Theses and Dissertations at Montana State University (MSU)
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Item Biochar as a renewable carbon additive for biodegradable plastics(Montana State University - Bozeman, College of Engineering, 2022) Kane, Seth Douglas; Chairperson, Graduate Committee: Cecily Ryan; This is a manuscript style paper that includes co-authored chapters.Biochar - a carbon material produced from pyrolysis of biomass - is a promising alternative to petroleum-derived filler materials in biobased and biodegradable plastics. In this application, biochar can replace materials such as carbon black, with a material that is compatible with end-of-life degradation of bioplastics, while reducing costs and improving material properties. Specifically, high electrical conductivity biochar has the potential to be applied to create highly electrically conductive and biodegradable biochar-bioplastic composite materials. Herein, two critical gaps to development of biochar-bioplastic composites are addressed: the high variation in biochar electrical conductivity and poor thermal interactions between bioplastics and biochar that reduce the bioplastics molecular weight and mechanical properties. To this end, biochars are produced from a variety of feedstocks and their chemical structure and electrical conductivity are extensively characterized. The relationship between feedstock chemical properties, biochar chemical properties, and biochar electrical conductivity is examined. Feedstock oxygen and inorganic content are found to play a critical role in developing highly electrically conductive biochar. The impact of these biochars on the thermal behavior of bioplastics is then examined in detail, and multiple hypotheses for the reduction in thermal behavior that have been proposed in past studies are tested. Biochar moisture content is found to have a limited impact on polymer thermal degradation, while alkali and alkaline earth metals present in biochar reduce the thermal degradation temperature of common bioplastics. A simple washing method was developed to remove these metals and improve the thermal stability of biochar-bioplastic composites. Finally, the environmental benefits of biochar-plastic composites are examined with life cycle assessment methodology, and the developed biochar is examined as a conductive additive in lithium-ion batteries. This work addresses two critical issues that limited the potential of biochar to reduce environmental impacts of rapidly growing classes of materials, as well as demonstrating its applicability in critical applications of petroleum-derived materials. Biochar-bioplastic composites show a unique combination of high electrical conductivity and biodegradability, with strong potential for development of applications in diverse industries from agriculture to biomedical applications.Item Biochemical and biophysical characterization of plastic degrading aromatic polyesterases(Montana State University - Bozeman, College of Letters & Science, 2019) Topuzlu, Ece; Chairperson, Graduate Committee: Valerie Copie; Brandon C. Knott and Mark D. Allen were authors and Japheth Gado, Harry P. Austin, Erika Erickson, Bryon S. Donohoe, Nicholas A. Rorrer, Fiona L. Kearns, Graham Dominick, Christopher W. Johnson, Valerie Copie, Christina M. Payne, H. Lee Woodcock, Gregg T. Beckham and John E. McGeehan were co-authors of the article, 'Structural and biochemical characterization of MHETASE' submitted to the journal 'Proceedings of the National Academy of Sciences of the United States of America' which is contained within this dissertation.As the world is producing more plastics than it can recycle, accumulation of manmade polymers in the environment is becoming one of the greatest global threats humanity is facing today. One of the major contributors to the plastics pollution problem is polyethylene terephthalate (PET), an aromatic polyester widely used in the packaging, beverage, garment and carpeting industries. As a response to the onslaught of plastics in the environment, fungi and bacteria are evolving metabolic pathways to convert plastics into useable energy sources. One of these organisms, a bacterium, Ideonella sakaiensis 201-F6, has recently been identified to convert PET into its monomers, terephthalic acid (TPA) and ethylene glycol (EG), and to use these compounds for energy and growth. I. sakaiensis' ability to convert PET is made possible by two enzymes, named PETase and MHETase. As a first step, PETase breaks down the insoluble substrate PET into a soluble major hydrolysis product - mono-(2- hydroxyethyl) terephthalate (MHET), which is then further hydrolyzed by MHETase into TPA and EG. Crystal structure of PETase, as well as some of its biochemical features, have been reported several times to date, but MHETase has remained largely uncharacterized. This work focuses on further discovery-driven biophysical and biochemical characterization of PETase, visualization of PETase activity on various polyester surfaces, as well as the structural and biochemical characterizations of the MHETase enzyme. We have found that several aspects of PETase-mediated substrate surface modification hydrolysis mechanisms differ depending on the specific mechanical and material characteristics of the substrate. We have also found that PETase is inhibited by BHET. Additionally, we have solved the crystal structure of MHETase. MHETase consists of an alpha/beta hydrolase domain, and a 'lid' domain, commonly seen in lipases. Molecular dynamics simulations revealed the mechanism of MHETase action. Through bioinformatics approaches, we have also identified mutants of interest for improved MHETase activity. Coincubation of MHETase with PETase affects PET turnover in a synergistic fashion. Taken together, this work provides additional insights into the mechanisms of action of the PETase and MHETase enzymes, which may open new avenue for bioremediation and removing plastics from the environment in a sustainable manner.