Synergistically Modified High‐Density Polyethylene Composites by Basalt Fibers and Scales for Marine Engineering Applications

High‐density polyethylene (HDPE) is widely applied in marine engineering infrastructures, but its service in sustained dynamic impact scenarios is severely constrained by the inherent mismatch among tensile strength, impact toughness, and environmental stress cracking resistance (ESCR). To break through this performance bottleneck, this work develops a synergistically modified HDPE composite using basalt scales (BS) and basalt fibers (BF) as reinforcing phases, paired with a hybrid compatibilizer system of polyethylene‐grafted maleic anhydride (PE‐g‐MAH) and polyolefin elastomer‐grafted maleic anhydride (POE‐g‐MAH). A coupled “3D skeleton + 2D barrier” model is proposed to elucidate the reinforcement mechanism: one‐dimensional (1D) BF dominates axial stress transfer, while two‐dimensional (2D) lamellar BS restricts planar slippage of molecular chains, collectively achieving improvement in strength and rigidity without severe toughness loss. Meanwhile, the hybrid compatibilizer system establishes a “firm adhesion + flexible buffering” interfacial regime: PE‐g‐MAH forms chemical bonding between basalt fillers and the HDPE matrix, whereas POE‐g‐MAH elastomer domains induce the formation of crazes and shear bands to dissipate impact energy, thus markedly enhancing impact toughness. At the optimal formulation, the composite delivers a tensile strength of 54.89 MPa, a flexural strength of 24.9 MPa, and a notched Izod impact strength of 51.5 kJ/m 2 , with an ESCR failure time up to 202 h. Its volume wear rate is reduced by more than 77% compared with neat HDPE. The composite can be processed into marine components such as antifouling rollers via injection molding. A 12‐month real‐sea service test in the Bohai Sea of China confirms that the material remains intact without obvious cracking or wear and can endure sustained dynamic loads driven by tides and ocean currents. This work provides a novel design strategy and performance support for HDPE‐based composites serving in harsh marine engineering environments.