Application of supercritical CO2 as the processing medium to tune impact fracture behavior of polypropylene/poly(ethylene-co-octene) blends

Abstract

The objective of the present work is to study the effectiveness of the application of scCO₂ as the processing medium to tune the fracture behavior of polypropylene/poly(ethylene-co-octene) (PP/POE) blends. Three types of POE were selected to blend with PP to test the feasibility of this approach. A tandem extrusion system was employed for the thermal blending of PP/POE blends, and an integrated slit die rheometer was used to measure the viscosity of pure PP and POE without or with scCO₂ for viscosity ratio calculation. Scanning electron microscopy (SEM) was applied to investigate the phase dispersion and also the fractured morphologies after impact tests. The notched Izod impact tests were carried out at different temperatures to confirm the effectiveness of application of scCO₂ on the alteration of the fracture behavior of PP/POE blends. It was found that PP has a higher affinity for scCO₂ than POE does, and that consequently, for POE originally with a lower apparent viscosity than PP, the phase dispersion of the PP/POE blends was improved upon injection of scCO₂, and thus the fracture behavior alteration from brittle to tough was observed at suitable temperatures. In comparison, for POE originally with a higher apparent viscosity than PP, the phase domains of the PP/POE blends were increased in size upon injection of scCO₂, and resultantly, the fracture mode transition from tough to brittle was observed at suitable temperatures. Hence, this study confirmed the effectiveness of application of scCO₂ to tune the fracture behavior of PP/POE blends, which is of great significance from both fundamental and industrial perspectives.