Renewable materials have been put into the spotlight as the demand for environmentally responsible feedstocks grows yearly. Lignin, an abundant and renewable aromatic polymer, which can source a diverse cast of derivative structures, has yet to rise to the potential it possesses as a material in high technological applications. The expansion of studies and growing interest in its versatility has brought forth materials such as lignin nanoparticles, coatings, films, second generation alcohols, phenolic building blocks for drug synthesis, and many others. Among the many valorization methods thus far pursued, photochemical methods have received relatively low representation, incurring several challenges stemming from less desirable interactions of lignin as a substrate directly with light. As the search for clean, low-emissive processes with high scale-up potential for lignin valorization continued, advances and studies on the benefits and challenges on the use of photochemistry with this class of compounds became the focus of this work. This thesis will primarily aim to highlight our efforts to find photocatalytic materials and systems to achieve lignin valorization, discuss its limitations and benefits, and provide a pathway towards potential applications of these reactions. Our core values were to find conditions that worked well, but also translating that success into systems that could be greener and less dangerous or environmentally impactful. We can report to have achieved single-product yields of over 2% in protolignin valorization reactions using Pd and Au based nanoparticles, supported on niobium-based materials. We have also reached up to 2% yields in visible-light reactions using CdSe quantum dots. While literature reports tend to overwhelmingly focus on lignin models, we have kept ours on real lignin, which while more complex and challenging, does present more relevant results in the long run for this field. These results, in addition to molecular model valorization experiments, present a promising prospect for the application of photocatalysis in lignin valorization for the future.

This thesis delves into exploring lignin's potential as a sustainable substitute for bitumen within asphalt mixtures, with the overarching goal of reducing the environmental footprint of the asphalt industry. By conducting a meticulous blend of literature reviews and comprehensive laboratory experiments, the research examines the performance and ecological sustainability of lignin-infused asphalt mixtures. The primary objective is to assess lignin's efficacy as a binding agent in asphalt pavements and its potential to create more sustainable and environmentally friendly road materials. Key inquiries encompass comparative analyses of lignin-based asphalt mixtures against conventional bitumen-based counterparts, alongside an exploration of the environmental advantages and challenges associated with lignin utilization. Through laboratory assessments and analyses, including examinations of tensile strength, permanent deformation and air voids, the study evaluates the performance and sustainability of lignin-infused mixtures. Notable findings indicate significant environmental benefits, such as reduced CO2 emissions and enhanced water resistance. However, despite promising results meeting Swedish Transport Administration requirements, further optimization is essential to enhance competitiveness.

Lignans are a structurally diverse group of phenylpropanoid metabolites widely distributed throughout the plant kingdom. Their biogenetic pathway has generally been viewed to occur via coupling of two monomeric moieties, with subsequent modifications as required to afford the various Iignan skeleton structures. Podophyllotoxin is a tetrahydronaphthalene lignan found in Podophyllum species, and its derivative etoposide is widely used medicinally for skin cancer and venereal warts (Condyloma acuminatum). In this investigation, the biogenetic pathway to podophyllotoxin was investigated using whole plants, as well as callus and rhizome tissue. In contrast to previous claims in the literature, no active metabolism leading to podophyllotoxin formation in vivo in callus culture was observed. Similar findings were also noted for rhizome tissue. With whole plants, experiments investigating podophyllotoxin formation have been limited to employing lignan substrates, labeled specifically with carbon-14 and tritium. No stable isotopes, e.g carbon-13 or deuterium, have been used because of low incorporations. / Master of Science

Lignin degradation, is quite common in nature and is an important link in the natural carbon cycle. A large variety of microorganisms are know to degrade lignin in nature as well as in contrived fermentation systems. White-rot and soft-rot fungi, as well as Actinomycetes, are apparently the most active lignin degraders in nature. The large, cross-linked, polymeric structure of the lignin macromolecule makes its direct uptake, during the initial stages of its degradation, by microbial cells improbable. Moreover, the fact that the lignin macromolecule is composed of different monomeric units linked by a large variety of non-hydrolyzable intermonomeric bonds precludes hydrolytic cleavage of the biopolymer. Despite the fact that many extracellular and membrane-bound enzymes have been suspected in the initial breakdown of lignin, such activities have not yet been found. A close review of the literature indicates that the initial breakdown of the lignin macromolecule may be nonenzymatic. In addition, the degradation of the lignin polymer appears to follow an exo-degradation mechanism. That is, many lignin degrading microorganisms are apparently incapable of splitting the lignin molecule into intermediate molecular weight polyphenolic moieties which are further degraded; instead, they attack the periphery of the macromolecule. The possible involvement of reduced oxygen species produced by white-rot fungi in the initial breakdown of the lignin macromolecule, during its biodegradation, was investigated. Using Coriolus versicolor as a representative of white-rot fungi, I demonstrated that C. versicolor exports superoxide radical and hydrogen peroxide during lignin degradation, into the lignolytic medium. Results presented in this study indicate that a correlation between the concentration of extracellular superoxide radical in the medium and the extent of lignin degradation may exist. Moreover, I have shown that superoxide radical is produced in the cell membrane, and not the organism's mitochondria. This precludes the possibility that such reduced oxygen species are produced as a result of normal respiration by the organism. An investigation of the effects of aeration and agitation indicated that agitation has a detrimental effect on the extent of lignin degradation. On the other hand, increased oxygen tension in lignolytic cultures appeared to enhance the extent of lignin degradation. Another interesting finding was the fact that conditions leading to the formation of reproductive fruits in the lignolytic microorganism favored the degradation of the lignin fraction in lignocellulosic materials. A comparative study of two different fennentation schemes, designed to degrade lignin in 1ignocellu1osic materials on a large scale, indicated that solid state fermentation of such materials led to greater lignin degradation. Fluidized bed fermentations, on the other hand, appeared to favor the degradation of the carbohydrates rather than the lignin fraction of lignocellulosic materials. Studies of the biodegradation of monomeric lignin model compounds do not shed light on the initial step(s) involved in the breakdown of the lignin polymer. Such studies assume that microbial breakdown of lignin model compounds is similar to microbial breakdown of lignin an assumption that may not be correct. It is true that degradation of monomeric lignin model compounds can conceivably elucidate the mode of degradation of low molecular weight moieties resulting from initial breakdown of the lignin macromolecule. However, the chemical identities of these low molecular weight intermediates are not yet known. The efficacy of studies using aromatic, monomeric lignin model compounds in attempts to identify intracellular pathways for metabolism of lignin depends on the assumption that lignin breakdown products are indeed mononuclear phenolic materials. Careful analysis of soluble and insoluble residual lignin resulting from lignin fermentations is a critical step in assessing the lignolytic ability of microorganisms. Furthermore, such analyses are essential in understanding the steps involved in lignin metabolism by microorganisms. To date the methods for residual lignin analyses are complex, time consuming and error prone. There is an urgent need to develop a quick and simple method for residual lignin analysis that will yield accurate and reproducible results capable of elucidating structural changes in residual, biodegraded lignin. The development of such an analysis technique will undoubtedly lead to a better understanding of the complex problem of lignin biodegration. / Ph. D.

Non-ionic surfactants are known to enhance the biochemical conversion of lignocellulosic (LC) biomass to bioethanol. Their mechanisms of action, however, are incompletely understood. This research was conducted to elucidate the effects of the non-ionic surfactant Tween 80 on the enzymatic hydrolysis of cellulose and LC substrates. Model cellulose substrates were prepared from cellulose nanocrystals (CNCs) obtained by sulfuric acid hydrolysis of wood pulp. Two methods were developed for the removal of the sulfate groups on the CNCs, resulting from the use of sulfuric acid in their preparation. The effect of sulfate groups, which may be introduced into LC biomass during pretreatment with sulfuric acid, on the enzymatic hydrolysis of cellulose was studied with model cellulose substrates prepared from CNCs with different sulfate group densities. Adsorption of cellulases onto sulfated substrates increased with increasing sulfate group density but their rate of hydrolysis decreased. The decrease indicated an inhibitory effect of sulfate groups on the enzymatic hydrolysis of cellulose, possibly due to non-productive binding of the cellulases onto the substrates through electrostatic interactions instead of their cellulose binding domains. The effect of Tween 80 on the adsorption of cellulases onto lignin, often present as residual lignin in pretreated biomass, was studied with model lignin substrates, prepared from kraft lignin, organosolv lignin, and milled wood lignin. Cellulases appeared to adsorb onto the lignin substrates via both hydrophobic and polar interactions. Tween 80 molecules on the lignin substrates seemed to hinder cellulase adsorption via hydrophobic interactions and reduced the adsorption rate. Finally, the effects of lignin and Tween 80 on the enzymatic hydrolysis of cellulose and LC substrates were studied. Lignin hindered both the adsorption of cellulases onto the substrates and the enzymatic hydrolysis of the substrates. Tween 80 was found to form surfactant–protein complexes with cellulases in solution without compromising cellulase activity. Either substrate-adsorbed or in solution, Tween 80 had no effect on the hydrolysis of cellulose by cellulases. Substrate-adsorbed Tween 80 increased the apparent enzymatic hydrolysis rates of LC substrates but the ability of Tween 80 to increase their apparent hydrolysis rate depended strongly on their structural properties and the chemical properties of the lignin. Hence, Tween 80 may be able to mitigate the inhibitory effect of lignin on the enzymatic hydrolysis of pretreated biomass. / Ph. D.

The study of lignin with the aim of correlating data, which may lead to a greeter utilization of this wood waste product, has been the subject of investigations since 1838. Previous investigations by Othmer, Harris, Sherrard and others have indicated that chlorinated lignin had potential value as a plastic. The purpose of this investigation was to study the chlorination reaction of lignin obtained from the black liquors of the sulfate process of paper manufacture. Results of preliminary experimental work indicated that the optimum method of chlorinating lignin was by suspending or dissolving the lignin in methyl alcohol. The sulfate lignin was chlorinated in two liter wolff flask which was equipped with a motor driven stirrer, and the chlorine flow was measured by a calibrated U-tube differential gage. The flask was charged with the alcohol-lignin mixture and chlorinated from one to seven hours. The rates of chlorine flow for the tests were 0.472, 0.85 and 1.084 gm. Cl₂/min at temperatures of 25 and 65ºC. The reactant gases were passed through a condenser to return the vaporized alcohol to the reaction flask and then into a 3 normal sodium hydroxide solution to react the excess chlorine gas. Samples of the reaction gas, which were analyzed for chlorine, were collected in a 1.5 normal sodium hydroxide solution at 10 minutes intervals. With this information the progress of the reaction could be plotted and the rate of chlorination measured. The chlorination of a suspension of lignin in methyl alcohol in a ratio of l to 20 was possible at 25°C. The critical temperature above which the lignin would not stay in solution was 43°C. The reaction was exothermic and produced an orange colored product containing 25 per cent chlorine. Increasing the rate of chlorine flow from 0.85 to 1.084gm. Cl₂/min. increased the chlorine consumption from 0.74 to 0.833 gm Cl₂/min. The chlorination of lignin dissolved in methyl alcohol produced two chlorinated products. One was precipitated as an orange red powder from solution during the chlorination reaction, and had a chlorine percentage as high as 29 per cent. The other lignin remained dissolved in the alcohol solution. When precipitated from solution by ice water this chloro-lignin was a light yellow powder with a chlorine percentage as high as 28.0 per cent. Increasing the rate or chlorine flow trom 0.472 to 1.084 gm Cl₂/min. during tests at 25°C resulted in increasing the rate of chlorination from 0.454 to 0.935gm Cl₂/min. Adding ferric chloride, as a catalyst, increased the chlorine consumption from 0.768 to 0.967 gm Cl₂/min. Raising the reaction temperature from 25 to 65°C decreased the chlorine consumption trom 0.935 to 0.768 gm. Cl₂/min. The chlorinated product showed definite bonding value when mixed with sawdust and pressed at a temperature or 112°C and pressures from 1000 to 5000 lb/in². The percentage lignin in the samples was varied from 5 to 60 per cent. The lignin-sawdust samples were light yellow in color and firmly bonded and water resistant. / Master of Science

Star-like macromers were prepared from hydroxypropyl lignin by reaction with propylene oxide. The average number of arms per macromer was controlled by partial capping with diethylsulfate, and the average arm length by the degree of chain extension with propylene oxide. Six methods of analysis were applied for characterizing of the star-like macromers: total hydroxyl (by titration), vapor pressure osmometry, hydriotic acid/gas chromatography, ultraviolet spectroscopy, proton-nuclear magnetic resonance spectroscopy and thermal analysis. Number average molecular weights were measured by vapor pressure osmometry. Total hydroxyl content was determined after acetylation by potentiometric titration. Based on HPL molecular weight and hydroxyl content it was estimated that the average HPL molecule generates a star-like structure ("macromer”) with an average of 6 arms. Hydriodic acid/gas chromatography proved to be the most appropriate method for the quantitative determination of the degree of capping. Based on this technique it was possible to classify star-like macromers with between two and six radiating arms per average molecule. The same method could also be applied for the determination of arm length. Two different propoxylation reaction conditions produced macromers with an average of 2.5 and 3.5 propylene oxide units per arm. Ultraviolet spectroscopy was the simplest and most rapid method of analysis investigated. The decrease in copolymer absorptivity coefficient was found to be related to an increase in non-UV absorbing mass after capping and/or chain extension. Results indicated that H-NMR spectroscopy is an adequate method of analysis for star-like macromers. Macromer arm length was calculated from the ratio of signals representing the methyl group of acetyl (i.e. hydroxyl) and propoxyl functionality. Two levels of propoxylation produced star-like macromers with 2.2 - 2.5 and 3.9 - 4.0 propylene oxide units per arm. Thermal analysis by DMTA of lignin derivative-containing blends with ethylene-vinyl acetate copolymer indicated that the glass transition behavior of the star-like macromers follows the Gordon-Taylor relationship for copolymers. Although variable, the results revealed a consistent decrease in T_g as a consequence of an increase of propylene oxide chain length. / Master of Science

In nature, it has long been assumed that p-hydroxycinnamyl alcohols occur exclusively in their trans (E) stereoisomeric form. However, in beech bark (Fagus grandifolia Ehrh.) only the corresponding cis (Z) monomers were found. Experiments with beech bark and 2-¹⁴C-labelled E ferulic acid, E coniferaldehyde, and E coniferyl alcohol revealed that these compounds were efficiently incorporated into both E and Z isomers of coniferyl alcohol. On the other hand, low incorporation of 2-¹⁴C-labelled Z ferulic acid indicated that this isomer was not a preferred substrate. Our results suggest that Z coniferyl alcohol is produced by E + Z isomerization of the corresponding E isomer. Experimental evidence excluded the possibility of this unusual isomerization occurring by either chemical or photochemical means; instead it is concluded that isomerization is enzymatically mediated by a novel isomerase. / M.S.

Lignin based polyurethane films were synthesized by solution casting from hydroxypropyl lignins and diisocyanates. Kraft and steam explosion lignin, hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI), were used for the study. It was found necessary to use stoichiometric excess amounts of diisocyanates in the synthesis of the thermosetting polyurethanes. The investigation primarily addresses the effect of synthesis variables and soft segment incorporation on the thermal and mechanical properties. The first part of the study examined the effect of lignin type, of diisocyanate type and of composition (NCO/OH ratio). Stoichiometric excess was found to cause a significant increase in the glass transition temperature. Use of HDI resulted in films with lower moduli as compared to TDI. NCO/OH stoichiometry variation had no noticeable effect on modulus or tensile strength. In the second part of the study involving incorporation of soft segments, four polyethylene glycols were used. No soft segment phase in the network was detectable by differential scanning calorimetry or dynamic mechanical analysis. The glass transition temperature of lignin phase dropped by as much as 70°C for HDI and 115°C for TDI based polyurethanes with inclusion of glycols up to 25% of the polyol weight. The swelling tendencies showed an expected increase with glycol content. Effect on mechanical properties were more pronounced in HOI than in TDI based polyurethanes. The modulus and tensile strength decreased, and the ultimate strain values increased with polyethylene glycol content. Last part of the study involved synthesis and characterization of kraft polyurethanes with polybutadiene glycol with functionality in excess of 2.0. The miscibility of this phase with hydroxypropyl lignin phase was found to be poor as observed by scanning electron microscopy. Glass transition temperature for the lignin phase increased with polybutadiene glycol content of the polyurethane in contrast to observations on polyethylene glycol modified polyurethanes. There were no significant improvements in tensile properties. The incompatibility of soft segments was seen to result in a more condensed lignin phase, and was thus found to be the major limitation in its applicability in modification of the network properties. The study demonstrates the utility of concept of network modification in the synthesis of lignin based thermosetting polyurethanes. By proper choice of synthesis variables, and with the use of glycols of sufficient compatibility, significant improvements in properties can be realised in these polyurethanes. / M.S.

M.S.