# Mechanical and Conductive Behavior of Graphite Filled Polysulfone-Based Composites
## 1 Introduction
Polymer composites can replace metals as fuel cell materials by ensuring adequate electrical and thermal conductivity, good processability of bipolar plates, and light weight [14; 15]. Conductive fillers such as Gr, CB, CNT, nGr and CF can improve the electrical characteristics of CPCs [16]. Bipolar plates can be made from a wide range of materials. Pure graphite was initially selected because it has a good combination of thermal and electrical properties, is available in a wide range of shapes and sizes, and is simple to obtain using conventional processes. However, it is not economically feasible to produce in large quantities due to its inherent brittleness and costly machining methods [17]. Commercially available composite bipolar plates can be based on various polymer matrices, such as polypropylene (PP) [18], polyphenylene sulfide (PPS) [19], polyvinylidene fluoride (PVDF) and phenolic resin [20]. The employment of big graphite particles as the matrix's major filling component, or vice versa, was also investigated by many researchers. They found that mixing a larger primary conductive filler together with a smaller secondary conductive filler could improve the composite electrical conductivity while also improving its mechanical qualities. [PERSON] et al. [21] investigated the effect of conductive filler size combinations on the electrical conductivity of materials for bipolar plate applications in fuel cells. In their investigation, [PERSON] et al. employed various graphite particle sizes and discovered that electrical conductivity increased as the graphite particle size increased [22]. [PERSON] et al. studied the electrical characteristics of composites containing expanded graphite (EG) of various sizes (30, 50, 150 and 300 \(\upmu\)m) and phenolic resin as a matrix and discovered that the EG/phenolic composites with the largest EG size of 300 \(\upmu\)m had the highest electrical conductivity [23]. Particle size and density are important factors that influence the rheology of composite materials. Smaller particles often have higher viscosities and viscoelastic elastic modulus than bigger particles because of their larger surface area and tendency to agglomerate [24]. Particle size effects and powder loading are strongly related. [PERSON] et al. investigated the effects of the 316L feedstocks' solid loading content and powder particle size distribution on rheological properties. This only applied to powder loadings above 65 vol.%; for lower powder loadings, viscosity changes were less pronounced. They also observed that an increase in composite viscosity is caused by a decrease in particle size [25]. It is possible to create nanocomposites with superior qualities using carbon nanofibers (CNFs), which are considerably larger than carbon nanotubes (CNTs) but considerably smaller than regular carbon fibers. This might lead to the development of numerous new applications. They come in sizes between 70 and 200 nm, and their length is thought to be between 50 and 100 \(\upmu\)m. It has already been shown that CNFs can be used as reinforcements to enhance the qualities of a number of polymer matrix systems, including polycarbonate, epoxy, polyethylene, polypropylene, polymethyl methacrylate, polyether ether ketone, and polystyrene [26]. The results show enhancement in mechanical [27], thermal [28], and dielectric/electrical [29] properties. Because of their exceptional mechanical properties and heat stability, high-performance polymers, such as polysulfone (PSU), are particularly notable among thermoplastics. PSU is widely used in modern technology because of its excellent characteristics, including its thermal, mechanical, chemical, strength, and toughness properties as well as its ability to construct polymeric membranes with a range of functions [30; 31].