|dc.description.abstract||Epoxy resins (ERs) are one of the most versatile thermoset polymers which are widely used in variety of applications from electrical and electronics (insulation and circuit boards) to construction and civil engineering works (coating of concrete floors), automotive (structural glue), and aircraft (carbon fiber reinforced composites) industries due to their superior properties such as toughness, mechanical strength, flexibility, chemical and thermal resistance and adhesion. The global epoxy production is projected to be 3 million tons by 2017 with a market size of USD 21.5 billion. Today epoxy and other plastic production processes rely on petroleum-based chemicals. Current petroleum use is large and creates significant problems such as air pollution, promotion of the greenhouse effect, and depletion of petroleum reserves. Therefore, environmental concerns, as well as instability in the petrochemical market, have recently increased in using more sustainable and renewable chemical resources.
Bio-oil is a liquefied biomass produced by decomposition of lignocellulosic biomass through thermomechanical liquefaction processes, and it could be used as a biopolyol to synthesize bio-based epoxy resin due to its high hydroxyl number (OHN). The main hypothesis was that the reaction behavior and the consequent physical, mechanical, and thermal properties of resulting epoxy resin depend on the interaction between OH group availability in bio-oil and epoxy group in epichlorohydrin Therefore, the objectives of this dissertation were to (i) produce a high quality bio-oil via thermomechanical liquefaction of lignocellulosic biomass, (ii) investigate the source and variation of hydroxyl (OH) groups in bio-oil, and (iii) utilize the bio-oil as an alternative to petroleum-based polyols for the synthesis of bio-based epoxy resin.
Bio-oils from different thermomechanical liquefaction processes, organic solvent liquefaction (OSL) and hydrothermal liquefaction (HTL), were studied. In Chapters 3 and 4, OSL of loblolly pine in ethylene glycol (EG) using atmospheric reactor and Parr® reactor at different liquefaction time and temperature was studied, respectively. It was found that bio-oil from OSL process (OSL-bio-oil) had a high hydroxyl number (11.3 – 26.4 mmol/g); however, gas chromatography–mass spectrometry (GC-MS) results revealed that unreacted liquefying solvent (EG) left in the OSL-bio-oil was the major source of the high OHN, and accounted for the 70 – 95% of the total OHN. 31P-NMR analysis of OSL-bio-oils showed that the majority of OH groups was aliphatic type. The focus of Chapter 5 was on the HTL process of loblolly pine. HTL was performed in water and water/ethanol medium at different temperatures. For the first time, 31P-NMR and 19F-NMR were employed to understand the effect of ethanol on the formation bio-oil. It was found that addition of ethanol significantly increased the yield of bio-oil (from 25 to 68 wt.%) and decreased the residue yield (from 39 to 2 wt.%), increased the hydroxyl concentration (from 3.91 to 7.42 mmol/g), and decreased the carbonyl concentration (from 3.46 to 2.53 mmol/g). Analysis showed that more aliphatic and less phenolic type OH was obtained when ethanol was used as a co-solvent in HTL process.
Utilization of bio-oil in ER systems was studied in Chapters 6 and 7. A commercial epoxy resin (EPON828) was cured using a pyrolysis bio-oil (Chapter 6). The resulting cured ER exhibited superior thermal and mechanical properties. The glass transition temperature (Tg), crosslink density, and storage modulus at room temperature was found to be 120 ᵒC, 1891 mol/m3, and 2.55 GPa, respectively, using dynamic mechanical analysis (DMA). In the last chapter, Chapter 7, synthesis and characterization of a novel bio-oil-based self-curing epoxy resin was presented. For the first time, HTL-bio-oil was utilized as an alternative to bisphenol-A (BPA) in epoxy synthesis. It was found that the resulting bio-oil-based epoxy resin could be cured without using a curing agent. Differential Scanning Calorimetry (DSC) analysis proved the self-curing phenomena, and the activation energy for curing was calculated to be 95 – 98 kJ/mol, using Kissinger model of kinetic analysis. Self-curing phenomena of bio-oil-based epoxy resin was attributed to etherification reaction based on the evidences obtained from Fourier Transform Infrared Spectroscopy (FT-IR) and curing kinetic analysis. Tg, crosslinking density, and the storage modulus of self-cured epoxy resin were obtained from DMA to be 96 ᵒC, 58.7 mol/m3, and 845 MPa, respectively.||en_US