Investigation of Shape Memory Recovery in Thermally Activated PLA-TPU Blends Using Fused Granular Fabrication (FGF)

The current paper presents a study on the shape memory effect (SME) on thermally activated PLA-TPU polymer blends that have been produced using the emerging additive manufacturing technique of Fused Granular Fabrication (FGF) as a new pellet-based technique. The melt mixing and pelletization processes were conducted to prepare three ratios of blend (90:10, 80:20, 70:30 PLA: TPU), and then 3D printed as cubic specimens with different infill patterns (honeycomb, triangular and grid) and density (10%, 25%, 40%). The specimens were mechanically programmed under three levels of compressive strain (10%, 25%, 40%), then activated in hot water. The peak compressive strength (PCS) was measured alongside shape fixity ratio (Rf), recovery ratio (Rr) and overall SME. To analyze the effect of the four inputs in a systematic way, a Taguchi L27 orthogonal array was used to analyze the results, followed by statistical analysis using ANOVA and Grey Relational Analysis (GRA). It was found that the compression ratio produced the largest impact on shape restoration (70.71% impact) and the infill density and pattern only impacted heavily on the mechanical compressive strength. The optimum combination comprised of 30% TPU, 40% infill density, honeycomb-pattern combined with 25 to 40% compression that had SME values of over 75% and showed improved fidelity of recovery. These results support the idea regarding the use of PLA-TPU blends in the use of 4D printing of programmable structures and smart materials, particularly in those applications that require compressive deformation and thermal recovery.