Towards Dimensionally Stable 3D ‐Printed HDPE Composites: Synergistic Warpage Mitigation by Carbon Fiber and Polyolefin Elastomer via Transcrystalline Formation

In this work, efforts were made to mitigate the warpage of high‐density polyethylene (HDPE) to render it suitable for 3D printing. The results showed that the combination of polyolefin elastomer (POE) and carbon fiber (CF) significantly decreased the coefficient of thermal expansion (CTE) and warpage rate of HDPE. The HDPE/POE/CF composite with a CF loading of 18 wt.% (HDPE/POE/CF‐18) exhibited the lowest CTE (65 × 10 −6 /K) and warpage rate (0.3%), which is only 0.34 times and one‐ninth that of neat HDPE (190 × 10 −6 /K and 2.7%). This was attributed to the synergistic effect of CF and POE. The rigid CF network restricted HDPE chain mobility and crystallization shrinkage, while the POE phase reduced residual stress mainly via inducing transcrystalline at CF surfaces, rather than through the lowered crystallinity. Thus, HDPE/POE/CF‐18 was successfully 3D printed into high‐fidelity gears and knee joint models with minimal deformation, whereas neat HDPE displayed obvious warpage and dimensional distortion. This work provides an effective strategy for preparing high‐performance HDPE‐based composites for 3D printing of functional components with complex geometries.