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Source: Fraunhofer-Gesellschaft Wood waste, oil and sugar residues, glycerine from biodiesel production – the bacteria in Dr. Susanne Zibek’s laboratory at the Fraunhofer IGB in Stuttgart has already been fed a wide variety of residues. The carbon-based feed sources stimulate the bacteria to produce certain endogenous storage granules, so-called polyhydroxyalkanoates (PHA). These special biopolymers are at the center of the “SusPackaging” research project. In cooperation with the Fraunhofer IVV in Freising, the University of Stuttgart and the LCS Life Cycle Simulation from Backnang, the researchers at the Fraunhofer IGB want to produce bio-based and biodegradable plastic alternatives for the cosmetics industry – and that in a completely green value chain. Such an overall concept with a focus on sustainability is new, emphasizes Dr. Ana Lucía Vásquez-Caicedo from the Fraunhofer IGB: “Many studies focus on individual aspects, but you rarely see the entire process chain up to the evaluation of the material quality.” The process starts with bacterial cultivation. Dr. Susanne Zibek, head of the working group Bioprocess Development, is investigating together with Dr. Thomas Hahn explains which microorganisms produce which PHAs with which structures and how their properties can be controlled through the choice of feed: “In principle, our aim is to produce as new structural variants as possible so that we can then check whether the respective plastic can be used as a packaging material suitable, «explains Zibek. The working group receives support from researchers from the University of Stuttgart, who are investigating the various properties of the microorganisms more closely, for example to what extent they adapt to toxic substances that may be contained in natural feed sources they must first be extracted from the microorganisms. This is the specialty of Vásquez-Caicedo, head of the food technology department at Fraunhofer IGB. In general, this so-called purification process takes place with solvents such as chloroform, but Vásquez-Caicedo emphasizes: “Our goal is to get away from these environmentally harmful solvents.” Therefore, she has developed a purely mechanical-physical method for disrupting the cells, the pressure change technology. Here, the fermentation broth in which the microorganisms are located is first provided with a working gas and pressurized so that the gas penetrates into the cytoplasm of the cells. If the pressure in the mixture is then abruptly reduced again, the cells are destroyed and the PHA is released. Once the purification is complete, the material is sent as a white powder to the Fraunhofer IVV in Freising. Here it is processed into granules and finally into films. Initial tests of the material properties have already been carried out on the basis of small plates. Among other things, the heat resistance, deformability and various barrier properties that are later to prevent the cosmetic ingredients from drying out are examined. Cornelia Stramm from Fraunhofer IVV is satisfied with the test results so far: “The mechanical properties show that some types of PHA are currently still somewhat difficult to process. We still have to readjust a little. As far as the barrier properties are concerned, however, the PHAs are very promising compared to other biopolymers. ”She reports her results back to Stuttgart together with recommendations for further action and the process chain begins again. Zibek’s work group at the Fraunhofer IGB was able to use the data to determine its feed strategy of the Fraunhofer IVV already adapt. The bacteria now receive an additional co-substrate, which increases the proportion of valerate in the PHA and thus makes the end product more flexible. Optimization with each feedback loop The quantities produced are still very small and production takes a lot of time. However, the process is further optimized with each feedback loop. Once all steps have been finalized, a life cycle analysis by the external project partner LCS Life Cycle Simulation is used to evaluate the energy efficiency and sustainability of the overall process and to compare it to existing processes. The three researchers agree that PHAs have great potential. Especially with small single-use packaging, they could represent a real alternative to conventional petroleum-based plastics in the future.


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