Biodegradable Poly(L-lactic acid)/Poly(butylene succinate-co-adipate) blends:: Miscibility, morphology, and thermal Behavior

Blends of two biodegradable and semicrystalline polymers, poly(L-lactic acid) (PLLA) and poly(butylene succinate-co-adipate) (PBSA), were prepared by solvent casting in different compositions. The miscibility, morphology, and thermal behavior of the blends were investigated using differential scanning calorimetry and optical microscopy. PLLA was found to be immiscible with PBSA as evidenced by two independent glass transitions and biphasic melt. Nonisothermal crystallization measurements showed that fractionated crystallization behavior occurred when PBSA was dispersed as droplets, evidenced by multiple crystallization peaks at different supercooling levels. Crystallization and morphology of the blends were also investigated through two-step isothermal crystallization. For blends where PLLA was the major component, different content of PBSA did not make a significant difference in the crystallization mechanism and rate of PLLA. For blends where PBSA was the major component, the crystallization rate of PBSA decreased with increasing PLLA content, while the crystallization mechanism did not change. (c) 2007 Wiley Periodicals, Inc.