Masters Theses

Yuh-Chen Shen

Date of Award

6-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

James L. White

Committee Members

D. C. Bogue, H. Pih, J. F. Fellers

Abstract

The properties of crosslinked polymers are greatly dependent on their network structures. Knowledge of the relationships between characteristics, curing conditions, compositions, structural and mechanical properties is required to evaluate uses for critical and demanding appli cations. The characterization of properties of crosslinked polymers like epoxy resins has received great attention in past decades. However, due to their increasing important uses for engineering purposes such as composite matrices and adhesives in aerospace structural components, characterization of properties is becoming critical.

The effect of residual stresses on the properties of metals and glass has received extensive studies for a long time. The residual stress distribution in slabs of epoxies due to the cooling process was studied. In order to measure the residual stress, both layer removal and photoelastic methods were used. A theoretical solution for the residual stresses, which is based on the assumption of a low modulus elastic rubbery state at temperatures above the softening point and a low temperature glassy state, was derived and compared to the results of the experiments. The agreement was good. The effect of the residual stress distribution on the impact strength of epoxies was also studied. It was found that residual stresses increase the impact strength.

The Influence of the stochiometric ratio (the curing agent, NMA to the epoxy resin, EPON 828) and the curing conditions such as cure temperature, postcure on the structure (as specified by swell index, density, Tg, etc.) and mechanical properties was studied. The kinetics of the curing reaction of epoxies was also examined by using the differential scanning calorimetry. The morphology of network structure was investigated in the scanning electron microscope and a globular structure was observed.

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