Synthesis of PLLA/PEG-Blockcopolymers by Reactive Extrusion and Scale-up of the Reactive Extrusion Process for the Synthesis of PLLA-Homopolymers
Maren Heinemann, Sandra Weinmann, Zhidong Chen, Hans-Gerhard Fritz
Institut fuer Kunststofftechnologie, University of Stuttgart, Germany
Germany
Keywords: polylactide, reactive extrusion, scale-up
In this work the former investigations of the reactive extrusion process for the production of poly(L,L-lactide) (PLLA) by
ring-opening polymerization of L,L-lactide are extended to the synthesis of PLLA/poly(ethylene glycol) (PEG)-blockcopolymers
by reactive extrusion and to the investigation of different process concepts for the scale-up of the PLLA-production by reactive
extrusion.
Pure PLLA is a stiff and brittle polymer that can only be used for few applications. The incorporation of prepolymerized
PEG-molecules offers one way to vary the properties of PLLA in a wide range from brittle to viscoelastic behavior. In this work
different PLLA/PEG-blockcopolymers were synthesized using a closely intermeshing twin-screw extruder with a screw diameter
of 25 mm. The effect of the content and the nature of the PEG components in the blockcopolymers on the thermal, mechanical
and rheological properties, as well as the influence of process parameters on the properties of the resulting blockcopolymers
were investigated. Special focus was put on the influence of the presence of hydroxyl groups in the reaction mixture caused by
the addition of the PEG. Already low contents of PEG result in strong changes in the mechanical properties of the
PLLA/PEG-blockcopolymers in comparison to pure PLLA.
Two different scale-up scenarios of the reactive extrusion process of PLLA-homopolymers were analyzed. The first process
set-up consisted of a closely intermeshing twin-screw extruder with a screw diameter of 40 mm equipped with a static mixer
at the tip of the screws. For the second process concept a Buss co-kneader was installed in front of the twin-screw extruder.
Thermal, rheological, and molecular properties of the produced PLLA-homopolymers were determined. Using the second
process set-up PLLA-homopolymers with a weight-averaged molecular weight of 50.000 to 100.000 g/mole were synthesized.
Long-term stability of this process was investigated.