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 (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.

Development of a Material Design Space for 4D-Printed Bio-Inspired Hygroscopically Actuated Bilayer Structures with Unequal Effective Layer Widths

“…For most of these material systems, the influence of basic geometric changes such as layer thickness are well understood, enabling computational reproduction of observed curvatures based on Timoshenko's model for bimetal bending, adapted for hygromorphic materials [12,16,17,[21][22][23]. This knowledge allows for designing new demonstrators with planned and timed curving behavior [18].…”

Moisture-sensitive mechanical metamaterials with unusual and re-programmable hygroscopic deformation modes

“…Timoshenko et al proposed a method for calculating the deformation of a bi-material strip with different coefficient of thermal expansion (CTE) upon heating. 43 Similarly, the curvature change induced by moisture change Δ φ is quantitatively determined by the modified equation which replaces CTE with CHE: 44–48 where β 2 , β 1 , E 2 , E 1 , t 2 , and t 1 denote CHE, Young's module, and the thickness of the outer (subscript 2) and inner materials (subscript 1). The linear CHE can be expressed by the ratio of the strain to the change of moisture.…”

“…Timoshenko et al proposed a method for calculating the deformation of a bimaterial strip with different coefficient of thermal expansion (CTE) upon heating. 43 Similarly, the curvature change D 1 r induced by moisture change Dj is quantitatively determined by the modified equation which replaces CTE with CHE: [44][45][46][47][48]…”

The Design of 4D‐Printed Hygromorphs: State‐of‐the‐Art and Future Challenges

“…Poppinga et al ( 2020) [63] • Short wood and cellulose fibers & ABS [64] • PLA and Short cellulose or arbocel fillers & ABS…”

“…These techniques are also adequate for immersed actuators, as the optical methodologies proposed later on tend to feature images diffracted by the water. Another technique, named measure on photos, consists in taking images of the specimens while deforming and measuring the curvature, [8,18,56,58,59,79,81,108,119,130,133] the twisting angle, [81,119,354] the bending angle, [48,62,74] the deflection [64,67,150,167,323] and the position [139] representative of the deformation. The postprocessing of these images is usually conducted by using commercial codes, such as Fiji.…”