Processing - Structure - Property Relationships in Catalyst Cured Epoxy Systems (Morphology)
Wu, Ching-Shiun
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https://hdl.handle.net/2142/71820
Description
Title
Processing - Structure - Property Relationships in Catalyst Cured Epoxy Systems (Morphology)
Author(s)
Wu, Ching-Shiun
Issue Date
1985
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Abstract
The present investigation addresses the characterization of the low temperature relaxation behavior, glass transition behavior, stress-strain behavior, bulk density and morphology for catalyst cured epoxy systems based on diglycidyl ether of bisphenol A (DGEBA). The methods of thermally stimulated discharge (TSD) analysis, free oscillation torsion pendulum, differential scanning calorimetry (DSC), tensile mechanical test, and transmission electron microscopy (TEM) were employed in the investigation.
Three series of epoxy networks were used in this investigation. One series provides a baseline for examing the effect of mixing. The second series deals with the effect of extent of cure in terms of postcure temperature. The last series provides the study of the effect of distance between crosslinks by varying the molecular length of the epoxy resins.
The investigation on the effect of mixing indicate that the glass transition temperature, room temperature density, tensile mechanical properties in the rubbery state and nodular morphology are significantly affected by the extent of homogeneity of the system. A correlation between the properties and the size of nodular domain thus has been established. Based on experimental data, we propose that the glass transition temperature, density, and tensile mechanical properties in the rubbery state are directly dependent on the size of nodular domain. A network system with higher nodule size has higher glass transition temperature, tensile strength and Young's modulus in the rubbery state, but lower room temperature density and ultimate elongation in the rubbery state.
In the investigation on the effects of postcuring, postcure temperature, mixing condition, and distance between crosslinks on the low temperature relaxation behavior, five relaxation processes designated as (beta) ((beta)(,x) and (beta)(,OH)), (gamma), (beta)', and (beta)'' have been observed, and their molecular origins have been discussed in detail. Based on these observations, an inhomogeneity morphological model has been proposed which relates the curing process and postcure temperature to the properties and morphology. Furthermore, in the investigation on the temperature dependence of tensile mechanical properties, a fracture envelope was obtained which provide practical information for better design epoxy network system in regards to their engineering applications.
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