Showing papers in "Rubber Chemistry and Technology in 1975"
TL;DR: In this article, an anionic mechanism is proposed for those systems where there is good reason to assume that the metal is strongly electropositive relative to the carbon (or other) atom at the tip of the growing chain.
Abstract: Addition polymerizations involving soluble organometallic species have received intensive attention in recent years with special reference to the type of counterion and solvent. An anionic mechanism is proposed for those systems where there is good reason to assume that the metal is strongly electropositive relative to the carbon (or other) atom at the tip of the growing chain. Hence, the metal, e.g. lithium, becomes a cation either in the free state or coupled with the growing carbanion. Under the appropriate experimental conditions, spontaneous termination is avoidable in many of those systems when one of the metals of Group I is used as the counterion. The alkali metals sodium and potassium were revealed to be polymerization initiators of isoprene in the disclosures of Matthews and Strange in 1910 and Harries in 1911. The first unambiguous report of the use of lithium in reactions with diolefins appears to be that of Ziegler and coworkers in 1934. Their work consisted of an investigation of th...
372 citations
TL;DR: In this paper, the authors show that surface modifications of carbon black with a wide variety of groups have shown only minimal effects on rubber-reinforcing ability, giving cured vulcanizates of high crosslink density.
Abstract: 1. Heat treatment of carbon black-rubber mixtures is a method of “in process” polymer grafting which gives a definite improvement in the dynamic properties of vulcanizates. 2. The heat treatment process can be more effective if chemical promoters are used. These chemical promoters function as coupling agents between filler surface and rubber. 3. With very unreactive butyl rubber an effective interaction is produced both by the addition of chemical promoters and by the use of specially active surface-modified carbon black. 4. In normal unsaturated rubbers, surface modifications of carbon black with a wide variety of groups has shown only minimal effects on rubber-reinforcing ability. Halogenated blacks have a pronounced effect on vulcanization kinetics, giving cured vulcanizates of high crosslink density. 5. Carbon black surfaces can be deactivated by calcining at high temperatures. The loss of surface-bound hydrogen may not account for this loss in surface activity. 6. Grafting of polymers to the...
280 citations
TL;DR: A survey of the results of the most important of these experimental studies, particularly in regard to the effect of experimental variables on 2C1 and 2C2 can be found in this paper.
Abstract: There has been a very large number of experimental studies of the elastic properties of amorphous polymer networks in uniaxial deformation, particularly elongation, over the past few decades. In spite of these efforts, and related theoretical investigations, major questions remain unanswered with regard to stress-strain isotherms over the range of moderate deformations. The major question in this area is the molecular basis or interpretation of the phenomenological constants 2C1 and 2C2 used to represent the experimentally observed isotherms. It is hoped that the present survey of the results of the most important of these experimental studies, particularly in regard to the effect of experimental variables on 2C1 and 2C2 will encourage additional work, leading to an unambiguous solution to this important unsolved problem in the area of rubberlike elasticity.
151 citations
TL;DR: The interaction between fumed silica and silicone elastomer after various treatments of the silica surface has been investigated in this article, and the results indicated that the interaction is much more intensive than in carbon black-hydrocarbon rubber systems.
Abstract: The interaction between fumed silica and silicone elastomer after various treatments of the silica surface has been investigated. The effect of the treatments was determined by measuring bound rubber, an interaction coefficient by means of the oscillating disk rheometer, the mechanical properties of the vulcanizates, the morphology of the silica aggregates, and the use of an hydroxyl-terminated silicone rubber. The results indicated that the interaction is much more intensive than in carbon black-hydrocarbon rubber systems. This is demonstrated by much higher bound rubber values (by a factor of 2–3) and a higher interaction coefficient. It is shown that the major effect on this interaction coefficient is the specific interaction by hydrogen bonding, between silica surface silanol groups and the polydimethylsiloxane chain. In this bonding the isolated hydroxyl groups should play the major part. Partial inactivation of these isolated silanol groups leads to improved strength but lower modulus. Maxi...
150 citations
TL;DR: In this paper, the effect of silica filler structure on the effective crosslink density and on mechanical properties was studied, and the effects of silicone filler structures on crosslink densities and mechanical properties were investigated.
Abstract: This work was undertaken to study the effect of silica filler structure on the effective crosslink density and on mechanical properties. Vulcanizates of silicone, SBR, and EPM were include...
149 citations
TL;DR: In this article, the compatibility of various compositions of polystyrene (PS)-poly (vinyl methyl ether) (PVME) films and the thermally induced phase separation of such mixtures have been studied using several methods.
Abstract: The compatibility of various compositions of polystyrene (PS)-poly (vinyl methyl ether) (PVME) films and the thermally induced phase separation of such mixtures have been studied using several methods. Density measurements indicate extensive mixing of the PS and PVME chains in compatible PS-PVME films. Vapor sorption measurements have enabled calculation of the PS-PVME interaction parameter X′23 as a function of composition and temperature. The parameter X′23 is negative for compatible PS-PVME films in the composition range 35-65 wt % PVME satisfying the thermodynamic criterion for stability in a binary mixture. The temperature dependence of X′23 for the PS-PVME system suggests the existence of a lower critical solution temperature and an upper critical solution temperature. Vapor sorption measurements also indicate that the diffusion of benzene into a 45.3:54.7 PVME-PS film is Fickian, supporting the notion of extensive mixing of PS and PVME chains in the compatible mixture. Temperature-dependen...
103 citations
TL;DR: A ground rice hull ash prepared by a new burning process has been found to be a moderately reinforcing filler for rubber as mentioned in this paper, which is made by a controlled incineration process in which the bulk of the organic components of the rice hulls are removed, leaving the skeletal silica structure of the hull intact and in the amorphous state.
Abstract: A ground rice hull ash prepared by a new burning process has been found to be a moderately reinforcing filler for rubber. This filler, 85-90% amorphous silica and 10-15% carbon, is made by a controlled incineration process in which the bulk of the organic components of the rice hulls is removed, leaving the skeletal silica structure of the hull intact and in the amorphous state. The resultant ash is easily ground to produce fine particles, generally in the range of 0.1-2.0 μm. This filler does not adversely affect either the vulcanization characteristics or the aging of SBR, natural rubber, nitrile rubber, butyl rubber, neoprene, EPDM, and propylene oxide rubber compounds. As it is predominantly silica, it responds effectively to silane coupling agents in improving properties of the rubber compounds. It is concluded that RHA filler is a satisfactory substitute for MT black and that, in blends with blacks, it can be effectively used as a partial replacement for finer and more reinforcing blacks.
62 citations
TL;DR: In this paper, a combination of DSC, TG, and DTG was used to analyze fully compounded stocks on a time scale consistent with routine quality control, with a scan rate of 10°C/min.
Abstract: We have shown in this and the preceding paper that fully compounded stocks can be analyzed for all main constituents by use of a combination of DSC, TG, and DTG. Further, this can be achieved on a time scale consistent with routine quality control. DSC gives information on cure characteristics, sulfur, and accelerator levels in approximately five minutes. Elastomer, elastomer ratio, carbon black, oil/plasticizer, and inorganic pigments are determined in about 35 minutes by TG/DTG, at a scan rate of 10°C/min. This time can be reduced by increasing the scan rate, but interference from highly exothermic reactions can be a limiting factor. Each compound must be treated individually to determine the maximum scan rate that can be used without impairing reproducibility. Clearly limitations exist for identification of unknown blends by DTG. The main problem is that many commercial elastomers have very similar thermal stabilities, which results in DTG peaks in the same temperature range. Further work is b...
61 citations
TL;DR: In this paper, total thermal analysis is used for the identification of the polymers in tire treads or black sidewalls, using DTG curves to confirm the findings of DSC and Tg.
Abstract: Total thermal analysis provides a reasonably accurate method for the identification of the polymers in tire treads or black sidewalls. DSC curves in nitrogen distinguish SBR, BR, or blends from NR or IR. Tg then distinguishes between these polymers, although confusion may arise in the case of blends of SBR/BR with a high proportion of BR. DTG curves confirm the findings of DSC and Tg. Thus, by combining all the techniques mentioned, it should be possible to establish the nature of the polymers with reasonable accuracy. The method is rapid, requires no sample preparation or treatment of the sample, and operator attention is not necessary once the experiment is started. An estimate of the proportion of carbon black in the recipe may also be obtained from the TG curve or by weighing the sample after DSC experiment in nitrogen.
43 citations
TL;DR: In this article, the microstructural changes occurring in cis- and trans-1,4-polyisoprenes during uncatalized thermal oxidation in the solid phase were investigated.
Abstract: An investigation was conducted concerning the microstructural changes occurring in cis- and trans-1,4-polyisoprenes during uncatalized thermal oxidation in the solid phase. The investigation made use of approaches based on proton and carbon-13 NMR spectroscopy. The oxidation of squalene and dihydromyrcene in the liquid phase was also studied. The studies provide the first NMR spectroscopic evidence for the presence of epoxy and peroxide, hydroperoxide, and alcohol groups within the oxidized polyisoprene chain.
40 citations
TL;DR: The smoke inhibitory activity of hydrated fillers in SBR is centered primarily in condensed phase processes and is analogous to the generally accepted mechanism of flame retardation by the hydrates as mentioned in this paper.
Abstract: The smoke inhibitory activity of hydrated fillers in SBR is centered primarily in condensed-phase processes and is analogous to the generally accepted mechanism of flame retardation by the hydrates. Dissipation of heat, which disfavors pyrolysis and favors competing crosslinking reactions is probably involved. These reactions should occur chiefly among polybutadiene segments of the polymers. In addition, the smoke-suppressant efficiency of hydrated fillers should depend upon the crosslinking efficiency of the rubber. Finally, although smoke generation in latex rubber goods presents a challenge, substantial practical reductions in visible smoke can be achieved through the selection of proper hydrated fillers.
TL;DR: This review represents an attempt to summarize and discuss some of the literature on the batch operated internal rubber mixer, with the primary view of studying processing conditions and processing conditions.
Abstract: This review represents an attempt to summarize and discuss some of the literature on the batch operated internal rubber mixer, with the primary view of studying processing conditions and h...
TL;DR: In this article, the authors demonstrate that DSC is a convenient and rapid technique for the study of elastomer vulcanization characteristics, and they have found the diurethane cure of natural rubber to be exothermic and amenable to DSC study.
Abstract: Our objective has been to demonstrate that DSC is a convenient and rapid technique for the study of elastomer vulcanization characteristics. Although we have been concerned only with NR and NR-BR blends, the observation of exothermicity in sulfur vulcanization is quite general. Similar observations on sulfur vulcanization of IIR, SBR, EPDM, CSM, and NBR rubbers have been made in our laboratory. In non-sulfur vulcanization systems, we have found the diurethane cure of natural rubber to be exothermic and amenable to DSC study. As reported by Bruce et al., the magnesium oxide cure of chloroprenes is exothermic, but magnesium oxide-diamine vulcanization of fluoroelastomers is characterized by very low exothermicity. Future studies of the effect of various additives on soft rubber cure could make a significant contribution to our understanding of the complex cure mechanism. Successful kinetic analysis of DSC scans is perhaps the major hurdle to be overcome before the DSC technique can be meaningfully ...
TL;DR: In this paper, it was shown that there is a unique relationship between unit work and in-process properties of the compound such as Mooney viscosity, die swell, etc.
Abstract: (1) Compounds mixed under high-shear conditions in a laboratory Brabender Plastograph or in larger Banbury mixers can be quantitatively compared on the basis of work input per unit volume. This quantity, unit work Wu, is proposed as a useful parameter for characterizing the effects of polymer, filler, and other ingredient on mixing performance. (2) This work supports the principle that, independent of the size and speed of a mixer, there is a unique relationship between unit work and such in-process properties of the compound as Mooney viscosity, die swell, etc. It has been shown that this relationship extends to other high-shear mixers, such as the Shaw Intermix and a cam-head type Brabender Plasticorder. (3) Practical unit work ranges for passenger tire-tread mixing found typical of factory operations are: first stage, 300–800 MJ/m3; second stage, 150–400 MJ/m3; final mix, 2000–4500 MJ/m3. Mixing to these unit-work levels in the laboratory achieved mixing quality that closely duplicated large-s...
TL;DR: In this article, the experimental results show that the bulk modulus K for four different rubbers tested increases almost linearly with carbon black content while the Young's modulus E increases much more rapidly as shown in Figure 3.
Abstract: The experimental method developed is mostly suitable for measuring K of relatively incompressible materials such as members of the elastomer family. The accuracy of K values are estimated to be within ±3% for all rubber specimens. Its use can be extended to plastics with somewhat reduced accuracy. The results show that bulk modulus K for the four different rubbers tested increases almost linearly with carbon black content while the Young's modulus E increases much more rapidly as shown in Figure 3. It is interesting to note that Poisson's ratio v calculated using K and E does not fall below 0.4940 (Figure 5), and the value of v=0.4997 as quoted in engineering handbooks would be reasonable to use for most practical applications where the carbon black content is not excessive.
TL;DR: In this paper, the authors draw attention to three different reasons why measurements of fracture energy by different methods may not agree: (1) When the test involves propagation of a tear by stored strain energy, as in the method shown in Figure 1, the energy available to cause rupture will be less than that supplied, because of dissipation within the elastomer.
Abstract: Attention has been drawn here to three different reasons why measurements of fracture energy by different methods may not agree: (1) When the test involves propagation of a tear by stored strain energy, as in the method shown in Figure 1, the energy available to cause rupture will be less than that supplied, because of dissipation within the elastomer. Calculation of the fracture energy on the basis of input energy would then lead to an overestimate, by about 100 per cent or more for typical filled elastomers. (2) As shown in Figures 4a and 5, the tear path is sometimes wider than the thickness of the test sheet. In consequence, fracture energy calculated from the sheet thickness would be too large, by about 40 per cent in the cases considered here. (3) Even when allowance is made for the true width of the tear path, measurements of fracture energy in shear (Mode III) are about 50 per cent larger than in cleavage (Mode I). This is attributed to frictional work expended in sliding the rough torn s...
TL;DR: In this paper, a theory of bound rubber formation was developed which treats the effect as random adsorption of structural units of polymer on reactive sites which are assumed to exist on the surface of filler particles.
Abstract: A theory of bound rubber formation has been developed which treats the effect as random adsorption of structural units of polymer on reactive sites which are assumed to exist on the surface of filler particles. Equations are derived for the fraction of bound rubber and for the molecular weight distribution of free (unbound) rubber. The theory contains only one adjustable parameter, the filler surface area per reactive site, A0. It is shown for the case of the Schulz distribution that the amount of bound rubber depends but slightly on the dispersion parameter of the polymer and is determined essentially by the adsorption index MwcP/A0NA, where c is the filler concentration, P is its specific surface area, and NA is the Avogadro number. All of the experimentally observed features of the bound rubber effect, including preferential adsorption of large molecules, are correctly predicted, the quantitative agreement of the theoretical equations with available experimental data being satisfatory. This supports the underlying assumption that the processes involved in the polymer–filler interaction may be approximated by a random-process model.
TL;DR: In this paper, the authors describe friction experiments on smooth icy surfaces at various temperatures and show that the WLF transformation can be applied to friction on ice, and friction-temperature curves may be interpreted as being part of the friction master curve on smooth solid surfaces.
Abstract: The paper describes friction experiments on smooth icy surfaces at various temperatures. Speed and temperature variations for NR gum rubber shows that in principle the WLF transformation can be applied to friction on ice, and friction—temperature curves may be interpreted as being part of the friction master curve on smooth solid surfaces. Very near the melting point the friction decreases rapidly for all polymers, and this appears to be associated with changes in the nature of the icy surface. At low temperatures, the friction—temperature curves do not only agree in shape with curves obtained on glass but reach similar values in magnitude also. Black and oil extension effects are also similar to those expected from friction experiments on other surfaces. The blending of polymers, either in the gum state or filled with carbon black, broadens the region of high friction, enveloping the friction curves of the two polymers making up the blend. Depending on the temperature region, either one of the c...
TL;DR: In this article, it was shown that scrap rubber vulcanizates, typical of today's tires, can be depolymerized to a product which is essentially a carbon black dispersion in oil.
Abstract: Experimental results are presented which indicate that scrap rubber vulcanizates, typical of today's tires, can be depolymerized to a product which is essentially a carbon black dispersion in oil. The depolymerization is free radical in nature and requires an efficient chain transfer agent to prevent hardening of the vulcanizate and to increase the rate of depolymerization. The product, termed “Depolymerized Scrap Rubber” (DSR), should be useful, particularly as a rubber compounding ingredient and as a fuel oil extender.
TL;DR: In this paper, a theory was proposed to explain the observed changes in viscosity and extrusion shrinkage of rubber stocks based on the concept of occluded rubber which is rich in high molecular weight polymer and behaves as a part of filler volume during viscous flow.
Abstract: 1. A direct correlation between bound rubber content and molecular weight of soluble polymer was found for a wide range of carbon black samples and processing conditions in SBR. 2. No significant polymer degradation occurred during the ineorporation of carbon black into SBR rubber. 3. A theory was proposed to explain the observed changes in viscosity and extrusion shrinkage of rubber stocks. This theory is based on the concept of occluded rubber which is rich in high molecular weight polymer and behaves as a part of filler volume during viscous flow.
TL;DR: In this article, a surface analysis of vulcanized NR compounds by ATR was performed and the results were consistent with a scavenger or protection-layer mechanism for antiozonant protection.
Abstract: This work reports a direct surface analysis of ozonization of vulcanized NR compounds by ATR. On ozonization of a vulcanized NR compound without clay filler or AO a degraded rubber layer, which contains ozonides and carbonyl compounds, is formed on the surface. This reaction is considerably slower than that of raw NR. When clay filler is added, the first effect is a decrease of rubber on the surface and a corresponding increase in the surface concentration of clay. With further ozone exposure, ozonides and carbonyl compounds appear. When a compound containing N,N′-dioctyl-p-phenylenediamine AO is ozonized, a film is seen, which has an ATR spectrum essentially identical to that of the ozonized liquid AO. There is no evidence of ozonized NR products, or of complex reaction products between AO and ozonized NR. These results are consistent with a scavenger or protection-layer mechanism for antiozonant protection.
TL;DR: In this paper, the strength behavior of rubbers is discussed in terms of fracture mechanics which treats fatigue and tensile failure as crack growth processes from small flaws, and crack growth can be influe...
Abstract: The strength behavior of rubbers is discussed in terms of fracture mechanics which treats fatigue and tensile failure as crack growth processes from small flaws. Crack growth can be influe...
TL;DR: In this article, measurements of the moduli of these networks in the unswollen state gave results supporting the theory of rubberlike elasticity developed by Flory and coworkers, rather than the corresponding theory due to James and Guth.
Abstract: A recently reported study described the preparation of elastomeric networks by crosslinking poly(dimethylsiloxane) chains in both the undiluted state and in solution. Measurements of the moduli of these networks in the unswollen state gave results supporting the theory of rubberlike elasticity developed by Flory and coworkers, rather than the corresponding theory due to James and Guth. These results were not entirely unambiguous, however, because of complications due to departures (“2C2 corrections”) from the expected elastic equation of state. Much of this uncertainty has now been removed by measurements of the moduli of such networks in the swollen state, a condition under which the effects of the 2C2 contributions are known to be minimized. These new results strongly support the earlier conclusion that the Flory theory is the more nearly correct. Nonequilibrium effects, as well as the 2C2 corrections, diminish upon incorporation of a diluent into the crosslinked network; similar decreases occu...
TL;DR: Capillary rheometry of carbon-black-filled butadiene copolymers at 125°C was performed over a wide shear rate range as mentioned in this paper, and the data were corrected for pressure loss in the barrel and at the capillary entrance, and for the non-Newtonian velocity profile.
Abstract: 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...
TL;DR: 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 size and, incidentally, also aggregate size distributions as discussed by the authors.
Abstract: 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.
TL;DR: In this article, the degree of carbon-black particle aggregation in conventional vulcanizates varies with the nature of the elastomers, which is revealed by the variation of (Gm′−G∞−G ∞−ƒ′), which is a measure of the transient structure.
Abstract: The degree of carbon—black particle aggregation (transient structure) in conventional vulcanizates varies with the nature of the elastomers. This is revealed by the variation of (Gm′−G∞ƒ′), which is a measure of the transient structure. The relationship between Gm″ and (Gm′−G∞ƒ′) as well as that between strain work and normalized modulus show similarity to earlier work in which the polymer type was not varied. This suggests that carbon-black structural elements act as energy storage units and are of the same type in all these polymers. While the decrease of in-phase modulus is primarily caused by carbon-black particle units, tan δ reflects also the effect of the polymeric matrix.
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TL;DR: In this article, the stereospecific polymerization of isoprene with simple alanes and poly (N-alkyliminoalanes) (PIA) and TiCl4 is critically reviewed and related to the more recent finding on the cage structure and composition of PIA's.
Abstract: The stereospecific polymerization of isoprene with simple alanes and poly (N-alkyliminoalanes) (PIA) and TiCl4 is critically reviewed and related to the more recent finding on the “cage” structure and composition of PIA's. In particular, the polymer yield was found strictly dependent on the structure of the PIA, which in turn depends on the nature of the alkyl groups bonded to nitrogen. The effects of the chemical composition of the PIA and of the halogen level in its halogenated derivatives on the activity of the catalyst and on the possibility of side reactions is discussed with reference to conventional aluminum alkyl catalysts. The identification of new structures within this class of cocatalysts is discussed
TL;DR: EPR has been used to measure molecular phenomena during fracture of elastomers as mentioned in this paper, including the role of filler-matrix interaction in fracture of filled elastomer, and to study ozone-stress-induced cracking of rubber.
Abstract: EPR has been used to measure molecular phenomena during fracture of elastomers. To date, because of various technical limitations, the studies have been largely confined to identification of the polymer chain scission site during fracture at low temperature in rubbers, to studying ozone-stress-induced cracking of rubber, to development of a micro-macro Griffith-type failure criteria for this type of failure, and lastly to systematic investigation of the role of filler-matrix interaction in fracture of filled elastomers. It is hoped that the brief outline presented here will give the reader some insight into the uses and potential of the EPR methods for the study of fracture. As a final note, while we have concentrated almost totally on EPR fracture studies in rubbers, there has been fairly extensive EPR work on fracture in oriented plastic, fibers, and films. Even though some of this knowledge may be transferable, directly or indirectly, to elastomers, it has not been reviewed here, but important...
TL;DR: In this paper, a new synthesis of D2-carborane-siloxanes is described which overcomes many of the disadvantages of previous synthetic methods, and linear polymers with molecular weights up to 250,000 can now be prepared using silanol-silylurea condensation reactions.
Abstract: A new synthesis of D2-carborane—siloxanes is described which overcomes many of the disadvantages of previous synthetic methods. Linear polymers with molecular weights up to 250,000 can now be prepared using silanol-silylurea condensation reactions. Elastomers with useful general properties and good retention of mechanical properties after heat aging in air at 315°C for 300 hr were produced. The property profile and ease of vulcanization suggest utility in high-performance sealant, gasket, O-ring, and coating applications.