Molecular structure, crystallinity and morphology of polyethylene/polypropylene blends studied by Raman mapping, scanning electron microscopy, wide angle X-ray diffraction, and differential scanning calorimetry.
The present study is aimed at investigating the mol. structure, crystallinity, and morphol. of polyethylene (PE) and polypropylene (PP) blends by using Raman mapping, SEM, wide-angle x-ray diffraction (WAXD), and differential scanning calorimetry (DSC). In this study, three kinds of PEs, high-d. polyethylene (HDPE), linear low-d. polyethylene (LLDPE), and metallocene polyethylene (MEPE) were used. MEPE is one of the LLDPEs but its d. is very low and its melt flow index (MFI) is very high. Blends of each PE and PP with a PP content ranging from 20 to 80 wt.% with an increment of 20 wt.% were prepd. Raman mapping images and SEM images show that the 80/20 blends of HDPE/PP and LLDPE/PP have similar dispersibility behavior and that only the 80/20 blend of MEPE/PP shows a different behavior in this respect. For the 20/80 blends, the differences are not so large. For the Raman mapping, the intensity ratio of the two bands at 1128 and 974 cm-1 was used. The former is due to a sym. C-C stretching mode of all-trans -(CH2)n- groups of PE while the latter is assigned to a CH3 rocking mode of PP. MEPE/PP blends yield quite different X-ray diffraction patterns compared to HDPE/PP and LLDPE/PP blends; the MEPE/PP blends show that with increasing MEPE content the cryst. size of PP become smaller. DSC curves of MEPE/PP show that the peak area changes linearly with the blending ratio and that the crystn. temp. does not change for any blend. These results mean that the d. and MFI of PE influences the blend properties.
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