Doctor of Philosophy / Department of Grain Science and Industry / X. Susan Sun / Biobased polymers derived from renewable resources are increasingly important due to acute concerns about the environmental issues and limited petroleum resources. Poly(lactic acid) (PLA) is such a polymer that has shown great potential to produce biodegradable plastics. However, low glass transition temperature (Tg), low thermal stability, slow biodegradation rate, and high cost limit its broad applications. This dissertation seeks to overcome these limitations by reinforcing PLA with inorganic nanoparticles and low-cost agricultural residues. We first synthesized PLA nanocomposites by in situ melt polycondensation of L-lactic acid and surface-hydroxylized nanoparticles (MgO nanocrystals and TiO2 nanowires) and investigated the structure-property relationships. PLA grafted nanoparticles (PLA-g-MgO, PLA-g-TiO2) were isolated from the bulk nanocomposites via repeated dispersion/centrifugation processes. The covalent grafting of PLA chains onto nanoparticle surface was confirmed by Fourier transform infrared spectroscopy and thermalgravimetric analysis (TGA). Transmission electron microscopy and differential scanning calorimetry (DSC) results also sustained the presence of the third phase. Morphological images showed uniform dispersion of nanoparticles in the PLA matrix and demonstrated a strong interfacial interaction between them. Calculation based on TGA revealed that more than 42.5% PLA was successfully grafted into PLA-g-MgO and more than 30% was grafted into PLA-g-TiO2. Those grafted PLA chains exhibited significantly increased thermal stability. The Tg of PLA-g-TiO2 was improved by 7 °C compared with that of pure PLA. We also reinforced PLA with low-value agricultural residues, including wood flour (WF), soy flour (SF), and distillers dried grains with solubles (DDGS) by thermal blending. Tensile measurements and morphological images indicated that methylene diphenyl diisocyanate (MDI) was an effective coupling agent for PLA/WF and PLA/DDGS systems. MDI compatibilized PLA/WF and PLA/DDGS composites showed comparable tensile strength and elongation at break as pure PLA, with obviously increased Young’s modulus. Increased crystallinity was observed for PLA composites with SF and DDGS. Such PLA composites have similar or superior properties compared with pure PLA, especially at a lower cost and higher biodegradation rate than pure PLA. The results from this study are promising. These novel PLA thermoplastic composites with enhanced properties have potential for many applications, such as packaging materials, textiles, appliance components, autoparts, and medical implants.

Master of Science / Department of Grain Science and Industry / Xiuzhi Susan Sun / Plant oil-based raw materials have become more attractive alternatives in polymer industry as fossil resources depletion and environmental concerns continue to arise. Camelina (camelina sativa L.) seed contains about 45% of oil and about 90% of the oil is unsaturated fatty acids such as linoleic acid, α-linolenic acid, and erucic acids. It also provides the advantages of low cost and low fertilizer demand. Functionalized oils such as epoxidized camelina oil (ECO) and di-hydroxyl camelina oil (DCO) can be used for resins, adhesives, coatings, etc. The objectives of this work were to synthesize and characterize ECO and DCO from camelina oil. The epoxidation reaction of camelina oil was completed with formic acid and hydrogen peroxide. Catalyst ratio, reaction time, and temperature effects on the epoxidation reaction were studied. The optimum epoxy content of 7.52 wt% with a conversion rate of 76.34% was obtained from camelina oil using excess hydrogen peroxide and a molar ratio of formic acid of less than 1 for 5 hours in 50 °C. Camelina oil yields higher epoxy content (7.52 wt%) than soybean oil (6.53 wt%); however, soybean oil had a higher conversion rate of 80.16% compared to camelina oil because of uniform fatty acids distribution. In this study, we found that epoxidation efficiency is significantly affected by fatty acids composition, structure, and distribution. DCO was synthesized from ECO with different reaction parameters. The ring opening of ECO was performed with water, perchloric acid, and THF as proton donor, catalyst, and solvent respectively. Hydroxyl value of DCO was measured, and the maximal hydroxyl value was 369.24 mg KOH/g. physical properties of DCO were characterized by acid value and moisture content; thermal properties of DCO were obtained using different scanning calorimeter (DSC), thermalgravimetric analysis (TGA). Amount of solvent and acid catalyst addition affected the hydroxyl value and residual acid in DCO. Heat capacity, phase transition temperatures, and thermal stability of DCO were obtained and showed higher values than ECO’s. The DCO showed higher peel adhesion when it was formulated with epoxidized soybean oils through UV curing because camelina oil allows higher epoxy content, which results in higher hydroxyl values.

Master of Science / Department of Chemical Engineering / Jennifer L. Anthony / A polymer has drastically different physical properties above versus below some characteristic temperature. For this reason, the precise identification of this glass transition temperature, T[subscript]g, is critical in evaluating product feasibility for a given application. The objective of this report is to review the behavior of polymers near their T[subscript]g and assess the capability of predicting T[subscript]g using theoretical and empirical models. It was determined that all polymers begin to undergo structural relaxation at various temperatures both nearly above and below T[subscript]g, and that practical assessment of a single consistent T[subscript]g is successfully performed through consideration of only immediate thermal history and thermodynamic properties. It was found that the best quantitative structure-property relationship (QSPR) models accurately predict T[subscript]g of polymers of theoretically infinite chain length with an average error of less than 20 K or about 6%, while T[subscript]g prediction for shorter polymers must be done by supplementing these T[subscript]g (∞) values with configurational entropy or molecular weight relational models. These latter models were found to be reliable only for polymers of molecular weight greater than about 2,000 g/mol and possessing a T[subscript]g (∞) of less than about 400 K.

Doctor of Philosophy / Chemical Engineering / Mary E. Rezac / Membrane contact reactors (MCRs) have been evaluated for the selective hydro-treating of model reactions; the partial hydrogenation of soybean oil (PHSO), and the conversion of lactic acid into commodity chemicals. Membranes were rendered catalytically active by depositing metal catalyst onto the polymer "skin" of an asymmetric membrane. Hydrogen was supplied to the support side of the membrane and permeated from the support side to the skin side, where it adsorbed directly onto the metal surface. Liquid reactant was circulated over the membrane, allowing the liquid to come into direct contact with the metal coated surface of the membrane, where the reaction occurred. Our membrane contact reactor approach replaces traditional three-phase batch slurry reactors. These traditional reactors possess inherent mass transfer limitations due to low hydrogen solubility in liquid and slow diffusion to the catalyst surface. This causes hydrogen starvation at the catalyst surface, resulting in undesirable side reactions and/or extreme operating pressures of 100 atmospheres or more. By using membrane reactors, we were able to rapidly supply hydrogen to the catalyst surface. When the PHSO is performed in a traditional slurry reactor, the aforementioned hydrogen starvation leads to a high amounts of trans-fats. Using a MCR, we were able to reduce trans-fats by over 50% for equal levels of hydrogenation. It was further demonstrated that an increase in temperature had minimal effects on trans-fat formation, while significantly increasing hydrogenation rates; allowing the system to capture higher reaction rates without adversely affecting product quality. Additionally, high temperatures favors the hydrogenation of polyenes over monoenes, leading to low amounts of saturated fats. MCRs were shown to operator at high temperatures and: (1) capture high reaction rates, (2) minimize saturated fats, and (3) minimize trans-fats. We also demonstrated lactic acid conversion into commodity chemicals using MCRs. Our results show that all MCR experiments had faster reaction rate than all of our controls, indicating that MCRs have high levels of hydrogen coverage at the catalyst. It was also demonstrated that changing reaction conditions (pressure and temperature) changed the product selectivities; giving the potential for MCRs to manipulate product selectivity.