Study of the miscibility, morphology, crystallization, and melting behavior of blends of poly(3-hydroxybutyrate) and poly(vinylidene fluoride)

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Virginia Tech

This thesis reports on the results of thermal, optical, and spectroscopic studies on poly(vinylidene fluoride)/poly(3-hydroxybutyrate) (PVDF/PHB) blends prepared by melt and solution blending techniques. The blends exhibit - a single, composition dependent Tg. Dynamic crystallization studies indicate that PVDF crystallizes first in all blends containing more than 30% PVDF, and that the blends exhibit single phase behavior in the liquid state. Studies of the melting of isothermally crystallized samples indicate a melting point depression for melt blended PVDF/PHB but no equilibrium melting point depression for the solution blends. Growth rate studies on the α phase of PVDF reveal that its radial growth rate decreases with increasing PHB blend content. Morphological studies demonstrate that the ring spacing of the PVDF α phase increases with increasing temperature and PHB blend content. The different behavior of the meit and solution blends and the previous findings on the thermooxidative degradation behavior of PHB by Kunioka and Doi [1] indicated that PHB may have degraded during the melt blending process. NMR spectra reveal that PHB's chemical composition had not been affected by either blending procedure, but intrinsic viscosity studies indicate a dramatic decrease in PHB's viscosity average molecular weight after melt blending and a smaller decrease after solution blending. FT-IR studies were conducted to determine if PHB did crystallize in the same temperature range as PVDF. FT-IR spectra reveal PHB does crystallize in the same temperature range as PVDF in the solution but not in the meit blends, and the PVDF γ phase content is higher in the solution blends. Finally, TGA studies were performed to determine the effect of PVDF on the degradation of PHB. These findings indicate that PVDF retards the rate of PHB degradation in both types of blends.