In the last years, the opportunities and behavior of self-transforming materials, especially in the area of shape memory alloys have been widely studied. However, there are also bioinspired approaches to develop smart, autonomously moving biomaterials. The origin of the movement is mostly the response to external stimuli or an environmental change, such as temperature, moisture or light.
In this context, the presented poster will show the process from the biological role model, the pine cone, to the manufactured material. The material under investigation is called Cottonid. It is created by parching untreated cellulosic fibers with different solutions to increase the hygroscopicity. In the next step, the material is arranged into a bilayered composite. If the structure is now exposed to a different humidity, it shows a moisture-driven curvature like movement, based on the different hygrometric expansion coefficient of the single layers. To optimize that movement, the processing parameters, e.g. time in the parchment bath, temperature and concentration of the parchment solution and the pressure, with which the layers are bonded together, are varied to set the hygrometric expansion coefficient. The resulting material is characterized by infrared spectroscopy, thermogravimetric analysis and x-ray diffraction. In superimposed medial loading tests the passive movements of Cottonid-based bilayer structures in reaction to moisture are evaluated qualitatively and quantitatively concerning parameters such as, angle of deflection, repeatability, and saturation. In addition, an impression of occurring structural mechanisms during manufacturing and actuating is given with the help of scanning electron microscopy (SEM) and computer tomography (CT) to investigate process-structure-property-relationships.
The aim is to develop a structurally optimized biopolymer composite with pronounced actuation movements in reaction to alternating humidity. Furthermore the results lead to a profound understanding of biomechanics. On this basis, tailor-made functional materials shall be generated in the future where anisotropy and hygroscopicity can be adjusted throughout the manufacturing process.