Thesis (doctoral)--Åbo Akademi University, 2007. / Includes bibliographical references. Also available on the World Wide Web.

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Thesis (Ph. D.)--University of Western Sydney, Hawkesbury. / "A thesis submitted to the University of Western Sydney Hawkesbury in fulfillment of the requirement for the degree of Doctor of Philosophy." Includes bibliographical references (leaves 204-224).

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.

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.

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This thesis aims to utilize graphene nanoplatelets (GNPs) in biobased and biodegradable thermoplastic polylactide (PLA) matrix for improved properties and multifunctionalities. A comprehensive comparative study was carried out on the effect of the addition of GNPs with different sizes. The mechanical, electrical, thermal and barrier properties of resulting PLA/GNP nanocomposites and their inter-relationship with the microstructure of the composites is revealed. The effect of annealing on dynamic percolation and conductive network formation of PLA/GNP composites including the effect of hybrid GNP fillers of different size is reported, indicating the underlying mechanisms for different behaviours of GNP fillers of different size. Multifunctional engineering biopolymers with improved performances (mechanical and electrical) and added functionalities (barrier properties) were successfully developed through controlled filler distribution and orientation using multilayer co-extrusion technology. Changes in mechanical properties of the PLA/GNP multilayer nanocomposites were successfully correlated with GNP orientation in the filled layers. Multilayer PLA/GNP nanocomposites demonstrated excellent mechanical and barrier properties with low filler loadings compared to traditional mono-extruded films.