Sustainable electrostatic zipping actuators - biodegradable polymer films and power-efficient actuation

As the prominence of soft robotics steadily increases in modern research, electrostatic zipping actuator designs so far are all plagued by the same drawback, as they rely on petroleum-based polymer films. Furthermore, steady state actuation entails considerable power losses due to being restricted mostly to a.c. actuation. Remedying those shortcomings would improve the sustainability of electrostatic zipping actuators and bring them in line with a more environmentally-conscious approach for industry.
In this thesis I explore options to increase sustainability in electrostatic zipping actuators. First, I investigate several biodegradable polymer films for their potential use as actuator materials. Following, I examine their compatibility with gelatin-based hydrogel electrodes as a biodegradable alternative to conventional metal electrodes. From this analysis two polymer films emerge as good options: BOPLA and a biopolyester blend by Naturabiomat with dielectric strengths of 559 V/µm and 213 V/µm and dielectric constants at a frequency of 1 Hz of 2.87 and 5.43 respectively. Hydrogel electrodes were found to be viable alternatives to copper electrodes, however they lead to a lower breakdown strength of the solid dielectrics. Additionally, I use the biopolyester blend to enable a power-efficient driving method for electrostatic zipping actuators using d.c. It is applied in a device for unidirectional liquid transport, which is inspired by the skin of the Texas Horned Lizard. Here, a capillary channel network allows for passive liquid flow, which can be blocked by an inflatable membrane that is hydraulically coupled to the actuator. The actuator is able to sustain a constant pressure even when powered by d.c. and completely stops the flow of the liquid on the surface. Turning off the power allows the flow to continue through the channels.
This result showcases that sustainable electrostatic zipping actuators can be made from completely biodegradable materials and even be actuated in a more energy-efficient manner than previous designs. This thesis enables future works to incorporate these polymers and principles into newer actuator designs.