Dr. Andreas Geißler, Project Manager at the Department of Macromolecular and Paper Chemistry at the TU Darmstadt, is coordinator of the “BioPlas4Paper” project and heads the “Paper Technology” sub-project.

Dr. Kristina Lachmann, Head of Medical Technology and Pharmaceutical Systems at the Fraunhofer IST, is responsible for the sub-project “Process Development and Optimization”, which is primarily being worked on by Martin Bellmann, research associate at the Fraunhofer IST.

Dr. Jörn Appelt heads the “Thermochemical Conversion” working group at the Thünen Institute of Wood Research and the “Biogenic Precursors” sub-project.  

Andreas Geißler, what is the aim of the overall project “BioPlas4Paper” and what significance does it have for society?

Geißler: The aim of the research project was to functionalize papers for future applications (primarily to make them hydrophobic) without thereby counteracting the intrinsic sustainability of the material. For the finishing of paper, coatings or additives of petrochemical origin are currently used - which we wanted to avoid at all costs.

Through the utilization of natural raw materials (plant extracts) – for the extraction and processing of which modern technologies (sCO₂ extraction and atmospheric-pressure plasma polymerization) were used – we have succeeded impressively.

Unfortunately, the “BioPlas4Paper” project cannot abruptly solve the problems that we as a society have accumulated over the last few decades, but it is an important and correct step towards bioeconomy and sustainability. We present a holistic approach to the value-adding utilization of natural raw and residual materials, which will soon also be of interest to other industries.

The project is divided into three sub-projects. What are the individual aspects?

Geißler: How do the precursor molecules actually fragment when energy is applied, how do they react to form a polymer network, and what properties does the resultant material have as a paper coating? These are the questions that the sub-project in Darmstadt is addressing. It thereby ranges from the reaction mechanisms and the kinetics of plasma polymerization, through basic polymer characterization and microscopic evidence of distribution in the fiber structure, up to functional testing of the modified papers in interaction with water. 

Lachmann: In the Fraunhofer IST sub-project “Process development and optimization”, the plasma source system, the coating process and carrier gases for the polymerization of biogenic precursor molecules were developed, selected and optimized. The functionalization and coating of paper substrates was subsequently performed by means of PECVD (Plasma Enhanced Chemical Vapor Deposition). The applied layers were analyzed with regard to their surface topography and surface chemistry. In addition, the gas-phase chemistry in both the plasma process and the process exhaust air was investigated. In conclusion, a pilot-plant setup was used to devise a conceptual design for process integration.

Appelt: The sub-project conducted by the Thünen Institute encompasses the strategic selection of suitable technical by-products and residues such as pyrolysis oil, tall oil and robinia bark or robinia wood for the polymerization of biomimetic structures. This includes chemical and physical characterization of the precursors. In addition, suitable fractions are isolated from these complex biogenic residues and by-products. A number of variants are tested with regard to the requirements placed on the feedstock and the extraction success. To conclude, an analysis is performed in order to identify the potential dangers during recycling and during the utilization of the new products.

What results have you achieved so far and what are the next steps? 

Appelt: We were able to show that various fractions with differing viscosities and compositions could be obtained from pyrolysis oil by means of supercritical CO₂ extraction. It was also possible to extract fractions rich in fatty acids from crude tall oil - a viscous and sticky mass. For both feedstocks, it was determined that the skillful selection of extraction parameters and the segregation of precursors from the gas stream can have an influence on the composition and physical parameters such as viscosity. It became clear that biogenic subsidiary or residual streams can be fractionated gently and that these mixtures can then also be applied in plasma polymerization. For further follow-up projects, the question arises as to the extent to which we can also make precursors available from solid residual products and by-products – such as bark or residual wood – for coating by means of plasma.   

Bellmann: The project result of the second sub-project is an innovative atmospheric-pressure plasma process that creates homogeneous and reproducible layers under the exclusion of ambient air. Depending on the precursor used, these bio-based layers can be hydrophilic, hydrophobic or even antibacterial and can be applied to thermosensitive materials such as paper. It is thereby important to select gentle parameters in order to preserve the potential biomimetic characteristics of the feedstock. Thanks to the operating principle of the novel plasma source, the process remains stable to a certain degree against drag air, which occurs at higher process speeds.

Through close contact with 4evergreen – a cross-industry association of more than 100 members representing the entire life cycle of packaging made from fibers – as well as the packaging and textile industries, the existing potential is to be fully exploited and, in further research projects, intensified. The packaging and textile industries are already expressing keen interest in the topic.

Geißler: We have succeeded in coating papers with the smallest possible quantities of plant extracts (oils) in atmospheric-pressure plasma, thereby making them sustainably hydrophobic. We were able to characterize the resulting polymer networks and to confirm their covalent attachment to the cellulose. Through the selection of the precursors and the plasma process parameters, it was possible to influence the properties of the coatings in terms of thickness, topography and functionality. Ultimately, it was possible to transfer the entire coating concept to an inline process in which the paper web was treated at speeds of up to 16 m/min.

Based on these results, diverse options arise both on the research side and with regard to up-scaling and industrial application. As the “BioPlas4Paper” project is currently being concluded, we are planning follow-up projects that will take an even closer look at the variety of potential precursors, will provide for extended functional testing of the coatings under normal conditions of use, and will include substantiated considerations of the end-of-life scenarios for these materials. 

To conclude, a personal question: What will stay in your memory, what was your personal highlight during the project?

Geißler: In the five years from the initiation of the project to its completion, there were many positive things that stick in my mind. The trusting collaboration, the get-togethers and events, the committed doctoral students, the great publications and, of course, the fact that we succeeded in turning the vision of the project into reality. If I had to pick one highlight, I would choose the final roll-to-roll coating experiment at PTS. Although the preparation and coordination for this was carried out exclusively online, all the manufactured components fitted and the trial ran smoothly. To see how a project idea “suddenly” turned into a continuous coating process was very impressive.

Lachmann: I was really impressed by the good cooperation and the high level of motivation - especially among the doctoral students. In particular, I will always remember the project meetings in person. The guided tours on site always provide exciting insights into the work of the partners involved and help to enable a better understanding of their technologies and challenges. Another highlight was a joint workshop in which we collected various ideas that we can collaboratively address in the future.  

Bellmann: The positive atmosphere that was already prevalent at the beginning of the brainstorming and application process was further consolidated during the course of the project. This led to a smooth interlocking of the necessary work. The interdisciplinary cooperation between all the participants was always interesting and motivating. The friendly interaction created an optimal basis for future cooperation. My conclusion: the project could not have run any better. I would like to thank everyone involved for the excellent collaboration and I am looking forward to future projects!

Appelt: From the application phase through to the completion of the project, we had a very productive and results-oriented working method in a great team comprised of all project members. This yielded very good results as well as publications and conference contributions. The project meetings, whether online or in person, were characterized by this mutual togetherness. This helped us through the tricky times – which occur in every research project – and led to success. In addition to the superb scientific results, one highlight for me was seeing how far you can get with an idea combined with a structured and focused way of working. Namely, so far that a multitude of ideas for further projects have emerged that we want to collaboratively pursue in the future.  

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