In this study, using a developed mathematical model, the non-isothermal behavior of a nonNewtonian fluid flow in the conveying elements of an intermeshing co-rotating twin screw extruder (TSE) is simulated based on the combination of mixed finite elements and fictitious domain methods. The flow equations are solved employing the standard Galerkin method and a streamline-upwind/Petrov-Galerkin technique is used in the solution scheme of the energy equation to reduce numerical oscillation. This model is combined with the Carreau rheological model to solve governing equations of continuity, momentum, and energy in a 3D Cartesian coordinate system. Using a developed mathematical model, the velocity and pressure fields are simulated for a non-isothermal flow in a corotating TSE. The shear rate distribution as a criterion for viscous dissipation and also the temperature distribution is calculated based on the simulated flow fields. The applicability of this model is verified by the comparison of experimentally measured pressures and mass flow rates with the simulation results for a highdensity polyethylene melt. This comparison shows a good correlation between experimental data and model predictions.

The aim of this research was to establish a balance between scratch resistance and scratch damage visibility in the wollastonite-filled heterophasic polypropylene copolymers.The influences of various factors including the surface hardness, elasticity, friction coefficient, and combinations thereof on the scratch behavior (scratch resistance and scratch visibility) were elucidated. Using micro-scale and nano-scale scratch tests and image analysis techniques, the scratch hardness, scratch depth, and scratch visibility of the composites were characterized.It was found that the introduction of wollastonite in the polypropylene copolymer matrix contributes to ductile fracture behavior because of an induced crystallization alteration. Accordingly, the scratch resistance of reinforced composites revealed an increase as a result of higher stiffness of the wollastonite as well as contribution of new crystalline structure. The addition of siloxane to the composites improved the resistance to surface damage by lowering the surface friction coefficient originated from enhanced chain mobility. Simultaneous addition of high density polyethylene and siloxane induced a significant influence on the resistance to the scratch damage.

This study was devoted to the effect of extensional flow during film extrusion on the formation of the b-crystalline phase and on the piezoelectric properties of the extruded poly(vinylidine fluoride) (PVDF) films after cold drawing. The PVDF films were extruded at different draw ratios with two different dies, a conventional slit die and a two-channel die, of which the latter was capable of applying high extensional flow to the PVDF melt. The PVDF films prepared with the two-channel die were drawn at different temperatures, strain rates, and strains. The optimum stretching conditions for the achievement of the maximum b-phase content were determined as follows: temperature ¼ 908C, strain ¼ 500%, and strain rate ¼ 0.083 s À1. The samples prepared from the dies were then drawn under optimum stretching conditions, and their b-phase content and piezoelectric strain coefficient (d 33 ) values were compared at equal draw ratios. Measured by the Fourier transform infrared technique, a maximum of 82% b-phase content was obtained for the samples prepared with the two-channel die, which was 7% higher than that of the samples prepared by the slit die. The d 33 value of the two-channel die was 35 pC/N, which was also 5 pC/N higher than that of the samples prepared with the slit die.

The flow behaviour of a polymer melt in the conveying region of an intermeshing corotating twin screw extruder was studied using the combination of mixed finite element and fictitious domain method. The model was a combination of the governing equations of continuity and momentum with Carreau rheological model in a three-dimensional Cartesian coordinate system. The equations were solved by the use of a mixed Galerkin finite element technique. The Picard's iterative procedure was used to handle the non-linear nature of the derived equations. The particle tracking technique was used to obtain residence time distribution and analyse distributive mixing in conveying region. The shear rate distribution was investigated as a criterion for dispersive mixing. The applicability of this model was verified by the comparison of experimentally measured pressure and simulation results for high density polyethylene melt. This comparison shows that there is a good adequacy between experimental data and model predictions.

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