Additive manufacturing and investigation of shape memory properties of polylactic acid/thermoplastic polyurethane blend

The fused filament fabrication (FFF) process is one of the most widely used additive manufacturing (AM) methods in producing parts with relatively complex geometry due to its low cost and high capability. Using this blend along with the 3D printing method to make complex shapes can have a high potential in medical applications such as stents, so the goal of the following study is to investigate the shape memory properties of Polylactic Acid/Thermoplastic polyurethane (PLA/TPU) blend. The printed samples with 100/0, 80/20, and 60/40 PLA/TPU composition ratios were comprehensively evaluated based on their structural, thermal, and shape memory properties. A differential scanning calorimetry (DSC) test was conducted to determine the glass transition temperatures and crystallization temperature zone of the blends. A full factorial design of experiments was employed to investigate the effect of three variables called composition ratio, printing angle, and filling percentage on shape memory behavior. Using the three-point flexural test, the shape memory behavior of printed samples with composition ratios 100/0,80/20, 60/40, and filling percentages of 50, 75, and 100%, along with printing angles of zero, ±45, and 90°, was evaluated and measured. The annealing process increased the force required to change the shape and crystallization percentage, such that not being processed, no crystals were observed in the X-ray diffraction (XRD) analysis of the samples, while after being annealed, up to 38% of the crystals were formed. Increasing the percentage of TPU and temperature led to the softening of the samples, reducing the strength and elastic modulus, as well. Enhancing the percentage of TPU also decreases the hydrophilic properties of the samples. The results showed that the best shape memory performance is related to the 20 weight percentage of TPU composition, and the maximum recovery force ratio belongs to the sample with such a composition, zero printing angles, and 75% filling percentage, which equals 81.56%, while it equals 74% using compression molding (CM) in all three production blends.