Masters Theses

Date of Award

8-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

Joseph E. Spruiell

Abstract

This work encompasses the effect of additives and melt orientation on the crystallization from the melt and subsequent Form II-Form I crystal-crystal transformation of polybutene-1. Key components in this work are: structural development during secondary crystallization and transformation, and enhancement of the crystallization and transformation rates by compounding of additives as well as melt induced orientation.

To study these effects several experiments were performed. Blends of polybutene-1 (Shell BR200S) and selected additives were mixed in a Brabender screw extruder. The additives studied were polypropylene, diphenyl ether, a-chloronaphthalene, 1-naphthalene acetamide, carbon black, sodium benzoate, and stearic acid. The transformation kinetics in compression molded sheets were followed at 0, 23, 45, and 60 °C by WAXS techniques. The crystallization behavior was studied by differential scanning calorimetry. Structural development was examined by small-angle x-ray (SAXS) and small-angle laser light scattering (SALS) techniques in the BR200S resin.

Fibers were melt spun to various spin draw ratios to study the influence of orientation on the kinetics of the Form II-Form I phase transformation. These results were compared to previous studies on the effect of cold rolling by Hong and Lee of this university. The transformation was followed by wide-angle x-ray diffraction (WAXS) using a Rigaku diffractometer with a fiber attachment. Crystalline orientation factors were determined from wide-angle x-ray diffraction azimuthal scans.

Important conclusions from this work can be summarized as follows. From the quiescent melt state, an initial crystalline structure develops which undergoes secondary crystallization and transformation to create a well developed ordered structure. The -2 possibility of a very small fraction (10-2 %) of voids is shown through invariant analysis of the small-angle x-ray scattering results for the fresh and fully aged samples. This small amount of voids detected does not appreciably affect the crystallinities calculated from density measurements.

The crystallization rate was most affected by crystalline additives. Therefore, it seems by the nature of the effective additives, that the crystallization is nucleation rate controlled. The relative effectiveness of the crystalline additives may be attributed to crystallization temperatures as well as the possible epitaxial nucleation abilities.

Dependent on the nature of the material added, both the enhancement of nucleation and molecular mobility are important factors involved in the acceleration of crystal transformation by blending.

Sample dimension is also shown to affect both secondary crystallization and transformation rates. Samples with higher surface to volume ratios undergo these processes faster. The rate constants of the transformation can be related to the surface to volume ratio of the sample by a relationship developed using an Avrami analysis. The assumptions involved are that the nuclei are instantaneously present at the surface of the sample and that the crystals grow through the lamellar ribbon with a one-dimensional constant growth rate.

Lastly, increasing the melt orientation also increases the rate of secondary crystallization and transformation; however, solid state deformation, specifically cold rolling, seems to be a more effective method of increasing the rate of crystal-crystal phase transformation.

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