Structure-property-processing relationships in extruded liquid crystal polymer film

2021 ◽  
pp. 096739112110070
Author(s):  
Anthony Sullivan ◽  
Anil Saigal ◽  
Michael A Zimmerman

Liquid crystal polymers (LCPs) derive favorable mechanical, chemical, and electrical behavior from long-range molecular ordering. The microstructure gives rise to anisotropic bulk properties that are problematic for industrial applications, and thus the ability to model the polymer directionality is essential to the design of isotropic material manufacturing processes. This investigation proposes a modeling methodology to simulate the 3D director field in full-scale film extrusion geometries. Wide-angle x-ray scattering (WAXS) is used to validate the predicted orientation for a standard coat-hanger die, and is compared with macroscopic mechanical, thermal, and dielectric testing of LCP film to illustrate the morphological dependence of the polymer properties. The highly anisotropic orientation state resulting from cast film extrusion is both predicted by the model and confirmed experimentally, and this preferred orientation is shown to correlate with observed anisotropy in the bulk properties. Additionally, a practical implementation of the modeling tool is presented to simulate directionality in two alternative die geometries designed to improve bulk isotropy, and it is demonstrated that the model is capable of simulating the resulting order for large, irregular domains typical of industrial processing.

Author(s):  
Anthony Sullivan ◽  
Anil Saigal ◽  
Michael A. Zimmerman

Liquid crystal polymers (LCP’s) comprise a class of melt-processable materials that derive specialized mechanical, chemical, and electrical properties from long-range molecular ordering. This unique microstructure gives rise to anisotropic bulk behavior that can be problematic for industrial applications, and thus the ability to model the orientation state in the polymer is necessary for the design of isotropic material manufacturing processes. Previous efforts to model LCP directionality have been primarily restricted to structured grids and simple geometries that demonstrate the underlying theory, but fall short of simulating realistic manufacturing geometries. In this investigation, a practical methodology is proposed to simulate the director field in full-scale melt-processing set-ups, specifically cast film extrusion, to predict the bulk material orientation state. The hybrid approach utilizes separate simulations for the polymer flow with commercial computational fluid dynamics (CFD) software, and the material directionality through a user-defined post-processing script. Wide-angle x-ray scattering (WAXS) is used to experimentally validate the simulated directionality during extrusion processing. It is shown that the model is capable of predicting both the direction and degree of orientation in the polymer resulting from processing, and the model produces strong agreement with experimental measurement of the polymer orientation state.


MRS Advances ◽  
2018 ◽  
Vol 3 (39) ◽  
pp. 2311-2316
Author(s):  
Anthony Sullivan ◽  
Anil Saigal ◽  
Michael A. Zimmerman

AbstractLiquid crystal polymers (LCP’s) comprise a class of materials that derive desirable, but anisotropic, engineering properties from long-range molecular ordering. The ability to model the polymer texture is essential to the design of manufacturing processes for isotropic material production. Previous efforts to model LCP directionality have been primarily restricted to structured grids and simple geometries that demonstrate the underlying theory, but fall short of simulating realistic manufacturing geometries. In this investigation, a practical methodology is proposed to simulate the director field in full-scale melt-processing domains and wide-angle x-ray scattering (WAXS) is used to experimentally validate modeling results. It is shown that the model generates good agreement with experimental measurements of both the orientation state and degree of order.


Author(s):  
Anthony Sullivan ◽  
Anil Saigal ◽  
Michael A. Zimmerman

Abstract Liquid crystal polymers (LCPs) form a class of high-performance plastics that exhibit comparable mechanical, chemical, and electrical characteristics to engineering metals and ceramics arising from their mesoscopic ordering. The unique hierarchal LCP microstructure leads to anisotropic bulk behavior and an understanding of the development of this morphology during manufacturing, as well as the subsequent effect on polymer properties, is essential to the design of isotropic material manufacturing processes. In this investigation, the preferred orientation in injection molded LCP plaque samples was measured using wide-angle x-ray scattering (WAXS). The direction of preferred alignment was observed from the WAXS scattering patterns and the degree of orientation in the material was quantified using an anisotropy factor. In addition, the mechanical, thermal, and dielectric bulk behavior was measured with respect to the mold direction (MD) and transverse direction (TD). To investigate the effects of processing geometry on microstructural development, and the resulting macroscopic properties, plaques of three different thicknesses were analyzed. In addition, the influence of melt rheology was probed through the comparison of two different commercial LCP resins. It is shown that a strong correlation exists between material performance and both the bulk polymer texture and the individual regimes of the hierarchal structure. The effects of processing geometry and polymer rheology also demonstrate the structure-property-processing dynamics at work in injection molded LCPs.


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