Properties Of High-density Polyethylene Nanocomposites Research Articles

Size effects of graphene nanoplatelets on the properties of high-density polyethylene nanocomposites: morphological, thermal, electrical, and mechanical characterization.

High-density polyethylene (HDPE)-based nanocomposites incorporating three different types of graphene nanoplatelets (GnPs) were fabricated to investigate the size effects of GnPs in terms of both lateral size and thickness on the morphological, thermal, electrical, and mechanical properties. The results show that the inclusion of GnPs enhance the thermal, electrical, and mechanical properties of HDPE-based nanocomposites regardless of GnP size. Nevertheless, the most significant enhancement of the thermal and electrical conductivities and the lowest electrical percolation threshold were achieved with GnPs of a larger lateral size. This could have been attributed to the fact that the GnPs of larger lateral size exhibited a better dispersion in HDPE and formed conductive pathways easily observable in scanning electron microscope (SEM) images. Our results show that the lateral size of GnPs was a more regulating factor for the above-mentioned nanocomposite properties compared to their thickness. For a given lateral size, thinner GnPs showed significantly higher electrical conductivity and a lower percolation threshold than thicker ones. On the other hand, in terms of thermal conductivity, a remarkable amount of enhancement was observed only above a certain filler concentration. The results demonstrate that GnPs with smaller lateral size and larger thickness lead to lower enhancement of the samples’ mechanical properties due to poorer dispersion compared to the others. In addition, the size of the GnPs had no considerable effect on the melting and crystallization properties of the HDPE/GnP nanocomposites.

A comparative study on different ionic liquids used as surfactants: Effect on thermal and mechanical properties of high-density polyethylene nanocomposites

Dialkyl imidazolium and alkyl phosphonium salts were synthesized to be used as new surfactants for cationic exchange of layered silicates, such as montmorillonite (MMT). The synthesized phosphonium (P-MMT) or imidazolium ion (I-MMT)-modified montmorillonites display a dramatically improved thermal degradation with respect to commonly used quaternary ammonium salts. This thermal degradation window can still be shifted toward higher temperatures after washing of modified clays. Two kinds of organic species can be identified onto clay: physically adsorbed species versus chemically adsorbed species. To evidence the impact of these thermally resistant ionic liquids, the modified montmorillonites were introduced in a great commodity polymer, i.e., high-density polyethylene. Thermoplastic nanocomposites with a very low amount of nanofillers were processed in melt by twin screw extrusion. If the thermal stability of polyethylene is slightly increased with only 2 wt.% of thermostable made clays, the stiffness–toughness compromise is well improved since a strong increase in modulus is achieved with both thermostable clays without loss of fracture properties. But these mechanical performances are mainly obtained with unwashed thermostable clays because the physically adsorbed organic species onto clay surfaces behave like a compatibilizer that helps both the dispersion into the PE matrix and improves the clay/matrix interface quality.