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.
