Compatibilizing capability of poly(β-hydroxybutyrate-co-ε-caprolactone) in the blend of poly(β-hydroxybutyrate) and poly(ε-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 transesterification in solution phase. The melting point [T-m] depression, which was not observed in PHB/PCL blend without compatibilizer, was observed when PHB/PCL copolyesters as compatibilizers were added to the PHB/PCL blend system. As the amount of compatibilizer added to the blend increased, the crystallization 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 gradually reduced. When the sequence length of PHB block and PCL block in the PHB/PCL copolyester increased, the miscibility of the blend increased. This is 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 polarizing optical micrographs, the phase separation in PHB/PCL blend was observed. However, in the presence of PHB/PCL copolyester, the spherulite of PHB grows in equilibrium with one phase melt.