4D printing of shape memory polymers: A comparative study of programming methodologies on various material properties

The emergence of 4D printing has enabled the fabrication of various components that can change in response to external stimuli. Fused filament fabrication is one of the methods for creating shape-changing components using shape-memory polymer (SMP) filament. In order to exhibit the phenomenon of the shape memory effect, programming plays a crucial role. This article discusses two programming concepts, programming during printing (PDP) and programming after printing (PAP), for SMP processed by fused deposition modeling (FDM). We investigated the shape memory properties and other material behavior of PAP and PDP samples considering different thicknesses. We observe that PDP outperforms PAP in terms of shape memory properties based on various characterization tools like Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and field emission-scanning electron microscopy (FE-SEM), which are used for macro and microstructural features. Whereas, PAP shows better mechanical properties based on Nanoindentation analysis. The PDP samples achieved a maximum shape recovery of 99.25%, which is 44% higher than PAP for a 4 mm thick sample, and showed a 28% improvement in recovery compared to PAP for a 2 mm thick sample. Statistical analysis reveals significant differences in the means of recovery ratio and shape memory index between PAP and PDP, and no statistically significant difference is found for the fixation ratio. A shape recovery cycle life measurement has been carried out for a PDP bending actuator, which showed recovery until 140 cycles before complete failure. Finally, a working prototype demonstrating effectiveness of PDP and PAP for programming the same SMP in two different ways has been presented.