## 1 Introduction  
Aromatic polyamide fiber, abbreviated as aramid fiber (PPTA), is the second-generation high-performance reinforcement fiber following carbon fiber [1; 2; 3]. As one of the three major high-performance fibers in the world, aramid fiber possesses superior properties, such as low density, high tensile strength, high modulus, excellent thermal stability, abrasion resistance, chemical corrosion resistance, and outstanding ballistic performance [4; 5; 6; 7]. Consequently, it is widely used in the manufacturing of advanced composite materials for aerospace, civil engineering, armored protection, and other fields [8; 9; 10; 11; 12; 13]. However, in practical applications, due to the rigid molecular structure, high crystallinity, smooth surface, and low-molecular-surface active functional groups of aramid fiber, it exhibits certain drawbacks, such as surface chemical inertness [14; 15]. This results in poor interfacial adhesion between the reinforcement phase and the resin matrix when used in composite materials, making it difficult to fully transfer stress and affecting the overall performance of the composite materials, thereby greatly limiting its further application [16; 17; 18; 19]. Therefore, while fully exploiting the excellent mechanical properties of aramid fiber, improving the interfacial adhesion performance of fiber-reinforced resin-based composite materials has become a hot research topic both domestically and internationally [20; 21; 22; 23; 24; 25]. Currently, the most commonly used technique involves modifying the surface of aramid fiber through chemical or physical methods to enhance the interfacial adhesion performance of composite materials [26; 27; 28; 29; 30], such as acid treatment [31; 32], acid anhydride etching [33], plasma modification [34; 35], high-energy radiation modification [36], etc. Different from the strong acid and acetic anhydride etching commonly used in many previous studies, the Friedel-Crafts acylation reaction refers to a type of reaction where hydrogen or other functional groups in aromatic compounds are replaced by acyl groups [37; 38; 39]. The reaction between phthalic anhydride and PPTA fiber is an example of the Friedel-Crafts acylation reaction. The amide bond (-CO-NH-) in the molecular chain of PPTA fiber possesses strong electron-donating ability, which can induce changes in the electron cloud density of the benzene ring and enhance the reactivity of the ortho position of the benzene ring [40; 41]. Under the action of electrophilic reagents (such as phthalic anhydride), acylation reactions occur, resulting in the generation of -OH groups [42; 43]. At the same time, partial amide bonds undergo hydrolysis, leading to the formation of -COOH groups. The reaction mechanism is illustrated in Figure 1. The anhydrous AlCl\({}_{3}\) is the most representative catalyst for acylation reactions, widely used to increase the yield of the reaction product (ortho-benzoylic acid) between benzene and phthalic anhydride [44]. However, there is currently no research on the use of anhydrous AlCl\({}_{3}\) for the reaction between phthalic anhydride and PPTA fiber. The catalytic mechanism of anhydrous AlCl\({}_{3}\) for acylation reactions involves the carbon of the acyl group (-CONH-) on the benzene ring of PPTA fiber becoming a carbocation under the action of anhydrous AlCl\({}_{3}\), promoting the occurrence of aromatic electrophilic substitution reactions, effectively increasing the reaction rate and yield, thereby shortening the modification time, and introducing more polar oxygen-containing functional groups on the fiber surface, increasing the number of active sites on the fiber surface [45; 46]. This article investigates the effects of different concentrations of phthalic anhydride on etching plain-woven aramid fiber fabrics. Additionally, it innovatively explores the use of an anhydrous AlCl\({}_{3}\)-catalyzed fiber modification process, examining the impact of different catalytic modification times on the performance of PPTA/DGEBA composite materials.