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Elastomers based on polyesters produced by the bacterium Pseudomonas oleovorans
Abstract
This dissertation has explored the structure property relationships of as extracted and chemically modified polyesters produced by the bacteria Pseudomonas oleovorans. The as extracted polymers are considered biodegradable thermoplastic elastomers. The two polymers studied were: poly($\beta$-hydroxyoctanoate), PHO, and poly($\beta$-hydroxyoctanoate-co-$\beta$-hydroxyundecylenic acid), PHOU. A fed batch biosynthesis was developed and the polymer yield was increased tenfold by optimizing feeding times of the carbon source(s). Batch-to-batch consistency was evaluated using GC, GPC, DSC, and TGA techniques. Mechanical property evaluations included the determination of tensile properties, tensile set, and hardness. The physical network structure was elucidated through equilibrium modulus determination coupled with rubber elasticity theory. The testing results revealed a material that compared well to other commercially available thermoplastic elastomers (also tested) but the elastic recovery was relatively poor. A thermal analysis of stretched samples provided possible explanations for the moderate elastic response exhibited by the material. The adhesive properties of PHO to paper were also evaluated and compared to several commercial tapes. Crystallization studies were conducted to understand the kinetics of crystallization and the effect of thermal history on the material properties. Several nucleating agents were evaluated to try and increase the rate of crystallization. The bacterial polyesters were chemically crosslinked in order to improve the elastic recovery. PHO, a totally saturated polymer, was crosslinked with a variety of peroxides both with and without multifunctional coagents. A controlled level of unsaturation was incorporated into the polymer by growing the bacteria on a mixture of carbon sources yielding PHOU. Using these reactive moieties, various crosslinking reactions were evaluated including sulfur vulcanization in addition to the peroxide crosslinking reactions. The modified polymers displayed better elastic response than the as extracted thermoplastic elastomer. The network structure was evaluated using a dynamic mechanical analysis technique called impulse viscoelasticity. Preliminary results of a study aimed at determining if PHO and PHOU biodegrade and the effect of crosslinking on the biodegradation of these materials are included. The study is being conducted jointly with the Microbiology Department at the University of Massachusetts, Amherst.
Subject Area
Materials science|Plastics|Microbiology
Recommended Citation
Gagnon, Karla Drew, "Elastomers based on polyesters produced by the bacterium Pseudomonas oleovorans" (1993). Doctoral Dissertations Available from Proquest. AAI9408275.
https://scholarworks.umass.edu/dissertations/AAI9408275