates Crosslinked under Strain
Authors: Yanai H. Steve
Published: February 2011

The two network model of Berry, Scanlan, and Watson has been generalized by utilizing the simplified non-Gaussian, three-chain model of Treloar. The generalized two network model provides : (1) the relationship between effective stretch and applied stretch with a given precrosslink level, (2) the stress strain relationship of stretched, crosslinked elastomer, and (3) the relationship between anisotropic swelling behavior and the stretch-crosslinking conditions. Experimental results are in fair agreement with theory. However, due mainly to premature failure of specimens during the tensile test, the results are not quite enough to test the present theory adequately. Therefore additional experimental data are desirable, preferably from specimens with a wider range of the variables.
Viscoelastic Behavior of Segmented Elastomers
Authors: Cooper Stuart L. , Tobolsky Arthur V.
Published: February 2011

Viscoelastic behavior of linear segmented elastomers was examined. The unusual properties found in spandex systems are also observable in hydrocarbon block co-polymers, indicating that hydrogen bonding interactions are perhaps not essential. Low temperature properties of segmented systems are governed by the structural nature of the associated flexible segments, which determines the value of the major glass transition temperature (Tg). It appears that an association of the hard segments provides a broad temperature range of enhanced rubbery modulus. This occurs between the major Tg and a secondary high temperature transition.
Constitutive Equations for Viscoelastic Fluids for Short Deformation Periods and for Rapidly Changing Flows: Significance of the Deborah Number
Authors: Metzner A. B. , White J. L. , Denn M. M.
Published: February 2011

The proper forms and asymptotic characteristics of constitutive equations which may be useful for the description of viscoelastic fluids in flow fields of engineering interest are considered. It is seen that the Deborah number emerges as a natural ordering parameter which determines, on the one hand, whether simple approximations explicit in stress may suffice to describe the fluid properties or, on the other hand, whether implicit or integral equations are required. Methods of scale up are discussed.
Milling Behavior of Gum Elastomers: Experiment and Theory
Authors: Tokita Noboru , White James L.
Published: February 2011

When an uncompounded elastomer is processed on a two roll mill, four different regions of mechanical behavior are observed, depending upon the temperature and the severity of the nip deformation. This behavior is observed on materials with a wide variety in chemical composition, though the severity varies. The flow at high temperatures is typical of melt or polymer solution behavior. At lower temperatures unstable flow and elastic solidlike regions are observed. By presuming the elastomer to be an isotropic viscoelastic medium, stress and velocity fields were computed in the polymer melt region. The unstable regime was found to correspond to a critical value of the ratio of viscoelastic to viscous forces. The mathematical analysis, done in terms of the Green-Rivlin-Noll theory of viscoelastic media, extends earlier studies of deformation in this geometry by Gaskell and Bergen.
Viscoelasticity and Flatspotting
Authors: Howard William H. , Williams Malcolm L.
Published: February 2011

Flatspotting involves delayed elasticity, so conventional principles of polymer viscoelasticity should be applicable. The strain behavior of the tire cord material during the complex stress and thermal history of the tire is idealized in a model, assuming flatspotting is caused mainly by the tire cord material and that the strains in the cord in the footprint area are less than the strains in the cords elsewhere in the tread. A flatspot index based on this model is empirically correlated with tire performance. It is shown here that this commonly used empirical index can be quantitatively interpreted in terms of a viscoelastic property of the tire cord material, in this case, creep compliance of nylon 66. Flatspotting depends on the shape of the viscoelasticity function, which is governed by chemical composition, stress differences in the tire, and the effect of environmental variables on the time scale. The most important environmental variables are temperature and moisture content. Certain qualitative predictions of tire behavior can be made on this basis.
Quantitative Measurement of Tire Flatspotting
Authors: Brownlee J. L. , Perry Eli
Published: February 2011

Equipment was developed to measure the flatspotting of tires quantitatively on an indoor wheel. It provides close control over all of the important variables and has the virtue of simulating driving conditions for all seasons of the year. Good correlations between quantitative values from the indoor wheel and subjective jury tests on the road are obtained when wheel speeds are adjusted to give the same maximum tire temperature as in the road test for a given ambient temperature. The tire cord was of primary importance in controlling the depth of flatspot. Other variables exerted their influence via their effect on cord properties. For nylon 66 cord, flatspot depth was decreased by high ambient temperatures, high tire air pressure, low loads, and moderate run-in conditions. Change in the moisture content of the nylon cord improved or worsened flatspot depending on the ambient temperature of test. Factors such as cord processing conditions, cord twist, tire bias angle, number of plies, building drum width, postinflation conditions, and temperature of cure had minor effects on the flatspot. A nylon 66 copolymer (Monsanto 88N) showed a large reduction in tire flatspotting.
Heats of Transport of the Rare Gases in a Rubber Membrane
Authors: Bearman Mirion Y. , Bearman Richard J.
Published: February 2011

Revised values for heats of transport, Q*, of the rare gases He, Ne, Ar, Kr, and Xe in rubber are presented. In the case of helium, it is shown that, within experimental error, there is no pressure dependence of heat of transport in the pressure range 25-65 cm. The apparent Q* varies slightly with temperature difference across the membrane. Nevertheless, departures from linearity in the local phenomenological equations seem to be negligible even though the temperature gradients range up to 900°/ni.
Electron Microscope Investigation of States of Distribution in Elastomer Blends
Authors: Kiyek H. , Schoon Th G. P.
Published: February 2011

High polymers that possess high elastic deformability are referred to as elastomers. They have a glass transition between —40° and —70° C. Uberreiter1 has appropriately described their aggregate state as “liquid with fixed structure”, since within the temperature range of elastic deformability individual chain segments of a macromolecule do describe, to be sure, a disordered temperature motion, corresponding to that found in liquids. Yet the macromolecule as a whole is not mobile, because of strong intermolecular forces. When elastomer blends are prepared by mixing the components on a mill or in an internal mixer, technical interest is mainly limited to technological properties, such as softening point, shear modulus, abrasion, etc. But it also seems important to obtain information about the distribution of the components in the blends, in order to evaluate more accurately the basic miscibility of elastomers in general, as well as the intrinsic strength of such multi-phase systems. A solution to the problem may best be obtained by electron microscope investigations since they permit observation of very minute structures representing constant and characteristic values for a given polymer, and can thus serve as a means of identifying a given polymer, even in mixtures. Schoon and Kretschmer have already found that a relation exists between microstructure (observed with an electron microscope) and molecular weight of high polymers.
Theoretical Consideration of Interfacial Forces Involved in Coalescence of Latex Particles
Authors: Vanderhoff J. W. , Tarkowski H. L. , Jenkins M. C. , Bradford E. B.
Published: February 2011

The Dillon, Matheson, and Bradford and the Brown hypotheses for the mechanism of film formation of latexes are extended, two latex particles in a drop of water being given as a model. As the water evaporates, the particles are brought together, so that their stabilizing layers are in contact and their further approach is hindered. The pressure forcing the particles together is increased by the further evaporation of water (that is, by the forces arising from the water air interfacial tension), until the stabilizing layers are ruptured and a polymer polymer contact is formed. Once this occurs, the pressure exerted upon the particles is increased further by the forces arising from the polymer water interfacial tension. Numerical values for the pressure exerted upon the particles are calculated as a function of latex particle size, degree of coalescence, and interfacial tensions both of water against air and polymer against water. Similar calculations with a latex particle coalescing against a flat surface (for example, a substrate) as a model demonstrate the importance of the contact angle between the polymer and the flat surface. The hypotheses developed are used to explain various experimental observations.
Porous Sprayed Sheets and Coatings
Authors: Satas D.
Published: February 2011

In the past few years, porous plastic films have been actively extended into a wide variety of uses, both in sheeting and in coatings. Some porous films, especially films of poly (vinyl chloride), have been used for quite some time in such specialized applications as battery separators. At present, the use of porous plastics in the apparel and footwear industries is of special importance. Large amounts of elastomers in sheet and film form, including coated textiles, are consumed by these industries. Nonporous products are not entireiy satisfactory for uses in which breathability or ability to transmit water vapor is required for comfort. Porous plastic materials in these areas not only improve the suitability and the functioning of plastic sheeting already used, but also replace some of the established materials used for apparel and footwear. It is not surprising, therefore, that a considerable activity is noticeable in this area, particularly in regard to processes for introducing porosity into polymeric films and coatings.
Determination of Carbon Black Particle Size by Reflectance
Authors: Studebaker Merton L. , Nabors Lester G.
Published: February 2011

A simple technique of sample preparation using dry carbon black samples has been developed which gives a carbon black surface of reasonably reproducible reflectance, using a commercially available and reasonably priced reflectance meter. The reflectance values were calibrated against particle size determined by Kraus and Rollmann using the calorimetric procedure of Harkins and Jura.
Effect of Temperature on Stress-Optical Properties of Styrene Butadiene Block Copolymers
Authors: Fischer E. , Henderson J. F.
Published: February 2011

Stress, strain, and optical properties of three elastomeric styrene butadiene block copolymers containing 31, 40 and 49 wt per cent styrene were studied as a function of temperature. Mechanical and optical properties indicate that these materials are two phase systems in which the polybutadiene chains form an elastomeric phase and the polystyrene a glassy phase with the latter providing physical crosslinks. Birefringence measurements indicate that decreases in modulus and strength of these materials are associated with decrease in concentration of elastically effective network chains. Independence of stress-optical coefficient of temperature suggests that the decrease in concentration of elastically effective chains is not due to onset of rubberlike behavior or flow within the polystyrene regions themselves, at least for temperatures below about 70° C. Rather, the decrease seems to be associated with increased mobility of the polybutadiene chains at higher temperatures, which also leads to an increase in the rate of stress relaxation. Birefringence measured during extension and retraction showed that stress strain hysteresis is due to restricted mobility of polybutadiene chain segments rather than to permanent viscous flow or to change in the effective network structure of the block copolymers. The ultimate properties of these rubbers were well correlated with the effective network structure in undeformed specimens.