Moving Die Rheometer Research Articles

The Effect of Excess Silane-69 Used for Surface Modification on Cure Characteristic and Mechanical Properties of Precipitated Silica Filled Natural Rubber (PSi/NR)

This research is concentrated on the effect of concentration of silane-69 used for surface modification on precipitated silica (PSi), on cure characteristic and mechanical properties of PSi filled NR. The PSi content in this study was fixed at 20 phr in order to reveal the effect of silane used to modify PSi, on NR compound and vulcanizate. Moving Die Rheometer (MDR) was used to characterize cure characteristic of rubber compounds. Generally, scorch and cure time of NR would increase with the addition of PSi due to the absorption of accelerator on its surface whereas the addition of Si-69 modified PSi would reduce both scorch and cure time. It was found in this research that the excess amount of Si-69 used increased scorch and cure time of rubber compounds. This was thought to be that the excess of Si-69 led to the formation of polysiloxane clusters which could absorb accelerator in rubber compound and resulted in a prolonged scorch and cure time. In term of vulcanized rubber, it was found that maximum torque increased with the concentration of Si-69 up to 6 %. The polysiloxane formed during the cure characterization test was responsible for the slightly decreased torque after 6% of Si-69 treatment. Nonetheless, even with high concentration of Si-69 used, torque was still higher than that of untreated PSi filled NR. This is widely understood that sulfur atoms in Si-69 molecule are able to participate in the bonding between rubber and silane molecules resulted in the enhancement of crosslink density of the vulcanizate rubber. The increased of modulus at 200 % elongation, tensile strength under tension, with the silane concentration, was evidence of the crosslink enhancement. Tear strength and hardness of the vulcanizates exhibiting the increment, with the silane used, also clearly confirmed the bonding between Si-69 and rubber molecules. It was elucidated from the research that excess of Si-69 would lead to polysiloxane formation, cluster form of silane and crosslinking density. Scanning Electron Microscope (SEM) micrographs and swelling test are also presented to confirm the phenomena.

Influence of various crosslinking systems on the mechanical properties of gas phase EPDM/PP thermoplastic vulcanizates

AbstractDynamically cured thermoplastic elastomers or thermoplastic vulcanizates (TPVs) are widely used nowadays for their unique characteristics. In this paper, gas phase ethylene–propylene–diene terpolymer (GEPDM)/Polypropylene (PP) TPVs with various crosslinking systems have been extensively studied to optimize the curative level in each crosslinking system with special reference to their mechanical properties. Optimized systems were compared for heat aging, recyclability, crosslink density, morphology studies, and dynamic mechanical analysis. Crosslinking by peroxide in the presence of triallyl cyanurate as a coagent gives best overall performance with reference to excellent heat aging behavior, tension set, and compatibility between GEPDM and PP. Conventional EPDM/PP system was also compared with GEPDM/PP system. GEPDM/PP system was found to exhibit better behavior in all respects. Significant correlations were obtained between delta torque values obtained from Moving Die Rheometer and modulus or cross link density of TPVs irrespective of the nature of crosslinking agent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5463–5471, 2006

Rheometers in scanning mode for cure of rubbers with low enthalpy: effect of heating rate and rubber–die contact

Rheometers are usually run under isothermal conditions for the cure of rubbers, in spite of the following drawbacks: three experiments at least are necessary at different temperatures selected within a narrow temperature window, and it takes some time for thermal equilibrium to establish between the rubber sample initially at room temperature and the dies. In scanning mode, the dies of the rheometer and the sample should be heated from room temperature up to the selected final temperature at a constant rate. The effect of the value given to the heating rate, which is the main factor in this new method, is especially studied, as well as the quality of the contact between the dies and the sample. The rubber used in the present study is a natural rubber vulcanised with 2% sulphur with a low enthalpy. The kinetic parameters of this cure reaction have been previously determined by isothermal rheometry, and the enthalpy measured by calorimetry. The state of cure–temperature curves in scanning mode have been calculated using a numerical model taking into account the conduction heat transfer through the rubber, the coefficient of heat transfer at the die–rubber interface, and the kinetics of the heat evolved from the cure reaction with the enthalpy. The kinetic parameters are determined from the state of cure–temperature curves, which are similar to the torque–temperature curves, using a least squares method. The values of the kinetic parameters obtained by this last calculation, based on the mathematical treatment of these curves, are the same as those introduced for obtaining these curves using the numerical model. Thus, whatever the heating rate, ranging from 2 to 10 K min –1 , and the value of the coefficient of heat transfer at the die–rubber interface expressing the quality of the contact, in scanning mode the moving die rheometer (MDR) can be used to determine the kinetics of the cure of rubbers.

Simulation of Crosslink and Graft Mechanism of Hydrogenated-NBR/ZINC Di-Methacrylate Composites by Moving Die Rheometer

Abstract This paper studies the crosslink and graft mechanism of hydrogenated-NBR/zinc di-methacrylate (HNBR/ZDMA) composites. The experiments to determine the rate constants of crosslink and graft reaction formulas are from Moving Die Rheometer (MDR) data. Comparison with experimental data and the solution of simultaneous ordinary differential equations for the crosslink and graft reactions are performed. Genetic algorithm optimization of the reaction rate constants allowed for simulation of crosslinking and graft reaction process. This simulation predicts that the HNBR/peroxide cure system will contain 0.1052-mole/l crosslink between matrix HNBR polymer at 2 phr.-peroxide concentration. The crosslink concentration of 0.1052-mole/l is composed of 0.0308-mole/l-addition reaction and 0.0744-mole/l-termination reaction. Moreover, the HNBR/ZDMA cure system contains 0.0148-mole/l graft of poly-ZDMA to HNBR and 0.0903-mole/l crosslink between matrix HNBR polymer at a 2 phr.-peroxide concentration.

New way of using rheometers in scanning mode for the cure of rubbers

Rheometers, especially the moving die rheometer (MDR), is used under isothermal conditions for the cure of rubbers. Thus, at least three experiments are necessary at different temperatures selected within a rather narrow temperature window, for determining the kinetic parameters of the cure. Moreover, it takes some time for the sample to attain the selected temperature, and for a high temperature of the dies, the reaction takes place before thermal equilibrium has reached. With this new way of using the rheometer, the dies with the rubber samples in them are heated from the room temperature up to the selected final temperature, with a constant heating rate. Calculations have been done for evaluating the performances of this method. The kinetic parameters such as the activation energy and the pre-exponential factor, as well as the order of the overall reaction, are obtained from only one experiment. The temperature in the sample is constant and nearly the same as that of the heating dies. The profiles of temperature and of the state of cure developed through the sample thickness are rather flat during all the processes. The parameter of interest, with the value of the heating rate, should be between 2 and 10°C/min, and perhaps much better between 2 and 5°C/min.

A Thorough Examination of a Torsional Dynamic Rheometer with a Closed Oscillating Cavity

The so-called Rubber Process Analyser, RPA 2000®, is a torsional dynamic rheometer, whose test cavity design is similar to that of the Moving Die Rheometer, a well known rotorless vulcameter, and the only available device which offers the possibility to test very stiff materials, in dynamic conditions. The paper systematically investigates the test conditions prevailing in the instrument, with respect to basic rheology principles, in order to identify the possible sources of errors and to quantify them. Using a monodisperse polymer melt, an experimental comparison is made with conventional cone-and-plan rheometers and data obtained with the RPA are found similar. A numerical simulation of the instrument test cavity is made in order to evaluate the error associated with the closed rim and the associate pressurisation. Results obtained show that rheological functions can be evaluated with a confidence of around 10%.

Study of process of cure of EPDM rubbers in moving die rheometer

Rheometers, especially moving die rheometers (MDR), are widely used for evaluating the kinetic parameters of the cure of rubbers. Experiments are run under isothermal conditions at three temperatures and the reaction is followed by measuring the torque as a function of time. The kinetic parameters can be determined, except the enthalpy of cure. However, the total heat generated by the overall cure reaction can be obtained by calorimetry. Using numerical models and taking all the known facts into account, i.e. the heat transfer by conduction and heat evolved from the cure reaction, profiles of temperature and of state of cure developed through the samples in the MDR have been calculated. The profiles of state of cure were calculated at various times, especially at the time necessary for the torque modulus to attain the value of 95%, and thus a comparison is made between these two pieces of information. Three EPDM compounds were used, containing 2, 9, and 19% peroxide and having different cure enthalpies. The effect of a change in the thickness of the rubber sheet and in the value of the heat transfer at the die/rubber interface was also determined. Rather good correlation was obtained between the results obtained from MDR and the values of the state of cure. The thickness of the sample plays an important role on the process of cure.

Fatigue, resilience and hardness properties of unfilled SMR L/ENR 25 and SMR L/SBR blends

The fatigue, resilience and hardness properties of natural rubber/epoxidized natural rubber (SMR L/ENR 25) and natural rubber/styrene-butadiene rubber (SMR L/SBR) blends were studied with a blend ratio from 0 to 100% rubber. A semi-efficient vulcanization system was used throughout the study. The cure time of the rubber compound was determined by using the Moving-Die Rheometer (MDR 2000). The fatigue life of the unaged and aged samples was determined by using a Fatigue To Failure Tester (FTFT), whereas the unaged samples of resilience and hardness were measured by a Wallace Dunlop Tripsometer and a Wallace Dead Load Hardness Tester, respectively. Results indicate that before ageing, fatigue life passes through a maximum at 50% ENR and SBR for both blends. This observation is attributed to the “synergistic” effect of mutual reinforcement due to strain-induced crystallization in the former system, whereas for the latter system, compatibility accounts for the observed maximum. Ageing lowers the fatigue life for both blends, a phenomenon which is associated essentially with the breakdown of crosslinks. Resilience decreases with increasing blend ratio, whereas the reverse behaviour is observed for the hardness experiment.

Cure and tear properties of ENR 25/SMR L and ENR 50/SMR L blends

Curing characteristics of two rubber blends, namely, epoxidized natural rubber (ENR) 25/SMR L and ENR 50/SMR L were studied using a Monsanto Moving Die Rheometer (MDR 2000), and the blend ratio was varied from 0–100% ENR. Also, a systematic study of tear strength of the blends was carried out before and after ageing at 100°C for 48 h. A Monsanto Tensometer (Model T10) operating at 50 cm/min was used to determine the tear strength of the standard crescent test piece. The results indicate that scorch time and cure time decrease with increasing ENR contents, whereas maximum torque and torque difference show the contrary. This observation is attributed to the activation of an adjacent double bond by the epoxide group in ENR (shorter scorch and cure time) and consequently enhances cure to produce higher crosslink density (higher torque values). The effect of activation is more significant in ENR 50 than in ENR 25, due to the presence of more epoxide groups in the former. From viscous torque and loss tangent data, better resilience property of the blend can be obtained if the ENR content is less than 25%, or more than 50%. The tear strength increases with the ENR content up to a maximum value at about 50% ENR in the blend. This finding is ascribed to the increased energy dissipation, as indicated by the increase in tan δ with % ENR. However, tear strength of aged sample decreases with increasing ENR contents, due to the poor aging property of the ENR, especially ENR 50.

The Effect of Accelerator/Sulphur Ratio on the Cure Time and Torque Maximum of Epoxidized Natural Rubber

The cure time of accelerated sulphur vulcanization of Epoxidized Natural Rubber (ENR 25) was studied while one grade of unmodified natural rubber– Standard Malaysian Rubber Light (SMR L) was used as a control. Five accelerators, viz. 2-mercaptoben-zothiazole (MBT), tetramethylthiuram disulphide (TMTD), zinc dimethyldithiocarbamate (ZDMC), N-tert-butyl-2-benzothiazylsulphenamide (TBBS) and diphenylguanidine (DPG) were used in the study and the vulcanization systems used were conventional vulcanization (CV), semi-efficient vulcanization (semi-EV) and efficient vulcanization (EV). Monsanto Moving-Die Rheometer (MDR 2000) was used to determined the cure time in the temperature range of 100-180°C. The results indicate that cure time decreases exponentially with increasing temperature for the two rubbers studied. At a fixed curing temperature, ENR 25 shows shorter cure time compared to that of SMR L. This has been attributed to the activation of the double bond by the adjacent epoxide group in ENR 25. Studies of the effect of varying amounts of M Bata a fixed sulphur concentration show that cure time decreases as the accelerator concentration increases. ENR 25 shows higher torque maximum than SMR L. This observation can be related to the oxirane group which is bulky and thus accounts for increased glass; transition temperature with increase in the level of epoxidation. Of the vulcanization systems, CV shows the highest torque maximum followed by semi-EV and than EV. This trend can be attributed to the amount of active sulphurating agent which increases with increasing accelerator concentration. It was also found that the influence of accelerator/sulphur ratio becomes less significant as vulcanization temperature increases.

Injection Moulding of Rubber Compounds1

Abstract The aim of this study is to show the relevant physical parameters related to rubber injection moulding, and especially compressibility, vulcanisation and wall slippage. Three materials are studied: an SBR compound, without and with a lubricant, and an EPDM compound. The viscosity is determined by capillary rheometry. The modified SBR exhibits wall slippage. Rheological vulcanisation kinetics are determined with a Moving Die Rheometer. Precise moulding experiments are carried out with an injection moulding machine and a mould equipped with pressure and temperature transducers. At low flow rate, the influence of the curing reaction on the pressure appears clearly especially for the fast curing EPDM. The conditions in which surface scorch defects appear are determined. The SBR with lubricant needs a lower pressure to fill the cavity than without lubircant. A model of mould filling is developed. The material is purely viscous, with a state of cure dependence of the viscosity. A Norton friction law is introduced to take into account a possible slippage at the cavity walls. A compressible calculation in the injection chamber allows a realistic evaluation of the flow rate at the entry of the cavity. The comparison with the experimental data confirms the importance of the compressibility, and the influence of the vulcanisation on the viscosity at low flow rate. In moulding conditions for which vulcanisation is not activated during the filling stage, despite uncertainties on the friction law parameters appropriate to the cavity wall roughness, the agreement with experiments is better when wall slippage is taken into account.

Cure characteristics of unaccelerated sulfur vulcanization of epoxidized natural rubber

The curing characteristics of unaccelerated sulfur vulcanization of ENR 25 and ENR 50 were studied in the temperature range from 100–180°C. The range of sulfur loading was from 1.5 to 6.5 phr. The scorch time was determined by Mooney Shearing Disk Viscometer whereas the initial cure rate, maximum torque, and reversion properties were obtained from the Moving Die Rheometer (MDR 2000). Results shows that ENR 25 gives a longer scorch time than ENR 50, an observation similar to that in an accelerated system reported earlier. For temperature < 120°C, scorch time depends exponentially on sulfur loading for both rubbers. However, this dependence diminishes as temperature is increased. This observation is attributed to the availability of activated sulfur molecules for vulcanization. The initial cure rate and maximum torque increases with increasing sulfur loading. ENR 50, however, exhibits higher value than ENR 25, suggesting faster cure in the former. For a fixed sulfur loading, reversion is a time and temperature-dependent phenomenon. It decreases with increasing sulfur loading because of the increase of cross-linking density for both rubbers stuided. © 1996 John Wiley & Sons, Inc.

Cure characteristics of unaccelerated sulfur vulcanization of epoxidized natural rubber

The curing characteristics of unaccelerated sulfur vulcanization of ENR 25 and ENR 50 were studied in the temperature range from 100–180°C. The range of sulfur loading was from 1.5 to 6.5 phr. The scorch time was determined by Mooney Shearing Disk Viscometer whereas the initial cure rate, maximum torque, and reversion properties were obtained from the Moving Die Rheometer (MDR 2000). Results shows that ENR 25 gives a longer scorch time than ENR 50, an observation similar to that in an accelerated system reported earlier. For temperature < 120°C, scorch time depends exponentially on sulfur loading for both rubbers. However, this dependence diminishes as temperature is increased. This observation is attributed to the availability of activated sulfur molecules for vulcanization. The initial cure rate and maximum torque increases with increasing sulfur loading. ENR 50, however, exhibits higher value than ENR 25, suggesting faster cure in the former. For a fixed sulfur loading, reversion is a time and temperature-dependent phenomenon. It decreases with increasing sulfur loading because of the increase of cross-linking density for both rubbers stuided. © 1996 John Wiley & Sons, Inc.

Finite Element Evaluation of the State of Cure in a Tire

Abstract Curing is one of the most important steps in the tire manufacturing process. During this process, a green tire is formed to the desired shape and the compound is converted to a strong, elastic material to meet tire performance needs. The process of curing, commonly called vulcanization, is usually accomplished under pressure and an elevated temperature provided by the mold. The curing process is energy-consuming and has a strong effect on material properties. To attain an optimal state of cure for different compounds of various dimensions at minimal capital and energy costs requires proper evaluation of the state of cure in a tire. Various numerical models have been proposed to determine the state of cure of rubber compounds in molds. Their applications are limited to simple geometry and boundary conditions. For a tire, which has complex shape and variable boundary conditions, the finite element method appears to be an ideal candidate because of its versatility. In this paper, a commercial finite element code, ABAQUS, is used to determine the temperature history of a tire in the curing press. In order to evaluate the state of cure throughout a tire, a user subroutine, HETVAL, is implemented. In the subroutine, the state of cure is determined based on the temperature history using a selected kinetic model, whose cure rate parameters are obtained from moving die rheometer (MDR) measurements. The heat generation due to chemical reaction is also included. The evaluation of the state of cure using the finite element method is benchmarked using a number of rubber compounds with simple geometries and boundary conditions. Both isothermal and nonisothermal conditions are tested. The predicted temperature history of a tire is then verified by the temperature history obtained from the thermocouples embedded in the tire. Parametric studies are carried out to evaluate the effect of various temperature histories on the state of cure in a tire. The results are used to shorten the curing cycle.