Showing papers in "Rubber Chemistry and Technology in 1998"
TL;DR: In the past few years, an enormous amount of work has been reported on the progress in the application of conventional fillers and the development of new products to improve the reinforcement of rubber, dynamic properties in particular as mentioned in this paper.
Abstract: In the past few years, an enormous amount of work has been reported on the progress in the application of conventional fillers and the development of new products to improve the reinforcement of rubber, dynamic properties in particular. While all agree that the filler as one of the main components of the filled-rubber composite, has a very important role in improving the dynamic performances of the rubber products; many new ideas, theories, practices, phenomena, and observations about how and especially why the filler alters the dynamic stress-strain response have been presented. This, of course, suggests that not only is the real world of the filled rubber complex and sophisticated but also multiple mechanisms may be involved. However, it must be admitted that the possibility exists for explaining the effect of all fillers on rubber properties ultimately in similar and relatively nonspecific terms, i.e., the phenomenon related to all filler parameters should follow a general rule or principle. I...
861 citations
TL;DR: In this article, in situ silica incorporation by the in situ sol-gel reaction of tetraethoxysilane with TESPTS was found to have a much higher reinforcing efficiency than did conventional mechanical mixing and the in- situ method without tesPT, attributed to the formation of a silica-rubber network.
Abstract: Bis(3-triethoxysilylpropyl)tetrasulfide (TESPT) was found to affect the curing characteristics and the physical properties of styrene-butadiene (SBR) gum rubber and xin situ silica-filled SBR vulcanizates. Silica incorporated by the in situ sol-gel reaction of tetraethoxysilane with TESPT showed a much higher reinforcing efficiency than did conventional mechanical mixing and the in situ method without TESPT. The higher reinforcing efficiency is attributed to the formation of a silica-rubber network, which also changed the dynamic mechanical behavior of the SBR vulcanizates. Transmission electron microscopy observations showed in situ silica incorporation of very fine particles in comparison to the sol-gel process without TESPT.
198 citations
TL;DR: In this article, the role of fillers in elastomer compounds is reviewed and discussed, particularly concerning silica observed by atomic force microscopy and scanning probe microscopy, and recent transmission electron microscopy results concerning furnace carbon black.
Abstract: The present stand on the understanding of the role of fillers in elastomer compounds shall be reviewed and discussed. Unpublished results of our laboratory are also introduced in this review paper, particularly concerning silica observed by atomic force microscopy and scanning probe microscopy and recent transmission electron microscopy results concerning furnace carbon black and its inception and growth.
122 citations
TL;DR: In this paper, crosslinked samples of natural rubber (NR, SMR-5L) and a synthetic cis-1,4-polyisoprene (IR, Natsyn 2200, The Goodyear Tire & Rubber Company) were crystallized at −25 °C at various strains.
Abstract: Crosslinked samples of natural rubber (NR, SMR-5L) and a synthetic cis-1,4-polyisoprene (IR, Natsyn 2200, The Goodyear Tire & Rubber Company) were crystallized at −25 °C at various strains...
98 citations
DSM1
TL;DR: In this paper, the network density in EPDM vulcanizates was studied by the following methods: low resolution, proton T2 NMR relaxation, Mooney-Rivlin analysis of stress-strain curves, and equili...
Abstract: The network density in unfilled EPDM vulcanizates was studied by the following methods: low resolution, proton T2 NMR relaxation, Mooney—Rivlin analysis of stress—strain curves, and equili...
61 citations
TL;DR: In this paper, a crumb rubber of high surface area and a diameter between 100 and 200 µm was incorporated into uncured natural rubber (NR) or acrylonitrile-butadiene (NBR) containing silica.
Abstract: The recycling of rubber from waste tires and other products has been of commercial and environmental interest for several decades. For recycling, bulk properties are most relevant; whereas, for crumb incorporation both bulk and matrix-crumb interface phenomena are important, which are dealt with in this study. We have taken a crumb rubber of high surface area and a diameter between 100 and 200 µm and incorporated it into uncured natural rubber (NR) or acrylonitrile—butadiene (NBR) containing silica. This non-black reinforcing filler was used to allow a better modulus match between crumb and matrix than would exist for a non-filled system, while allowing visual contrast between the two phases for microscopic examination. The micromechanics of deformation can be investigated using scanning electron microscopy. The crumb rubber was either added as received or used after a surface chlorination step. The matrix was also used unmodified or with a compatibilizer used to facilitate homogenization of pola...
56 citations
TL;DR: In this article, the interactions of silica filler in zinc activated, sulfur vulcanized cis-1,4-polyisoprene (IR) were characterized using Fourier Transform Infrared (FTIR)-Attenuated Total Reflectance (ATR) spectroscopy.
Abstract: The interactions of silica filler in zinc activated, sulfur vulcanized cis-1,4-polyisoprene (IR) were characterized using Fourier Transform Infrared (FTIR)-Attenuated Total Reflectance (ATR) spectroscopy. The variables examined were increased levels of silica and quality of mixing of the batch. The increased silica level resulted in band broadening and a frequency shift to lower wavenumbers of the silica absorbance region (1250-1000 cm−1) due to a combination of physical and chemical adsorption of the rubber and parts of cure system on the silica surface. The peaks that appeared near 1040 and 1017 cm−1 were attributed to physical interactions between silica and the natural rubber. However some chemical bonding of the IR was present as a result of a free radical reaction that takes place during the milling process. Inefficient mixing had an affect comparable to adding less filler, according to the results above. That is, there was less “effective” filler in the poorly mixed samples because poor di...
44 citations
TL;DR: In situ silica reinforcement was applied to the acrylonitrile-butadiene rubber (NBR) vulcanizates as mentioned in this paper, where the presence of γ-mercaptopropropyltrimethoxysilane (γ-MPS) increased the conversion of TEOS in the sol-gel reaction.
Abstract: In situ silica reinforcement was applied to the acrylonitrile—butadiene rubber (NBR) vulcanizates. The amount of in situ silica introduced in the NBR vulcanizates was limited due to the high polarity of NBR. The presence of γ-mercaptopropyltrimethoxysilane (γ-MPS) in the NBR vulcanizate increased the conversion of TEOS in the sol-gel reaction and resulted in the higher amount of in situ silica, compared to the system without γ-MPS. The obtained silica was very fine and dispersed very homogeneously. In situ sol-gel reaction of TEOS in the NBR vulcanizates mixed with a conventional silica (VN-3) was also carried out. The reinforcement efficiency in this system increased with the increase of the amount of mechanically mixed conventional silica. Interestingly, the hysteresis loss decreased by the in situ filling of silica.
39 citations
TL;DR: Semi-crystalline polyolefins, e.g., polypropylene in its isotactic and syndiotactic forms, become brittle at low temperature due to their inherent crystallinity and relatively high Tg as discussed by the authors.
Abstract: Semi-crystalline polyolefins, e.g., polypropylene in its isotactic and syndiotactic forms, become brittle at low temperature due to their inherent crystallinity and relatively high Tg. It ...
38 citations
TL;DR: In this paper, the effects of heating and cooling rates on the structure of N660 and N299 carbon black particles have been investigated using Raman spectroscopy, X-ray scattering, and the BET technique.
Abstract: The effects of heating and cooling rates on the structure of N660 and N299 carbon black particles have been investigated using Raman spectroscopy, X-ray scattering, and the BET technique. ...
38 citations
TL;DR: In this article, the dispersion of carbon black agglomerates suspended in polydimethyl siloxane (PDMS) or polybutadiene (PBD) liquids has been studied.
Abstract: The dispersion of carbon black agglomerates suspended in polydimethyl siloxane (PDMS) or polybutadiene (PBD) liquids has been studied. Agglomerates comprised of either a low-structure or a high-structure carbon-black were subjected to simple shear flow. Two characteristic length scales that affect the dispersion process are identified. One length scale (Lp) is a measure of the ease with which fluid can flow through the porous agglomerate structure. The second (δ) is a measure of the depth to which processing fluid has soaked into the agglomerate. Values of Lp were found to be independent of types or viscosity of the polymer but were sensitive to the structure and packing density within agglomerates. The parameter δ, which varies with time of immersion in the processing fluid, was found to be smaller at comparable immersion times for matrix fluids with high viscosity. Shearing experiments showed two kinetic regimes (fast and very slow dispersion). For each type of matrix liquid, there exists a cri...
TL;DR: A meshless formulation based on the Reproducing Kernel Particle Method is applied to the large deformation and contact analysis of elastomeric components, and the discretization can be performed without the need of a structured mesh.
Abstract: A meshless formulation based on the Reproducing Kernel Particle Method (RKPM) is applied to the large deformation and contact analysis of elastomeric components. In this approach, a kernel estimate that ensures the completeness requirement of a linear field is introduced to construct the global Reproducing Kernel shape functions of the displacements. The Galerkin approximation of the variational equation is formulated using the Reproducing Kernel shape functions, and the discretization can be performed without the need of a structured mesh. In this paper, a RKPM formulation for rubber materials including frictional contact conditions is presented. The contact constraint equations and essential boundary conditions are formulated in the nodal coordinate using a direct transformation method. The global Reproducing Kernel shape functions expressed in a material description are used in the total Lagrangian formulation of hyperelasticity. By the use of the smooth Reproducing Kernel shape functions, the...
TL;DR: In this article, three hyperelastic constitutive models, the Arruda and Boyce model, the Yeoh model, and the Ogden model, are used to simulate the response of vinyl elastomers in large, non-homogeneous deformation states.
Abstract: Three hyperelastic constitutive models, the Arruda and Boyce model, the Yeoh model, and the Ogden model, are used to simulate the response of vinyl elastomers in large, non-homogeneous deformation states. A single uniaxial compression test is used to characterize the elastomers to obtain model constants. Drucker stability is enforced by restriction of the coefficients for the Yeoh and Ogden models to produce physically feasible uniaxial results. The ability of the models to predict the global force versus deformation responses and deformed shapes for large deformation shear, tensile deformation of a long bar with fixed grips, and inflation of a thin disk is examined. The experiments used in this study are designed to provide known boundary conditions to eliminate ambiguity in the modeling. We demonstrate for the first time that each of these models may be sufficiently characterized via a simple, homogeneous compression test to allow accurate predictions of large, non-homogeneous deformations invo...
TL;DR: The physical relationship between wet skid resistance of filled rubber compounds and the dynamics of the corresponding bulk polymers in the rubber-glass transition zone is investigated in this article, where wet grip data and their ratings correlate with dynamic glass transition temperatures in the N(uclear)M(agnetic)R(esonance) time scale for the spin-spin relaxation time T2 that characterizes the relaxation of transverse magnetization.
Abstract: The physical relationships between wet skid resistance of filled rubber compounds and the dynamics of the corresponding bulk polymers in the rubber—glass transition zone are investigated. We show how wet grip data and their ratings correlate with dynamic glass transition temperatures in the N(uclear)M(agnetic)R(esonance) time scale for the spin—spin relaxation time T2 that characterizes the relaxation of transverse magnetization. The corresponding frequency is independent of the Larmor frequency of the NMR experiment. The amount of the frequency is located in the frequency region of the glass—rubber transition and depends on the microstructure of the used polymers. Finally, some molecular aspects of the network dynamics in the transition zone are considered. Damping curves of different rubbers can be predicted using the bead-spring-model of Kloczkowski, Mark and Frisch (KMF), considered as an extented Rouse-model of an entanglement network with tree-like connectivity and a certain number of subch...
TL;DR: In this article, the intrinsic viscosity of DPNR with only K2S2O8 decreased from 7.2 to 5.5 after 2 hours and then increased to 6.5 by 3 hours.
Abstract: Low molecular-weight natural rubber (LNR) and LNR latex was prepared by oxidative degradation of de-proteinized natural rubber (DPNR) latex in the presence of 1 phr of K2S2O8 and 15 phr of propanal, by shaking at 60 °C. The intrinsic viscosity [η] of DPNR with only K2S2O8 decreased from 7.2 to 5.5 after 2 h and then increased to 6.5 after 3 h. By the addition of propanal, DPNR showed a significant decrease in the [η] value of LNR with [η] of about 0.5 after 5 h of the reaction, while rubber from high-ammonia natural rubber (HANR) latex showed a slight decrease in [η]. The concentration of latex and the kind of surfactant used for stabilizing the latex had little effect on the degradation rate of DPNR latex. The LNR latex is stable as the latex form and the dried rubber coagulated from latex is transparent and colorless. The LNR was a telechelic polymer containing aldehyde and ketone groups at both terminals as determined by NMR and molecular weight analyses.
TL;DR: In this paper, the authors have developed new theories of contact mechanics to relate the interfacial force induced deformation to the thermodynamic work of adhesion both for elastic and viscoelastic solids.
Abstract: Contact mechanics deals with the deformation of solid bodies in contact. In recent years, significant advances have been made both in the theoretical and experimental areas of contact mechanics, especially in the area of soft solids, in relating the contact deformation to interfacial adhesion. On the theoretical front, new theories of contact mechanics have been developed to relate the interfacial force induced deformation to the thermodynamic work of adhesion both for elastic and viscoelastic solids. On the experimental front, several new techniques have been developed to measure the interfacial forces and the interfacial-force-induced deformations. These techniques have been used, with the aid of the theories of contact mechanics, to measure directly the surface and interfacial energies of a variety of polymers and other model surfaces. These experimental and theoretical developments have also been exploited to measure quantitatively the effect of interfacial chain diffusion on the adhesion of ...
TL;DR: In this paper, a review is made of the literature describing surface discoloration problem and approaches to formulate a black sidewall compound to eliminate this surface degradation upon exposure to ozone.
Abstract: The tire black sidewall is the outer surface that protects the casing against weathering. It is formulated for resistance to weathering, ozone aging, abrasion, tearing and cracking, and for good fatigue life by using blends of natural rubber and cis-butadiene rubber. Protection against ozone aging is of particular interest since reaction with these olefinically unsaturated elastomers results in polymer decomposition via chain scission. Use of N-alkyl, N′-aryl-para-phenylenediamine antiozonants has proved most effective. However, their use also results in a surface discoloration, and thus they can be used in only limited amounts when tire appearance is also an important factor. A review is made of the literature describing this surface discoloration problem and approaches to formulate a black sidewall compound to eliminate this surface discoloration upon exposure to ozone. Methods include use of non-staining antiozonants, and uses of elastomers with saturated backbones such as ethylene-propylene-d...
TL;DR: In this article, the double networks of a black-filled natural rubber composition have been prepared by partially curing a sheet, stretching it, and then completing cure, and upon release, a double network retracts to a residual extension ratio, αr.
Abstract: Double networks of a black-filled natural rubber composition have been prepared by partially curing a sheet, stretching it, and then completing cure. Upon release, a double network retracts to a residual extension ratio, αr. Samples cut perpendicular to the stretch direction have stress—strain responses like the isotropic single network, while parallel samples have enhanced stiffness and tensile strength, and reduced extensibility. Tensile strength is rather weakly dependent on αr. Tear strengths of the double networks, determined using edge-cut strip specimens, exceed that of the single network for low αr. However, when αr is high, double networks have very low tear strengths. Consistent with previous studies, high tear strengths are associated with extensive longitudinal cracking.
TL;DR: A series of carbon-silica dual phase fillers have been analyzed using electron spectroscopy for chemical analysis (ESCA) and IR as discussed by the authors, which revealed that the silicon in these materials is consistent with that in silica, and the predominant carbon in the carbon phase is similar to the dominant carbon in carbon black.
Abstract: A series of carbon—silica dual phase fillers have been analyzed using electron spectroscopy for chemical analysis (ESCA) and infrared spectroscopy (IR). These techniques reveal that the silicon in these materials is consistent with that in silica, and the predominant carbon in the carbon phase is similar to the predominant carbon in carbon black. ESCA and IR experiments demonstrate that the carbon—silica dual phase fillers are comprised of composite aggregates, each containing carbon and silica phases. In these dual phase aggregates the silica phase is intimately distributed with the carbon phase. Quantitative ESCA reveals that these dual phase fillers have excess oxygen over the expected stoichiometric amount for the silica present. This excess oxygen is likely due to oxygen groups on the carbon phase. Analysis of the ESCA oxygen Auger lines in combination with various chemical treatments substantiate the presence of carbon phase oxygen groups on the dual phase fillers. Quantitative ESCA in comb...
TL;DR: Rubbers are soft polymeric materials having generally 100 MPa of Young's modulus for the normally applied temperature range and are widely used for the buffer position between high modulus materials such as metals, plastics, glasses, etc., in energy transmission, liquid delivery, and energy isolation positions.
Abstract: Various elastomers are used for automotive components because of their physical properties, chemical properties, durability, etc. There are belts to transmit energy, seals to support radial or reciprocating parts, gaskets and O-rings to seal in oils and fuels, hoses to deliver liquid and gases and diaphragms to control them. Figure 1 shows one example of elastomers for gasoline engines reported by Akema and Yoshida. Rubbers are soft polymeric materials having generally 100 MPa of Young's modulus (shown in Figure 2) for the normally applied temperature range. They are widely used for the buffer position between high modulus materials such as metals, plastics, glasses, etc., in energy transmission, liquid delivery, and energy isolation positions. The materials are selected for their resistance to fuels, oils, and heat; as well as their cold flexibility and sealing ability. However, different materials are sometimes selected for the same device depending upon such factors as applied temperature, cla...
TL;DR: In this article, the effects of lower cure temperatures on the crosslink distributions through the cure in natural rubber (NR)/cis-poly(butadiene) (BR) blend vulcanizates are considered.
Abstract: Crosslink distributions in gum natural rubber (NR)/cis-poly(butadiene) (BR) blend vulcanizates have been studied previously for cure states ranging from times shortly after the onset of cure to over-cure at 150 and 175 °C, respectively. The effects of lower cure temperatures on the crosslink distributions through the cure in NR/BR blend vulcanizates are considered here. The results of this and the previous work indicate that at temperatures above 140 °C the BR phase in gum NR/BR blends begins curing before and at a faster initial rate than the NR phase. Below 140 °C it is the NR phase which attains high crosslink densities first and maintains this increased level over BR until over-cure. The effect of cure temperature on crosslink distribution at maximum state of cure is also presented.
TL;DR: A modification of acoustic cavitation and flow modeling of ultrasonic devulcanization of styrene-butadiene rubber (SBR) is proposed using a concept of effective viscosity characterizing the flow of vulcanized particles as discussed by the authors.
Abstract: Continuous ultrasonic devulcanization of styrene-butadiene rubber (SBR) is considered. Experiments are performed under various processing conditions. Two recipes of SBR with different amounts of polysulfidic linkages are utilized. Gel fraction and crosslink density of devulcanized rubbers are measured and a unique relationship between them is established. This relationship is found to be in agreement with the 3D percolation theory. Die characteristics with and without imposition of ultrasonic waves are determined. A modification of acoustic cavitation and flow modeling of ultrasonic devulcanization of SBR is proposed using a concept of effective viscosity characterizing the flow of vulcanized particles before devulcanization combined with a shear rate, temperature, and gel fraction dependent viscosity of devulcanized rubber. Velocity, shear rate, pressure, and temperature field along with gel fraction, crosslink density, and number of bonds broken are simulated. Predicted data on gel fraction, cr...
TL;DR: In this article, the authors showed that the incorporation of linked stearoyl group stimulated the crystallization of synthetic cis-1,4-polyisoprene (IR) at −25 °C.
Abstract: Natural rubber (NR) contains linked fatty acids, composed of mainly saturated fatty acids, in conjunction with a mixture of free saturated and unsaturated fatty acids The crystallization of synthetic cis-1,4-polyisoprene (IR) is accelerated by the addition of 1 wt % mixture of saturated fatty acid as a nucleating agent and unsaturated fatty acid as a plasticizer As an NR model, IR was esterified with stearic acid selectively at the 3,4-isoprene units after introduction of hydroxyl group by hydroboration The linked stearoyl group stimulated the crystallization of IR at −25 °C, while linked fatty acids other than stearoyl group showed no stimulating effect on the crystallization The addition of methyl linoleate to the stearoyl-esterified IR gave the highest rate of crystallization at −25°C A rapid crystallization of NR is presumed to originate from the mixed saturated and unsaturated fatty acids composition present and the presence of saturated fatty acids linked to NR
TL;DR: In this paper, the fracture energies of a partially-cracked rubber disk are derived in terms of the shear modulus μ, radius r of the still-uncracked portion, and rotation angle ϕ, assuming that the rubber compound is linearly elastic.
Abstract: When a thin bonded rubber disk is subjected to repeated torsional strains by rotating one end-piece with respect to the other, an initial circumferential crack grows inwards. This is the basis of a new test method for determining rates of growth of a fatigue crack in rubber. Values of torsional stiffness K for a partially-cracked disk are computed here by FEA and corresponding fracture energies G are deduced in terms of the shear modulus μ, radius r of the still-uncracked portion, and rotation angle ϕ, assuming that the rubber compound is linearly elastic. Values obtained for G are shown to vary with r2, and thus decrease rapidly as the crack grows and the radius of the uncracked portion decreases. They are approximately the same as values obtained when the cracked disk is assumed to be equivalent to a solid disk having a slightly larger radius than the actual uncracked portion. For thin disks the correction in radius for K is approximately 0.22h, and for G approximately 0.33h, where h is the dis...
TL;DR: In this paper, a methodology was developed to estimate individual hysteresis contributions arising from the carbon black network, polymer free chain ends and effective polymer network chains, which was applied to rubber compounds formulated with linear polymers of varied number-average molecular weight.
Abstract: A methodology was developed to estimate individual hysteresis contributions arising from the carbon black network, polymer free chain ends and effective polymer network chains. The estimation technique was applied to rubber compounds formulated with linear polymers of varied number-average molecular weight (Mn) from each of three different series. The three series corresponded to polymers modified with either zero, one or two tin ends per chain. In general, the relative hysteresis contributions depend on strain amplitude and Mn. For unmodified polymers at strain amplitudes from 0.02 to 0.07, and with Mn in the neighborhood of 150 kg/mole, each of the three hysteresis sources contributes about one-third of the total tan δ. With respect to shear loss modulus (G″), the carbon black network contributes about 60%, while free chain ends and the effective polymer network chains each contribute about 20%. At the same Mn and strain conditions, tin end-modified polymers reduce G″ and tan δ by as much as 60...
TL;DR: In this article, reaction-stage modeling was used to study the mechanism of accelerated vulcanization, namely Reaction-Stage Modeling (RSM) by carefully studying the reactivity of relevant model compounds under selected conditions.
Abstract: This paper reports a novel approach for the study of the mechanism of accelerated vulcanization, namely, Reaction-Stage Modeling (RSM). By carefully studying the reactivity of relevant model compounds under selected conditions, detailed knowledge about a particular reaction stage of vulcanization can be obtained. Background, experimental details and synthesis of model compounds are described. An RSM study after cross-link formation in the thiuram- and dithiocarbamate type vulcanization has been performed, and the role of zinc compounds herein was investigated. In contrast to earlier studies, it has appeared that at 140 °C, cross-links form from cross-link precursors solely via disproportionation. Allylic substitution was not observed. Zinc compounds act as catalysts for disproportionation, but especially ZDMC can be regarded as an efficient, soluble molecular turntable for sulfur atoms.
TL;DR: In this paper, the morphologies of reinforced elastomers prepared from emulsions were found to depend greatly on how the silica phases were introduced, and these morphological differences were used to explain the different shapes of the stress-strain isotherms of these materials in simple elongation.
Abstract: The morphologies of the reinforced elastomers prepared from emulsions were found to depend greatly on how the silica phases were introduced. More specifically, blending colloidal silica into the elastomer prior to film formation was found to yield a highly unusual elastomer in which the continuous phase was the silica and the dispersed phase the elastomer. This is the opposite of the usual case in which, for example, the silica is generated in-situ within the continuous elastomeric phase. These morphological differences were used to explain the different shapes of the stress—strain isotherms of these materials in simple elongation. Results on the crosslinking effects of gamma radiation demonstrated that this treatment represents another useful technique for optimizing the properties of these emulsion-derived materials.
TL;DR: In this article, a simple torsion test is described in which a thin bonded rubber disk is subjected to repeated torsional strains by rotating one end-piece with respect to the other through a fixed angle.
Abstract: A simple torsion test is described in which a thin bonded rubber disk is subjected to repeated torsional strains by rotating one end-piece with respect to the other through a fixed angle. An initial circumferential cut then grows inwards as a fatigue crack. From measurements of crack depth as a function of number of strain cycles, relations are obtained for the rate of crack growth dc/dn vs. fracture energy G for three representative rubber compounds: unfilled natural rubber, unfilled SBR and a carbon-black-filled SBR. The results are closely similar in all cases to previously-published values, obtained from tensile fatigue experiments. This is an important finding, because the present specimen is subjected to simple shear strains and the agreement obtained validates the use of a fracture energy criterion for crack growth under complex states of strain. Moreover, the test method itself has marked advantages. The strain cycle is well-defined, even for relaxing materials. The crack slows as the tes...
TL;DR: In this article, the phase morphology of unvulcanized natural rubber (NR)/high-density polyethylene (HDPE) blends were investigated under scanning electron microscopy (SEM).
Abstract: Phase morphology is an important factor in the determination of properties of polymer blends. In this work, methods for determining phase morphology of unvulcanized natural rubber (NR)/high-density polyethylene (HDPE) blends were investigated. Small, quick-quenched samples were taken from the internal mixer for examination under scanning electron microscopy (SEM). There was almost no interruption of the mixing because the sampling device was designed for preventing the coalescence of dispersed particles. Three specimen-preparation methods for SEM were considered: (i) OsO4 vapor staining, followed by carbon coating; (ii) toluene etching of NR phase at room temperature, followed by coating of the surface with a platinum alloy; (iii) crosslinking of NR phase by S2Cl2 vapor and then etching of HDPE phase by using boiling xylene. Method (i), OsO4 staining of cryogenic microtomed samples, was selected for the work on the kinetics of dispersion during the mixing process. Vast differences in phase morpho...
TL;DR: In this paper, the shear rate and temperature dependent viscosity function based on the modified Cross model is fitted to experimentally measured viscosities data. But the authors did not consider the post-filling phase of a natural rubber compound.
Abstract: Experimental and theoretical results are obtained for the cavity filling of a natural rubber (NR) compound. The shear rate and temperature dependent viscosity function based on the modified Cross model is fitted to experimentally measured viscosity data. A nonisothermal vulcanization model with nonisothermal induction time is fitted to the nonisothermal curing kinetic data obtained by differential scanning calorimetry (DSC). These data are utilized in the simulation of the cavity filling and curing stages. The pressure traces at various locations in the mold during cavity filling are obtained at different inlet and mold temperatures. The predicted results for the pressure traces are in good agreement with those measured in the cavity, but significantly lower than those measured in the nozzle. Evolution of the state of cure in the post-filling stage is predicted and compared with experimental data measured in moldings obtained at various cycle times. The measured states of cure in the moldings are...