Mechanical and tribological properties of nanocomposites based on ultra high molecular weight polyethylene (PEUAMM) and two-dimensional materials based on carbon

Abstract

This project is a request to continue a master's project (2017/14640-2 process) that was evaluated and indicated, due to its extreme potential, to become a doctoral project. Therefore, some results obtained until this moment will be used as a scientific basis for this project presented here. Ultra High Molecular Weight Polyethylene (UHMWPE) is a polymer with high tribological properties (wear resistance and low coefficient of friction) when compared to polymers with not so high molecular weight. Its good wear resistance and low coefficient of friction allow it to be applied in various segments of the industry, acting as a coating of machinery or composing parts of machinery. Therefore, its performance is still unsatisfactory for some applications due to its low wear resistance compared to materials (steel, titanic, glass, grit, ores etc.) in which it is in contact. Several studies have shown that the addition of nanofillers to the polymers, when well dispersed and distributed, allows developing materials with excellent tribological properties. The UHMWPE, due to its high viscosity, does not flow even at high temperatures and is not processable by the conventional melt mixing and conformation methods (extrusion, torque rheometer, injection etc.), which may be a limiting factor for some applications. Achieving a good homogeneity of filler in the UHMWPE matrix has been the major hurdle in obtaining a new high performance material. The results obtained during master's project present advances in the direction of developing a new material that presents better properties than the UHMWPE. First, blends formed by two high molecular weight polyethylenes, UHMWPE and High Molecular Weight Polyethylene (HMWPE), were produced during this period via melt mixture. In this stage the developed blends already presented tribological results superior to HMWPE and similar to UHMWPE. In order to achieve superior performance, graphene oxide with multilayers (mGO) was added to the HMWPE and the blends. Nanocomposites formed by only HMWPE/mGO presented slightly better tribological properties than UHMWPE. However, the nanocomposites formed by the HMWPE/UHMWPE blends did not show the expected increase in the properties with the addition of the mGO. These nanocomposites presented large agglomerates of mGO, because of that the properties of the blends were not modified with the insertion of the filler. This project intends to solve this problem in two ways, seeking a better homogeneity of the filler in the polymer matrix and improving the adhesion of the polymer-filler interface. To improve the dispersion and distribution of the filler in the matrix will be used a graphene oxide with greater control of the number of layers stacked, without the presence of particles not properly exfoliated, leading to a greater surface area. To improve adhesion between materials, the GO will be functionalized with specific alkyl chain chemical groups. Moreover, taking advantage of the good mechanical and tribological properties already achieved for HMWPE-UHMWPE (20%wt.) blends and based on the high capacity of reinforcement of the carbon nanotube for this system, it will be developed in this work nanocomposites of HMWPE and HMWPE-UHMWPE (20%wt.) containing carbon nanotube not functionalized and functionalized with an alkyl chain chemical groups. With these complementary strategies we intend to obtain a processable material in equipment commonly used in the plastics processing industry and that present mechanical and tribological performance superior to UHMWPE making it easy to access and of greater diversity of applications. (AU)