Viscoelastic characterization of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The viscoelastic properties of microbial biodegradable copolymers containin g 3-hydroxybutylate (3HB) and 3-hydroxyvalerate (3HV) were investigated as well as the reference homopolymer, poly(3-hydroxybutylate) (PHB), by plotti ng the first normal stress difference (N-1) versus shear stress (tau(s)) an d the storage modulus (G') versus the loss modulus (G "). At low shear rate s, the N(1)s of the copolymers were higher than that of PHB, and at high fr equencies, the G's of the copolymers were lower than that of PHB. To examin e the rheological properties of biodegradable copolymers, we used a modifie d Cole-Cole plot (N-1 versus tau(s) and G' versus G "). From these plots, w e found that the elastic behavior from steady shear experiment is closely r elated to that of the dynamic oscillatory experiments for the biodegradable copolymer. (C) 1999 Elsevier Science Ltd. All rights reserved.