Doctoral Dissertations

Date of Award

8-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Polymer Engineering

Major Professor

James L. White

Committee Members

D. C. Bogue, J. E. Spruiell

Abstract

Biaxial orientation and mechanical properties of amorphous polymers have been investigated. Biaxial orientation dealt with the influence of the stretching conditions on the degree of orientation. These conditions include stretching mode, rate, ratio and temperature. The influence of biaxial orientation on the mechanical properties was investigated. Since the stretching of the films was accompanied by quenching to freeze in the orientation, the effect of aging and residual stresses that might accompany quenching was studied. The amorphous polymers studied were polystyrene, polycarbonate, polysulfone, poly(methyl methacrylate), R high impact polystyrene and BarexR.

Birefringence was used as a measure of the orientation of the films stretched under various conditions. The stretching stress was found to correlate linearly with the birefringence. The stress optical coefficient was found to be greater for uniaxially stretched films than for the biaxially stretched films. This has been attributed to greater relaxation of the stretching stress of biaxially stretched films than in uniaxially stretched films.

The tensile properties of the films were measured. The modulus^ tensile strength, yield stress and percent elongation to break improved substantially with orientation. Brittle polystyrene and poly(methyl methacrylate) exhibit a transition to ductile failure after they became oriented.

The volumetric aging was monitored on stretched and unstretched sheets that were quenched. The rate of volumetric aging is smaller in stretched sheets than in unstretched sheets. The effect of aging on the mechanical properties of the stretched films was negligible. The relaxation of the stretching stress was predominant in the effect on the mechanical properties of the stretched films.

Nonhomogeneously cooled poly(methyl methacrylate) was prepared by quenching large slabs in ice water bath. The birefringence profiles were determined as an indirect measurement of the residual stress. The birefringence and residual stress profile indicated tension throughout the thickness of the slab with the greatest tension at the center of the slab. This was interpreted as a result of combined effect of flow induced orientation, plastic defomnation and thermal strain.

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