Fabrication of 3D-Printed Hygromorphs Based on Different Cellulosic Fillers

Abstract The aim of this work is to characterize the moisture-dependent actuation behavior of bioinspired and additively manufactured hygromorphs based by following deductive and inductive design approaches. Fused Filament Fabrication is employed to print bilayered structures consisting of swellable active layers and rigid passive layers. The active layer is composed of a polylactic acid matrix filled with different hygroscopic cellulosic materials up to a filler content of 50 m%. Acrylnitril-Butadien-Styrol-Copolymer is used for the passive layer. The Fused Filament Fabrication process allows the generation of desired differential swelling properties in the composites upon moisture absorption. The moisture dependent actuation strain of the printed bilayers was determined by video analyses. Some influencing geometrical factors that contribute to the actuation were deduced from x-ray diffraction and micro computed tomography. The investigation of the mean cellulose microfibril orientation on the surface of the active layer suggested a preferential orientation with respect to printing direction. Furthermore, a gradient of cellulosic material within a single printed layer was observed, which indicates fiber sedimentation. Comparison with a thermomechanical model shows that the computational prediction of the moisture dependent actuation is considerably accurate for most selected cellulosic materials and filler contents.