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.
Electric-field-induced changes in thickness have been measured interferometrically for thin films of ferroelectric VDF/TrFE copolymers. For sinusoidal fields high enough to induce ferroelectric switching, the strain x in the thickness direction draws a hysteresis loop of butterfly shape while the electric displacement D draws a conventional square D–E hysteresis loop. The x is shown to be proportional to D
2. Their ratio gives the electrostriction constant κ33 ranging from -2.1 to -2.5 m4/C2. Low-field measurements for poled samples with remnant polarization P
r yield a linear relationship between x and D. The piezoelectric constant given by the ratio x/D coincides with 2κ33
P
r, implying that the piezoelectric activity of VDF copolymers originates from electrostrictive coupling as does that of traditional ferroelectrics. The role of the dimensional effect in both piezoelectricity and electrostriction is discussed.
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