Studies on Spherulitic Morphology and Crystallization Kinetics of Poly(3-hydroxybutyrate) Blended with a Medium-Molecular-Weight Poly(ethylene oxide)

Abstract

ABSTRACT Spherulitic morphology and crystallization kinetics of poly(ethylene oxide)/poly(3- hydroxybutyrate) blends, PEO/P(3HB), were investigated using differential scanning calorimeter (DSC), polarized optical microscope (POM) and scanning electronic microscope (SEM). A single glass transition temperature was observed for all the blends and the Gordon-Taylor equation follows the Tg-composition dependence very well. Furthermore, the melting point of P(3HB) was depressed by the addition of PEO component and from which the interaction parameter χ12 was calculated to be -0.059 using the Nishi-Wang equation. Thus, it can be concluded that P(3HB) and PEO are miscible in the level of molecular mixing. From POM and SEM observations, P(3HB) spherulites exhibit a banded texture due to the twisting of lamellar crystals. The band spacing is almost a constant, ca. 20 μm, when the crystallization temperature is below 90 oC, at which the maximum growth rate of P(3HB) spherulites occurs. When P(3HB) is blended with PEO, the growth rate of P(3HB) spherulites decreases because of the dilution effect and a decrease in the degree of undercooling. According to the polymer-diluent theory, the nucleation factor Kg and the folded surface free energy σe of P(3HB) crystals are calculated to be 5.648 x 105 K2 and 47.2 erg/cm2 , respectively. Both values decrease when PEO is added.