Optimization of tribological and mechanical properties of nanocomposites of polyurethane/poly(vinyl acetate)/CaCO3.

Properties of samples containing polyurethane (PU), poly(vinyl acetate) (PVAc) and nanosize particles of calcium carbonate (CaCO3) are correlated with concentrations of these components. Interphase phenomena in PU/PVAc/CaCO3 nanohybrids have been studied before, we focus here on wear and scratch resistance. In addition to polymer blends containing CaCO3, the effects of adding CaCO3 with grafted PVAc, and CaCO3 with grafted silane and PVAc in varying ratios are also evaluated. For blends that do not contain the filler, a hypothesis explaining the concentration dependence of friction called the Bump Model is advanced and supported by the experimental results. In particular, we explain how creating a blend containing only 10% of a second polymer results in a dramatic drop of friction of the majority polymer. In single scratch testing, above 3% the filler displays 'its own' resistance to scratching. Chemical modification of the filler results in shallower residual depths--a consequence of improved interaction of the filler with the polymeric matrix. In sliding wear determination, strain hardening is seen for blends as well as for filler-containing composites. In tensile testing, addition of an unmodified filler increases the elongation at break and thus lowers the brittleness; the effect is even larger for chemically modified fillers.