###### Abstract  
Although aramid fiber has the advantage of excellent chemical and mechanical properties, the performance of the composites may be reduced due to the low interfacial adhesion between the fabric and the matrix. The surface of the aramid fiber was modified to improve the interfacial properties. The surface of the aramid fibers was treated with ZnCl\({}_{2}\) and polydopamine. After the pretreated fabrics were made into a composite material by the vacuum-assisted resin transfer molding (VARTM) process, their mechanical performance was investigated. The highest impact energy was shown in the concentration of 6 wt% ZnCl\({}_{2}\) and 1.5 g/L polydopamine, which is 20% better than that of the untreated material. In the bending strength, the condition of 1.5 g/L polydopamine resulted in the highest value and increased by 13% compared to the untreated material. The hybrid surface treatment of ZnCl\({}_{2}\) and polydopamine did not significantly affect the tensile strength. aramid fiber; hybrid modification; mechanical properties; Zinc chloride; polydopamine +
Footnote †: journal: Applied  
the current research trend to enhance the interfacial bond between fiber and resin by means of surface treatment. Surface decontamination, roughness change and surface activation are the main factors to increase surface free energy and improve adhesion. Additionally, Plasma treatment is beneficial to improve the mechanical properties of fabric-reinforced composites, such as shear strength and impact energy absorption [6; 7; 8]. Additionally, different conditions of plasma treatment, such as low-temperature plasma, cold plasma and room temperature plasma, to improve the wettability, roughness, the degree of surface activation are different [9; 10; 11]. [PERSON] et al. showed the effect of aramid fiber hybridization on the mechanical behavior of basalt fiber-reinforced epoxy resin composites under impact [12]. [PERSON] et al. reported that the tensile strength of the aramid fiber composites put into seawater, 30% concentration of sulfuric acid, and sodium hydroxide, respectively, had different tendencies to decrease with increasing time [13]. [PERSON] et al. reported that aramid fiber was pretreated with LiCl and then coated with low molecular weight malleated polybutadiene liquid (MLPB) or butadiene-vinyl-pyridine emulsion (VPL) rubber to improve the interfacial adhesion to influence the fatigue behavior of the composites [14]. Ultrasonic treatment can increase interlaminar shear strength (ILSS) of aramid fiber/epoxy resin composites by 13% without reducing the tensile strength [15]. [PERSON] et al. investigated the effect of the strength with treatment time and concentration by treating the aramid fiber with CaCl\({}_{2}\) ethanol solution. It is proved that Lewis acid treatment can improve the aramid fiber [16]. [PERSON] et al. reported that enhancement of interfacial shear strength by direct fluorination of aramid fiber surface to induce fluorine-related radicals and chemical grafting of carbon nanotubes [17]. [PERSON] et al. reported that Lewis acid treatment etches aramid fibers and increases their surface area and surface activity [18]. [PERSON] et al. and [PERSON] et al. reported that the wettability of aramid fiber surface was enhanced by air dielectric barrier discharge (DBD) plasma at atmospheric pressure [19; 20]. [PERSON] and [PERSON] enhanced the mechanical strength and stiffness of the fabric composites by immersing the fabrics in an aqueous dopamine solution to increase the interfacial adhesion between the fabric and epoxy resin by depositing PDA on the fabric surface [21]. The Lewis acid treatment effectively enhances the roughness and interfacial adhesion of the fabric surface, while the PDA treatment forms reactive chemical bonds on the fabric surface, which all can enhance the performance of the composite. In this study, in order to improve the interfacial adhesion between the aramid fiber and the epoxy resin, the surface of the aramid fiber was treated with a ZnCl\({}_{2}\) solution [22].