Effect of Bulk Miscibility on the Surface Composition of Polypropylene/Poly(ethylene-co-propylene) Blends

Abstract

The surface composition profiles of bulk miscible and immiscible blends of atactic polypropylene (aPP) with aspecific poly(ethylene-co-propylene) rubber (aEPR) were studied by differential scanning calorimetry (DSC), sum frequency generation surface vibrational spectroscopy (SFG), and X-ray photoelectron spectroscopy (XPS). SFG spectra of blends of aPP and aEPR show that aPP preferentially segregates to the air/polymer interface, for both the bulk miscible and immiscible systems. The SFG spectra also indicate that methyl side branches assume a preferred configuration at the air/polymer interface, which may play a role in the high surface activity of aPP. Bulk miscibility is shown to control the thickness of the surface enrichment layer, with thicker enrichment layers detected by XPS on bulk immiscible blends. The thickness of the surface enrichment layer measured in the bulk miscible systems is in agreement with the thickness calculated using existing depth profiling models based on Flory-Huggins energy of mixing.

Effect of composition and component structure on thermal behavior and miscibility of polypropylene catalloys

“…By blending PP with elastomer such as ethylene‐propylene random copolymer (EPR), ethylene–propylene–diene monomer (EPDM) etc, the impact properties of blends could be improved to some extent. The miscibility for these blends has been studied experimentally and theoretically 1–8. In recent years, a novel in‐situ polypropylene blend named polypropylene catalloys (PP‐cats) has drawn great interest because they can provide better mechanical properties and considerably cheaper production costs than polypropylenes modified generally by mechanical blending with thermoplastic elastomer 9–12.…”

“…On the basis of various characterizations such as small‐angle neutron scattering (SANS), small‐angle light scattering (SALS), nuclear magnetic resonance spectra (NMR), dynamic mechanical analysis (DMA), differential scanning calorimeter (DSC), and morphology analysis, some studies on the miscibility of ethylene‐propylene (EP) copolymer,17 PP/EPR,1–8 have been conducted. The results show that the composition and chain structure has a great effect on the miscibility, and some miscible blends with special composition could be obtained 6, 10.…”

Solvent‐ and interface‐induced surface segregation in blends of isotactic polypropylene with poly(ethylene‐co‐propylene) rubber

“…The equilibrium surface compositions of polymer blends have extensively been studied, both experimentally1–5 and theoretically 6–9. In practical applications, however, a polymer blend may be far from equilibrium, and factors related to the processing conditions may dictate the surface composition.…”

Combined Atomic Force Microscopy and Sum Frequency Generation Vibrational Spectroscopy Studies of Polyolefins and Hydrogels at Interfaces

“…The blend components include atactic polypropylene (aPP), isotactic polypropylene (/PP), and aspecific poly(ethylene-co-propylene rubber) (aEPR) 10 . In this polymer system, AFM experiments distinguish aPP and aEPR by their differences in viscoelastic properties, and are used to characterize lateral morphology (phase separation) at the interface.…”

“…For comparison, we have also characterized these surfaces by XPS. 10 Like SFG spectroscopy, XPS results obtained from the carbon valence band region also distinguish between aPP and aEPR based on differences in CH 3 content. In contrast though, the XPS experiements have a surface sensitivity that is determined by the mean free path of photoelectrons generated in the polymer film (in this particular case -5-7 nm -much deeper than the monolayer sensitivity of SFG experiments).…”