# The Influence of Copper Oxide Particle Size on the Properties of Epoxy Resin
## 1 Introduction
Epoxy resins exhibit better wettability, leading to increased strength parameters and enhanced resistance to water. Additionally, after curing, epoxy resins do not contain ester groups, which significantly improves their corrosion resistance. An analysis of various studies provides pertinent information on the comparison of wettability between epoxy and polyester resins. [PERSON] [8] found that bifunctional epoxy displays superior wettability among thermoset resins, regardless of the surface structure of the carbon nanotube material. Additionally, [PERSON] [9] highlighted the improved wettability achieved by curing epoxy resin with specific surface sizing, indicating its effectiveness in fostering adhesion with carbon fibers. Furthermore, [PERSON] et al. [10] characterized the wettability between carbon fibers and an epoxy resin matrix, emphasizing the significance of dynamic contact angle measurements in evaluating their interface. In contrast, [PERSON] et al. [11] and [PERSON] et al. [12] discussed the challenges arising from poor wettability between polyester resins and materials such as thiolenic resins and natural fibers, respectively. These studies emphasized the importance of addressing wettability issues to enhance the performance of composite materials. Overall, the literature suggests that epoxy resin generally exhibits superior wettability characteristics compared to polyester resin, attributable to factors such as resin structure, curing processes, and surface treatments. It is essential to understand and optimize wettability to achieve robust interfacial bonding and enhance the overall performance of composite materials. These advantages make epoxy resins suitable for replacing polyester resins in the production of prepregs, which are used in the aviation industry. Table 1 provides a comparison of the mechanical properties of the most commonly utilized thermosetting resins. Epoxy resins offer several advantages when used with a hardener. They have a longer working time, which facilitates application, and exhibit low shrinkage during the hardening process. Additionally, they can be hardened at temperatures as low as 7 \({}^{\circ}\)C, which makes them suitable for use in colder environments. However, they come with some drawbacks, including their higher price, which is typically double that of polyester resin. Moreover,the amine hardeners used with epoxy resins can be toxic, and the need to use thinners and plasticizers increases the overall cost [9]. Epoxy composites also incorporate reinforcement in the form of particles, such as silica particles. These particles may be used individually or in conjunction with a fibrous reinforcement to enhance the strength and durability of the material [10; 11; 12; 13]. [PERSON] et al. examined the influence of the size and volume fraction of spherical silica particles on the fracture toughness of epoxy composites. The researchers incorporated fractions ranging from 1.56 \(\upmu\)m to 240 nm and volume fractions from 0 to 0.35 into the epoxy resin. The study revealed that the fracture toughness significantly improved with an increase in volume fraction and a decrease in diameter. It was observed that as the volume fraction of small particles increased, so too did the fracture toughness. Furthermore, the researchers noted that the size of the particles played a role in the enhancement of strength when smaller particles were utilized [14]. [PERSON] et al. conducted a study comparing the properties of mineral silica-based composites to conventional fused silica composites, which are commonly used as filler materials. The study examined the effect of three different particle shapes--angular, cubic, and elongated--on tensile strength, modulus, flexural strength, modulus, thermal stability, and Tg at filler contents ranging from 15 to 45 wt%. The results showed that the addition of particulate filler increased the mechanical properties of the composites while also reducing the coefficient of thermal expansion.