Alain Michel

Bulk polymerization of ε-caprolactone: Rheological predictive laws

The rheological behavior during bulk polymerization of e-caprolactone with titanium tetrapropoxide as the initiator was studied in connection with the kinetics of the reaction (conversion rate and molecular weight variations). The viscoelastic properties of the melt polycaprolactone performed by this reactive system was predicted reasonably well using phenomenological models such as the Yasuda–Carreau or relaxation spectrum models and a molecular dynamic model based on a blending law of the relaxation function. The evolution of these viscoelastic properties during bulk polymerization was calculated by combining these viscoelastic models with the kinetic laws of the system. By taking into account the dilution effect caused by the presence of a monomer, a global rheological predictive model was then achieved. It was shown to give a reasonably good depiction of the viscoelastic properties [‖η*(t)‖, G′(t) and G″(t)] whatever the processing conditions (temperature, frequency, initiator concentration, etc.) are.

Polymerization of ∊-Caprolactone in a Twin Screw Extruder

The purpose of this work is to model the bulk polymerization of epsilon -caprolactone in a corotating twin screw, extruder: Starting from kinetic data and rheological laws previously defined, we nse a twin screw flow modelling software to calculate the progress of the polymerization along the extruder Experiments are performed to assess the influence of processing conditions (feed rate, screw speed, barrel temperature, initiator concentration) and to validate the model. They put in evidence the control of the polymerization process by the temperature and the residence time in the extruder. It is shown that a good correlation between theoretical and experimental results can only be obtained if accurate kinetic and rheological data are used in the model.Abstract The purpose of this work is to model the bulk polymerization of ∊-caprolactone in a corotating twin screw extruder. Starting from kinetic data and rheological laws previously defined, we use a twin screw flow modelling software to calculate the progress of the polymerization along the extruder. Experiments are performed to assess the influence of processing conditions (feed rate, screw speed, barrel temperature, initiator concentration) and to validate the model. They put in evidence the control of the polymerization process by the temperature and the residence time in the extruder. It is shown that a good correlation between theoretical and experimental results can only be obtained if accurate kinetic and rheological data are used in the model.

New morphologies in immiscible polymer blends generated by a dynamic quenching process

Abstract New types of morphology in immiscible polymers blends, obtained by a process named dynamic quenching process [Cassagnau P, Michel A. French Patent, No 0004420, 6 April 2000], are presented. The dynamic quenching process consists of crystallizing under shear or elongational flows, a semi-crystalline polymer (or solidifying an amorphous polymer) dispersed in melt thermoplastic matrix. Using this new process, polybutylene terephthalate (PBT) and polycarbonate (PC) have been dispersed in an ethylene vinyl acetate (EVA) copolymers matrix in a twin-screw extruder. A coral structure of the PBT domains and a fine nanoscale (100×300 nm 2 ) of PC rods have been so elaborated. The development of the morphology during processing was qualitatively discussed in terms of crystallization under shear or elongational flows of fine PBT droplets dispersed in a melt EVA matrix. Coral PBT structure forms a network-type structure, which confers to the material an yield stress behavior. Considering EVA/PC blends, the mechanism of the morphology development is different. As PC is an amorphous polymer, the viscosity ratio and the elasticity of the PC phase considerably increases with decreasing temperature to the PC glass temperature. Furthermore, the dynamic quenching process can be used as a way to control and to form a rod morphology at high concentrations of PC.

Reactive blending by in situ polymerization of the dispersed phase

Abstract The formation of a polyethylene/polyurethane blend polymer via in situ polymerization of diols and diisocyanate monomers dispersed in a molten polyethylene matrix was investigated in an internal mixer. Two urethane systems were used in this study. The evolution of the blend morphology with increasing molecular weight of the polyurethane phase was discussed. The difference in viscosity between the minor and major phases has a controlling influence on the qualitative compounding behaviour exhibited. Furthermore, the viscosity ratio appears to be the physical parameter which governs the blend morphology development. The phase inversion was observed at η d gh m = 0.05 . Beyond the phase inversion point, Wus model (Polym. Eng. Sci., 1987, 27, 335) quantitatively predicts the decrease of the size morphology with increasing molecular weight of the polyurethane phase. Nevertheless, high solubility of isocyanate monomers and low solubility of alcohols in molten polyethylene induce an imbalance stoichiometry which limits the degree of polymerization (molecular weight) during the blending process. A pre-polymerizing step of the urethane system limits this solubility phenomenon.

Mechanical properties of plasticized poly(vinylchloride): effect of drawing and filler orientation

Abstract Reinforcement of plasticized poly(vinylchloride) was achieved by the use of two anisotropic fillers: talc and a lead carboxylate. The orientation of such fillers was developed during the extrusion processing. Then, in the present paper, we studied the correlations between extrusion conditions (draw ratio, temperature), development of particle orientation (talc, lead stabilizer) and tensile properties of a plasticized polyvinylchloride. X-ray diffraction measurements have allowed us to analyse orientation of the particles which also became evident through tensile property results. This work shows that talc is a good candidate for filling PVC formulations. Furthermore, good orientation is achieved with the extrusion conditions used. Moreover, the orientation of the lead stabilizer which has a lamellar shape leads to an increase in Youngs modulus. The enhancement of the Youngs modulus obtained by these two fillers is well modelled by the Halpin and Tsai law, considering that the platelets are oriented in the stretching direction. Concerning drawing, the stretching temperature has proved to be of particular importance, especially when it is above or below the temperature of the ‘gel-liquid’ transition of PVC, found to be around 205°C.

Diffusion of plasticizer in elastomer probed by rheological analysis

A free volume approach of the diffusion of organic molecules in polymers above their glass transition temperature (Tg) is addressed in this work. The idea that molecular transport is regulated by free volume was first introduced by Cohen and Turnbull [M. H. Cohen and D. Turnbull, J. Chem. Phys. 31, 1164 (1959)]. Our hypothesis is that the diffusion of small molecules, like plasticizers, in a polymer, here the copolymer of ethylene and vinyl acetate (EVA) above Tg, can be described by Fick’s classical law. The experiments were carried out on a parallel plate geometry rheometer. We studied the diffusion of the diethyl 2-hexyl phtalate (DOP) into the melted EVA at four different temperatures. Using Fick’s law, the concentration of the plasticizer was established for any given point of the thickness of the swelling elastomer at any time. Using a one-dimensional grid to solve continuous equations that describe the different rheological contributions of each abscissa, we determined the linear viscoelastic respo...

Melt Temperatures and Residence Times in an Extruder by Infrared Spectroscopy

Abstract This article presents melt temperature measurements with an infrared thermometer during extrusion and investigates the influence by the surface emissivity and the rotating screw. This influence can be used for on line residence time measurements in the extruder line, to measure the number of revolutions of the screw, and to measure both the surface temperature and the bulks temperature. The results show that colouring the PE with a high emisffisivity tracer allows us to measure the melts surface temperature and minimise the influence of the rotating screw. Its influence is weaker in complete filled section as in partial filled sections of the extruder and the mean bulks temperature is measured when the emissivity is lower than one. Furthermore it is shown that it is possible to measure the residence time distribution on line with an infrared thermometer, by taking advantage of its sensibility on a changing surface emissivity. Measurements with classical methods shows the same residence time distribution as obtained with the infrared spectroscopy. The advantage of this method is its wide range of applications, such like as the use in pressure zones, for a wide range of temperature and to measure on line the local residence time distribution all along the screw.

Bulk and Dispersed Phase Polymerization of Urethane in Twin Screw Extruders

Abstract The bulk and dispersed phase polymerizations of urethane were investigated in a co-rotating twin screw extruder. The residence time has predominant influence on the bulk polymerization in twin screw extruders. Furthermore, the polyurethane polydispersity decreases going down the screws, as the result of the extent of the reaction and mixing in the extruder. As expected, the polyurethane polydispersity at the die exit of the extruder is close to the theoretical value (Ip = 2). In the case of urethane polymerization in molten polyethylene matrix, the residence time distributions showed that the two monomers (isocyanate and alcohols) have different behaviors in the extruder in presence of PE due to the solubility of isocyanate and non-solubility of alcohols in PE. Furthermore, this solubility phenomenon PE induces an imbalance stoichiometry which limits the degree of polymerization (molecular weight) and a broadening of the molecular weight distribution during the blending process in extruder. Slip phenomenon was also observed at the die because of the presence of polyurethane, with low molecular weights, at the sample surfaces. An in-situ pre-polymerizing step of isocyanate/alcohols tends to eliminate this phenomenon. Then, the aim of the present work was to study the formation of a polyethylene/polyurethane blend polymer via in situ polymerization of diols and diisocyanate monomers dispersed in a twin screw extruder.

Lubrication and slip flow during extrusion of plasticized PVC compounds in the presence of lead stabilizer

Abstract The main point of interest when discussing lubrication is to understand what lubricants do in a compound, particularly during processing. Among lubricants, we can find metal soaps, which are often heat stabilizers of PVC. In order to study the influence of lubricants on the flow properties, it is of particular interest to analyse the behaviour of the material at the die walls, where slip may be observed. Then, in the present paper, the lubricating ability of a lead stabilizer during extrusion of a plasticized PVC formulation was investigated through an instrumented die, which allowed us to have the apparent flow properties at the wall. Rough and smooth surfaces of the die were used in order to prevent or promote slip at the metal surface. From this method, it was possible to observe the slip phenomenon above a critical concentration, whereas the analysis of the die surface through SEM coupled energy dispersive x-ray spectroscopy shows that lead stabilizer migrates even at low concentration. So, slip occurs when the lubricant layer forms a continuous solid layer which modifies the polymer–metal interface properties.

Structure and dynamics of melt poly(ε-caprolactone) from inverse rheological calculation

The linear viscoelastic behavior of poly(∈-caprolactone) (PCL) in situ synthesized between the plates of the rheometer was investigated. The polymerization of ∈-caprolactone was initiated and catalyzed by titabium tetrapropoxide. These polymers are very sensitive to hydrolysis of the alkoxy-titanium bonds of PCL can be studied : hydrolyzed or non-hydrolyzed PCL. Howevern only tge molecular weight distribution (MWD) of the hydrolyzed chains can be accessed from size exclusion chromatography (SEC) analysis. The MWD of the in-situ synthesized poly (∈-caprolactone) was calculated by solving the inverse problem of determination of the MWD from rheological data. A continuous form of the relaxation function was derived and an a priori shape (Wesslau or bi-modal Wesslau) of the MWD was assumed. Then MWDs calculated from complex moduli curves were used to investigate the structure of the poly (∈-caprolactone) at the end of the polymerization process. About 85 % of the polymer chains consist of a single branched linear structure. The remaining 15 % are assumed to be mainly two fold branched. The presence of star structures cannot be precluded. The presebt work describes an illustrative example of the suitability of the quasi on-line estimation of the MWD from the inversion data.