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Research project (§ 26 & § 27)
Duration : 2020-11-01 - 2023-10-31

Lignin is the most common renewable aromatic biopolymer. The molecule is still undergoing significant changes through various industrial conversion processes of wood or annual plants in the pulp and paper industry. As a result, lignin is obtained in large quantities and chemically modified form as "technical lignin". At present, an annual production of approx. 70 million tons worldwide is assumed. Despite large-scale availability, over 95% of the lignin obtained is used for energy production. As a result of the energy obtained and returned from this process, processes in the pulp and paper industry are considered to be largely energy self-sufficient. The discrepancy between availability and the very limited real use of lignin has posed a major challenge for academic and industrial research for decades - with varying degrees of intensity and success. Due to a worldwide rethinking, caused by the climate crisis and increasing carbon dioxide emissions, a clear trend towards a sustainable use of raw materials and a bio-economic overall design of various processes is becoming apparent. As a result, lignin has gained new momentum as a source of raw materials and is considered a "key player" in the substitution of petroleum-based raw materials and materials by renewable raw materials. This can be seen from the increase in research intensity and the resulting exponential growth of lignin patents in recent years. However, the implementation of existing, undoubtedly practicable ideas and their large-scale applications is progressing much more slowly. Therefore the question arises whether and why we are not yet able to fully understand and use technical lignins analogous to cellulose or petroleum? While we have had process chains for cellulose and its products for more than a hundred years to produce cellulose-based products such as paper, fibers or other derivatives, lignin is merely a waste product. Its high energetic value has been used thanks to the positive energy balance of the processes, but has otherwise only found a real material application as a niche product (lignosulfonate). Through processes such as Lignoboost (Thomani, 2009), which are already available and in use on a large scale, the isolation of technical lignins from the waste liquors of the kraft pulp process has become possible and makes technical lignin available for further processing practically worldwide.
Research project (§ 26 & § 27)
Duration : 2020-07-01 - 2022-06-30

Oxidative modification of cellulose The aim of the planned work is to achieve Lean and cost-efficient and green chemical routes to improve the properties of kraft pulp for thermoplastic materials. The cellulose chain is intrinsically rigid, which is one of the causes of its high Tg and Tm. The offered research targets to increase the mobility of the cellulose chain through oxidation chain cleavage methods, that decrease H-bonds in which the anhydroglucose units are involved and induce a major release of molecular motions within and between the chains.
Research project (§ 26 & § 27)
Duration : 2020-06-01 - 2021-10-24

Mechanical and functional gradients are reasons for the abundance of functionalities and extraordinary mechanical properties in nature. Mechanical gradients are spatial smooth transitions from mechanically weak to strong structures resulting in materials with remarkable mechanical performance. In case of the in vivo cell environment, the extra-cellular matrix, there are not only mechanical gradients present but also functional gradients, such as an increasing concentration of a bio-active molecule in one dimension. These gradients play an important role in the organization of cells into functional tissues and organs. The imitation of these multidimensional structures by biocompatible and shapeable materials in a straightforward way is a critical challenge that will be addressed in this proposal. The research hypothesis is the development of a novel gradient printing approach, named 5D Click Printing, combining cutting-edge bioprinting technology with state-of-the-art materials and crosslinking chemistry. This will be realized by using functional nanocellulose and polyoxazoline as ink formulations to produce 3D objects with mechanical (+1D) and functional gradients (+1D). The proposed ink formulations are based on functional cellulose nanofibrils and polyoxazolines. These materials were chosen because of their established biocompatibilities, printabilities and the resemblance to the two main components of the extra-cellular matrices, fiber-forming proteins and non-fibrous glycoproteins. The functional groups on the polymers were carefully selected to allow gelation by spontaneous click chemistry, which can be conducted in the presence of living cells. The 5D Click Printing technology will be further developed to fabricate multidimensional hydrogels with various functionalities. These gels will be used to assess and compare diverse characterization techniques to establish a methodology to visualize gradients in multidimensional objects. In conclusion, the developed technology will be the first straightforward avenue to shaped hydrogels with functional and mechanical gradients. 5D Click Printing will be used to fabricate, bioinspired and sophisticated tissue models for biomedical application, and to produce graded membranes for chromatographic separation of complex biopolymer mixtures.

Supervised Theses and Dissertations