In situ FTIR microscope study on crystallization of crystalline/crystalline polymer blends of bacterial copolyesters

This study describes in situ observation of crystallization in a spherulite of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] and poly(3-hydroxybutyrate-co-3-hydroxypropionate) [PHBP] by FTIR microscopy. In order to trace the crystallization processes of blend components separately, PHBV was deuterated. The C–D and CO stretching bands in the IR spectra, respectively, show the crystallization behavior of PHBV and the whole blend. D-PHBV containing 6 and 8% HV [D-PHBV6 and D-PHBV8] are blended with PHBP containing 11% HP [PHBP11]. The crystallization rates of D-PHBV6, D-PHBV8 and PHBP11 decrease in this order. In case of the blend of D-PHBV8 and PHBP11 the crystalline peaks of C–D and CO bands grows simultaneously during crystallization, and the growth rates are rather close to that of D-PHBV8. The results indicate that D-PHBV8, which is the component that shows higher crystallization rate in the pure state, leads the cocrystallization of the blend. For D-PHBV6/PHBP11, on the other hand, the crystalline peak of C–D band grows faster than that of CO band, indicating that the crystallization of D-PHBV6 proceeds before the crystallization of PHBP11. During the crystallization of D-PHBV6, PHBP11 molecules get away from the growing front of the spherulite, i.e. the phase segregation precedes the crystallization. These results demonstrate that FTIR microscopy is a powerful tool to trace the formation of different crystalline phases, such as cocrystallization and phase segregation.