Moisture-induced deformation of 3D printed hygro-responsive bi-material actuators

Several past research studies have demonstrated the fast fabrication of hygroscopic actuators using additive manufacturing (AM) technology. However, further insight is needed to assess the confounding effect of material types on the structure-property correlations in AM-produced hygroscopic bi-material actuators (BA). Premised on the above, this study sets out to quantify the responsiveness of BA produced by fused filament fabrication (FFF). The primary aim is to assess the influence of two FFF process parameters and the choice of materials on the BA’s responsiveness. In this vein, the investigation examined the effect of FFF’s layer height and extrusion width on the hygroscopic swelling coefficient of wood-filled polylactic acid polymers, pure polylactic acid (PLA) and thermoplastic polyurethane (TPU) polymers. Carried out also is the quantification of the hygromorphic response of monolithic FFF-printed BA derived from these materials. Deformation tests on the BA revealed its responsiveness to correlate positively with printing layer height, extrusion width, and the materials’ hygroscopic coefficient of expansion. Besides, the monolithic BA derived from the combination of the Wood-filled PLA/TPU composite specimens were found to generate mean/maximum tip deflections of 6.44 mm/9.5 mm, which are 4% and 11% more than what was obtained for the Wood-filled PLA/PLA composite specimens.