3D Printing with Core-Shell Filaments Containing High or Low Density Polyethylene Shells

Polyolefins dominate the market for commodity plastics due to their low cost and suitable properties, but polyolefins are rarely used in 3D printing due to issues with deformation of the printed structure during crystallization from the large volume change. Here, we demonstrate that filaments containing approximately 50% of either high density or low density polyethylene (HDPE/LDPE) as a shell with a polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blend core can be printed using standard fused filament fabrication methods with adequate to good dimensional accuracy, improved impact resistance, and enhanced elongation at break relative to samples printed with PC/ABS alone. The combination of lower crystallinity (28%) of LDPE in comparison to HDPE (62%) and lower crystallization temperature of LDPE (89 degrees C) than HDPE (117 degrees C) leads to improved dimensional accuracy of the printed part. However, the elastic modulus of the composite containing LDPE is only 48% of the part printed with only PC/ABS for flat (XY) orientations, whereas the reduction in modulus with the HDPE shell is significantly less. The mechanical behavior can be rationalized in terms of aligned fiber composite theory where anisotropic modulus is expected to be dependent on the angle between stretching direction and fiber axis. The low cost of LDPE and HDPE along with the ability to increase impact strength and extensibility of printed parts further demonstrate the promise of composite core-shell filaments for additive manufacturing.