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Lamellar Structure and Thermal Behaviour of Poly (hydroxybutylate) Studied by Infrared Spectroscopy and Wide-Angle X-ray Diffraction

Yukihiro OZAKI School of Science and Technology, and Research Center for Environment Friendly Polymers, Kwansei-Gakuin University, Japan

The present study aims at investigating the importance of C-H•••O=C hydrogen bonding in the crystalline and lamella structure and its relation to the thermal behavior of PHB and P(HB-co-HHx) (HHx=2.5, 3.5, 10.5 and 12 mol%) by means of WAXD and IR spectroscopy. The existence and the reversibility of the C-H•••O=C hydrogen bonding between the C=O group and the CH3 group along the a axis is explored through the temperature-dependent variations in the a and b lattice parameters by the WAXD measurements. Moreover, the sizes of the a and b lattice parameters are compared for PHB and P(HB-co-HHx). The strength and variation of the C-H•••O=C hydrogen bonding are analyzed also by temperature-dependent IR spectra in the CH and C=O stretching vibration regions. We have found that there is clear linear relation between the temperature-dependent change in the a lattice parameter and that in the CH3 asymmetric stretching band near 3009 cm-1 for PHB and P(HB-co-HHx).
In the temperature dependence of x-ray diffraction of P(HB-co-HHx), it was found that the thermal expansion is much larger in the a lattice parameter than in the b lattice parameter and that the values of the a lattice parameter at room temperature before the heating process and after the cooling process are almost the same while the value of the b lattice parameter varies. It was found that the variations in only the a lattice parameters show reversibility during the heating and cooling processes of PHB and P(HB-co-HHx).