The present study is aimed at investigating structure, dispersibility, and crystallinity of
poly(3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) blends by using FT-IR microspectroscopy
and differential scanning calorimetry (DSC). Four kinds of PHB/PLLA blends with a PLLA content of
20, 40, 60, and 80 wt % were prepared from chloroform solutions. Micro-IR spectra obtained at different
positions of a PHB film are all very similar to each other, suggesting that there is no discernible segregated
amorphous and crystalline parts on the PHB film at the resolution scale of micro-IR spectroscopy. On
the other hand, the micro-IR spectra of two different positions of a PLLA film, where spherulite structures
are observed and they are not observed, are significantly different from each other. PHB and PLLA have
characteristic IR marker bands for their crystalline and amorphous components. Therefore, it is possible
to explore the structure of each component in the PHB/PLLA blends by using micro-IR spectroscopy. The
IR spectra of a position of blends except for the 20/80 blend are similar to that of pure PHB. On the other
hand, the IR spectra of another position of the blend consist of the overlap of those of pure PHB and
PLLA. For the 20/80 blend, it is difficult to find a position whose spectrum is similar to that of pure
PHB. However, a crystalline peak due to the CO stretching band is observed at 1718 cm-1. This means
that PHB crystallizes as very small spherulites or immature spherulites under such blend ratio. DSC
curves of the blend show that the heat of crystallization of PHB varies with the blending ratio of PHB
and PLLA. The recrystallization peak is detected for PLLA and the 20/80 blend respectively at 106.5 and
88.2 °C. The lowering of recrystallization temperature for the 20/80 blend compared with that of pure
PLLA suggests that PHB forms small finely dispersed crystals that may act as nucleation sites of PLLA.
The results for the PHB/PLLA blends obtained from IR microspectroscopy indicate that PHB crystallizes
in any blends. However, crystalline structures of PHB in the 80/20, 60/40, and 40/60 blends are different
from those of the 20/80 blend.
We report on the Raman spectra of water under high temperature and pressure conditions and show a discontinuity in the pressure dependence of the OH stretching frequency. As pressure increases, the strength of hydrogen bonding increases rapidly in the pressure ranges up to 0.4+/-0.1 GPa at 25 degrees C, 1.0+/-0.1 GPa at 100 degrees C, and 1.3+/-0.1 GPa at 300 degrees C and slowly above these pressures. This finding clearly demonstrates the existence of discontinuities in the pressure response of the hydrogen bonds of water, which suggests a possible structural change under these conditions.
ABSTRACT:The present study is aimed at investigating the molecular structure, crystallinity, and morphology of polyethylene (PE) and polypropylene (PP) blends by using Raman mapping, scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). In this study, three kinds of PEs, high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and metallocene polyethylene (MEPE) were used. MEPE is one of the LLDPEs but its density 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 prepared. 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 À1 was used. The former is due to a symmetric C-C stretching mode of all-trans -(CH 2 ) n -groups of PE while the latter is assigned to a CH 3 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 crystalline size of PP become smaller. DSC curves of MEPE/PP show that the peak area changes linearly with the blending ratio and that the crystallization temperature does not change for any blend. These results mean that the density and MFI of PE influences the blend properties.
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