@phdthesis{Graglia2017,
  author    = {Graglia, Micaela},
  title     = {Lignin valorization},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-104863},
  school      = {Universit{\"a}t Potsdam},
  pages     = {133},
  year      = {2017},
  abstract  = {The topic of this project is the use of lignin as alternative source of aromatic building blocks and oligomers to fossil feedstocks. Lignin is known as the most abundant aromatic polymer in nature and is isolated from the lignocellulosic component of plants by different possible extraction treatments. Both the biomass source and the extraction method affect the structure of the isolated lignin, therefore influencing its further application. Lignin was extracted from beech wood by two different hydrothermal alkaline treatments, which use NaOH and Ba(OH)2 as base and by an acid-catalyzed organosolv process. Moreover, lignin was isolated from bamboo, beech wood and coconut by soda treatment of the biomasses. A comparison of the structural features of such isolated lignins was performed through the use of a wide range of analytical methods. Alkaline lignins resulted in a better candidate as carbon precursor and macromonomers for the synthesis of polymer than organosolv lignin. In fact, alkaline lignins showed higher residual mass after carbonization and higher content of the reactive hydroxy functionalities. In contrast, the lignin source turned out to slightly affect the lignin hydroxyl content. One of the most common lignin modifications is its deconstruction to obtain aromatic molecules, which can be used as starting materials for the synthesis of fine chemicals. Lignin deconstruction leads to a complex mixture of aromatic molecules. A gas chromatographic analytical method was developed to characterize the mixture of products obtained by lignin deconstruction via heterogeneous catalytic hydrogenolysis. The analytical protocol allowed the quantification of three main groups of molecules by means of calibration curves, internal standard and a preliminary silylation step of the sample. The analytical method was used to study the influence of the hydrogenolysis catalyst, temperature and system (flow and batch reactor) on the yield and selectivity of the aromatic compounds. Lignin extracted from beech wood by a hydrothermal process using Ba(OH)2 as base, was functionalized by aromatic nitration in order to add nitrogen functionalities. The final goal was the synthesis of a nitrogen doped carbon. Nitrated lignin was reduced to the amino form in order to compare the influence of different nitrogen functionalities on the porosity of the final carbon. The carbons were obtained by ionothermal treatment of the precursors in the presence of the eutectic salt mixture KCl/ZnCl2 Such synthesized carbons showed micro-, macro- and mesoporosity and were tested for their electrocatalytic activity towards the oxygen reduction reaction. Mesoporous carbon derived from nitro lignin displayed the highest electrocatalytic activity. Lignins isolated from coconut, beech wood and bamboo were used as macromonomers for the synthesis of biobased polyesters. A condensation reaction was performed between lignin and a hyper branched poly(ester-amine), previously obtained by condensation of triethanolamine and adipic acid. The influence of the lignin source and content on the thermochemical and mechanical properties of the final material was investigated. The prepolymer showed adhesive properties towards aluminum and its shear strength was therefore measured. The gluing properties of such synthesized glues turned out to be independent from the lignin source but affected by the amount of lignin in the final material. This work shows that, although still at a laboratory scale, the valorization of lignin can overcome the critical issues of lignin´s structure variability and complexity.},
  language  = {en}
}
@phdthesis{ChaleawlertUmpon2018,
  author    = {Chaleawlert-Umpon, Saowaluk},
  title     = {Sustainable electrode materials based on lignin},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-411793},
  school      = {Universit{\"a}t Potsdam},
  pages     = {114},
  year      = {2018},
  abstract  = {The utilization of lignin as renewable electrode material for electrochemical energy storage is a sustainable approach for future batteries and supercapacitors. The composite electrode was fabricated from Kraft lignin and conductive carbon and the charge storage contribution was determined in terms of electrical double layer (EDL) and redox reactions. The important factors at play for achieving high faradaic charge storage capacity contribute to high surface area, accessibility of redox sites in lignin and their interaction with conductive additives. A thinner layer of lignin covering the high surface area of carbon facilitates the electron transfer process with a shorter pathway from the active sites of nonconductive lignin to the current collector leading to the improvement of faradaic charge storage capacity. Composite electrodes from lignin and carbon would be even more sustainable if the fluorinated binder can be omitted. A new route to fabricate a binder-free composite electrode from Kraft lignin and high surface area carbon has been proposed by crosslinking lignin with glyoxal. A high molecular weight of lignin is obtained to enhance both electroactivity and binder capability in composite electrodes. The order of the processing step of crosslinking lignin on the composite electrode plays a crucial role in achieving a stable electrode and high charge storage capacity. The crosslinked lignin based electrodes are promising since they allow for more stable, sustainable, halogen-free and environmentally benign devices for energy storage applications. Furthermore, improvement of the amount of redox active groups (quinone groups) in lignin is useful to enhance the capacity in lithium battery applications. Direct oxidative demethylation by cerium ammonium nitrate has been carried out under mild conditions. This proves that an increase of quinone groups is able to enhance the performance of lithium battery. Thus, lignin is a promising material and could be a good candidate for application in sustainable energy storage devices.},
  language  = {en}
}