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Mehdi Razzaghikashani - One of the best experts on this subject based on the ideXlab platform.
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Vulcanization kinetics of nano silica filled styrene butadiene rubber
Polymer, 2014Co-Authors: Seyed Mostaffa Hosseini, Mehdi RazzaghikashaniAbstract:Abstract It was shown that the physical filler-polymer and filler–filler interactions, apart from the filler surface chemistry, has a substantial role in controlling the Vulcanization kinetics of styrene butadiene rubber filled with nano-silica in a sulfur Vulcanization system. Kinetic studies by the oscillating disc rheometer, differential scanning calorimeter, and swelling tests revealed that the Vulcanization rate goes through a maximum as loading of silica increases, but conversion in crosslinking continuously decreases as the amount of silica increases. The effect of silica loadings on the Vulcanization reactions was linked to the immobilization of rubber chains around particles as well as in a polymer-mediated filler network, which were differentiated by the nonlinear viscoelastic behavior of rubber vulcanizates. By surface modification of nano-silica, the accelerating/decelerating effects of nano-silica on the Vulcanization reactions were altered corresponding to the non-linear viscoelastic behavior of the vulcanizates. Therefore, a mechanism was proposed which correlates Vulcanization kinetics of rubber to the dynamics of chains influenced by the reinforcing fillers.
Gabriele Milani - One of the best experts on this subject based on the ideXlab platform.
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Quasi-analytical kinetic model for natural rubber and polybutadiene rubber blends
Reaction Kinetics Mechanisms and Catalysis, 2018Co-Authors: Gabriele Milani, Federico MilaniAbstract:A very simple kinetic model for natural rubber (NR) and polybutadiene (PB) blends is presented. The model is characterized by a completely uncoupled curing between NR and PB, NR being modeled with a primary Vulcanization and a subsequent de-Vulcanization and PB only by a simple first order model of Vulcanization. The assumptions made are roughly in agreement with the actual experimental behavior of the constituent materials in a rheometer chamber, where PB exhibits a quite stable behavior even at high curing temperatures and long Vulcanization times. As a result of the simplifications assumed into the curing model adopted, the numerical approach uses only on three kinetic constants, two for NR and one for PB. Such assumptions allow for a quite straightforward determination of the kinetic constants by means of a simple semi-analytical approach. The reliability of the procedure proposed is benchmarked on some 70% NR- 30% PB blends with two different accelerants ( N -terbutyl, 2-benzothiazylsulfenamide TBBS and N , N -diphenylguanidine DPG) in different concentrations tested experimentally on a standard rheometer chamber at 170 and 180 °C. Quite good match is found between numerical predictions and normalized rheometer curves, with a clear practical impact into the Finite Element FE modelling of Vulcanization of real items.
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parabola hyperbola p h kinetic model for nr sulphur Vulcanization
Polymer Testing, 2017Co-Authors: Gabriele Milani, F MilaniAbstract:Abstract A Parabola-Hyperbola (P-H) kinetic model for NR sulphur Vulcanization is presented. The idea originates from the fitting composite Parabola-Parabola-Hyperbola (P-P-H) function used by the authors in [1,2] to approximate experimental rheometer curves with the knowledge of a few key parameters of Vulcanization, such as the scorch point, initial Vulcanization rate, 90% of Vulcanization, maximum point and reversion percentage. After proper normalization of experimental data (i.e. excluding induction and normalizing against maximum torque), the P-P-H model reduces to the discussed P-H composite function, which is linked to the kinetic scheme originally proposed by Han and co-workers [3]. Typically, it is characterized by three kinetic constants, where classically the first two describe incipient curing and stable/instable crosslinks and the last reproduces reversion. The powerfulness of the proposed approach stands into the very reduced number of input parameters required to accurately fit normalized experimental data (i.e. rate of Vulcanization at scorch, Vulcanization at 90%, maximum point and reversion percentage), and the translation of a mere geometric data-fitting into a kinetic model. Kinetic constants knowledge from simple geometric fitting allows characterizing rubber curing also at temperature different from those experimentally tested. The P-H model can be applied also in the so-called backward direction, i.e. assuming Han's kinetic constants known from other models and deriving the geometric fitting parameters as result. Some existing experimental data available, relying into rheometer curves conducted at 5 different temperatures on the same rubber blend are used to benchmark the P-H kinetic approach proposed, in both backward and forward direction. Very good agreement with previously presented kinetic approaches and experimental data is observed.
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mechanistic modeling of reversion phenomenon in sulphur cured natural rubber Vulcanization kinetics
Polymer Testing, 2013Co-Authors: Gabriele Milani, Eric Leroy, F Milani, Remi DeterreAbstract:Abstract A novel kinetic model of natural rubber sulphur Vulcanization is proposed. The modeling approach takes into account current knowledge on the different polysulfidic structures present during Vulcanization, and the associated individual reactions. A simplified scheme is proposed, giving a mechanistic view of the reversion phenomenon, which results in a decrease of the elastic modulus (related to the sulphur crosslink density) for long Vulcanization times at high temperature. The resulting set of differential equations is solved by an appropriate numerical method to predict the evolution of the degree of Vulcanization for isothermal cure conditions. The Vulcanization kinetics of a model natural rubber compound was characterized experimentally by rheological measurements, in order to test the proposed kinetic model. A remarkable agreement between model predictions and experimental data is observed. The identified kinetic parameters corresponding to the individual reactions taken into account by the mechanistic model are consistent with those of an existing, less refined, pseudo-mechanistic model. The proposed model thus allows bridging the gap between the prediction of macroscopic variations of the elastic modulus and the evolution of molecular scale structure during Vulcanization when the reversion phenomenon is present.
F Milani - One of the best experts on this subject based on the ideXlab platform.
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parabola hyperbola p h kinetic model for nr sulphur Vulcanization
Polymer Testing, 2017Co-Authors: Gabriele Milani, F MilaniAbstract:Abstract A Parabola-Hyperbola (P-H) kinetic model for NR sulphur Vulcanization is presented. The idea originates from the fitting composite Parabola-Parabola-Hyperbola (P-P-H) function used by the authors in [1,2] to approximate experimental rheometer curves with the knowledge of a few key parameters of Vulcanization, such as the scorch point, initial Vulcanization rate, 90% of Vulcanization, maximum point and reversion percentage. After proper normalization of experimental data (i.e. excluding induction and normalizing against maximum torque), the P-P-H model reduces to the discussed P-H composite function, which is linked to the kinetic scheme originally proposed by Han and co-workers [3]. Typically, it is characterized by three kinetic constants, where classically the first two describe incipient curing and stable/instable crosslinks and the last reproduces reversion. The powerfulness of the proposed approach stands into the very reduced number of input parameters required to accurately fit normalized experimental data (i.e. rate of Vulcanization at scorch, Vulcanization at 90%, maximum point and reversion percentage), and the translation of a mere geometric data-fitting into a kinetic model. Kinetic constants knowledge from simple geometric fitting allows characterizing rubber curing also at temperature different from those experimentally tested. The P-H model can be applied also in the so-called backward direction, i.e. assuming Han's kinetic constants known from other models and deriving the geometric fitting parameters as result. Some existing experimental data available, relying into rheometer curves conducted at 5 different temperatures on the same rubber blend are used to benchmark the P-H kinetic approach proposed, in both backward and forward direction. Very good agreement with previously presented kinetic approaches and experimental data is observed.
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mechanistic modeling of reversion phenomenon in sulphur cured natural rubber Vulcanization kinetics
Polymer Testing, 2013Co-Authors: Gabriele Milani, Eric Leroy, F Milani, Remi DeterreAbstract:Abstract A novel kinetic model of natural rubber sulphur Vulcanization is proposed. The modeling approach takes into account current knowledge on the different polysulfidic structures present during Vulcanization, and the associated individual reactions. A simplified scheme is proposed, giving a mechanistic view of the reversion phenomenon, which results in a decrease of the elastic modulus (related to the sulphur crosslink density) for long Vulcanization times at high temperature. The resulting set of differential equations is solved by an appropriate numerical method to predict the evolution of the degree of Vulcanization for isothermal cure conditions. The Vulcanization kinetics of a model natural rubber compound was characterized experimentally by rheological measurements, in order to test the proposed kinetic model. A remarkable agreement between model predictions and experimental data is observed. The identified kinetic parameters corresponding to the individual reactions taken into account by the mechanistic model are consistent with those of an existing, less refined, pseudo-mechanistic model. The proposed model thus allows bridging the gap between the prediction of macroscopic variations of the elastic modulus and the evolution of molecular scale structure during Vulcanization when the reversion phenomenon is present.
B Herrero - One of the best experts on this subject based on the ideXlab platform.
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Vulcanization kinetics of natural rubber organoclay nanocomposites
Journal of Applied Polymer Science, 2003Co-Authors: Miguel A Lopezmanchado, M Arroyo, B Herrero, J BiagiottiAbstract:The effect of the incorporation of a bentonite on the Vulcanization kinetics of natural rubber was investigated by means of both cure-meter testing and differential scanning calorimetry (DSC) under dynamic and isothermal conditions. The Vulcanization curves showed that the modified clay behaved as an effective vulcanizing agent, accelerating the Vulcanization reaction of the elastomer. A marked decrease in the induction time and optimum cure time of the elastomer were observed in the presence of the organoclay. Although the octadecylamine itself accelerated the Vulcanization process, the octadecylamine-modified clay gave rise to a further noticeable increase in the Vulcanization rate, which could be attributed to a synergetic effect between the filler and the amine. Moreover, in the presence of the organoclay, a dramatic increase in the torque value was obtained because of the formation of a higher number of crosslinks, which could be attributed to the confinement of the elastomer chains within the silicate galleries and, consequently, to better interactions between the filler and the rubber. However, no significant changes were observed in the unmodified clay composite. These results were in concordance with those obtained by DSC. In addition, the activation energy of the Vulcanization process was also calculated by means of both techniques. A clear decrease in the activation energy was observed when the organoclay was added to the nanocomposite, which indicated that the layered silicate favored the processing of the elastomer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1–15, 2003
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organo montmorillonite as substitute of carbon black in natural rubber compounds
Polymer, 2003Co-Authors: M Arroyo, Miguel A Lopezmanchado, B HerreroAbstract:Abstract The use of octadecylamine modified montmorillonite as substitute of carbon black in natural rubber (NR) compounds is studied. Rubber with 10 parts per hundred resin (phr) of pristine (clay) and octadecylamine modified montmorillonite (organoclay) were compared with 10 and 40 phr carbon black as filler. The modified silicate is analysed by X-ray, FTIR and thermogravimetric analysis. Vulcametric curves show that the organoclay and carbon black accelerate the Vulcanization reaction and, furthermore, give rise to a marked increase in the torque, indicating a higher degree of crosslinking as was also confirmed by swelling measurements and DSC. The vulcanisation rate and torque value of the organoclay compound are sensibly higher than the carbon black compound even at high contents (40 phr). Mechanical characterization shows the strong reinforcing effect of both fillers up to 350% in the strength in relation to NR. The mechanical properties of NR with 10 phr organoclay are comparable to the compound with 40 phr carbon black. Moreover, the organoclay improves the strength of the NR without hardly any reduction in the elasticity of the material.
Seyed Mostaffa Hosseini - One of the best experts on this subject based on the ideXlab platform.
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Vulcanization kinetics of nano silica filled styrene butadiene rubber
Polymer, 2014Co-Authors: Seyed Mostaffa Hosseini, Mehdi RazzaghikashaniAbstract:Abstract It was shown that the physical filler-polymer and filler–filler interactions, apart from the filler surface chemistry, has a substantial role in controlling the Vulcanization kinetics of styrene butadiene rubber filled with nano-silica in a sulfur Vulcanization system. Kinetic studies by the oscillating disc rheometer, differential scanning calorimeter, and swelling tests revealed that the Vulcanization rate goes through a maximum as loading of silica increases, but conversion in crosslinking continuously decreases as the amount of silica increases. The effect of silica loadings on the Vulcanization reactions was linked to the immobilization of rubber chains around particles as well as in a polymer-mediated filler network, which were differentiated by the nonlinear viscoelastic behavior of rubber vulcanizates. By surface modification of nano-silica, the accelerating/decelerating effects of nano-silica on the Vulcanization reactions were altered corresponding to the non-linear viscoelastic behavior of the vulcanizates. Therefore, a mechanism was proposed which correlates Vulcanization kinetics of rubber to the dynamics of chains influenced by the reinforcing fillers.