The Linear Viscoelastic Behavior of a Series of 3-Hydroxybutyrate-based Copolymers

Abstract

The thermal and linear viscoelastic behavior of a series of synthetically produced 3-hydroxybutyrate-based copolymers is reported. The comonomers employed include 4-hydroxybutyrate (4HB), 5-hydroxyvalerate (5HV), and 6-hydroxyhexanoate (6HH). The polymers investigated differed in the concentration of comonomer randomly distributed within the material and in the length of the carbon backbone of the comonomer. The glass transition temperature follows the Fox equation and decreases with increasing comonomer concentration. The molecular weight between entanglements M _e was determined from the linear viscoelastic data for each copolymer, and a mixing rule was used to determine M _e for homopolymers made from the comonomers studied. Depending on comonomer type and concentration, M _e can be varied systematically, resulting in a wide range of potential applications depending on the chemistry employed. Using the complex viscosity data, master curves were constructed for both the zero-shear viscosity and the shear-thinning behavior depending upon the temperature and the molecular weight between entanglements. The analysis of rheological results and polymer properties based upon copolymer content provides an opportunity to process bio-based materials for a wide range of applications.