Masters Theses

Young D. Lee

Date of Award

3-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

Joseph E. Spruiell

Abstract

The effects of rolling on the crystal transformation from the tetragonal to the hexagonal phase as well as on structure and properties of fully transformed polybutene-1 have been studied. Compression-molded sheets of polybutene-1 were rolled via two different process routes. In Path I freshly molded and quenched samples were immediately rolled. In Path II the quenched samples containing the unstable tetragonal phase were aged and transformed to the stable hexagonal phase prior to rolling. For each rolling route, three different rolling temperatures were applied. In addition, the effects of annealing the cold rolled Path I samples were studied. The mechanical properties and structure were characterized by use of tensile testing, density measurements, and wide- and small-angle x-ray diffraction analysis.

The calculation of the crystal transformation rate from wide-angle x-ray diffraction scans indicated that light rolling at room temperature resulted in severe crystal transformation, but increasing the holding or rolling temperature decreased the transformation rate. The enhancement of the transformation rate was explained on the basis of the nature of roll pass.

It was found that rolling of PB-1 produced an increase in the yield strength and tensile strength and a decrease in the extensibility in the rolling direction. With increasing rolling temperature it is possible to obtain a more rigid and stronger film.

In general, rolling via Paths 1 or 11 makes little difference in the final morphology and properties except for one consideration. The processability in Path 11 is relatively lower than that in Path 1, especially at higher rolling temperatures, due to the rigid property of the hexagonal phase. Thus higher ultimate reductions could be achieved via Path 1 with resulting higher strength and modulus at these higher reductions.

Wide-angle x-ray diffraction analysis indicated that the orientation development process is characterized by initial orientation of the (300) poles along the normal direction followed by rotation of the crystals so as to orient their chain axes toward the rolling direction. This ultimately leads to single crystal texture with the (300) planes parallel to the rolling plane and the chain axes parallel with the rolling direction. At higher rolling reductions the lamellae are tilted in the ND-RD plane, producing four point SAXS patterns with the incident beam parallel to the transverse direction.

Annealing of cold rolled Path 1 samples at higher temperatures tends to develop a more sharply defined single crystal texture. It also transforms the SAXS patterns from a four point pattern into a "near" two point pattern, indicating stacks of lamellae parallel to the rolling direction of the sheets.

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