Advancing sustainable materials: developing pathways for renewable and bio-based polymers

Abstract

This thesis covers several interrelated studies that collectively aim to address challenges of sustainable material production and the improvement of biorefinery technologies. Each study focused on innovative approaches for recycling, transforming, and valorizing polyolefins and lignocellulosic biomass, providing potential solutions to environmental and economic concerns. The first study focused on the biorefining of hybrid poplar, a lignocellulosic woody biomass resource. We investigated a two-stage alkaline-oxidative pretreatment at a larger scale (20-L reactor volume) to understand the effects of reaction conditions in each stage and interstage mechanical refining on downstream processes. This pretreatment involved an initial alkaline pre-extraction stage, followed by Cu-catalyzed alkaline hydrogen peroxide treatment. By varying alkali loadings, temperatures, and H 2 O 2 loadings, we explored the influence of pre-extraction severity and pre-treatment oxidation on mass solubilization, lignin solubilization, lignin properties, fiber properties, and enzymatic hydrolysis yields. In the second study, we addressed the challenges of recycling polyolefins, which are notorious for their persistence in the environment. We introduced a two-stage process that converts polyolefins into valuable biodegradable polyesters. In the initial stage, we utilized aqueous oxidative depolymerization of polyolefins to break them down into ethanol-soluble waxes and water-soluble oxygenated compounds that can serve as feedstock for biological conversion. Our research investigated the conversion process, with a particular emphasis on the generation of oxygenated compounds, a less-explored aspect in this context. Our work explores the potential of the oxidative depolymerization method and its impact on chemical functionality, thermal properties, and molecular size of the resulting oxygenated products. The final stage involved the utilization of Thermus thermophilus HB8 to biologically convert the water-soluble oxygenated products into polyhydroxyalkanoates (PHAs). These biodegradable products hold promise as precursors for recyclable plastics. Our work demonstrated that T. thermophilus is capable of consuming water-soluble oxygenated products as a sole carbon source and producing PHA granules. This work represents a significant step toward reducing the environmental impact of polyolefin waste and promoting the use of sustainable and bio-based materials.