Karolina Gaska

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

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.

Gas Barrier, Thermal, Mechanical and Rheological Properties of Highly Aligned Graphene-LDPE Nanocomposites

This contribution reports on properties of low-density polyethylene-based composites filled with different amounts of graphene nanoplatelets. The studied samples were prepared in the form of films by means of the precoating technique and single screw melt-extrusion, which yields a highly ordered arrangement of graphene flakes and results in a strong anisotropy of composites morphology. The performed tests of gas permeability reveal a drastic decrease of this property with increasing filler content. A clear correlation is found between permeability and free volume fraction in the material, the latter evaluated by means of positron annihilation spectroscopy. A strong anisotropy of the thermal conductivity is also achieved and the thermal conductivity along the extrusion direction for samples filled with 7.5 wt % of GnP (graphene nanoplatelets) reached 2.2 W/m·K. At the same time, when measured through a plane, a slight decrease of thermal conductivity is found. The use of GnP filler leads also to improvements of mechanical properties. The increase of Young’s modulus and tensile strength are reached as the composites become more brittle.

Enhanced thermal conductivity of graphene nanoplatelets epoxy composites

Abstract Efficient heat dissipation from modern electronic devices is a key issue for their proper performance. An important role in the assembly of electronic devices is played by polymers, due to their simple application and easiness of processing. The thermal conductivity of pure polymers is relatively low and addition of thermally conductive particles into polymer matrix is the method to enhance the overall thermal conductivity of the composite. The aim of the presented work is to examine a possibility of increasing the thermal conductivity of the filled epoxy resin systems, applicable for electrical insulation, by the use of composites filled with graphene nanoplatelets. It is remarkable that the addition of only 4 wt.% of graphene could lead to 132 % increase in thermal conductivity. In this study, several new aspects of graphene composites such as sedimentation effects or temperature dependence of thermal conductivity have been presented. The thermal conductivity results were also compared with the newest model. The obtained results show potential for application of the graphene nanocomposites for electrical insulation with enhanced thermal conductivity. This paper also presents and discusses the unique temperature dependencies of thermal conductivity in a wide temperature range, significant for full understanding thermal transport mechanisms.

Novel electrical properties of extruded LDPE-GnP filled nanocomposites

This work presents the impact of shear rate variation during extrusion process of nanocomposite of low density polyethylene (LDPE) filled with graphene nanoparticles on its electrical properties. The obtained nanocomposites show, independently of the shear rate used during extrusion, field dependent non-linear behavior of the electric transport, which starts dominating the conduction current at about 20 kV/mm and become stronger with increasing filler content. However, at electric field strength below 20 kV/mm the nanocomposites extruded at higher shear rate exhibit increased level of conduction current as compared to those extruded at lower one.

Dielectricproperties of graphene nanoplatelets filled LDPE

This work presents studies on electrical properties of nanocomposites of low density polyethylene (LDPE) filled with graphene nanoplatelets (GnP) of different content. As compared to pure LDPE, significant reductions of the conductivity are found for the composites at relatively low electric fields (<20 kV/mm). A crossover effect is however seen at higher fields (>20 kV/mm), where a strongfield dependentnon-linear behavior dominates, yielding higher conduction currents that increase with increasing filler content. Results of investigations of dielectric response confirm the differences found in polarization currents during the measurements of dc conductivity.