BIODEGRADATION OF SYNTHETIC POLYMERS: THE INFLUENCE OF MORPHOLOGY ON THE RATE AND MECHANISM OF BIODEGRADATION

Date of Completion

January 1983

Keywords

Chemistry, Polymer

Degree

Ph.D.

Abstract

The mechanism of the biodegradation of polycaprolactone (PCL) was investigated in terms of morphological and molecular weight changes that occur during the biodegradation process. The polymer was prepared in three forms for study: films, single crystals, and crosslinked films. Morphology was monitored by Scanning Electron Microscopy (SEM), Small Angle X-Ray Scattering (SAXS), and turbidity measurements. Molecular weight changes were measured by Gel Permeation Chromatography (GPC). Degradation was monitored by suspension turbidity, GPC peak area loss, and weight loss. The degrading organisms used were a Fusarium isolate and Cryptococcus Laurentii.^ It was found that PCL biodegradation is a selective process in which amorphous regions are degraded more rapidly than crystalline material. In contrast to chemical selective degradation, the enzyme system appears to include a cofactor which helps break down crystalline material comparatively rapidly. Although crosslinking was shown to reduce crystallinity, it was also shown to reduce the biodegradation rate. This is due to the inability of crosslinked sites to fit into the enzyme active site, which may require several repeat units. The single crystal investigations revealed that degradation proceeds by attacking the amorphous surface layer most rapidly until it is depleted. Degradation continues at a pseudo-zero order rate at the edge of the crystallite where the only available hydrolyzable linkages remain. ^

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