4D printing of porous PLA-TPU structures: effect of applied deformation, loading mode and infill pattern on the shape memory performance

Abstract

For the first time, the synergy of shape memory polymer (SMP) blending, 4D printing, and cold programming (CP) are investigated for improving the functionality of the shape memory effect (SME), increasing medical applications of porous structures, direct programming, and removing current limitations. Porous PLA-TPU structures with different printing patterns and applied deformation were CPed under constrained and non-constrained compression modes at room temperature and were recovered in the rubbery phase. The shape fixity and shape recovery ratios were calculated and the cross-section morphology was examined with scanning electron microscopy (SEM). The shape fixity values were in the range of 39.75%-71.27%, while almost complete shape recovery ratios (100%) were observed for all porous samples. Low shape fixity ratios can be justified due to the existence of two steps of spring-back and structure relaxation after unloading in cold programming, resulting from elastic and viscoelastic behavior. The glass transition temperature of the PLA-TPU blend was 69 °C and shifted to raw materials, indicating the possibility of some interaction between the two components. SEM images showed the uniform distribution of TPU particles and matrix-droplet morphology in the PLA-TPU blend. After printing, TPU droplets were stretched and the sea-island morphology was observed in some segments.