BIODEGRADABLE POLYMER BLENDS OF POLY(3-HYDROXYBUTYRATE) AND HYDROXYETHYL CELLULOSE-ACETATE

The melting and crystallization behaviour and phase morphology of poly (3-hydroxybutyrate) (PHB) and hydroxyethyl cellulose acetate (HECA) bl ends prepared by casting films have been studied by differential scann ing calorimetry (d.s.c.), Fourier transform infra-red (FTi.r.), scanni ng electron microscopy and polarizing optical microscopy. The melting temperatures of PHB in the blends were independent of the blend compos ition with PHB contents above 20%. The melting enthalpy of the blends decreased with increase in the HECA component and was close to the add itive value of the enthalpy of the two components. The glass transitio n temperatures of PHB in the blend were constant at about 8 degrees C. No specific interaction between the two components was found by FTi.r . The crystallization of PHB in the blend was affected by the HECA com ponent, especially in the PHB/HECA (20/80) blend. During the d.s.c. co oling run at a lower cooling rate, two separate transitions were found for PHB/HECA (80/20), (60/40) and (40/60) blends, which corresponded to the crystallization of PHB and the phase transition of HECA from an isotropic phase to a mesophase in the blends, respectively. The phase transformation of HECA from an isotropic phase to a mesophase was alm ost independent of the PHB component. (C) 1997 Elsevier Science Ltd.