Electrical, Mechanical, and Thermal Properties of LDPE Graphene Nanoplatelets Composites Produced by Means of Melt Extrusion Process

Abstract

Composites of LDPE filled with different amounts of graphene nanoplatelets (GnP) were prepared in form of films by means of precoating technique and single screw melt-extrusion using two types of screws, compression and mixing. This manufacturing process imposes strong anisotropy on the sample's morphology, in which the nanoplatelets become oriented along the extrusion direction. Such orientation of GnP in LDPE matrix is confirmed by scanning electron microscopy observations and it yields unique electrical properties. As compared to pure LDPE, significant reductions of the through-plane conductivity are found for the composites at relatively low electric fields (<20 kV/mm) at low filler concentrations. Above the field level of 20 kV/mm, a crossover effect is observed that results in a strong field dependency of the conductivity where the non-linear behavior starts to dominate. Moreover, differential scanning calorimetry (DSC) results indicate a decrease in polymer crystallinity of the composite matrix with increasing filler content, whereas thermogravimetric (TG) analysis shows a slight increase in the material's thermal stability. Application of GnP also leads to improvement of mechanical properties, manifested by the increase of Young's modulus and tensile strength in both types of samples.

Effect of Filler Orientation on the Electrical Conductivity of Carbon Fiber/PMMA Composites

“…The matrix material was PMMA Plexiglas 7N (Evonik Röhm GmbH, Darmstadt, Germany), with weight-average molar mass 99 kg/mol, density 1.19 g/cm 3 . polydispersity index = 1.52.…”

“…%). material was chopped carbon fibers with a diameter of 7 µm, an initial length of 6 mm, a density of 1.79 g/cm 3 and a specific resistance of 1.7 × 10 −3 Ω/cm, obtained from Tenax ® -JHT C493 6 mm (Toho Tenax Europe GmbH, Wuppertal, Germany).…”

“…These differences are explicitly stated in Figure 4 and are indicated with horizontal error bars in Figure 5. where ρCF = 1.79 g/cm 3 and ρCF = 1.19 g/cm 3 . The extrusion processing parameters (T = 200 °C, extrusion speed = 0.08 mm/s) were optimized for CF/PMMA composites [7,10] such that the porosity became very small and thus could be neglected in Equation (5).…”

“…Nowadays, the conductivity of CPCs is generally explained by "conductive pathways" in the composites, which are formed by conductive fillers [1][2][3][4][5]. When the filler fraction increases, the number of "conductive pathways" grows, and consequently, the conductivity of the composite also increases.…”

Robust measurements of electric conductivity in polyethylene based materials: measurement setup, data processing and impact of sample preparation

“…In the first extrusion, pellets of the master-batch were manufactured, which then were used in the second extrusion to obtain thin films with an average thickness of 100 m. The extruder temperatures from the hopper to the die were respectively: 115, 130, 140 and 140 °C . A constant speed of 5 rpm was kept for the compression screw [5]. The pressed specimens were prepared at KTH by compression molding (LabPro 400 Press, Frontlijne Grotnes) from LDPE pellets into 300 m thick film.…”