bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 c&lt;ccr. When strengths of edge-cut specimens were normalized by the regular (uncut) tensile strength, similar values were found for all three vulcanizates, when c&gt;ccr. 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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
Influence of Environmental Variables on Characterization of Polymer Decomposition by Thermogravimetry
Authors: Dudley M. A. , Smith Derek A. 
Published: February 2011

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.