Communications Project

Document Type:Dissertation
Name:Michael Allen McLeod
Title:Injection Molding of Pregenerated Microcomposites
Degree:Doctor of Philosophy
Department:Chemical Engineering
Committee Chair: Dr. Donald G. Baird
Committee Members:Dr. Donald G. Baird
Dr. William L. Conger
Dr. Richey M. Davis
Dr. Alfred C. Loos
Dr. Garth L. Wilkes
Keywords:injection molding, composite, pregenerated microcomposite, polymer blend, fiber spinning, thermotropic liquid crystalline polymer
Date of defense:December 18, 1997
Availability:Release the entire work for Virginia Tech access only.
After one year release worldwide only with written permission of the student and the advisory committee chair.


One portion of this work was concerned with injection molding pregenerated microcomposites composed primarily of poly(ethylene terephthalate) (PET) as the matrix and HX1000 as the thermotropic liquid crystalline polymer (TLCP). Several factors were examined to maximize the mechanical properties of these composites, including injection molding temperature, matrix viscosity, and nozzle tip exit diameter. In addition, concentrated strands of HX1000/PET (50/50 wt%) were diluted using both an injection molding grade of PET and an injection molding grade of PBT. From this work, it was determined that the best mechanical properties were produced when the microcomposites were processed at the lowest injection molding temperatures, diluted with PBT, and injection molded using a large nozzle tip exit diameter. The pregenerated microcomposite properties were compared against theoretical predictions as well as glass-filled PET. It was found that the pregenerated microcomposites had tensile moduli of approximately 70% of theoretical expectations in the machine direction. Additionally, the comparisons against glass-filled PET revealed that at the same weight fraction of reinforcement, the pregenerated microcomposites had lower properties. Still, the composites were found to have smoother surfaces than glass-filled PET and at temperatures up to 150C the storage and loss moduli of the pregenerated microcomposites were similar to those of glass filled PET. It was concluded that if the theoretically expected levels of reinforcement could be attained, the pregenerated microcomposites processing scheme would be a viable method of producing light weight, wholly thermoplastic composites with smoother surfaces than are obtained with glass reinforcement. An additional focus of this research was to evaluate the ability to modify the crystallization behavior of a high melting TLCP (HX6000, Tm = 332C) with a lower melting TLCP (HX8000, Tm = 272C). It was found that it was possible to tailor the crystallization behavior of these TLCP/TLCP blends by varying the weight fraction of each component, as determined by rheological cooling scans and differential scanning calorimetric cooling tests. Based on the analysis of these TLCPs at the maximum injection molding temperature of 360C, it was speculated that they had reacted with one another.

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