Processing characteristics and structure development in solid-state extrusion of bacterial copolyesters: Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Abstract

The bacterial copolyesters poly(3-hydroxybutyrate-co-3-hydroxyvalerate) have been successfully commercialized by ICI and are currently being distributed worldwide. Because of their bacterial origin, they are completely biodegradable. This has opened up numerous opportunities to develop new environmentally friendly products. The solid-state extrusion of a series of biodegradable copolyesters (P(3HB-3HV)) was performed in our laboratory with the aim of gaining fundamental understanding about their processability below their melting temperatures. The extrudability windows were found to span the temperature range from 135 to 150°C, depending on the composition of the samples under our experimental setup. The solid-state extrudates were found to exhibit an extra melting endotherm about 15–20°C above their normal melting temperature. This high temperature melting peak increasingly became dominant at lower extrusion temperatures. Wide angle X-ray diffraction studies did not indicate any phase change that might be responsible for this increase in the melting point. Contrary to the expectations, the solid-state extruded samples did not show significant chain orientation along the extrusion direction. This might be a result of fracture of the mass in the barrel into smaller pieces and their randomization during the course of their passage through the die. When the extrusion temperature was raised closer to the melting temperature, the quality of the extrudates was improved, and this was reflected in improvement of their mechanical properties. © 1996 John Wiley & Sons, Inc.