Masters Theses

Date of Award

3-1983

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

Donald C. Bogue

Committee Members

John F. Fellers, J. L. White

Abstract

When a molten polymer is quenched from the rubbery state to the glassy state, nonequilibrium properties are frozen into the material. Two such properties of considerable interest in character izing the behavior of the glassy state are the so-called "free volume" and the molecular orientation. Both of these properties were considered in this thesis. A major objective of the work was to develop a unified theoretical approach to connect the two states. Such a unified treatment provides the means through which the glassy state is directly related to the thermal and deformation history experienced in the rubbery state.

The time dependent volume behavior of polystyrene was investigated at 90°C, 70°C, and 25°C. Nonequilibrium free volume was frozen into the samples by quenching them in ice water from about 120°C. The decay of the free volume was then monitored at the above three temperatures. At 90°C and 70°C there was an initial period (100 hours or less) of rapid aging after which the change in free volume was very slow. At 25°C the aging was considerably slower.

An explicit form has been suggested for a general viscoelastic model including compressible effects. When the appropriate restrictions are imposed the model reduces to either incompressible visco-elasticity or to classical linear elasticity. Also, under certain circumstances, the general model reduces to a volume rate equation. The rate equation was used to fit the volume data described above, and also to predict the effect of the cooling rate on the glass transition temperature.

The incompressible form of the general model was used to analyze orientation aging data obtained by Potnis. The analysis involved following the history of the sample including the deformation in the rubbery state and cooling to the glassy state. The orientation, induced through the deformation and frozen into the glass, slowly decays with a corresponding shrinkage of the sample. The effect of an external load on the shrinkage was also considered. The analysis was shown to be capable of providing a good fit of the experimental shrinkage data.

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