4D printing of PLA-TPU blends: effect of PLA concentration, loading mode, and programming temperature on the shape memory effect

In this study, PLA-TPU blends with different component ratios were prepared and printed by melt blending and fused deposition modeling (FDM), respectively. The shape memory effect (SME) was investigated considering the effect of loading mode, programming deformation, and temperature for three combinations of PLA50, 70, and 90 wt%. The results of the thermal analysis showed that each compound had two glass transition temperatures in the range of −20 and 67 °C, which return to TPU and PLA, respectively. SEM results confirmed that TPU droplets are observed in the PLA matrix and the printed samples had stretched the TPU phase. In both loading modes, with the increase in PLA concentration, the fixity ratio increased and the highest shape recovery value was obtained in the PLA70 samples, although the values were very close to PLA50. The crystalline segments of PLA, as a net point, play an essential role in restoring the original shape, and by increasing the amount of PLA, stricter limitations are created. In the compression mode, although the programming stress was the highest in the cold-programmed sample, the highest stress was released in the warm-programmed samples. The maximum recovery stress value for PLA70 was 12.85 MPa, which can be effective in reducing the limitations of applications for shape memory polymers. The shape recovery ratio was in the 90.9–96.4% range under compression loading. Also, the cold-programmed samples showed the highest and lowest fixity and recovery ratios. The results of this research show that by changing the composition and programming temperature, the desired properties for different applications can be achieved so that the highest fixity, recovery, and stress recovery were obtained in hot, cold, and warm-programmed samples by manipulating the input energy and temperature.