# The Influence of Copper Oxide Particle Size on the Properties of Epoxy Resin
## 3 Results and Discussion
### Mechanical Properties
The increase in the elastic modulus as the filler content increased is attributed to the stiffening effect of the fillers on the polymer composite [31]. Research by [PERSON] and others focused on analyzing the impact of recycled copper particles. Their goal was to investigate how different particle sizes affect mechanical properties. The particle sizes were 10 \(\upmu\)m and 300-400 \(\upmu\)m, and the effects of mixing different particle sizes were studied. The results of the study showed that epoxy composites with a blend of recycled copper particles had higher flexural modulus values compared to composites whose filler consisted of recycled copper with a particle size of 10 \(\upmu\)m. Smaller filler particles contributed to the creation of a more compact structure, which in turn provided the composites with better strength. The presence of particles caused local changes in the stress field which could partially reduce the effects of cavitation deformation and instead initiate plastic deformation in the surrounding matrix during shear. Smaller particles have been shown to be more desirable due to their ability to provide better bonding; however, particles that are too small may require more polymers, resulting in reduced flexural strength. On the other hand, particles that are too large can act as discontinuities, which also reduces flexural strength. Differences between particle size groups are likely due to differences in packing density. A denser fill leads to less porosity of the composite, which in turn increases flexural strength. The results suggest that the fine filler in the mixture filled the gaps between the larger particle sizes, which contributed to the increased stiffness of the composites. The use of two different particle sizes allowed for a more even distribution of particle sizes, which in turn reduced agglomeration and increased the composite's resistance to cracking [32]. The presented test results and examples of other results available in the literature confirm the influence of particle size on bending properties while also showing that this influence is not clear and depends on many factors. The research results confirm the need to conduct this type of research due to gaps in the science related to the influence of particles on the properties being tested. A study conducted by [PERSON] et al. focused on the impact of food waste particle size on epoxy resin properties. The filler content was fixed at 15% by weight, and the particle size was varied, namely, (i) 100-250 mm, (ii) 350-500 mm, and (iii) 650-800 mm. The researchers investigated the effect of particle size on the impact strength of epoxy resin. It was observed that as the particle size decreased, the impact strength increased, indicating \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material** & **Density, g/cm3** & \begin{tabular}{c} **Impact Strength,** \\ **kJ/m2** \\ \end{tabular} & \begin{tabular}{c} **Flexural Strength,** \\ **MPa** \\ \end{tabular} & \
\begin{tabular}{c} **Flexural Modulus,** \\ **MPa** \\ \end{tabular} &
\begin{tabular}{c} **Deflection at** \\ **Failure, mm** \\ \end{tabular} \\ \hline EP & 1.157 \(\pm\) 0.001 & 8.66 \(\pm\) 1.32 & 63.9 \(\pm\) 0.9 & 3747 \(\pm\) 277 & 2.6 \(\pm\) 0.1 \\ \hline
10\% micro Cu & 1.265 \(\pm\) 0.005 & 14.93 \(\pm\) 2.11 & 72.4 \(\pm\) 4.0 & 4391 \(\pm\) 222 & 2.6 \(\pm\) 0.1 \\ \hline
10\% 40–60 nmCu & 1.301 \(\pm\) 0.005 & 12.10 \(\pm\) 1.51 & 83.4 \(\pm\) 9.3 & 4993 \(\pm\) 658 & 2.6 \(\pm\) 0.7 \\ \hline
10\% 10–30 nmCu & 1.267 \(\pm\) 0.002 & 16.86 \(\pm\) 3.82 & 79.8 \(\pm\) 3.9 & 4245 \(\pm\) 265 & 3.0 \(\pm\) 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results for basic physical and mechanical properties. better energy absorption during dynamic impact. Three potential reasons were proposed to explain this outcome: improved compatibility of the fine fillers with epoxy resin, reduced void content, and the finding that smaller particles do not readily detach from the matrix compared to larger particles [33].