Mechanical and rheological response of polypropylene/boehmite nanocomposites

In this study, the influence of synthetic boehmite alumina nanoparticles with various surface treatments on the morphology, crystallization behavior and mechanical properties of polypropylene copolymer nanocomposites was studied. In particular, a series of polypropylene/boehmite alumina nanocomposites, containing up to 10 wt% of untreated and of octylsilane-functionalized boehmite alumina nanoparticles, were prepared by melt compounding and film blowing. A third type of composite was produced by incorporation of boehmite alumina nanoparticles treated with benzene sulfonic acid. Scanning electron microscopy indicated that boehmite alumina nanoparticles were finely and uniformly dispersed, though agglomerated, in the polypropylene nanocomposites. Surface-treated boehmite alumina nanoparticles were better dispersed in the matrix than the untreated boehmite alumina nanocomposites. The melt viscosity of nanocomposites remained unaltered or decreased by nanofiller incorporation at low concentration (2.5 and 5 wt%), while it slightly increased at higher concentrations (10 wt%). Uniaxial tensile tests indicated that the nanoparticles can induce a remarkable stiffening effect even at a rather low filler content, especially in the case of surface-treated particles. The plane stress fracture toughness of the material, evaluated by the essential work of fracture approach, showed a noticeable improvement due to boehmite alumina incorporation, with an optimal effect for a filler concentration of about 2.5 wt%.