Recently, the opportunities and behaviors of self-transforming materials, especially in the area of shape memory alloys have widely been studied. But there are also bioinspired approaches to develop intelligent, autonomously moving biomaterials. The origin of the movement is mostly the response to an external stimuli or an environmental change, like temperature, moisture or light.
In this context, the presented poster will show the way from the nature-given ideal, the pine cone, to the manufactured hygromorph. The generated material is called Cottonid. It is made by parching untreated cellulosic fibers with different solutions to increase the hygroscopicity. In the next step the material is brought into an at least two-layered composite with different fiber orientations. 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 effect the processing parameters, e.g. time in the parch-ment bath, temperature and concentration of the parchment solution and the pressure, with which the layers are bonded together, are varied. The resulting material is characterized by infrared spectroscopy, thermogravimetric analysis and x-ray diffraction. In tests with super-imposed medial loading the passive movements of Cottonid-based bilayer structures in reac-tion to moisture are evaluated qualitatively and quantitatively concerning parameters, like angle of deflection, repeatability and saturation. In addition, an impression of occurring struc-tural mechanisms during manufacturing and actuating is given with the help of scanning elec-tron microscopy (SEM) and computed tomography (CT) to investigate process-structure-property-relationships.
The aim is to develop a structurally optimized biopolymer composite with pronounced actua-tion behavior in reaction to alternating humidity. Furthermore the results lead to a profound understanding of the biomechanics. On this basis, tailor-made functional materials shall be generated in future where anisotropy and hygroscopicity can be adjusted through the manu-facturing process.