Effects of metal ion-carbonyl interaction on miscibility and crystallization kinetic of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/lightly ionized PBS

Poly(butylene succinate) (PBS) and PBS-based ionomers (PBSi) with 1.0 and 3.0 mol% sodium sulfonate ionic group were synthesized and blended with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-HHx) via direct melt compounding. FT-IR analysis demonstrated that the sodium metal ion–carbonyl interaction between PHB-HHx and PBS ionomer increased in strength with the ionic group concentration. Both non-isothermal and isothermal analyses showed the crystallization rates of PHB-HHx to decrease as the strength of the sodium metal ion–carbonyl interaction increased. However, the constant value obtained for the Avrami exponent indicated that the presence of PBS ionomer did not interfere in any way with the nucleation mechanism or the geometry of the crystal growth of PHB-HHx. DMTA analysis confirmed that PBS ionomer reduced the crystallinity of PHB-HHx, and this phenomenon increased in proportion to the ionic group content. As the ionic group concentration increased, the sodium metal–carbonyl interaction between PHB-HHx and PBS ionomer became much stronger, resulting in the improvement of the miscibility for the blend. The interaction parameter obtained by analyzing the equilibrium melting temperature was negative for all bend systems, with the ionomer having ionic group content, displaying a more negative value. Based on the Lauritzen–Hoffman secondary nucleation theory, the regime of the PHB-HHx/PBS ionomer blend remained unchanged throughout the crystallization process. In addition, both the nucleation constant and surface free energy were found to decrease as both ionomer content and ionic group concentration increased.