1:30 pm – 4:30 pm:
M13-Extrusion: Twin Screw II
(Moderator: Michael Thompson)-Room S320F
1:30 pm – 2:00 pm:
3D Numerical Simulation of Multiphase Flow in Partially Filled Twin Screw Extruders
Hossam Metwally, ANSYS Inc.
Three dimensional (3D) flow simulation though twin screw extruders are inherently difficult. This is due to the transient nature of the flow, the non-Newtonian behavior of the polymer, the fact that the screws are never fully filled in addition to other flow physics that may also be present (e.g. viscous heating or chemical reaction). Current flow simulation technology limited the scope of flow simulation to fully filled twin screw extruders which is seldom a realistic scenario. In the current work, the newly developed Overset Mesh technique for modeling moving part in general is employed to simulate such complex motion of a twin screw extruder. The fact that the extruder is starve-fed is taking into account and thus the flow field represents both the liquid polymer as well as the air (gas) within the extruder. Emphasis is placed on the flow visualization within the twin screw, velocity field, polymer volume fraction, shear rates and mixing index developed. The overset mesh technique is also compared with the long standing mesh superposition technique (MST) typically used to model fully filled twin screw extruders. Results for a simple 2D fully filled system compared very well between the overset mesh and the superposition mesh techniques. Similarly, a 3D comparison between the fully filled system using MST and the partially filled system using overset mesh have been carried out and the differences have been highlighted.
2:00 pm – 2:30 pm:
Mechanical Properties of Ultra-high Molecular Weight Polyethylene Nascent Fibers at Different Screw Speeds
Fangke Liu, Beijing Institute of Technology
Ultra-high molecular weight polyethylene (UHMWPE) nascent fibers are the materials, which are spun and extruded by a twin-screw extruder, then extruded and cooled through spinneret without extracted, dried and hot-drawn. In this paper, UHMWPE nascent fibers were prepared by gel spinning method using twin-screw extruder at different screw speeds of 10rpm, 13rpm, 16rpm, 19rpm, respectively. The effects of different screw speeds on the mechanical properties of the nascent fibers were analyzed by tensile testing. The initial residence time inside the extruder and the diameter of nascent fibers were also used to study the relationship between the screw speed and the mechanical properties of fibers. The results showed that both tensile strength and modulus varied in a trend of increasing initially and decreasing afterwards as the screw speed increased.
Prakash Hadimani, Steer
Loss of molecular weight due to shear and hydrolytic degradation resulting in lower Intrinsic Viscosity (IV) is a matter of importance while working with PET resin. In applications that demand high levels of dispersion, for instance, addition of Carbon Black, drop in IV has been an unfortunate compromise to achieve the necessary dispersion, which is measured using a Filter Pressure Value (FPV). This study uses an advanced screw design to compare viscosity retention and effective dispersion of carbon black in Poly(ethylene terephthalate) (PET) resin against a screw design used for many years as an industry standard. The advanced screw design attempts to eliminate the presence of peak shear, which is considered as the leading factor for the degradation of PET and the resultant reduction in IV. PET was blended with carbon black and dispersed in the extruder at a barrel temperature of 220°C to 260°C with screw speeds of 200, 250 and300 rpm. The screw configuration resulting in reduced degradation of PET and the retention of molecular weight was evaluated along with the dispersion potential. These observations were evidenced from IV measurements on a Ubbelohde viscometers and Filter pressure value (FPV) for dispersion rating on a Collins FPV tester. Melt transducers were used to track melt temperature and pressure.Specific Mechanical Energy (SME) and extruder screw speed were also recorded from the extruder.
3:00 pm – 3:30 pm:
Enhancing Thermal Conductivity of PVDF/Graphene Nanocomposites by Water-assisted Mixing Extrusion
Han-xiong Huang, South China University of Technology
Water-assisted mixing extrusion was used to prepare thermal conductive poly(vinylidene fluoride)/graphene oxide (PVDF/GO) nanocomposites. The injected water not only improves the GO dispersion in the PVDF matrix, but also promotes in situ thermal reduction of the GO. As a result, the intrinsic thermal conductivity of the GO is significantly increased. The interfacial interaction between the GO and PVDF facilitates the nucleation of crystallites at the PVDF-GO interfaces, leading to reduced interfacial thermal resistivity. The thermal conductivity of PVDF/GO nanocomposites prepared with water injection is significantly improved. The nanocomposite with 1.0 wt% GO exhibits a thermal conductivity of 0.475 W/mK, which is much higher than those of the PVDF (0.206 W/mK) and the nanocomposite prepared without water injection (0.335 W/mK).
3:30 pm – 4:00 pm:
Effects of Novel Extensional Mixing Elements on Fiber Lengthe Distribution in Composite Extrusion
Molin Guo, Case Western Reserve University
A new extensional mixing element (EME) for twin-screw extrusion was applied to compound polypropylene (PP)/glass fibers (GF), polypropylene (PP)/carbon fibers (CF), and polyethylene oxide (PEO)/polyethylene terephthalate fibers (PET-F) composites, and the effects of EME on fiber length distribution have been studied compared to two kinds of shear flow dominated Kneading Blocks (KB) screw configurations. Composites structures were characterized, and good dispersion of the fiber fillers in the systems has been achieved. It was concluded that EME can reduce the breakage of the stiff glass fibers and carbon fibers in the mixing zone compared with the KB, resulting in longer fibers remained after passing through the EME than the KB based on optical fiber length distribution measurements. Although flexible polyethylene terephthalate (PET) fibers are hard to cut by conventional KB, EME can easily break them into small pieces by very high pressure generated.
4:00 pm – 4:30 pm:
Transition Metal Dichalcogenide Thermoplastic Composits Prepared Using Lab Scale Extrusion
Joshua Orlicki, Army Research Laboratory
Significant interest has been growing around the properties and potential applications arising from 2D materials. Molybdenum disulfide (MoS2) is a well-known transition metal dichalcogenide (TMD) that can exhibit tunable electrical, optical, and catalytic characteristics based on its method of preparation. Here we have prepared optical plaques of poly(methylmethacrylate) containing hydrothermally synthesized MoS2 nanoflowers, both neat and complexed with reduced Graphene Oxide (rGO), using a laboratory scale twin screw extruder and injection molder. Filler dispersion, composite optical properties, and thermal properties have been assayed as a function of MoS2 characteristics and loading.