Polymorphism and Enzymatic Degradation of Poly(1,4-butylene adipate) and Its Binary Blends with Atactic Poly(3-hydroxybutyrate) and Poly(vinyl phenol)

The influence of atactic poly­(3-hydroxybutyrate) (aPHB) and poly­(vinyl phenol) (PVPh) on the crystallization, phase transition, and enzymatic degradation behaviors of poly­(1,4-butylene adipate) (PBA) was studied. It was found that both aPHB and PVPh can lower the critical temperature of neat α-PBA crystallization from 34 °C for neat PBA to 32 °C for the blends. Also the critical temperatures of neat β-PBA crystallization decrease from 28 °C for neat PBA to 26 and 24 °C for the PBA/aPHB and PBA/PVPh, respectively. Moreover, the β-to-α phase transition can be accelerated by incorporation of PVPh and aPHB. The β-to-α phase transition completes at 55 °C during heating process for neat PBA, while the temperatures for a complete β-to-α transition of PBA in PBA/aPHB and PBA/PVPh are 50 and 45 °C, respectively. This result should be attributed to the decreasing melting point of PBA in its blends with aPHB or PVPh. Therefore, the melting of the original β-PBA and accompanied recrystallization into α ones should take place earlier and more quickly in the blends than that in neat PBA. The analysis of enzymatic degradation demonstrates that the degradation of PBA can be affected by crystalline morphology and the molecular chain mobility of PBA in the amorphous region. The restricted mobility of amorphous PBA imposed by aPHB and PVPh can slow down the degradation rate of PBA in the blends. The higher T_g and stronger intermolecular interaction between PVPh and PBA result in the slowest degradation of PBA in the PBA/PVPh blend. Furthermore, in neat PBA, PBA/PVPh, or PBA/aPHB, the degradation rate of α-PBA crystals obtained via annealing is slower than that of α-PBA prepared by isothermal crystallization and even slower than that of β-PBA.