# The Influence of Copper Oxide Particle Size on the Properties of Epoxy Resin
## 4 Conclusions  
Summing up the obtained test results, a positive effect of using copper particles as reinforcements in the context of strength parameters was noticed. An increase in mechanical properties was observed in relation to the control sample of a pure polymer for all tested composites. In addition, an upward trend in parameters was observed with reductions in individual particle sizes. The best strength parameters were achieved for composites reinforced with particles in the size range of 10-30 nm. For these materials, the best results in the static tensile test were recorded, which is consistent with the theory in the literature on the dependence of strength on adhesion forces and a larger contact surface between the matrix and the reinforcement. In addition, it was noted that larger particles cause agglomeration, which adversely affects strength properties. In the flexural strength tests, the composite modified with particles in the 40-60 nm range had the best strength. This is related to the examined structure of copper particles which, due to their developed dendritic surfaces, showed greater plastic properties. Thus, it can be concluded that the strength parameters depend not only on the size of the particles but also on their structural nature. Composites reinforced with copper oxide do not degrade under the influence of environmental conditions in the short term. Ultimately, the copper particles improve the thermal conductivity of the composite relative to the reference material. An increase of more than 18% was obtained for the material modified with particles in the 40-60 nm range, and a 16% increase was obtained for the material reinforced with particles in the 10-30 nm range, which means that reducing the particle diameter has a positive effect on thermal conductivity; however, it occurs at a certain critical value, blocking the formation of a continuous percolating network. The novelty of the field of copper-epoxy composites has been addressed in various studies. [PERSON] et al. [47] introduced a foamed copper-epoxy composite that showed improved wear resistance, making it a unique material for abrasion-resistance applications. [PERSON] and colleagues [32] also observed flexural strength and modulus improvements by incorporating mixed copper particles into epoxy composites, highlighting the potential for innovative material improvements. [PERSON] and [PERSON] investigated using copper(II) hexafluorosilicate-modified epoxy-amine composites for flame protection, which showed progress in increasing thermal stability through chemical interactions [48]. [PERSON] et al. 's study on adding copper slag filler to bamboo-epoxy composites showed improved physical and mechanical properties, suggesting the innovative development of composite materials [49]. [PERSON] and colleagues developed self-extinguishing copper(II)-coordinated epoxy-amine composites for pouring polymer floors, demonstrating progress in creating materials with improved properties [50]. [PERSON] et al. demonstrated a strengthening of the epoxy-copper heterojunction by incorporating sulfur-containing polymers, suggesting new approaches to improving material interfaces [51]. In summary, the research results presented, the discussion in this article, and the examples illustrated above highlight the need for the further development of epoxy composites modified with copper and copper oxides. These comparisons indicate the continuing need for research in this field and the need to create new copper-epoxy composites that can be used in various areas, ranging from wear-resistant materials and flame protection to composites with improved mechanical and thermal properties. The research studies mentioned above jointly contribute to the development of materials engineering by introducing innovative recipes and applications of copper-epoxy composites.