Effect of composition and comonomer type on the rheology, morphology and properties of isotactic polypropylene/ethylene-alpha-olefin copolymer blends.

摘要

The advent of single-site metallocene catalysts has enabled the production of polyolefins with unique properties and has opened new avenues in the area of product development for the plastics industry. The reported number of applications of these materials is continuously increasing and significant growth is anticipated in the area of blends of these polymers with other conventional polyolefins.;The present research aims at studying blends of high flow rate isotactic polypropylene homopolymer with metallocene-based ethylene-alpha-olefin copolymers (also termed polyolefin plastomers (POPs)). The effect of different types of POPS on the rheology, morphology, thermal and mechanical properties of the blends has been investigated.;Evaluation of the thermal properties of the blends by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) confirmed their two phase character in the solid state. Scanning Electron Microscope (SEM) characterization showed that PP/POP blends have droplet-matrix type morphology.;Studies of miscibility in the melt state, above the melting point of polypropylene (PP), have been conducted by using rheological techniques in the linear viscoelastic regime. Results indicate that thermoplastic polyolefin (TPO) blends are immiscible in the molten state. Dynamic oscillatory measurements reveal an enhancement of the elastic modulus at specific blend compositions. The rheological properties were correlated to blend morphology, by using the Palierne emulsion model. Based on the Palierne emulsion model fits, the interfacial tension between PP and POP was found to be 0.92 mN/m at 170°C and 0.59 mN/m at 230°C respectively.;The effect of blend composition and POP type on the mechanical properties has also been investigated. The significant improvements seen in the ductility and impact property of the blends with plastomer addition confirm good compatibility of these materials, without the need for any compatibilizers. Blends containing butene-based plastomers exhibit better mechanical properties.