Novel Bio-based Thermosets with Superior Performance Characteristics

Thermosetting materials are used extensively for adhesive, coatings, additive manufacturing, and high-performance composites applications. Petroleum-derived materials such as epoxy, unsaturated polyester, and vinyl ester (VE) resins that use styrene as a reactive diluent make up a large portion of the thermoset market. Though these materials are strong and have high heat resistance, they are highly cross-linked and brittle. Bisphenol A (BPA) and methylenedianiline (MDA) derived epoxies, and associated five monomers have a high viscosity that limits their processing. Additionally, BPA, MDA and styrene are known to be toxic and potentially carcinogenic and to negatively impact the human immune and reproductive systems. [17-18] This dissertation investigates the use of materials derived from naturally occurring feedstocks to create high performance polymers that are suitable for coatings, adhesives, composites, and additive manufacturing applications. A fundamental understanding of a range of bio-based feedstocks that are currently or potentially available and their unique properties was developed. These characteristics were used to design thermosetting polymers that combine the attributes of multiple bio-based feedstocks to obtain superior performance through formulation and molecular hybrid approaches. In this work, a new class of epoxy-amine monomers based on the bio-derived furan ring structure is introduced. Thermosets based on these monomers have exceptional performance characteristics that surpass standard petroleum-based systems. The unique nature of these materials lies in the unprecedented combination of high modulus, high yield strength, and high failure strain relative to incumbent systems. This behavior is attributed to the presence and interactions of the furan rings within the network structure. Crosslinking density analysis and X-ray scattering were conducted to probe potential intermolecular interactions within the polymer networks. Additionally, the furan-based systems exhibit remarkable char yields that could enable the widespread use of epoxies in fire protection and heat shield systems. This work also addresses the optimization of the synthesis of furan-based epoxies and amine curing agent to manufacture fully furan-derived polymer systems. The acidic condensation of furfuryl amine with aldehydes to prepare DFDAs was investigated, and the mechanism of high molecular weight by-product formation and the molecular structures of these byproducts were identified. A yield as high as 60% (previous yields reported in the literature ranged from 14-30%) was achieved by adjusting the pH of the aqueous solution during the separation process and controlling the synthetic pathways via stoichiometry to minimize high molecular weight by-product production. It was also discovered that the high molecular weight by-product contains secondary amine functionality and can be crosslinked into polymer networks, which greatly reduces material waste. Bioderived VE-resin systems were also investigated. Furan- and isosorbide-based methacrylate monomers were synthesized and found to exhibit significant benefits compared to BPA-derived five systems, which included low viscosity, high glass transition temperature, high modulus, and better toughness performance. This work highlights the potential of replacing BPA-derived methacrylate compounds in numerous applications with these bio-sourced methacrylate resin systems. For these monomers, a hybrid approach for the preparation of high-performance bio-based polymer systems was demonstrated. A series of isosorbide- and furan-based resin formulations were investigated as replacements of BPA-derived methacrylates and styrene copolymers in 3-D printing and composite applications. DLP (Digital Light Processing) printed parts with high glass transition temperature (>200°C) and fracture toughness Gic ~ 100 J/m² were obtained. These resin blends all possess low viscosity (below 0.12 Pa·s) and have also been used for glass fiber composite fabrication using liquid molding techniques.