This dissertation includes two research topics. This first topic focuses on fundamental studies of monolignols and lignin, including polymerization and degradation. The second part reports a polymeric material that was crosslinked but can be reprocessed. In order to understand lignin from a molecular level and promote biopolymer conversion, we investigated the dehydrogenative copolymerization and degradation of two monolignols: caffeyl (C) alcohol and p-coumaryl (H) alcohol. The copolymerization and degradation were monitored by a quartz crystal microbalance with dissipation (QCM-D). Atomic force microscopy (AFM) was applied to investigate the topologies of the copolymer and degraded films. Horseradish peroxidase (HRP) was used as the enzyme for the dehydrogenative polymerization of monolignols and chelator-mediated Fenton chemistry was used to degrade the lignin. With constant monolignol concentration, we found that as the fraction of H in the polymerization feed increased, the amount of lignin formed increased, and the films became more rigid. For the degradation process of the resultant lignins, the presence of more C-monolignol during polymerization facilitated greater degradation. This work demonstrated the chemical factors that influenced the physical properties of lignin and lignin degradation, which could impact biofuel production. We further investigated the surface-initiated dehydrogenative polymerization of a new monolignol 5-hydroxyconiferyl (5H) alcohol using a QCM-D. HRP was immobilized on gold sensors. Various experimental conditions were studied. The dehydrogenative polymerization of 5H-monolignol was influenced by the concentration of monolignols and temperature, but was not affected by the hydrogen peroxide concentration, which was different from other monolignols. We also compared the polymerization kinetics of 5H-monolignol and the topology of the resulting lignin thin films with other monolignols. Furthermore, we utilized enzymatic and chemical degradation methods to treat the 5H-lignin. The 5H-lignin film was degraded thoroughly via a chelator-mediated Fenton reaction. This study provided a comprehensive understanding of 5H-monolignol polymerization and degradation and could be used as a reference for the exploration of the applications of the 5H-monolignol. In this dissertation, a separate study involved a vitrimer. It was a crosslinked polymer, but could be reprocessed and reshaped. The new vitrimer was based on poly (methyl methacrylate-co-hydroxymethyl methacrylate). Aromatic disulfides that underwent a dynamic exchange reaction were incorporated as crosslinkers. The structure of the material was identified by proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared spectroscopy (FTIR). Thermal properties and mechanical properties were studied through thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and Instron tests. Furthermore, the chemical resistance was explored. Notably, that new material exhibited comparable mechanical performance for three cycles when reprocessed via a hot press to reprocess. / Doctor of Philosophy / Lignin is a complex phenylpropanoid polymer and is one of the most abundant biopolymers in nature. Conversion of lignin into biofuels or other fine chemicals has drawn significant attention in recent years. Understanding molecular details of lignin formation and degradation is of fundamental importance for the biorefinery. Although a number of studies have improved our knowledge about lignin, many important aspects remain unknown. Lignin arises from dehydrogenative polymerization of three types of monolignols, named p-coumaryl (H), coniferyl (G), and sinapyl (S) alcohols. Recently, a new monolignol, caffeyl (C) alcohol, has been found. In this work, the surface-initiated copolymerization of C-monolignol and H-monolignol was conducted through an in vitro synthesis. Furthermore, chelator-mediated Fenton reactions were applied to degrade the resulting lignin. The effect of C-lignin incorporation on degradation was studied. It was found that, when more C-lignin was incorporated, the percentage of degradation was larger. These findings are likely to guide the conversion of lignocellulosic biomass into value-added products. A new monolignol, 5-hydroxyconiferyl (5H) alcohol, was investigated in this dissertation. The surface-initiated dehydrogenative polymerization of 5H was conducted under various experimental conditions, including different temperature, monomer concentration, and hydrogen peroxide concentration. Furthermore, degradation by enzymatic and non-enzymatic methods were studied. It was found that the 5H-lignin was recalcitrant to enzyme, but can be degraded by a non-enzymatic procedure. The synthesis and degradation were monitored by a quartz crystal microbalance with dissipation (QCM-D), which is a label-free method and can provide real-time data. Thermosets are the materials that are chosen for many applications due to their structural stability and mechanical properties. However, due to their permanent crosslinkages, they cannot be reprocessed or recycled. In this dissertation, a new crosslinked polymer material called a vitrimer was reported. The material was developed based upon poly (methyl methacrylate) (PMMA) and aromatic disulfide linkages, which are exchangeable chemical bonds. The exchange reaction occurs very quickly at elevated temperature. As a result, the material can be easily reprocessed and also exhibited chemical stability and mechanical properties similar to conventional thermosets.

Anaerobic bioreactor landfills are the landfills with an increased moisture content in order to achieve a better biodegradation. Many Bioreactor landfills accept outside liquid wastes to achieve a higher moisture content . But the effect of these wastes on the degradation of landfill components is not known. In this study, the effect of sugar waste, surfactant waste and paint waste on the degradation of landfill components was investigated. Sugar waste, surfactant waste and paint wastes in different concentrations were added to the combination of paper, cardboard, office paper and plastic with a total moisture content of 70%. The samples were incubated, sampled and analytical parameters analyzed. Sugar waste having a COD of 250,000 mg/L in a concentration of even 5% of the total weight was found inhibitive due to a drop in pH and accumulation of volatile fatty acids. Reactors with surfactant concentrations ranging from 50 mg/L to 500 mg/L showed that a higher concentration of 500 mg/L or above may be inhibitive in nature and the inhibition increases with increase in the concentration of surfactant. However, paint waste with a concentration of even 7.5% highly inhibited the degradation in the reactors. This could possibly be because of some toxicity. / Master of Science

Switchgrass (Panicum virgatum L.) is a candidate bioenergy crop. Somatic embryogenic (SE) calli are used for genetic transformation in switchgrass. A superior switchgrass line, HR8, was developed using recurrent tissue culture selection from cv. Alamo. HR8 SE calli were genetically transformable using Agrobacterium at an efficiency of ~12%. We used HR8 somatic embryogenic calli for genetic improvement of switchgrass. The lignin content of feedstock has been proposed as one key trait impacting biofuel production. 4-Coumarate: Coenzyme A ligase (4CL) is one of the key enzymes involved in the monolignol biosynthetic pathway. Two homologous 4CL genes, Pv4CL1 and Pv4CL2, were identified in switchgrass. Gene expression patterns and enzymatic activity assays suggested that Pv4CL1 is involved in monolignol biosynthesis. Stable transgenic plants were obtained with Pv4CL1 down-regulated. RNA interference of Pv4CL1 reduced extractable 4CL activity by 80%, leading to a reduction in lignin content with decreased guaiacyl unit composition. The transgenic plants had uncompromised biomass yield. After dilute acid pretreatment, the low lignin transgenic biomass had significantly increased cellulose hydrolysis (saccharification) efficiency for biofuel production. Erect leaf is a desirable trait to adjust the overall plant architecture to perceive more solar energy and thereby to increase the plant biomass production in a field population. We overexpressed an Arabidopsis NAC transcriptional factor gene, LONG VEGETATIVE PHASE ONE (AtLOV1), in switchgrass. Surprisingly, AtLOV1 induced smaller leaf angle by changing morphologies of epidermal cells in the leaf collar region, affecting lignin content and monolignol composition, and also causing delayed flowering time in switchgrass. Global gene-expression analysis of AtLOV1 transgenic plants demonstrated an array of genes has altered expressions. Potential downstream genes involved in the pleiotropic phenotypic traits of the transgenic plants are discussed. / Ph. D.

Glycerol thermal processing (GTP) is studied as a novel biomass pretreatment method in this research with the purposes to facilitate biopolymer fractionation and biomass saccharification. This approach is performed by treating sweet gum particles on polymer processing equipment at high temperatures and short times in the presence of anhydrous glycerol. Nine severity conditions are studied to assess the impact of time and temperature during the processing on biopolymer structure and conversion. The GTP pretreatment results in the disruption of cell wall networks by increasing the removal of side-chain sugars and lignin-carbohydrate linkages based on severity conditions. After pretreatment, 41% of the lignin and 68% of the xylan is recovered in a dry powdered form by subsequent extractions without additional catalysts, leaving a relatively pure cellulose fraction, 84% glucan, as found in chemical pulps. Lignin structural analysis indicated GTP processing resulted in extensive degradation of B-aryl ether bonds through the C-y elimination, followed by abundant phenolic hydroxyl liberation. At the same time, condensation occurred in the GTP lignin, providing relatively high molecular weight, near to that of the enzymatic mild acidolysis lignin. Better thermal stability was observed for this GTP lignin. In addition to lignin, xylan was successfully isolated as another polymer stream after GTP pretreatment. The recovered water insoluble xylan (WIX) was predominant alkali soluble fraction with a maximum purity of 84% and comparable molecular weight to xylan isolated from non-pretreated fibers. Additionally, the narrow molecular weight distribution of recovered WIX, was arisen from the pre-extraction of low molecular weight water-soluble xylan. Additionally, a 20-fold increase of the ultimate enzymatic saccharification for GTP pretreated biomass was observed even with significant amounts of lignin and xylan remaining on the non-extracted fiber. The shear and heat processing caused a disintegrated cell wall structure with formation of biomass debris and release of cellulose fibrils, enhancing surface area and most likely porosity. These structural changes were responsible for the improved biomass digestibility. Additionally, no significant inhibitory compounds for saccharification are produced during GTP processing, even at high temperatures. While lignin extraction did not promote improvement in hydrolysis rates, further xylan extraction greatly increases the initial enzymatic hydrolysis rate and final level of saccharification. The serial of studies fully demonstrate glycerol thermal processing as a novel pretreatment method to enhance biomass saccharification for biofuel production, as well as facilitate biopolymer fractionation. Moreover, the study shows the impact of thermally introduced structural changes to wood biopolymers when heated in anhydrous environments in the presence of hydrogen bonding solvent. / Ph. D.

Guaiacol and hydroxypropyl-guaiacol were taken as model compounds for lignins and hydroxypropyl lignins to study their vinylation and copolymerization behaviors. Lignin model compounds and lignin were subjected to reaction with isocyanatoethyl methacrylate (IEM) using dibutyltin dilaurate as catalyst. The acrylate derivatives were characterized by elemental analysis, UV, IR, ¹H-NMR, and ¹³C-NMR spectroscopy. The acrylated lignin model compounds, guaiacol-IEM urethane (GIU) and hydroxypropyl-guaiacol-IEM urethane (HPGIU), were copolymerized with methyl methacrylate (MMA) and styrene (St) through free radical mechanism. Solution copolymerizations in 1,2-dichloroethane: ethanol were initiated by benzoyl peroxide. The monomer reactivity ratios were investigated for these copolymerization combinations. The copolymer compositions were analyzed by UV for GIU-co-MMA and HPGIU-co-MMA, while methoxyl content determination by HI-GC was used to determine compositions of styrene-based copolymers. The copolymers were characterized by gel permeation chromatography (GPC), and by IR and NMR spectroscopy. The reactivity ratios were computed by use of the Fineman-Ross linearization method, by the KelenTudos equation and by the Yezrielev-Brokhina-Roskin (YBR) numerical method. A comprehensive analysis with respect to the methods used to derive the ratios has shown that the Kelen-Tudos method and the YBR method produce diagnostic reactivity ratios. A great copolymerization tendency of lignins and hydroxypropylated lignins is predicted from the reactivity ratios of the lignin models. A statistical treatment of the model reactivity ratios lead to prediction for chain sequence length distribution of the copolymers formed. Hydroxybutyl lignin IEM urethanes (HBLIU's) were copolymerized with a vinyl-terminated poly(butadiene-acrylonitrile) macromer and MMA to study the copolymerization behaviors of macromolecular lignin acrylate derivatives. The crosslinked films with desired properties were cast from methylene chloride, with benzoyl peroxide as an initiator. The copolymerized network polymers were characterized by sol fraction measurements, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and by scanning electron microscopy (SEM). The influences of vinyl content in lignin acrylate derivatives and the ratio of lignin derivatives to vinyl monomer or macromer were studied with respect to structure-property relationship in the copolymers. / M.S.

Hydroxyakyl lignin derivatives were reacted with polymeric methylene diphenyl diisocyanate (PMDI) and hexamethoxy-methyl-melamine (HMMM) to form polyurethane and polyether wood adhesives respectively. Adhesive performance in shear block tests indicated: (a) that the combination of lignin and PHDI reduced the adhesive strength shown by neat PMDI. The HMMM failed to produce an acceptable wood adhesive in the absence of lignin, requiring 50-60% lignin derivative co-substrate for peak performance; (b) adhesive performance was related to molecular weight, if an organic solvent was the carrier, or solubility if the formulation was emulsified; (c) adhesive performance for the lignin based adhesives was better than a urea formaldehyde reference. Structure property relationships were determined by correlating data obtained by the analysis of (in vivo) cured adhesive films and (in vitro) adhesive strength data resulting from shear block testing. The results indicated that: (a) glass transition temperatures of the in vivo cured adhesives were inversely related to the strength of the adhesives cured in vitro; (b) variations in infrared analysis of the in vivo cured adhesives were used to determine the levels of products from the cross linking reaction. In vitro adhesive strength was directly related to the level of reaction products determined to be present in the in vivo wood adhesives; (c) the relationships between the analysis of in vivo and in vitro cured adhesives indicated that the lignin component may act as a soft segment blocks or domains in a more rigid polymer matrix. Particle board was produced with the lignin adhesives with: (a) properties equal to those produced with commercial OF resins; (b) spray application greatly reducing the effects of carrier compatibility; (c) none of the lignin based adhesives were water resistant. / Master of Science

A lignin epoxide resin was synthesized and characterized. The epoxidation reaction was studied by reacting hydroxypropylated guaiacol (a lignin-like model compound) and epichlorohydrin using a catalyst system of potassium hydroxide and a phase transfer catalyst in toluene. The parameters studied were different epichlorohydrin level and temperature. The reaction was followed by HPLC and the structure of the product was identified with IR, ¹H and ¹³C NMR spectroscopy. The lignin epoxide was synthesized by reacting hydroxyalkylated (hydroxypropyl and hydroxybutyl) lignin with epichlorohydrin using the reaction conditions defined by the model compound studies. The reaction was studied at different epichlorohydrin level and at elevated and room temperature. The epoxy content of the lignin epoxide was determined by titration with HBr and its structure was identified with IR, ¹H and ¹³C NMR spectroscopy. Lignin epoxides were cured by crosslinking with a diamine and with phthalic anhydride. An amine-terminated rubber was added as toughening agent. Sol fraction and swelling behavior, stress-strain behavior and dynamic mechanical behavior of the cured lignin epoxides were studied in relation to cure conditions. / M.S.

Lightweight design is an essential part of lowering CO2 emission, which is one of the mostimportant challenges that the automotive industry is facing today. Carbon fiber reinforcedplastics offer an enormous potential for replacing heavier structural materials like steel andaluminum, however due to their high cost and scarcity, carbon fibers are not a very feasibleoption to use in high volume production applications. It is thought that the introduction of arenewable, low-cost raw material, like lignin, as the carbon fiber precursor would not onlylower the cost but also increase supply compared to its PAN based counterparts. Properties ofthe fiber/matrix interface play a crucial role in governing the overall performance of thecomposite material. Good adhesion between the fiber and the matrix must be ensured in orderto maximize performance. In this study, plasma treatment of softwood lignin based carbonfibers was performed in order to increase the interfacial adhesion between the fiber and thematrix by incorporating functional groups onto the fiber surface. Plasma treatment time,plasma power, chamber pressure and plasma gas type were varied in order to investigate theireffects on the functionalization of the surface by various visual, chemical and mechanicalcharacterization methods. Observations with optical and scanning electron microscopiesshowed the cleaning effects of plasma treatment on the fiber surface by removal of flakes andsmoothing of the fiber surface. The smoothing effect of plasma treatment was later supportedby the subtle increase in the tensile strength of the plasma treated fibers and this wasattributed to the elimination of crack initiators on the surface by a so-called “polishing” effect.Contact angle measurements of the lignin based fibers showed that all plasma gases achieve acertain level of decrease in the contact angle values thus lowering the surface tension. X-rayphotoelectron spectroscopy (XPS) results were analyzed using a design of experimentssoftware with a PLS fit. For the highest amount of surface functionality to be achieved, it wasconcluded that oxygen plasma should be used with high plasma power, low pressure and ahigh treatment time. Detection of Na and S elements combined with unusually lowmechanical properties for all lignin based carbon fibers indicated insufficient carbonization ormolecular orientation for the softwood lignin based carbon fibers used in this study. / GreenLight

The effect of high organic liquid wastes on the overall performance of anaerobic bioreactor landfills is not known. In this study three different liquid wastes were added to mix of office paper, newspaper, cardboard and plastic in 3 different concentrations under anaerobic conditions to determine their effect on degradation of organics. The addition of buffer chemicals was found to improve degradation compared to data from an earlier study done without the addition of initial buffering. Paint waste with a COD 237,500 mg/L added at a concentration of 10% did not show any negative effect on the overall performance. The distillation waste with a COD of 812,500 mg/L added at 5% and higher concentration resulted in accumulation of volatile fatty acids and strong inhibition. The surfactant waste added at concentrations up to 1500 mg/L showed some inhibition but the overall performance was good. The surfactant waste also appeared to improve lignin degradation. / Master of Science

Hydroxypropyl lignins (HPLs) from several sources were reacted with propylene oxide to produce chain-extended ) hydroxypropyl lignin (CEHPL) copolymers with molar substitutions (MS) between 1 and 7 propylene oxide units. Isolated copolymers were characterized with respect to their chemical composition, molecular weight and thermal properties. These techniques confirmed the presence of a copolymer with between 20 and 67% lignin. Glass transition temperatures (Tgs) of the CEPHLs followed the behavior predicted by the Gordon-Taylor equation. Properties of the CEHPLs were independent of the original lignin source. The CEHPL copolymers were incorporated into lignin polyurethane networks (LPUs). The LPUs contained 17 to 43% lignin and showed a single Tg. Both the Tg and the Youngs modulus (MOE) of the LPUs were strongly correlated to the lignin content and type of diisocyanate used to prepare the network. Swelling studies indicated that the LPUs prepared from CEHPLs with a high MS (5-7) were not highly crosslinked networks. The LPU properties also appeared to be independent of the lignin source. In another set of experiments a HPL was separated into five fractions (F-HPLs) with molecular weights (MWs) between 1.5 and 10x10³ daltons. The Tg of the F-HPLs was correlated to molecular weight by the Fox-Flory equation. The fractionated HPLs were incorporated into polyurethane networks. The Tgs of these networks were related to the MW of the F-HPL. Swelling studies indicated that low molecular weight monofunctional fragments limited network formation. The LPUs were also used as one component in LPU/polymethyl methacrylate (PMA) interpenetrating polymer networks (IPNs). These IPNs varied in their LPU/PMMA composition and the presence of crosslinking. Dynamic mechanical and thermal analysis showed two phases in all of the IPNs. Mechanical properties were dependent on the IPN composition and phase crosslinking. For IPNs with a crosslinked LPU phase, the MOE values indicated the presence of dual phase continuity. A second series of IPNs was prepared to investigate the effects of lignin content on IPN properties. Phase separation appeared to be related to the lignin content. Mechanical properties were related to lignin content and not the phase behavior. / Ph. D.