Effect of amorphous/recycled polypropylene ratio on thermo-mechanical properties of blends for lubricant applications

This work focuses on the development of gel-like formulations for use as lubricating greases. These dispersions were formulated using mineral oil and recycled/amorphous polypropylene blends. In particular, the influence of the polypropylene concentration ratio (Wi) on the rheology, thermal and some lubricant performance properties of polymer/oil blends were studied. The rheological responses of these systems were quite different, influenced mainly by the concentration of amorphous polypropylene. At intermediate temperatures (25 °C, 50 °C) and high recycled polypropylene concentrations (Wi > 0.5), the evolution of small-amplitude oscillatory shear (SAOS) functions was very similar to those found with other commercial lubricating greases. Samples with lower concentrations of amorphous polypropylene (12.5%) present maximum GN° values in the temperature range studied. An Arrhenius-type equation can be used to quantify the thermal dependence of the linear viscoelastic functions of these gel-like dispersions. In general, sample formulations studied exhibited values of the friction coefficient comparable to those found for traditional lithium lubricating greases.