Polyolefin Toughened Polypropylene: Mixing Thermodynamcis

A series of poly(cyclohexyl ethylene-ran-ethylene) (CE) copolymers with similar statistical segment lengths were synthesized and then melt blended with isotactic polypropylene (iPP) at various loadings from 5 - 20 wt.%. Blend morphology was investigated using scanning electron microscopy (SEM). CE copolymers form well dispersed droplets with number average diameters of less than 0.4 μm at a loading of 20 wt.%. Blend mechanical properties were examined with tensile tests. CE copolymers composed of 50 - 70 weight percent of cyclohexyl ethylene are effective in iPP toughening, increasing the break strain from 20% to 400% at a loading of 5 wt.%, which might be attributable to shear yielding of the matrix triggered by cavitation of the uniformly dispersed CE copolymer particles. Blend rheology results were fitted to the Palierne model and interfacial tensions were obtained from the fitting parameter. The small interfacial tension values between CE copolymers and iPP were found to be closely correlated to relatively small interaction parameter χ caused essentially by density mismatch. These results suggest that blends with controlled morphology and good mechanical properties can be prepared by carefully balancing the density and statistical segment length mismatch between the components.