Enhanced dimensional accuracy and impact resistance of 3D printed polymers using core-shell filaments containing high density polyethylene

The limitation of using polyolefins in 3D printing results from the deformation of the printed structure caused by volume change during crystallization. We have previously described a route to partially circumvent this structural distortion using structured core-shell filaments with high density polyethylene (HDPE) shell that are printed with materials extrusion (MatEx) 3D printing. This improved performance was hypothesized to be a result of the core polymer acting as a composite reinforcement to inhibit bending from the stresses generated during the crystallization of HDPE. Here, we describe how the core selection influences the dimensional accuracy of the printed part using a shell of HDPE (at 50 vol%) and cores of polycarbonate-based polymer with increment of glass transition temperature (T_g). As might be expected, the highest T_g core material leads to the lowest warpage and provides the best overall dimensional accuracy. However, these differences in dimensional accuracy are strongly dependent on the details of the print shape. Through quantitative layer-by-layer analysis of complex object, we find that under most printing conditions, parts printed with cores of the highest T_g exhibit the lowest deviations.