Biodegradable polyesters as crystallization-accelerating agents of poly(l-lactide).

A series of biodegradable polyesters, poly[(R)-3-hydroxybutyrate] (PHB), poly(-caprolactone) (PCL), and polyglycolide (PGA), were found to be effective crystallization-accelerating agents for poly(l-lactide) (PLLA). Differential scanning calorimetry and polarized optical microscopy strongly suggested that the accelerated crystallization of PLLA in the presence of the three biodegradable polyesters is attributable to a nucleation-assisting effect of PCL and PGA and a spherulite growth-accelerating effect of PHB, although the incorporated PHB lowered the spherulite number of PLLA per unit area. The spherulite growth-accelerating effect of PHB probably resulted from the relatively high miscibility of PLLA with PHB and the low glass transition temperature of PHB compared to that of PLLA. The crystallization kinetics of PLLA varied only in the case of PLLA/PHB blends during cooling from the melt, as evidenced by the nucleation constant and radius growth rate values of the spherulites. The nucleation and growth types of PLLA crystallites are thought to be altered only in the case of PLLA/PGA blends during heating, as evidenced by Avrami exponent n values.