Processing Characteristics and Structure Development in Solid-state Extrusion of Bacterial Copolyesters: Poly( 3-hydroxybutyrate-co-3-hydroxyvalerate)

Processing Characteristics and Structure Development in Solid-state Extrusion of Bacterial Copolyesters: Poly( 3-hydroxybutyrate-co-3-hydroxyvalerate)

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 suc-
cessfully 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

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