Joint Project Proposal on: Development, Characterization and Applications of Cellular Fluoropolymer Films with Ferroelectret Properties Subproject on: Development of Cellular Fluoropolymer Films

埃尔兰根大学、波茨坦大学、达姆施塔特大学和林茨大学(后者是外国合作伙伴)的这一联合项目致力于开发一组新的具有泡状结构的氟聚合物薄膜，并提高了机电换能器应用的热稳定性和时间电荷稳定性。到目前为止，对蜂窝聚合物薄膜驻极体的研究大多是用PP进行的。然而，PP驻极体的热和时间驻极体稳定性不足以满足大多数应用。聚四氟乙烯和无定形氟聚合物薄膜的稳定性较高，但这些薄膜的制造技术困难，不适合大规模生产。在这项研究中，它将尝试将经过验证的泡沫型聚丙烯薄膜的加工工艺应用于含氟聚合物，以便从聚丙烯中已知的优化的空隙结构可以与含氟聚合物的优异稳定性相结合。为此，将使用以含氟乙烯丙烯共聚物(FEP)为基础的热塑性含氟聚合物。这些氟聚合物比聚四氟乙烯更容易制造，因为它们表现出热塑性行为。从含氟聚合物制备薄膜的合适工艺的开发和优化将通过两条路线进行。一种是挤出填充了无机填料的薄膜，然后进行双向拉伸，以产生泡孔，最好发生在颗粒上。另一种方法是使用物理发泡剂制备泡沫板，并由Rheoten在线拉伸泡沫板。所生产的薄膜将根据其细胞结构进行分析。通过与我们在波茨坦、林茨和达姆施塔特的项目合作伙伴的合作，他们的蜂窝结构将被优化，以适应作为驻极体的不同应用。除了为新的氟聚合物驻极体提供材料基础外，该项目还将产生广泛的成果，并对蜂窝状氟聚合物的总体发展产生影响，这也可能对其他应用产生影响。

This joint project of the Universities of Erlangen, Potsdam, Darmstadt, and Linz (the latter as a foreign partner) is concerned with the development of a new group of fluoropolymer films with cellular structure and improved thermal and temporal charge stability for electromechanical transducer applications. So far, most investigations on cellular polymer film electrets have been performed using PP. However, the thermal and temporal electret stability of PP electrets are not sufficient for most applications. Higher stabilities were found for PTFE and amorphous fluoropolymer films, but the manufacturing of these films is technically difficult and not suitable for large-scale production. In this investigation it will be attempted to adapt the proven processing of cellular polypropylene films to fluoropolymers so that the optimised void structure known from polypropylene can be combined with the superior stability of the fluoropolymers. For that aim thermoplastic fluoropolymers based an fluorinated ethylene propylene copolymers (FEP) will be used. These fluoropolymers can more easily be manufactured than PTFE, as they show a thermoplastic behaviour. The development and optimisation of suitable processes for the preparation of thin cellular films from fluoropolymers will be performed according to two routes. The one is the extrusion of films filled with inorganic fillers followed by biaxial stretching for the generation of cells preferably occurring at the particles. The other route is the preparation of foamed sheets using physical blowing agents and an in-line stretching of the foamed sheets by a Rheotens. The produced films will be analysed with respect to their cell structure. In cooperation with our project partners in Potsdam, Linz and Darmstadt their cellular structure will be optimised for different applications as electrets. Besides providing the material base for new fluoropolymer electrets this project will yield widespread results an the development of cellular fluoropolymers in general which could have an impact an other applications, too.