H. Craig Silvis

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).

Real-time cryo-deformation of polypropylene and impact-modified polypropylene in the transmission electron microscope☆

Abstract Dynamic plane-stress failure has been observed directly in the transmission electron microscope as a function of temperature using a commercially available cooling/straining holder in conjunction with a copper deformation cartridge. The low-temperature cooling stage permits studies of the ductile-brittle transition when the transition is between + 23 and − 170°C. A change in deformation mode was observed on the submicrometre level for polypropylene and impact-modified polypropylene. At room temperature, polypropylene and impact-modified polypropylene deform by shear yielding. Below the ductile-brittle transition the polymer chain mobility is curtailed and crazing dominates. The stage allows observation of the deformation at varying temperature, and events occurring during the deformation can be recorded in real time using a CCD camera.