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Obtaining a robust fiber/matrix interface is crucial for enhancing the mechanical performance of fiber-reinforced composites. This study addresses the issue by presenting a novel physical–chemical modification method to improve the interfacial property of an ultra-high molecular weight polyethylene (UHMWPE) fiber and epoxy resin. The UHMWPE fiber was successfully grafted with polypyrrole (PPy) for the first time after a plasma treatment in an atmosphere of mixed oxygen and nitrogen. The results demonstrated that the maximum value of the interfacial shear strength (IFSS) of the UHMWPE fiber/epoxy reached 15.75 MPa, which was significantly enhanced by 357% compared to the pristine UHMWPE fiber. Meanwhile, the tensile strength of the UHMWPE fiber was only slightly reduced by 7.3%, which was furtherly verified by the Weibull distribution analysis. The surface morphology and structure of the PPy in-situ grown UHMWPE fibers were studied using SEM, FTIR, and contact angle measurement. The results showed that the enhancement of the interfacial performance was attributed to the increased fiber surface roughness and in-situ grown groups, which improved the surface wettability between the UHMWPE fibers and epoxy resins. [ABSTRACT FROM AUTHOR]

• The UHMWPE fabric was modified by plasma treatment and polypyrrole grafting. • Low-velocity impact and residual compressive tests were conducted. • X-ray micro-computed tomography was used to quantify the microscopic void distribution. • Combined plasma treatment and polypyrrole grafting could improve the impact resistance. The physical–chemical method with plasma treatment and polypyrrole grafting was used to improve the low velocity impact resistance of the ultra-high molecular weight polyethylene (UHMWPE) fiber/epoxy laminates. The experimental impact force–time curves and impact force-central displacement curves were recorded. The microscopic void distribution of impact region was quantitatively counted by high-resolution X-ray micro-computed tomography (μCT). Then the residual compressive strengths for the laminates after low velocity impact were explored. Experimental results showed that the impact resistance and residual strength of the laminates treated by the combined plasma treatment and polypyrrole grafting were significantly improved by comparing with the plasma treatment alone, and the void fraction also reduced remarkably. In addition, the impact resistance with single physical plasma treatment method was more affected by the mixture ratio of nitrogen and oxygen. [ABSTRACT FROM AUTHOR]