Miscibility, melting, and crystallization behavior of poly(hydroxybutyrate) and poly(D,L-lactic acid) blends

Melting behavior and crystal morphology of poly(3-hydroxybutyrate)-poly(D,L-lactic acid) (PHB-RPLA) blends with various compositions have been investigated by modulated temperature differential scanning calorimetry (mt-DSC), polarized optical thermomicroscopy (POTM), modulated force thermomechanometry (mf-TM), and small angle X-ray scattering (SAXS). Thermal properties were investigated after fast cooling crystallization treatment. Multiple melting peak behavior was observed for all polymers. mt-DSC data revealed that PHB-RPLA blends undergo melting-recrystallization-remelting during heating, as evidenced by exothermic peaks in the nonreversing heat capacity. A decrease in degree of crystallinity due to significant melt-recrystallization was observed for blends. PHB-RPLA showed different crystal morphologies for various compositions. POTM results showed that the crystallization rates and sizes of spherulites were significantly reduced as RPLA content increased. mf-TM results confirmed miscibility of these two polymers. SAXS data provided evidence of lamella thickness of blends, which increased with increasing RPLA content.