Compatibilizing capability of poly(beta-hydroxybutyrate-co-epsilon-caprolactone) in the blend of poly(beta-hydroxybutyrate) and poly(epsilon-caprolactone)

In order to increase the miscibility in the blend of poly(-hydroxybutyrate) [PHB] and poly(epsilon-caprolactone) [PCL], PHB/PCL copolyesters were used as compatibilizers. These PHB/PCL copolyesters were synthesized by transes terification in solution phase. The melting point [T-m] depression, which w as not observed in PHB/PCL blend without compatibilizer, was observed when PHB/PCL copolyesters as compatibilizers were added to the PHB/PCL blend sys tem. As the amount of compatibilizer added to the blend increased, the crys tallization temperature [T-c] of PCL in the blend increased and T-c of PHB in the blend decreased. The difference in T-c between PHB and PCL was gradu ally reduced. When the sequence length of PHB block and PCL block in the PH B/PCL copolyester increased, the miscibility of the blend increased. This i s evidenced by the depression in the T-m of PHB and PCL in the blend and by the decrease in the difference of T-c between PHB and PCL. From the polari zing optical micrographs, the phase separation in PHB/PCL blend was observe d. However, in the presence of PHB/PCL copolyester, the spherulite of PHB g rows in equilibrium with one phase melt.