Mold filling characteristics and molecular orientation in injection molding of liquid crystalline copolyesters of poly (ethylene terephthalate)

The boundary layer effect on viscosity and injection molding studies in radial and unidirectional flows were investigated for liquid crystalline (ethylene terephthalate) using Instron model 3211 capillary rheometer. Two copolyesters of PET modified with 60 and 80 mole percent parahydroxy benzoate were examined. Melt viscosities were measured as a function of temperature and wall shear rates. Mold filling characteristics were investigated by introducing different fluid pigments into the melt before injection. Molecular orientation of the molded parts was studied by measuring the shrinkage of the microtomed samples at various temperatures, injection speeds, and cavity thicknesses for these two molds. For PET/60 mole % PHB, the viscosity was found to be some function of the capillary diameter, showing a marked decrease with decreasing capillary diameter at 275 C; this possible phenomenon is not found in most polymer melts. During mold filling stage, fluid pigments indicated that these liquid crystalline melts flow and split in the core before they approach the flow front. Molecular orientation studies showed that high shrinkage across the flow direction than that measured along the flow direction. Studies also indicated that there existed a relative maximum molecular orientation away from the surface of the parts, corresponding to the shear zone. As the cavity thickness decreases or injection speed increases, this relative maximum peak moves to the surface of the molded parts.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Chemical Engineering

Department dc:contributor.department

Chemical Engineering

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1982

Author dc:creator

• Nguyen, Chieu Dinh

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/80208

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/80208