Polypropylene/elastomer/poly(styrene-co-acrylonitrile) blends: manifestation of the critical volume fraction of SAN in dynamic mechanical, tensile and impact properties

The effect of the critical volume fraction vcr of poly(styrene-co-acrylonitrile) (SAN) on the mechanical properties of its blends with rubber-toughened polypropylene (RTPP) containing about 12% grafted ethylene-propylene copolymer was studied. To encompass a wide spectrum of mechanical properties, blend components were selected which are characterized with rather different viscoelastic, tensile and ultimate properties. The SAN volume fraction in blends covers the interval 0 to approximately 0.30; concentration dependencies of measured mechanical properties indicate vcr = 0.13. Experimental data on storage modulus Eb′, loss modulus Eb″, tensile modulus Eb, yield Syb and tensile Sub strength are in plausible accord with their simultaneous prediction based on a predictive scheme which operates with a two-parameter equivalent box model and the data on the phase continuity of components obtained from modified equations of the percolation theory. Strain at break, tensile energy to break and total impact energy of blends show a conspicuous drop in the interval 0 to approximately 15% of SAN where SAN forms a discontinuous component; further growth of the SAN fraction accounts for a reduction of the blend ultimate properties to the values typical of brittle polymers.