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 (FFF) is employed to print bilayered structures consisting of swellable active layers and rigid passive layers. The active layer is composed of a polylactic acid (PLA) matrix filled with different hygroscopic cellulosic materials (native and modified) up to a filler content of 50 m%. Acrylonitrile Butadiene Styrene (ABS) is used for the passive layer. The FFF 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 which contribute to the actuation were deduced from x-ray diffraction (XRD) and micro computed tomography (μCT). 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 the thermomechanical model derived from Timoshenko (1925) shows that the computational prediction of the moisture dependent actuation is considerably accurate for most selected cellulosic materials and filler contents.
Highlights
In nature plants have developed numerous kinds of movements to catch prey, to disperse seeds or to protect themself [1]
Bilayer fabrication Preliminary tests using pure and fiber filled polylactic acid (PLA) showed that the brittleness of the filaments prevented proper feeding
The brittleness of the PLA was adjusted by the addition of a terpolymer of vinyl acetate-ethylenevinyl versatate (10 m%), in order to improve the processability
Summary
In nature plants have developed numerous kinds of movements to catch prey, to disperse seeds or to protect themself [1]. Many of these motions occur without an external source of energy. They are only driven by environmental humidity gradients [2]. The materials and design approaches inspired by these phenomena are often of non-renewable origin [3–5] while several approaches describe the use of wood [6, 7] or cellulose-based materials such as cottonid, which is even more hygroscopic natural cellulose [8–10]. Hygromorphous structural materials respond to the relative humidity (Φ) of the environment by changing their dimensions, and their shape by swelling through the uptake of water. Pine cones are among the best known and well-described
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
