Mechanical and tribological properties of rubber blends composed of HNBR and in situ produced polyurethane

A peroxide curable hydrogenated nitrile rubber (HNBR) was modified by in situ produced polyurethane (PU), added in 50 and 100 parts per hundred rubber (phr). The crosslinked PU was formed from solid PU precursors, viz. polyol and blocked polyisocyanate, during curing of the HNBR rubber. Dynamic mechanical thermal analysis (DMTA) revealed that HNBR formed the continuous whereas PU the dispersed phase. Mechanical properties (hardness, tensile modulus, ultimate tensile strength and strain, tear strength) of the HNBR and HNBR + PU were determined and collated. Tribological properties were investigated in pin (steel)-on-plate (rubber) (POP), roller (steel)-on-plate (rubber) (ROP), oscillating cylinder (steel)-on-rubber plate (Fretting) and rolling ball-(steel)-on-plate (rubber) (RBOP) test configurations. Coefficient of friction (COF) and specific wear rate of the HNBR/PU systems were determined. It was found that the resistance to wear increased with PU hybridization. On the other hand, the COF did not change much with the PU content. The friction and wear characteristics strongly depended on the test configurations. The worn surface of the HNBR systems was inspected in scanning electron microscope (SEM) and typical wear mechanisms concluded.