Periodic Reporting for period 1 - PUZZLE MATERIALS (Puzzle cell nutshell waste for sustainable material solutions)
Reporting period: 2023-09-01 to 2025-02-28
The problem: 11 billion tonnes of plastic waste are projected to accumulate in the environment by 20251. A circular economy with biotransformation and biodegradation of oil-based plastics is as important as new bio-based and biodegradable materials. Another big problem is the increasing level of CO2 causing the climate change or global warming. Approaches to capture CO2 from the environment are as important as endeavours to reduce our carbon footprint by saving energy and using sustainable plant feedstock in all areas. The development of high-performance materials made from natural resources is increasing worldwide, among them plant fibre reinforced composites or nanocelluloses and lignins as ingredients for a wide range of material solutions. Challenges with using plant biomass, especially waste, are the diversity and variability as well as that new biomass streams and processing routes are needed. Currently, many products in everyday life as well as industrial processes are far away from CO2 neutral, zero pollution and energy and resource efficiency and companies as well as consumers have not enough possibilities to reduce their carbon and ecological footprints. To foster sustainability development that meets the needs of the present and future generations within the planet's physical boundaries, economic AND planetary welfare have to go hand in hand. The transition to sustainable resources, processes and products is urgently needed and included in the development of PUZZLE Materials.
The solution: Research into lignocellulosic biomass, and their transformation by green chemistry are important puzzle tiles in the transformation towards a sustainable economy and living. Among sustainable resources food loss and agri-residues are more and more in focus to synthesize materials. We consider nut shells (especially walnut) as exciting resource for biodegradable materials with low carbon footprint as they stand out by having high uniformity with only one cell type, the puzzle cell, which interlock and have a high surface area. In Europe (incl Turkey) 2021/22 walnut production exceeded 234 550 t (nutfruit.org) and around 130 000 t of shells would be available, but currently they end mostly on landfills or are burned. We envisage to exploit these walnut shells for innovative packaging and leather substitutes.
The solution: Research into lignocellulosic biomass, and their transformation by green chemistry are important puzzle tiles in the transformation towards a sustainable economy and living. Among sustainable resources food loss and agri-residues are more and more in focus to synthesize materials. We consider nut shells (especially walnut) as exciting resource for biodegradable materials with low carbon footprint as they stand out by having high uniformity with only one cell type, the puzzle cell, which interlock and have a high surface area. In Europe (incl Turkey) 2021/22 walnut production exceeded 234 550 t (nutfruit.org) and around 130 000 t of shells would be available, but currently they end mostly on landfills or are burned. We envisage to exploit these walnut shells for innovative packaging and leather substitutes.
Overall, we were able to explore and optimize some procedures towards new puzzle cell materials based on two waste resources: the lignocellulosic puzzle cells from walnut shells and fibrillary bacterial cellulose, a waste product in kombucha brewing. Developing such a composite involved to optimize several steps from dissolving the nutshells, to blending with bacterial cellulose and finally drying and forming the composites .
1) Dissolving the nutshells: We tested four different eutectic solvents to dissolve the grinded walnut shells and finally Cholin chloride: oxalid acid has proven as best choice to be blended at a mass ratio of 15:1 at 110°C for 1.5 hours to finally form the lignin slurry
2) Blending with kombucha cellulose: We aimed for composites with different ratios of bacterial cellulose/walnut shells. As different pellicles can differ in their water content and would shift the ratio away from the desired value in the end it was still essential to put 10g of each cellulose mass into the lyophilisator and measure the real water content to calculate the final cellulose:walnut ratio.
3) Drying of test specimen: To overcome the drying effects in composites with high cellulose content we finally used less material and produced thin films with different ratios of walnut shells/bacterial cellulose for tensile testing. As we also wanted to test the effect of the walnut shells on compression strength, we also tried several ways to prepare small stubs by drying in different ways and forms.
4) Recycling of DES: The collected mixture of DES with water is being filtered and distillated. In our approach to recycle the DES we noticed some problems to come up with the same composition (without impurities) and performance in solubility. Unfortunately we also saw an effect on the mechanical properties of the final composites Therefore, a further optimisation would be needed to come up with a reasonable quality of the recycled DES to be continuously used.
5) Material characterization: To come up with a better understanding of our in-going waste materials as well as the produced lignocellulosic composites we characterized our materials by microscopic techniques (Light Microscopy, electron microscopy), mechanical testing (tensile and compression testing), spectroscopic techniques (FT-IR spectroscopy, Raman microscopy) and to see the effect on barrier properties also water vapour permeability testing. Not all produced puzzle cell materials were suitable for mechanical testing as e.g. the materials produced out of pure lignin slurry have been very brittle, some samples too small, some samphttps://ec.europa.eu/research/participants/research/participants/research/participants/research/participants/grants-app/reporting/VAADIN/themes/sygma/icons/arrowOff.pngles too heterogeneous. We hypothesized that mainly the compression strength of materials will be improved by the incorporation of puzzle cells, as they are optimized on compression strength within the nutshell not to be cracked from outside. Beside the increase in brittleness with more lignified puzzle cells in the composite, it was also difficult to produce thicker samples from the different ratios for compression testing. The more cellulose we added the more shrinking during drying became relevant. Therefore, we finally produced mainly thin films and we observed an unexpected increase in tensile strength with the addition of more puzzle cells by 70-100%. Unfortunately the composites based on walnut shells derived from recycled DES showed significant lower tensile strength values, wherefore the recycling needs further improvement. Another parameter that was improved through the addition of the walnut puzzle cells was the water vapour permeability.
1) Dissolving the nutshells: We tested four different eutectic solvents to dissolve the grinded walnut shells and finally Cholin chloride: oxalid acid has proven as best choice to be blended at a mass ratio of 15:1 at 110°C for 1.5 hours to finally form the lignin slurry
2) Blending with kombucha cellulose: We aimed for composites with different ratios of bacterial cellulose/walnut shells. As different pellicles can differ in their water content and would shift the ratio away from the desired value in the end it was still essential to put 10g of each cellulose mass into the lyophilisator and measure the real water content to calculate the final cellulose:walnut ratio.
3) Drying of test specimen: To overcome the drying effects in composites with high cellulose content we finally used less material and produced thin films with different ratios of walnut shells/bacterial cellulose for tensile testing. As we also wanted to test the effect of the walnut shells on compression strength, we also tried several ways to prepare small stubs by drying in different ways and forms.
4) Recycling of DES: The collected mixture of DES with water is being filtered and distillated. In our approach to recycle the DES we noticed some problems to come up with the same composition (without impurities) and performance in solubility. Unfortunately we also saw an effect on the mechanical properties of the final composites Therefore, a further optimisation would be needed to come up with a reasonable quality of the recycled DES to be continuously used.
5) Material characterization: To come up with a better understanding of our in-going waste materials as well as the produced lignocellulosic composites we characterized our materials by microscopic techniques (Light Microscopy, electron microscopy), mechanical testing (tensile and compression testing), spectroscopic techniques (FT-IR spectroscopy, Raman microscopy) and to see the effect on barrier properties also water vapour permeability testing. Not all produced puzzle cell materials were suitable for mechanical testing as e.g. the materials produced out of pure lignin slurry have been very brittle, some samples too small, some samphttps://ec.europa.eu/research/participants/research/participants/research/participants/research/participants/grants-app/reporting/VAADIN/themes/sygma/icons/arrowOff.pngles too heterogeneous. We hypothesized that mainly the compression strength of materials will be improved by the incorporation of puzzle cells, as they are optimized on compression strength within the nutshell not to be cracked from outside. Beside the increase in brittleness with more lignified puzzle cells in the composite, it was also difficult to produce thicker samples from the different ratios for compression testing. The more cellulose we added the more shrinking during drying became relevant. Therefore, we finally produced mainly thin films and we observed an unexpected increase in tensile strength with the addition of more puzzle cells by 70-100%. Unfortunately the composites based on walnut shells derived from recycled DES showed significant lower tensile strength values, wherefore the recycling needs further improvement. Another parameter that was improved through the addition of the walnut puzzle cells was the water vapour permeability.
We were able to develop new materials based on two waste resources: walnut shells and kombucha cellulose. Yet, working with different ratios and tuning of material properties according to ratios was difficult as higher cellulose content and/ or higher lignin content seem to need different processing optimization. Best results have been achieved with thin films, in which we could improve tensile strength as well as barrier properties by adding walnut puzzle cells to kombucha cellulose. In the latter one we also found variability in water uptake and possibly also cellulose molecular and fibrillar structure. Overall, still further research and optimization is needed to come up with reproducible products with superior mechanical properties. The advantage of using waste and having a really green product has still potential.