Influence of mechanical blending method and consolidation temperature on electrical properties of the prepared graphene nanoplatelet/UHMWPE composite

The high performance of ultra-high molecular weight polyethylene (UHMWPE) has led to its use in aerospace, industrial and medical applications. Reinforced with conductive fillers, it has been used to develop conductive polymer composites through the formation of a segregated structure. For assessing the influence of processing conditions on electrical properties, coatings based on graphene nanoplatelet (GNP)/UHMWPE composites at a GNP content of 0.1 to 8 wt% were prepared, by two different mechanical blending methods, i.e., using a ball mill (BM) or blade mixer (BL), followed by a hot-compression process at different consolidation temperatures, 175 ºC or 240 ºC. Percolation thresholds at 0.5 wt% and 3.0 wt% were observed with the aforementioned mechanical techniques, respectively, with a jump in conductivity exceeding ten orders of magnitude. The use of the highest consolidation temperatures provided a decrease of the percolation threshold to 0.3 wt% in the composites prepared by ball mill, while maintain the same critical content by using the blade mixer technique. Images obtained by optical and scanning electron microscopy allowed to associate the former behavior to the different relative position of GNP and UHMWPE powder: the ball mill flaked the GNPs onto the surface while the blade mixer embedded the GNPs into voids in the fibrillary structure. Lock-in thermography (LIT) revealed on the surface of the composite manufactured by ball milling a better distribution of the graphene and the corresponding electrical paths, compared with the composites prepared by blade mixer.