Semi-Crystalline Polymer Blends for Material Extrusion Additive Manufacturing Printability: A Case Study with Poly(ethylene terephthalate) and Polypropylene

Semi-crystalline polymers are an important class of materials for engineering applications due to their high modulus and barrier properties. Traditional manufacturing methods process semi-crystalline polymers via rigid molds and well-controlled temperature and pressure environments to handle the significant change in specific volume occurring during crystallization; however, material extrusion additive manufacturing does not use these features. This often leads to warpage-induced build failure in fused filament fabrication (FFF). To enable FFF of semi-crystalline polymers, this work investigates characteristics of immiscible polymer blends (e.g., disparate crystallization behavior and phase separation) to mitigate warping failure during printing. A series of poly(ethylene terephthalate)/polypropylene/polypropylene–graft–maleic anhydride blends are explored and the effect of thermal and morphological characteristics on printability is analyzed. It is shown that these blends can be extruded into filament and printed into a 3D structure. Extrapolations indicate that phase-separated blends with increased total crystallization half-time are beneficial for FFF printing.