Masters Theses

Date of Award

6-1988

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

Paul J. Phillips

Committee Members

E.S. Clark, R.S. Benson

Abstract

Linear polyethylene has been crosslinked using bis(tertiary butyl peroxyisopropyl) benzene (Vul-Cup R ®)in weight to weight loadings ranging for 0.1 to 3.1 percent. Extractable levels (sol) range from 18 percent to three percent, and the average number of methylenes between crosslinks from 1200 to 100. Weight average molecular weights of the sol fractions have been found to vary from 9000 to 23,000. X-ray diffraction studies show no large scale crystal distortion for any of the systems, and all systems exhibited fairly high degrees of crystallinity ranging from 80 percent to 60 percent. Nonisothermal crystallization studies have shown that the crystallization temperature decreases with increasing peroxide loading, while nonisothermal melting studies indicate that the heat of melting decreases with increasing peroxide loading. Isothermal crystallization studies illustrate that multiple melting is possible in both the unextracted and gel fractions. Bulk crystallization kinetics have been analyzed using reciprocal halftime data assuming heterogeneous nucleation. Systems of the lowest levels of crosslinking show a significantly higher slope than for the uncrosslinked polymer, indicating a change from regime II growth to regime III growth. The regime Il-regime III transition can be observed in some of the crosslinked systems in the temperature range 109° to 114°C, dependent on the crosslink density. The morphology of the sol fractions is primarily axialitic, while that of the crosslinked systems is nonspherulitic, being sheaflike.

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