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International audience; The structure and properties of polypropylene (IPP) and ethylene propylene copolymer (IEPR) blends filled with nanosilica have been investigated. The nanocomposites were prepared via direct melt mixing using high shear corotating twin screw extruder. The effects of the process as well as adding amaleated-Polyethylene MAPE compatibilizer were assessed by morphology studies, thermal analysis and mechanical testing. From SEM and TEM investigations, a separate dispersion of filler and rubber in the PP matrix prevails in the PP/EPR/SiO2 systems. Encapsulation of the filler particles into the elastomer takes place when MAPE is used, promoting filler/polymer interactions and resulting in a simultaneous improvement in stiffness and toughness. Interestingly, the results indicated that high-shear processing is an effective method to improve the dispersion of the EPR phase and fillers through the matrix. The dispersed phase droplet size was reduced with the increase of the shear rate by varying the screw rotation speed from 300 to 800 rpm, which induces a high shear stress exerted onthe materials. To sum up, what is expected from an efficient compatibilization-process association is the reduction of the dispersed elastomer domains characteristic size, their stabilization by creation of an interphase and thus, enhanced mechanical properties.

International audience; Samples of polyethylene-1.4-cyclohexylenedimethylene terephthalate glycol (PETg) with different filler contents were prepared by a master batch process. The intercalated dispersion state of montmorillonite (MMT) was characterized using X-Ray Diffraction. Two different sample series are put in evidence with different basal distances (3.31 and 3.48 nm). The influence of nanofiller on ­ alpha and beta relaxations was studied by Dielectric Relaxation Spectroscopy and Differential Scanning Calorimetry. The use of these two techniques allowed us to determine accurately the fragility index m at the glass transition temperature Tg. For Tg, m, the Kauzmann temperature TK, and the relaxation time at Tg (Tg), we showed a decrease of the values more important for 3.48 nm basal distance than for 3.31 nm. The did not seem affected in its apparent activation energy Ea by the MMT addition.

The article addresses the issue of recycling of poly(ethylene terephtalate) (PET) by melt blending with polycarbonate (PC). PET/PC blends containing various amounts of the immiscible polymers were prepared in a twin-screw extruder. Selected compositions were also prepared in the presence of an Sn-based catalyst to assess the influence of transesterification during melt mixing. The degree of miscibility in the blends was studied using differential scanning calorimetry, scanning electron microscopy, and mechanical testing. PET/PC blends exhibit enhanced tensile properties in comparison to neat components for compositions of PET higher than 50% and these properties are improved by the addition of a transesterification catalyst. The PET/PC blend containing 20 wt% of PC, prepared with stannous octoate, shows the smallest size of the dispersed phase because of transesterification reactions that generate copolymer molecules at the interface between the immiscible polymers. The melting temperature of PET is decreased with the increase of the PC content in blends extruded in the presence of the catalyst. Also, the temperatures of the cold crystallization of PET are higher than those of similar blends without added catalyst. Both features give rise to better molding properties because of a shortening of the cooling time in the range of 50–90 wt% of PET. POLYM. ENG. SCI. 46:1378–1386, 2006. © 2006 Society of Plastics Engineers

Near infrared spectroscopy has developed in the polymer industry as a tool for in-line monitoring of processes, particularly extrusion. However, little work is dedicated to the monitoring of chemical reactions involving polymer melts. In this paper, we examine the suitability of NIR spectroscopy for monitoring the chemical modification (catalyzed esterification) of a molten ethylene–vinyl alcohol copolymer by octanoic acid in a twin screw extruder. Extrusion samples are characterized off-line, for calibration purposes, for the three species of interest (i.e. unreacted acid, OH groups, and ester functions formed on the polymer backbone) by means of two techniques: 1H NMR, allowing all three species to be quantified, and residual (free) acid titration. However, the mass balance of free acid is not straightforward, due to loss of mass by volatilization at the vent. Therefore, 1H NMR analysis and acid titration have to be combined to allow for determination of all concentrations. Multivariate calibration is implemented here to quantify and subsequently predict the analyte concentrations by using the NIR spectroscopic data. Our calibration, based on a partial least squares regression software, provides satisfactory results in terms of correlation between actual and predicted concentrations. This work demonstrates the potential of in-line NIR spectroscopy for monitoring chemical reactions with polymer melts in extrusion. POLYM. ENG. SCI. 46:1613–1624, 2006. © 2006 Society of Plastics Engineers

In recent years, experimental techniques based on microdielectrometry have attracted increasing interest for continuous monitoring, in a nondestructive way, of the advancement of the reaction of thermoset resins under cure. The extension of this technique for “in-situ” monitoring of the crystallization of thermoplastics has been carried out. A correlation between the evolution of the dielectric parameters of the material and its viscoelastic properties was done. A dynamic rheometer equipped with a dielectric cell and an instrumented slit die was designed. The crystallization process is depicted by a conductivity drop and by the occurrence of a maximum in the real permittivity. The decrease of the specific conductivity results from a modification of the conductive paths, whereas the increase of the permittivity is due to an interfacial polarization phenomenon (so-called Maxwell Wagner Sillars effect) between the amorphous phase and the growing crystalline entities. The sudden variation of the dielectric response is envisioned as a means for following the progression of the crystallization front within a mold. The description of the crystallization with Nakamura's model allowed the modeling of the crystallization inside a mold. The evolution of the temperature profile and of the crystallinity rate is modeled by a classical finite difference method. Dielectric measurements performed at controlled cooling rate experiments are in good agreement with the numerical simulation results and confirm the usefulness of dielectric measurements for “In-situ” monitoring of the crystallization process of a polymer inside a mold.

In injection molding, the pressure in the cavity usually reaches the atmospheric pressure before the ejection, therefore the thermal contact between polymer and mold is modified. This paper aims to evaluate the nature of the thermal contact between the polymer and the mold during the holding and cooling phase. An experimental plate mold has been designed to study this phenomenon. Thermal sensors facing each other and pressure sensors have been set in the mold. An inverse method is used to determine the heat flux density crossing the polymer mold interface, and the mold surface temperature. Then, a second inverse algorithm allows to determine the temperature profile at the end of the filling and the time evolution of the thermal contact resistance (TCR). Finally, the polymer temperature distribution in the thickness is determined between the thermal sensors. The results of this study show that the TCR between the polymer and the mold is not negligible and not constant with time. The polymer temperature at the surface can be 20°C higher than the mold surface temperature. Moreover, asymmetric air gaps have been observed when cavity pressure becomes equal to atmospheric pressure, therefore asymmetric temperature profile in the thickness are generated.