Characterization of Highly Filled PP/Graphite Composites for Adhesive Joining in Fuel Cell Applications

Abstract

In order to evaluate the suitability of graphite composite materials for use as bipolar plates in fuel cells, polypropylene (PP) was melt compounded with expanded graphite as conductive filler to form composites with different filler contents of 10–80 wt %. Electrical resistivity, thermal conductivity, and mechanical properties were measured and evaluated as a function of filler content. The electrical and thermal conductivities increased with filler content. Tensile and flexural strengths decreased with the incorporation of expanded graphite in PP. With higher graphite contents, however, both strength values remained more or less unchanged and were below the values of pure PP. Young’s-modulus and flexural modulus increased almost linearly with increasing filler content. The results of the thermogravimetric analysis confirmed the actual filler content in the composite materials. In order to evaluate the wettability and suitability for adhesive joining of graphite composites, contact angle measurements were conducted and surface tensions of composite surfaces were calculated. The results showed a significant increase in the surface tension of graphite composites with increasing filler content. Furthermore, graphite composites were adhesively joined and the strength of the joints was evaluated in the lap-shear test. Increasing filler content in the substrate material resulted in higher tensile lap-shear strength. Additionally, the influence of surface treatment (plasma and chemical) on surface tension and tensile lap-shear strength was investigated. The surface treatment led to a significant improvement of both properties.

Thermal Conductivity and Electrical Resistivity of Melt-Mixed Polypropylene Composites Containing Mixtures of Carbon-Based Fillers

“…These fillers have to form a thermally conductive network in the matrix in order to transfer their high conductivity into the composite. Next to high thermal conductivity, some applications require at the same time also high electrical conductivity, such as bipolar plates in fuel cells [3,4,5]. The electrical conductivity requires networks with neighboring conductive particles, which can be separated by thin polymer films with distances below the electron hopping and or tunneling distance (assumed to be around 2–8 nm) [6].…”

“…In this study, composite materials based on polypropylene (PP) containing different kinds of carbon-based fillers were prepared using small-scale melt mixing compounding. This investigation focused on PP, as it is a widely used material for bipolar plate applications [2,5,17,21] where both electrical and thermal conductivity play a role. In order to see general effects and enable the desired good melt processability, the filler content was limited to 7.5 vol%.…”

Highly conductive polypropylene‐based composites for bipolar plates for polymer electrolyte membrane fuel cells

“…The various conductive fillers were systematically tested concerning their effect on the electrical conductivity and flexural strength. Based on the literature [1–23] research and systematic in‐house investigation, a high amount of graphite (>40 wt%) and carbon nanotubes were selected as the main fillers of the composites. The effect of the additional fillers was thoroughly investigated in this paper.…”

“…As polymers are intrinsically and electrically insulating materials, apart from some special types such as polyaniline (PANI), they must be loaded with high amounts of conductive fillers in order to reach the required electrical conductivity values (≥50 S cm −1 in through-plane and ≥100 S cm −1 in-plane direction) [9]. There has been a large number of research studies and reviews on polymer, both thermoset-and thermoplastic-based composites for BPPs [10]. In general, thermosets usually show higher strength, can accommodate higher content of fillers, due to their low viscosity, but are quite brittle and usually require longer processing times [11][12][13].…”

Thermally enhanced polyolefin composites: fundamentals, progress, challenges, and prospects

“…A very high κ c of 12.4 W/m·K was reported for melt blended PP/EG composite containing 80 wt. % EG [ 113 ]. Wu et al fabricated low-temperature expandable graphite (LTEG)/low-density polyethylene (LDPE) composites with high κ c via an in situ expansion melt blending process followed by solid-state shear milling (S3M) for 20 cycles to produce GNPs/LDPE composites ( Figure 11 ) [ 114 ].…”