[PERSON]  
2 Digital Manufacturing and Materials Characterization Laboratory, School of Science and Technology, International Hellenic University, 14 km Thessaloniki, GR-570 01 N. Moudania, Greece; [EMAIL_ADDRESS] (K.T. ); [EMAIL_ADDRESS] (M.-E.G. ); [EMAIL_ADDRESS] (D.T.) [PERSON]  
2 Digital Manufacturing and Materials Characterization Laboratory, School of Science and Technology, International Hellenic University, 14 km Thessaloniki, GR-570 01 N. Moudania, Greece; [EMAIL_ADDRESS] (M.-E.G. ); [EMAIL_ADDRESS] (D.T.) [PERSON]  
2 Digital Manufacturing and Materials Characterization Laboratory, School of Science and Technology, International Hellenic University, 14 km Thessaloniki, GR-570 01 N. Moudania, Greece; [EMAIL_ADDRESS] (K.T. ); meggiorta@ihu. conductivity and mechanical properties of SCB-PE compared to the counterpart metal materials used in these systems limit its advantages and create the necessity for further improvement. More specifically, polymer materials used in geothermal piping systems, where ground heat exchange is a crucial parameter, should present adequate thermal conductivity combined with good temperature resistance and mechanical properties since these systems may experience changes in temperature (\(-\)4-46 \({}^{\circ}\)C) and pressure (up to 415 kPa) [4]. Adding a small amount of a reinforcing filler in a polymer matrix can lead to a multi-component system with enhanced physicochemical properties, depending on the selected filler's and matrix's properties separately. For this reason, during the last decades, polymer composites and nanocomposites have been extensively studied to gain insights into the factors that control and affect the reinforcement effect and subsequently develop new ways of improving these systems' fabrication. Carbon fillers such as graphene nanoplatelets (GNPs), expanded graphite (EG), carbon nanotubes (CNTs) etc., present outstanding mechanical performance, thermal and electrical conductivity and thus are widely used as a reinforcing material. Nonetheless, it is essential to mention that the extent of property reinforcement is inseparably linked to the filler's dispersion and the filler-matrix interactions, as many studies suggest [5; 6]. Many methods have been proposed in order to improve the filler's dispersion in the polymer matrix [7; 8; 9; 10]. However, ball-milling presents many advantages, i.e., it is environmentally friendly and industrially applicable [11; 12; 13]. Its operating principle is based on the mechanical forces generated by repeated events to the milling tools. These forces are then transferred to the inserted materials, the filler and polymer matrix, separating this way the filler's aggregates [14]. Based on the applied conditions (milling time, temperature, rounds per minute etc. ), various phenomena can occur, such as diffusion of the atoms, crack of the filler's particles, and intimate mixing [14]. The main characteristic of a polymer nanocomposite affected by the filler's dispersion is its mechanical properties. Improved distribution of the reinforcing particles leads to a more uniform distribution of the load transfer and an enhanced nanoconfinement effect [15; 16; 17]. [PERSON] et al. have shown that ball-milling induced better dispersion and stronger interfacial interaction of modified multiwalled nanotubes (MWNTs) in a Polyamide-6, 6 (PA66) matrix, which resulted in improved mechanical properties at a lower filler loading [18]. [PERSON] et al. have also prepared poly(butylene terephthalate) (PBT) nanocomposites containing modified nano-Sb\({}_{2}\)O\({}_{3}\) particles dispersed by high-speed rotating and high-energy ball-milling. The results showed that better dispersion was achieved for the nanocomposites prepared by ball-milling resulting in better mechanical properties [19]. Polyetheretherketone (PEEK) filled with nano-SiO\({}_{2}\) particles nanocomposites have also been fabricated by compounding via the ball-milling technique by [PERSON] et al. [20]. They reported substantial improvement in material stiffness [20].