Miscibility, melting and crystallization behavior of two bacterial polyester/poly(epichlorohydrin- co-ethylene oxide) blend systems

Abstract

The miscibility, melting and crystallization behavior of two bacterial polyester/poly(epichlorohydrin- co-ethylene oxide) (PECH–EO) blend systems was studied. PECH–EO containing 48 mol% of epichlorohydrin is miscible with poly(3-hydroxybutyrate) (PHB) and with poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) containing 14 mol% hydroxyvalerate. Both blend systems are characterized by the existence of a single glass transition temperature ( T g) and a depression of the equilibrium melting temperature of PHB or PHBV in each blend. The T g-composition dependence of the blends can be described by the Kwei equation. The interaction parameters obtained from melting point depression analysis are −0.089 and −0.075 for PHB/PECH–EO and PHBV/PECH–EO blends, respectively. The melting and cold crystallization behavior of PHB and PHBV during DSC heating runs is markedly affected by the addition of PECH–EO. During the non-isothermal crystallization process, the cold crystallization temperature ( T cc) of PHB first shows a slight decrease with increasing PECH–EO content from 0 to 50 wt.%, and then a significant increase with further increase of PECH–EO content to 90 wt.% in PHB/PECH–EO blends. For PHBV/PECH–EO blends, the T cc of PHBV increases with increasing PECH–EO content in the whole composition range studied during the process. For samples after cold crystallization, the phase crystallinity of PHB remains constant, while that of PHBV decreases significantly with increasing PECH–EO content. Under isothermal condition, the radial growth rates of bacterial polyester spherulites in the blends are lower than that of pure bacterial polyester samples at higher crystallization temperatures. Spherulitic growth kinetics is analyzed using the Lauritzen–Hoffman model, and the kinetic parameters are determined. Nucleation constant decreases with increasing PECH–EO content in both PHB/PECH–EO and PHBV/PECH–EO blends.