Graduate Theses & Dissertations

Novel Aliphatic Amides from Vegetable Oils as Bio-Based Phase Change Materials
Energy storage efficiency and sustainability require advanced technologies and novel materials. Recently, bio-based phase change materials (PCMs) have received significant attention for thermal energy storage (TES) uses. Vegetable oils are versatile renewable feedstocks that are well suited for the development of sustainable, functional PCMs. PCMs derived from vegetable oil, which compares favorably with paraffin waxes, the industry standard, are currently available. However, their melting points are typically below 80 °C preventing their wider integration in TES applications, particularly those requiring higher temperatures. The present work manipulated the structural building blocks of fatty acids to advantageously affect the intermolecular forces and increase the properties relevant to TES. The polar amide functional group was incorporated into fatty moieties to take advantage of the strong hydrogen bonds that it forms to increase intermolecular attractions and hence increase the phase change temperature and enthalpy as well as to improve thermal stability and thermal conductivity. A series of carefully designed lipid-derived monoamides and four series of lipid-derived diamides were synthesized via benign and simple amidation reactions. The purity of the amides and the intermolecular hydrogen bond strength were assessed using 1H NMR and FTIR. The properties relevant to TES such as thermal transition, crystal structure and polymorphism, thermal stability and thermal conductivity were measured using DSC, XRD, TGA and a thermal conductivity analyzer, respectively. The complex roles of the PCM’s constituting molecular building blocks in the phase behavior were elucidated and correlations between structure, processing conditions and macroscopic physicochemical properties, never before elucidated, were assembled in predictive relationships, drawing a unified picture of the rules that generally govern the phase behavior of lipid-derived PCMs. Practically, the prepared amides demonstrated desirable TES properties with substantial performance improvement over current bio-based PCMs. They presented increased phase change temperatures (79 - 159 °C), enthalpies of fusion (155 - 220 J/g) and thermal stability (234 - 353 °C). More importantly, the predictive structure-function relationships established in this work will allow the straightforward engineering of lipid-derived amide PCM architectures with judicious selection of molecular building blocks to extend the range of organic PCMs and deliver thermal properties desirable for TES applications. Author Keywords: LATENT HEAT THERMAL ENERGY STORAGE, LIPID-DERIVED AMIDES, PHASE CHANGE MATERIALS, RENEWABLE, SOLID LIQUID AMIDE PCMS, THERMAL PROPERTIES
Lipid-derived Thermoplastic Poly(ester urethane)s
Thermoplastic poly(ester urethane)s (TPEU)s derived from vegetable oils possess inferior physical properties compared to their entirely petroleum-based counterparts due to the structural limitations and lower reactivity of the precursor lipid-derived monomers. The present work shows that high molecular weight of TPEUs with enhanced performance can be obtained from lipid-derived monomers via (i) the synthesis of polyester diols with controlled molecular weights, (ii) the tuning of the functional group stoichiometry of the polyester diols and the diisocyanate during polymerization, (iii) the degree of polymerization (iv) the control of the hard segment hydrogen bond density and distribution via the use of a chain extender and (v) different polymerization protocols. Solvent-resistant TPEUs with high molecular weight displaying polyethylene-like behavior and controlled polyester and urethane segment phase separation were obtained. Structure-property investigations revealed that the thermal transition temperatures and tensile properties increased and eventually plateaued with increasing molecular weight. Novel segmented TPEUs possessed high phase separation and showed elastomeric properties such as low modulus and high elongation analogous to rubber. The response of the structurally optimized TPEUs to environmental degradation was also established by subjecting the TPEUs to hydrothermal ageing. TPEUs exhibited thermal and mechanical properties that were comparable to commercially available entirely petroleum-based counterparts, and that could be tuned in order to achieve enhanced physical properties and controlled degradability. Author Keywords: Hydrothermal degradation, Molecular weight control, Polyester diols, Renewable resources, Structure-property relationships, Thermoplastic poly(ester urethane)s

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