Biodegradable and eco-friendly sensors based on polylactide acid ferroelectrets with adjustable operating lifetime

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A large step towards an eco-friendlier future is the introduction of biodegradable plastic electronics. Such perspective can be seen in the growing demand for small sensors for collecting information from various locations at e.g. entire cities, agricultural infrastructures, manufacturing plants, public energy/water supply networks up to monitoring individual vital functions even inside the human body. Following this trend, this proposal focuses on mechanical-based sensors for quantities such as force, pressure, torque and acceleration. Due to their quasi-permanent built-in electric field, electrets and recently ferroelectrets establish a class of materials that allow for high efficiency and sometimes even independence of external power through energy-harvesting devices, as recently supported DFG-projects are indicating. The material base in those projects are polymers such as Teflon FEP and PTFE, which are not degradable (in a reasonable time period) and definitely contributing to a growing pollution as mentioned above. Therefore, we propose to study a new class of biodegradable electrets and ferroelectrets based on Polylactide Acid (PLA) and its derivatives. These have the potential of an adjustable biodegradability and suited electrical performance, i.e., sufficient charge storage and thermal charge stability. Based on our previous research and in order to obtain the energy efficient electromechanical conversion for these mechanical-based sensors, we propose using a polymer-air composite (hybrid) structure with geometrically defined air-filled and electrically charged voids. These mechanically soft hybrid systems allow achieving high piezoelectric coefficients even for very weak polar polymers such as PLA. Therefore, investigating and improving charge storage and its thermal stability is essential, since these are the most important properties to obtain high and persistent piezoelectric coefficients in biodegradable electret and ferroelectret hybrids to be used in mechanical-based sensors. We plan to identify a strategy for material processing, modeling, improving and characterizing PLA-based ferroelectrets with the aim to tailor charge stability. This will be done under normal environmental conditions raising the scientific question whether operation of PLA-based sensors also is possible under humid environmental conditions, while exposed to an ongoing degradation process. The objective here is tailoring the lifetime of a PLA-based sensor in the range of weeks to months.