Date of Award

Fall 1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)

Department

Mechanical Engineering

First Advisor

Kwabena A. Narh

Second Advisor

Rong-Yaw Chen

Third Advisor

Marino Xanthos

Fourth Advisor

Zhiming Ji

Fifth Advisor

E. S. Geskin

Abstract

In this study, a series of experiments was set up in order to analyze the morphology development and mechanical properties of poly(ethylene terephthalate) (PET)/ liquid crystalline polymer (LCP) blends. Simulations of the injection molded blends at various process conditions were performed using CMOLD. In order to determine the effect of the processing parameters on the deformation of the LCP domains during the injection molding, a new analytical method to analyze the melt flow in the advancing melt front (AMF) region was developed. By combining the simulations of the injection molding and analysis of the melt flow in the AMF region, velocity and deformation in the AMF region at various injection molding conditions were determined. A relationship between the aspect ratio of the LCP fibers and elongational strain was developed by assuming an affine deformation of the LCP domains. A new method was also developed to predict the tensile modulus of the injection molded blends by introducing the effects of injection molding parameters, based on the Halpin-Tsai composite model. The relationships between the structure and mechanical properties of the blends, between processing parameters, the properties and the structure, have been investigated.

Our studies show that injection speed and mold temperature have significant effects on the morphological development and mechanical properties of the PET/LCP blends. A 10 % increase in the tensile modulus could be obtained when the two parameters are changed at the same time. It was also found that melt temperature has a distinct effect on the strength of the blends. An effective way to enhance the modulus and strength of the blends is to increase LCP content but high LCP content results in an increase in the cost of the materials and a decrease in the elongation of LCP blends.

The efficacy of the new method to calculate the tensile modulus of the injection molded PET/LCP blends is demonstrated by comparing the theoretical predictions and experimental results. An agreement between the predictions and experimental data was obtained.

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