ABSTRACT:The effect of modifying polypropylene by the addition of long-chain branches on the rheological properties and performance of foam extrusion was studied. Three polypropylenes, two long-chain-branched polypropylenes and a linear polypropylene, were compared in this study. The modification was performed with a reactiveextrusion process with the addition of a multifunctional monomer and peroxide. The rheological properties were measured with a parallel-plate and elongational rheometer to characterize the branching degree. The change from a linear structure to a long-chain-branched nonlinear structure increased the melt strength and elasticity of polypropylene. Also, there was a significant improvement in the melt tension and sag resistance for branched polypropylenes. Foaming extrusion was performed, and the effect of the process variables on the foam density was analyzed with Taguchi's experimental design method. For this study, an L 18 (2 1 3 5 ) orthogonal array was used on six parameters at two or three levels of variation. The considered parameters were the polypropylene type, the blowing agent type, the blowing agent content, the die temperature, the screw speed (rpm), and the capillary die length/diameter ratio. As a result, the most significant factor that influenced the foam density was the degree of long-chain branching of polypropylene.

Three‐dimensional solid element analysis and the membrane approximated analysis employing the hyperelastic material model have been developed for the simulation of the thermoforming process. For the free inflation test of a rectangular sheet, these two analyses showed the same behavior when the sheet thickness was thin, and they deviated more and more as the sheet thickness increased. In this research, we made a guideline for the accuracy range of sheet thickness for the membrane analysis to be applied. The simulations were performed for both vacuum forming and the plug‐assisted forming process. To compare the simulation results with experiments, laboratory scale thermoforming experiments were performed with acrylonitrile‐butadiene‐styrene (ABS). The material parameters of the hyperelastic model were obtained by uni‐directional hot tensile tests, and the thickness distributions obtained from experiments corresponded well with the numerical results. Non‐isothermal analysis that took into account the sheet, temperature distribution measured directly from the experiments was also performed. It was found that the non‐isothermal analysis greatly improved the predictability of the numerical simulation, and it is important to take into account the sheet temperature distribution for a more reliable simulation of the thermoforming process.

In the resin transfer molding (RTM) process, preplaced fiber mat is set up in a mold and thermoset resin is injected into the mold. An important issue in RTM processing is minimizing the cycle time without sacrificing part quality or increasing the cost. In this study, a numerical simulation and optimization process for the filling stage was conducted in order to determine the optimum gate locations. The control volume finite element method (CVFEM), modeled as a 2‐dimensional flow, was used in this numerical analysis along with the coordinate transformation method to analyze a complex 3‐dimensional structure. Experiments were performed to monitor the flow front to validate the simulation results. The results of the numerical simulation corresponded with that of the experimental quite well for every single, simultaneous, and sequential injection procedure. The optimization analysis of the sequential injection procedure was performed to minimize fill time. The complex geometry of an automobile bumper core was chosen. A genetic algorithm was used to determine the optimum gate locations in the 3‐step sequential injection case. Taguchi's experimental design method was also used for determining the pressure contribution of each gate. These results could provide the information on the optimum gate locations and injection pressure in each injection step and predict the filling time and flow front.

ABSTRACT:The effects of SEBS as a compatibilizer on the interfacial tension and rheological properties of LDPE/PS blend have been studied. Interfacial tension was measured by the breaking thread method. The measured interfacial tension of the LDPE/PS blend was 8.26 dyn/cm. It decreased rapidly with SEBS contents to 1 wt % and then leveled off to a saturation value, 3.6 dyn/cm. Dynamic oscillatory shear, elongational viscosity, and recovery after elongation were measured as the rheological properties. Storage modulus at low frequencies decreased with SEBS contents to 1 wt %. More addition of SEBS, however, increased the storage modulus at low frequencies. Similar behaviors could be observed in elongation viscosity and recovery after elongation. Hardening of elongational viscosity and recovery after elongation were reduced with 1 wt % SEBS, and they enhanced again with more SEBS contents. This means that there is a critical concentration of SEBS that acts as a compatibilizer and reduces the interfacial tension. More SEBS than the critical concentration saturates the interface and increases the elasticity of the LDPE/PS blend, while maintaining the interfacial tension between LDPE and PS constant.

Summary: Polymer blend/clay nanocomposites were prepared by ultrasonic-assisted continuous extrusion process. This process was employed to enhance the compatibility between two polymers, and nano-scale dispersion between the polymer blend and organically modified clay. Materials were linear polypropylene and polystyrene with 3 phr loading of organophilic montmorillonite clay. The effectiveness of the proposed ultrasonic-assisted process on the polypropylene/polystyrene/clay nanocomposites was confirmed by rheological property measurements and structural analysis by scanning electron microscope and X-ray diffraction. The sonication during extrusion was effective in improving the compatibility between polypropylene and polystyrene. Also, it led to enhanced breakup of the clay agglomerates. The observed clay was in the exfoliated state from the X-ray diffraction analysis.