Effect of processing conditions on the structure, electrical and mechanical properties of melt mixed high density polyethylene/multi-walled CNT composites in compression molding

Abstract

(2017). Effect of processing conditions on the structure, electrical and mechanical properties of melt mixed high density polyethylene/multi-walled CNT composites in compression molding. Materials Testing, 59 (2) Department of Materials Science and Engineering, University of Sheffield, S1 3JD, UK Abstract: Melt mixed high density polyethylene (HDPE)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared via twin-screw extrusion and then compression moulded into sheets. The effect of heating temperature, pressing time and cooling rate on the structure, electrical and mechanical properties of the compression moulded nanocomposites was systematically investigated. Volume resistivity tests indicate that the nanocomposite with 2 wt% MWCNTs, which is in the region of the electrical percolation threshold, is very sensitive to the compression moulding parameters such that heating temperature > pressing time > cooling rate. Generally, the resistivity of nanocomposites decreases with increasing heating temperature and pressing time. Interestingly, the electrical resistivity of the rapidly cooled nanocomposite with 2 wt% MWCNTs is 1~2 orders lower than that of the slowly cooled nanocomposite with the same MWCNT loading. This can be attributed to the lower crystallinity and smaller crystallites facilitating the formation of conductive pathways. The tensile properties of the nanocomposite with 2 wt% MWCNTs are also influenced by the compression moulding parameters to some extent, while those of the nanocomposites with higher MWCNT loading are insensitive to the changes in processing conditions. The predicted moduli from Halpin-Tsai and Mori-Tanaka theoretical models show good agreement with the experimental results. This work has important implications for both process control and the tailoring of electrical and mechanical properties in the commercial manufacture of conductive HDPE/MWCNT nanocomposites.

Carbon Nanotube Reinforced High Density Polyethylene Materials for Offshore Sheathing Applications

“…Direction of extrusion is represented by the arrow on the top right of all the images ( Figure 2 ). In comparison to monolithic HDPE ( Figure 2 a), CNTs (and their aggregates) seem to be aligned in the direction of extrusion, which was also observed in other reports [ 26 , 27 , 28 ] as well.…”

“…Direction of extrusion is represented by the arrow on the top right of all the images (Figure 2). In comparison to monolithic HDPE (Figure 2a), CNTs (and their aggregates) seem to be aligned in the direction of extrusion, which was also observed in other reports [26][27][28] as well. Mechanical properties from tensile testing of the neat HDPE and CNT filled nanocomposites are shown in Figure 3; Figure 4.…”

“…For instance, the tensile strength after 600 h of exposure was found to be 16.75 or 16.71 MPs for 4 wt% and 6 wt% CNT-filled nanocomposites respectively. The cause of such minimal or nearly no improvement in mechanical properties is due to the agglomeration, as evident in Figure 2 d and reported in other publications [ 18 , 20 , 27 ]. Agglomerates ( Figure 2 d) reduce the surface area of CNTs interacting with the polymeric chains; hence, the mechanical properties were negatively affected ( Figure 3 and Figure 4 ).…”

A review of electrically conductive poly(ether ether ketone) materials

“…added thermally reduced graphene nanosheets modified by poly(ether sulfone) (PES) into PEEK and this produced an abrupt transition from electrical insulator to semiconductor behaviour at 1 wt%. Electrically conductive PEEK composites, like other conductive polymer composites, have different electrical percolation thresholds due to differences in parameters such as type and grade of nano‐filler, modification of the surface chemistry of the nano‐filler and the type and quality of mixing, which will be discussed in detail in the next sections 32–40 . In a few studies, other fillers such as Ag nanoparticles (AgNPs) and nanowires (AgNWs), Ni macroparticles and expanded graphite (EG) were loaded into PEEK to improve its electrical conductivity 41–45 .…”