• Friesenbichler, Walter
• Holzer, Clemens
• Schuschnigg, Stephan
• Battisti, Markus
• Winkler-Ebner, Joachim

Abstract

The aim of this research was the optimization of a co-rotating twin screw extruder for processing polypropylene with layered silicates. The various input parameters of the process itself such as screw speed, flow rate, temperature and pressure as well as the great variety of screw configurations lead to an enormous amount of experimental runs for the optimization. By using CFD simulations some of these parameters can be varied without the need for experiments. In order to verify the simulated results, experimental runs have been performed. The compounded materials consisted of 90 wt% PP (Bormed DM55 pharm or BB 412 E both from Borealis) with 5 wt% compatibilizer (BYK Scona TPPP 2112GA) and 5 wt% layered silicate (Rockwood Nanofil®5). The viscosity was measured using different rheometers, as an input parameter for the isothermal simulations. The pressure profiles, mixing index and dissipative energy input along the screw elements were simulated utilizing Polyflow simulation package from Ansys Inc.. The regions where the simulations showed zero pressure where assumed to be starved regions. These regions were also be verified in the “screw pull out” experiments. In addition the pressure was measured along the screw and compared to the simulations. The experiments where done with the polymer nanocomposites injection molding compounder (PNC-IMC), consisting of a Leistritz ZSE 27 MAXX 44D compounder and an Engel e-motion 740/180T injection molding machine. The final part (tensile specimen or plates for SAXS measurements) were processed directly with the PNC-IMC with only one plasticizing process. Instead of backward conveying elements, the optimized screw consisted of mixing and kneading elements leading to lower pressures and lower dissipative energy inputs and a longer residence time. The exfoliation of layered silicates and therefore the tensile strength of the material are often related to the shearing and residence time. However, the longer residence time in these experiments, did not compensate the lower dissipative energy input. The SAXS measurement also showed that the standard geometry had a higher exfoliation rate than the optimized screw.

Topics

• nanocomposite
• polymer
• experiment
• simulation
• extrusion
• twin screw extrusion
• strength
• layered
• viscosity
• tensile strength
• injection molding
• small angle x-ray scattering