Abstract: Fiber-reinforced composites have many advantages, such as good mechanical properties, corrosion resistance, high-temperature resistance, and high moldability. It is the fastest-developing and most widely used class of composite material. The technology of fiber-reinforced composites has gradually matured in all aspects since the 1960s and is one of the new materials focused on research and development worldwide. Fiber-reinforced composites continue to develop toward high performance, multifunctionality, and complexity. To meet this demand for the materials, academics at home and abroad have investigated fiber-reinforced composites in greater depth, and current research primarily focuses on modifying the interfaces of composites. The small size region of the composite interface makes it more difficult for researchers to characterize its chemical structure, physical properties, and mechanical properties. Characterization of interfacial properties is thus also one of the hot spots in academic research. There is still a need to explore and refine the relationship between the microscopic interfacial and macroscopic mechanical properties of composites.
We aimed to modify the glass fiber (GF) surface with a sodium hydroxide solution to improve the interfacial properties between GF and vinyl ester resin (VER). Glass fibers were soaked in sodium hydroxide solutions at concentrations of 1 mol/L, 2 mol/L, and 3 mol/L for 24 h, 48 h, 72 h, and 96 h. Glass fiber reinforced vinyl ester resin (GF/VER) composites were made by using vacuum-assisted resin infusion molding technique. The interfacial shear strength between the fibers and the resin matrix was investigated by using the characterization method for the interfacial property of fiber extraction. We aim to examine the effect of the modification treatment on the surface morphology and the chemical interaction of the GF by using scanning electron microscopy and infrared spectroscopy. Before and after modification, the GF/VER composites were tested for interfacial shear strength, flexural strength, and impact strength by using a single fiber strength machine, a universal material testing machine, and a pendulum impact testing machine. The effects of sodium hydroxide treatment on the interfacial and mechanical properties of GF/VER composites were investigated. It was found that after modification with a solution of sodium hydroxide (concentration of 2 mol/L, and treatment time of 48 h), the wettability of GF was improved, the surface became roughened, and the reactive groups on the surface increased. After the modification treatment, the interfacial properties of GF/VER composites were improved. The monofilament interfacial shear strength reached 5.00 MPa, and the fiber bundle interfacial shear strength reached 29.04 MPa, 25.31%, and 27.48% higher than the original samples before modification, respectively. The mechanical properties of the composites were improved, with the bending strength reaching 346.72 MPa and impact strength reaching 158 kJ/m2, which increased by 20.96% and 25.40%, respectively, compared with the initial samples before modification. Thus, it was shown that sodium hydroxide treatment positively improved the bonding strength between the fiber and the resin. These research findings provide a benchmark for modification processing methods for fiber-reinforced composites and ideas for enhancing composites' interfacial and mechanical properties.

Key words: glass fiber, vinyl ester resin, interfacial modification, mechanical properties, vacuum-assisted resin infusion molding

摘要： 为改善玻璃纤维(Glass fiber, GF)与乙烯基酯树脂(Epoxy vinyl ester resin, VER)间界面性能，使用氢氧化钠溶液对GF进行表面改性处理。借助扫描电镜、红外光谱仪、万能材料试验机、摆锤冲击试验机等，分析改性前后GF的表面形态与化学结构的变化。测试改性前后GF/VER复合材料的单丝和纤维束界面剪切强度、弯曲强度、抗冲击强度。研究氢氧化钠处理对GF/VER复合材料的界面性能和力学性能的影响。结果表明：经过氢氧化钠溶液处理后，GF浸润性得到改善，表面变得粗糙，表面活性基团增多。单丝和纤维束的界面剪切强度相比改性前分别提升了25.31%、27.48%。GF/VER复合材料的弯曲强度与抗冲击强度相比改性前分别提升了20.96%、24.48%。

关键词: 玻璃纤维, 乙烯基酯树脂, 界面改性, 力学性能, 真空辅助树脂灌注成型