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Abstract
The increasing concern for sustainability and progress of medical research has resulted in the emergence of a wide range of biopolymers. The
biodegradability of these alternative biopolymers requires investigation prior to their application in environmental and medical systems. This Thesis
describes biodegradation of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)), poly(3-
hydroxyoctanoate) (PHO), poly-DL-lactide (PDLL), poly-DL-lactide-co-glycolide (PDLLG) and ethyl cellulose (EC).
Polymers were buried in garden soil for in vivo biodegradation experiments and a mixed population of microbes from the soil were incubated in
laboratory in vitro biodegradation experiments.
In both systems the short chain length PHA’s degraded rapidly and the medium chain length PHAs
and other biomaterials displayed either slow or negligible weight loss. PHB and P(HB-co-HV) copolymers degraded to T50 6.7 to 9.7 times faster in
vitro than in vivo. After 380 days burial in soil PHO had lost 60 % of the original 20 mg weight, PDLL 28 % and PDLLG 35 %. Ethyl cellulose and
polystyrene did not biodegrade,
Polymer-microbe surface interactions were investigated. The faster degrading polymers PHB and P(HB-co-HV) attracted a higher coverage of
biofilm than the slower degrading polymers PHO, PDLL and PDLLG for both the in vitro and in vivo experiments. The non-degradable polymers
(EC and polystyrene) attracted no biofilm. In vitro and in vivo experiments demonstrated a positive correlation between biofilm coverage and
polymer weight loss. Additionally the rougher air sides of solvent cast films attracted more biofilm than the smoother dish sides.
Polymer surface changes were quantified with microscopy. Surface roughness of PHB, P(HB-co-8HV) and PHO increased during biodegradation,
primarily due to an increase in the waviness component for both in vitro and in vivo degradation. In vitro methods provided a rapid mechanism for
protocol development and sufficiently predicted both surface roughness changes and biofilm-biodegradation relationships in vivo.
PHB and P(HB-co-8HV) were blended with the biodegradable antifouling agent 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOI or Sea Nine 211).
DCOI leached slowly from the films into the soil delaying biodegradation of the films until a lower residual level of DCOI remained. Biofouling was
reduced on PHA films containing DCOI.