Polymerization of Lactide to Polylactic Acid and Co-Polymers of Polylactic Acid Using High Viscosity Kneader Reactors

Polymerization of lactide to polylactic acid (PLA) can be performed using conventional reactor technology such as stirred tank reactors, but the conversion and/or final molecular weight must be controlled to a lower level.  At higher conversion and/or molecular weight, the reaction mass will become very viscous , which limits the ability of conventional reactor technology to provide adequate mixing, minimize mass transfer effects on reaction kinetics, remove exothermic heat of reaction and ensure proper heat transfer in order to eliminate hotspots/thermal degradation.

Kneader reactor technology has been used over 60 years in many high viscosity applications such as reactions and polymerization, devolatilization, and drying.  This technology can handle the higher conversion and molecular weight polymerizations of lactide and other copolymers of lactide, while also providing the heat transfer required for proper temperature control.  Using model kinetics and rheology data, a study was performed that shows the capability of kneader reactor technology for lactide polymerizations as well as other copolymers.  Kneader reactor technology can also be used to remove the uncovered monomers from the polymer and expected results from the continuous operation of a polymerizer and finisher will be shown.