Ternary Blends of Polypropylene Copolymer, Polyethylene and Thermoplastic Polyurethane for Fused Deposition Modeling Three-Dimensional Printing Technology: Preparation, Printing and Properties.

A set of filaments for fused deposition modeling (FDM) three-dimensional (3D) printing was developed from the ternary blends of polypropylene random copolymer (PPR or P), high density polyethylene (HDPE or E), and thermoplastic polyurethane (TPU or T), formulated with different weight ratios of polymers, i.e., 80:20:0, 70:20:10, 60:20:20, and 50:20:30, respectively, and coded as P80E20T0, P70E20T10, P60E20T20, and P50E20T30, respectively. The blend composition was optimized to obtain both high-quality filaments with low ovality and FDM-fabricated objects with minimized warpage and good interlayer bonding. The crystallization and crystalline morphologies of individual polymers in the blend filaments were comprehensively analyzed by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized light optical microscopy (PLOM). It was found that HDPE acted as crystalline nuclei for PPR crystallization; PPR appeared to crystallize more readily at a slightly higher T with somewhat greater crystallinity. Meanwhile, TPU explicitly restricted the crystallization of both polyolefins; decreases in both the size and growth rate of their spherulites were observed. The PLOM and SEM results indicated that the surface morphology of the ternary blends was not absolutely phase-separated; an increasing number of TPU droplets inherently imbedded at the boundary of the polyolefin aggregate phase when a higher TPU quantity was integrated. Consequently, the warpage deformation and layer interfusion of the as-printed articles were most remarkably improved when P50E20T30 was used. Nonetheless, the incorporation of relatively flexible TPU material into the PPR-based filaments inevitably reduced their mechanical performance; the flexural strength and modulus of the highest-quality 3D-printed P50E20T30 object were fairly decreased by approximately 25% and 12%, respectively.