Development of binary and ternary polyester shape memory blends for additive manufacturing

The goal of this work was to create shape memory polymer blends for the additive manufacturing technology of fused filament fabrication. An iterative approach was taken to develop a binary blend of polycaprolactone (PCL) and thermoplastic urethane (TPU). The composition of equal parts by mass PCL and TPU exhibited the best mechanical and shape memory properties. It was then decided to compound a ternary blend of PCL, TPU, and polylactic acid (PLA) where all components were of equal parts by mass. Constituents were chosen because they are all long chain polyesters with similar Hildebrand solubility parameters, because they are biocompatible, and because they all have some level of shape memory properties on their own. Dynamic mechanical analysis was performed to determine the recovery temperature for specimens that were deformed at room temperature. Scanning electron microscopy was used to perform fracture surface analysis of spent tensile test specimens. X-ray diffraction was used to explore aspects related to crystallinity of the blend materials. Transmission electron microscopy was used to characterize the mixing of the blend constituents where both the binary and ternary blends were found to be immiscible. The work presented here demonstrates materials selection based on structure, polymer family, and solubility parameter as a strategy for the development of multi-constituent polymer blends without the use of compatibilizers.