Development of a simulation tool to analyze the orientation of LCPs during extrusion process.
Abstract: In this
thesis, different aspects of the rheology and directionality of the liquid crystalline
polymers (LCPs) are investigated. The rheology of LCPs are modeled with different
rheological models in different die geometries. The final goal in modeling the rheology
and directionality of LCPs is to have a better understanding of their rheology during
extrusion processing methods insid... read moree extrusion dies and eventually produce more isotropic
films of LCPs. An attempt to design a die geometry that produces more isotropic films
was made and it was shown that it is possible to use the inertia of the polymer to
generate a more isotropic velocity profile at the lip of the die. This isotropic
velocity profile can lead to alignment of directors along the streamlines and produce an
isotropic film of LCP. It is shown that the rheological properties of the LCP should be
altered to have a very low viscosity for this type of die to work. To be able to
investigate the effect of processing on directionality of LCPs, it is essential to
develop a method to simulate the directionality based on processing conditions. As a
result, a user defined function (UDF) code was added to ANSYS\textregistered
~FLUENT\textregistered~ to simulate the directionality of LCPs. The rheology of the LCP
is modeled using power-law fluid model and the consistency index (K) and power-law index
(n) were estimated based on the experimental measurements done with capillary rheometry.
Three main phenomena that affect the directionality namely effects of Franks elastic
energy, the effect of shear and the effect of movement of crystals with the bulk of
polymer are investigated. The results of this simulation are close to physical phenomena
seen in real LCPs. To quantify the directionality of the LCPs, the order parameter of
the domain were calculated and compared for different flow and fluid conditions. All
polymers including LCPs are viscoelastic fluids in molten state. To understand the
rheology of LCPs, a die-swell experiment was carried out using LCP material and
Polypropylene (PP). For this experiment a capillary die with two different land-lengths
was designed and built. The die-swell of the materials were measured optically according
to ISO standards and the dependence of the die swell for materials on rheological
properties is investigated. To simulate the viscoelasticity of LCPs numerically,
ANSYS\textregistered ~POLYFLOW\textregistered~ was used. ANSYS\textregistered
~POLYFLOW\textregistered~ has several viscoelastic models and is designed to simulate
extrusion processes. The geometry of the capillary die designed for the experiments was
modeled in ANSYS\textregistered ~POLYFLOW\textregistered~ and the results were compared
with the experimental results obtained for LCP and PP. It is shown that the morphology
of the polymer should be considered into account to have a correct simulation of die
Thesis (Ph.D.)--Tufts University, 2013.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Michael Zimmerman.
Committee: Anil Saigal, Mohammed Afsar, Meredith Dunbar, and Dan Ward.
Keywords: Engineering, Mechanical engineering, and Polymer chemistry.read less