The effects of short-chain branching and comonomer type on the interfacial tension of polypropylene-polyolefin elastomer blends

The imbedded fiber retraction method was used to assess the effect of increasing octene content and comonomer type on the compatibility of polypropylene-polyolefin elastomer (PP-POE) blends via direct measure of the interfacial tension. The interfacial tension was found to decrease monotonically with increasing octene content from a starting value of 1.5 +/- 0.16 dyn cm at an initial octene level of 9% down to 0.56 +/- 0.07 dyn cm at an octene content of 24%. These effects can be interpreted in terms of the effective decrease in the molecular weight between chain ends for the branched POE materials. The experimental data were found to be described well by a modification of the empirical relationship used to describe the effect of molecular weight on the interfacial tension for linear materials. The power-law parameter was found to be numerically equivalent for that obtained for the molecular weight dependence of linear materials. The measured interfacial tension was also found to be dependent on the type of comonomer used in the PP-POE systems. The interfacial tension ranged from 1.07 +/- 0.09 dyn cm for a PP-POE system made using ethylene-propylene down to 0.56 +/- 0.07 dyn cm for a PP-POE made using ethylene-octene (24% octene). (C) 1997 John Wiley & Sons, Inc.