The “Superlubricity State” of Carbonaceous Fillers on Polymer Composites

Abstract

In 2019 Ferreira et al. observed for the first time the influence of the superlubricity phenomenon of platelet‐like fillers on the properties of high molecular weight polyethylene (HMWPE) in the molten state. At the time, the study was carried out in the solid state of the polymer, analyzing the influence of the superlubricity phenomenon of oxide graphene and oxide graphite (GrO) agglomerates on the mechanical properties of the HMWPE. It was observed that the agglomerates, due to their superlubricity state, toughen the HMWPE polymer matrix. Here, mechanical tests (tensile), X‐ray microtomography, and scanning electron microscopy are carried out to elucidate this phenomenon. The same is observed for polystyrene containing very poorly dispersed GrO. The results presented here are a paradigm shift, as it has always been thought that the presence of agglomerates is harmful, but the opposite is proven here. In general, this paper can contribute a lot to the development of new composites and nanocomposites based on fillers that present the superlubricity phenomenon.

Role of Graphene Oxide on the Mechanical Behaviour of Polycarbonate-Urethane/Graphene Oxide Composites

“…As can be seen, the PCU + GO-2 composites mechanical performance results from the particle microdomains presence. Ferreira et al showed that carbonaceous filler microdomains have an important role in the mechanical properties development of polymer composites because of its superlubricity effect 68 . The domains are formed by the agglomeration of small GO blocks bonded by secondary forces, and it is possible that during a high deformation regime enough tension is reached to induce the GO block slipping, as shown in Figure 13.…”

High-Tribological-Performance Polymer Nanocomposites: An Approach Based on the Superlubricity State of the Graphene Oxide Agglomerates

“…Ferreira et al (2019 and 2020) recently studied the mechanical tensile properties of the high-molecular-weight polyethylene (HMWPE) nanocomposite containing 0.1 wt.% of mGO and graphite oxide (GrO), and they observed that due to the high viscosity of the matrix, this nanocomposite and composite had a high content of agglomerates but with satisfactory ultimate tensile properties [ 12 ]. Their research showed that the agglomerates are included in the HMWPE matrix and are not segregated at the boundary of the powders, not weakening the material.…”

“…Another essential feature of this system is that during the processing of the HMWPE nanocomposite, the polymer flow inside the extruder guides the agglomerates in the same direction, conducting the mGO agglomerated flakes, so they are organised parallel to each other, similar to playing cards. They also reported that agglomerates arranged in this way can act as lubricants by slipping between the agglomerated flakes (superlubricity phenomenon) [ 12 , 13 ]. Slips from the agglomerates can help the polymer achieve greater tensile toughness in the solid state and reduce viscosity in the molten state as they are present in small amounts [ 12 , 13 ].…”

“…They also reported that agglomerates arranged in this way can act as lubricants by slipping between the agglomerated flakes (superlubricity phenomenon) [ 12 , 13 ]. Slips from the agglomerates can help the polymer achieve greater tensile toughness in the solid state and reduce viscosity in the molten state as they are present in small amounts [ 12 , 13 ]. This study was a paradigm shift in the science of polymeric composites because it showed that agglomerates could act beneficially to the properties of polymers and not just as a defect.…”

“…HMWPE is a polyethylene matrix with intermediate molecular weight, i.e., it presents better tribological properties than low-molecular-weight polyethylene and a better processability than UHMWPE. In a previous study [ 12 , 13 ], despite the processing difficulty (mixing) of HMWPE nanocomposites in relation to HDPE, LDPE and LLDPE nanocomposites, it was observed that the agglomerates contained in HMWPE might present a superlubricity phenomenon, being beneficial to the properties of the polymer. A new study based on the superlubricity phenomenon of nanofiller agglomerates and its consequences on the tribological properties of polyethylene matrix nanocomposites was carried out here.…”