Poly(l-lactic acid) (PLLA), a biopolymer that can be derived from renewable resources, is known for its brittleness as a result of slow crystallization rates under supercooling conditions, which is associated with the formation of large spherulites. In addition, the glass transition temperature (T-g) of PLLA is 60 degrees C, such that the polymer chain is immobile at room temperature. These disadvantages make PLLA unsuitable for use in the food packaging sector. In this research, biopolymer blends based on PLLA and poly((R)-3-hydroxybutyrate) (PHB), together with tributyl citrate (TBC) as a plasticizer, were developed. TBC was added to increase polymer chain mobility, and to decrease PLLA T-g from 60 to 10 degrees C in blends. Furthermore, the addition of PHB as a nucleating agent to PLLA resulted in an increased proportion of smaller spherulites. Fourier-transform infrared (FT-IR) spectroscopy indicated that the carbonyl group and several other characteristic peaks in blends are shifted to lower wavenumber. In addition, polarized optical microscopy experiments confirmed the results of differential scanning calorimetry, FT-IR, and wide-angle X-ray diffraction, showing that PHB enhances the crystallization behavior by acting as a bionucleation. POLYM. ENG. SCI., 54:1394-1402, 2014. (c) 2013 Society of Plastics Engineers