Physical and Biochemical Strategies for Improving the Yield and Material Properties of Polyhydroxyalkanoate Biopolymers

Abstract

Polyhydroxyalkanoates (PHAs) are a diverse class of microbially synthesized biopolymers that are valued for their synthesis from renewable feedstocks and rapid biodegradation. As such, the commercial development of PHA plastics has potential to reduce the environmental impact of many, current polymers, which are non-biodegradable and rely on the use of unsustainable petroleum feedstocks. But despite the desirable traits of PHAs, the proliferation of these materials into commercial markets remains slow. Part of this is due to the greater cost of the renewable substrates used for PHA production versus the artificially low cost of petroleum-derived feedstocks. The other part of the challenge of promoting PHA utilization owes to the relatively limited diversity of physical and mechanical properties of PHAs that are currently available. As such, additional work is needed to develop new PHAs, which can satisfy the performance characteristics of many polymers already in use. Motivated by these two main challenges, 1.) to lower the production cost of PHAs and 2.) to broaden the range of unique PHAs materials available, the thesis presented herein details the development of new technologies to increase the substrate-to-product yield of PHA production and to expand the range of physical and mechanical properties of PHA-based materials. Chapter1 gives a broad introduction to polyhydroxyalkanoates and discuss various aspects of their production and application. Chapter 2 highlights the value of block-copolymers as a rich source for scientific discovery and technological development of PHAs. Methods are detailed in Chapter 3. The experimental results are presented in Chapters 4, 5, and 6, which focus generally upon: 4.) production of PHA copolymers in recombinant E. coli , 5.) fabrication and testing of PHA-graphene nanocomposites and 6.) production of PHA copolymers and block-copolymers directly from CO2 using Ralstonia eutropha. Finally, conclusions and prospects for future PHA research and development are given in Chapter 7. Taken all together, this thesis provides a solid foundation in theory and practice, for several technological approaches, which have great potential