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

迈向更加环保的未来的一大步是引入可生物降解的塑料电子产品。这种观点可以在对小型传感器的需求不断增长中看到，该小型传感器用于从例如整个城市、农业基础设施、制造厂、公共能源/供水网络的各个位置收集信息，直到监测甚至在人体内的个体生命功能。根据这一趋势，该提案侧重于力、压力、扭矩和加速度等量的机械传感器。由于它们的准永久内置电场，驻极体和最近的铁电驻极体建立了一类材料，其允许高效率，有时甚至通过能量收集装置独立于外部电源，如最近支持的DFG项目所示。这些项目的材料基础是聚合物，如Teflon FEP和PTFE，这些聚合物（在合理的时间内）不可降解，肯定会造成上述日益严重的污染。因此，我们提出研究一类基于聚乳酸（PLA）及其衍生物的新型生物可降解驻极体和铁电驻极体。这些具有可调节的生物降解性和合适的电性能的潜力，即，足够的电荷存储和热电荷稳定性。基于我们以前的研究，为了获得这些基于机械的传感器的节能机电转换，我们建议使用具有几何定义的空气填充和带电空隙的聚合物-空气复合（混合）结构。这些机械上柔软的混合系统允许实现高压电系数，即使是非常弱的极性聚合物，如PLA。因此，调查和改善电荷存储和其热稳定性是必不可少的，因为这些是最重要的属性，以获得高的和持久的压电系数的生物可降解的驻极体和铁电驻极体混合物中使用的机械传感器。我们计划确定一种材料加工，建模，改进和表征PLA基铁电驻极体的策略，目的是定制电荷稳定性。这将在正常的环境条件下进行，这提出了一个科学问题，即基于PLA的传感器在暴露于持续降解过程的同时，是否也可以在潮湿的环境条件下工作。这里的目标是在几周到几个月的范围内定制基于PLA的传感器的寿命。

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.