A response surface methodology study on 4D printing for layered PLA/TPU structures

Shape memory polymers (SMPs) are a new class of materials that have the ability to change their shape over time. The use of SMP in three-dimensional (3D) printing has resulted in the development of a new concept called four-dimensional (4D) printing. It is important to identify the main parameters affecting shape memory behavior in order to be utilized in new applications of SMP. In this study, polylactic acid (PLA) and thermoplastic polyurethane (TPU) were used as the main materials. A number of 3D printing parameters as well as the recovery temperature of the printed object have been investigated to explore how these factors affect shape memory behavior. For design of experiments (DOEs), the Box–Behnken method from response surface methodology (RSM) was used. RSM can be applied to model the effect of different parameters on the shape memory behavior to apply in the appropriate conditions. As part of the evaluation of the mechanical properties of the material, tensile tests were also performed. At higher layer heights, there was generally a decrease in the tensile modulus and strength of the material. Testing equipment was manufactured in order to conduct the testing. It was found that when the whole SMP was made of PLA, the fixity ratio increased. There was a significant correlation between the shape recovery ratio and the recovery temperature. Both shape fixity and recovery ratios were not significantly affected by layer height or infill angle, according to the analysis of variance (ANOVA). To determine the highest fixity and recovery ratios, an optimization was conducted. Using the optimized values, a sample was manufactured and compared with the values obtained from the RSM model.