Crystallization kinetics and morphology of biodegradable poly(butylene succinate-co-ethylene succinate) copolyesters: effects of comonomer composition and crystallization temperature

The crystallization kinetics and morphology of a series of biodegradable poly(butylene succinate-coethylene succinate) (P(BS-co-ES)) with ethylene succinate (ES) comonomer composition ranging from 13 to 28 mol% were investigated with various techniques and compared with those of the homopolymer poly(butylene succinate) (PBS) in this work. The crystal structures of P(BS-co-ES) are the same as that of neat PBS, but the crystallinity decreases slightly with increasing the ES composition. The glass transition temperature increases slightly while the nonisothermal melt crystallization peak temperature and melting point decrease for P(BS-co-ES) with increasing the ES composition; moreover, the equilibrium melting point temperature of P(BS-co-ES) is also reduced. The overall isothermal crystallization kinetics of P(BS-co-ES) was studied and compared with that of neat PBS. The crystallization mechanism does not change for either neat PBS and P(BS-co-ES) while the overall crystallization rates of P(BS-co-ES) decrease with increasing ES composition and crystallization temperature. The spherulite growth rates of P(BS-co-ES) also decrease with increasing ES composition and crystallization temperature. Both neat PBS and P(BS-co-ES) exhibit a crystallization regime II to III transition independent of ES composition; moreover, the crystallization regime transition temperature shifts to lower temperatures with increasing the ES composition.