Dynamic mechanical behavior and nanostructure morphology of hyperbranched-modified polypropylene blends

摘要

Polypropylene (PP) was modified utilizing two types of polyesteramide-based hyperbranched polymers (amphiphilic PS and hydrophilic PH). A maleicanhydride-modified PP (PM) was used as a reactive dispersing agent to enhance the modification by grafting the hyperbranched polymers onto the PP chains. Pure PP, two different non-reactively modified samples, i.e. excluding PM, and two different reactively modified samples, i.e. including PM, were studied. Investigating the morphology of the samples was performed by scanning electron microscopy. To follow the effect of the modification on the dynamic mechanical properties, dynamic mechanical analysis experiments both in the melt (rheometric mechanical spectrometry) and in solid state (dynamic mechanical thermal analysis) were carried out. In the next step, the nanocrystalline structure of the samples was studied by small angle X-ray scattering (SAXS) in two different modes, i.e. static and recrystallization. Hundreds of SAXS patterns were analyzed automatically using procedures written in PV-WAVE image-processing software. The chord distribution function (CDF) was calculated and the long period (/p) of the crystal lamellae was extracted from the COFs. The rheometric mechanical spectrometry results show that both hyperbranched polymers decrease complex viscosity rf and enhance liquid-like behavior. This happens more significantly when PM is included. The dynamic mechanical thermal analysis results reveal that Tg decreases when PS and PH are added. In the reactively modified samples this reduction is compensated most probably because of the crosslinked structure formed through the grafting reaction between the hyperbranched polymers and PM. Such structure is confirmed by SAXS data and calculated CDFs in the recrystallization mode. Static SAXS data also show enhancement in the crosshatched morphology of the crystalline lamellae of PP for reactively modified samples compared with non-reactively modified samples.