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

Abstract

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 °C) than HDPE (117 °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.

Effect of Porosity and Crystallinity on 3D Printed PLA Properties

“…Considering the numerous printing parameters, optimal printing conditions are challenging and may require several iterations of trial and error corrections before printing appropriately [10,16], especially when the polymer is semi-crystalline. Many polymers used for FFF are semi-crystalline, such as polylactic acid (PLA) [17,18], polycaprolactone (PCL) [19], polybutylene terephthalate (PBT) [20], polyethylene (PE) [21] and polypropylene (PP) [22]. Although a wide range of polymer filaments are commercially available for FFF, PLA is the most popular one due to its degradability and availability in various colors and textures.…”

Material Extrusion Additive Manufacturing of Wood and Lignocellulosic Filled Composites

“…Likewise, it is envisioned that syndiotactic or atactic PP could also be explored in extrusion-based 3D printing, though no results have yet been reported in the literature. Recently, low density polyethylene (LDPE) with a lower crystallinity (28%) was successfully added to high density polyethylene (HDPE) (62%) to improve the dimensional accuracy of 3D printed parts [ 76 ]. Additionally, some researchers have utilized post-print thermal annealing to overcome crystallization issues of some semi-crystalline 3D printed polymers [ 77 , 78 ].…”

Numerical Simulation of a Core–Shell Polymer Strand in Material Extrusion Additive Manufacturing

“…To overcome some of the mentioned drawbacks, a novel material design approach, namely core–shell structured filament, has recently been developed [ 10 ]. In this approach, a polymer resin, favouring from the high glass-transition temperature, such as polycarbonate (PC) [ 10 ] or a blend of PC and acrylonitrile-butadiene-styrene (ABS) [ 11 ], acts as the core to create a stiff skeleton, reinforcing the printed shape. Another polymer resin with a low glass-transition temperature, such as Surlyn [ 10 ] or high/low density polyethylene [ 11 ], is used as the shell to enable improved interdiffusion of polymers between adjacent layers.…”

“…In this approach, a polymer resin, favouring from the high glass-transition temperature, such as polycarbonate (PC) [ 10 ] or a blend of PC and acrylonitrile-butadiene-styrene (ABS) [ 11 ], acts as the core to create a stiff skeleton, reinforcing the printed shape. Another polymer resin with a low glass-transition temperature, such as Surlyn [ 10 ] or high/low density polyethylene [ 11 ], is used as the shell to enable improved interdiffusion of polymers between adjacent layers. The selected shell polymer should have both crystallinity and ionic functionality to provide routes to enhance the bridging across the interface [ 10 ].…”