Modeling and Simulation of Poly Lactic Acid Polymerization

Abstract

During the past 15 years, a number of aliphatic polyesters have aroused considerable interest due to their biodegradability and biocompatibility. Poly(lactic acid) (PLA) is the main biodegradable polyester of interest, primarily due to its biomedical and pharmacological applications. Since the syntheses of PLA by Carothers in 1932, hundreds of research papers and patents have appeared in the literature. Now large size PLA manufacturing units are being set-up. But, there is a lack of data concerning the rate constants for initiation, propagation and termination steps of PLA polymerization though some data about the apparent rate constant are available. Also, it is extremely difficult to experimentally find the absolute values of different rate constants. Thus, there is a need for mathematical modeling which when used with the readily available experimental data for the average molecular weights, can predict the polymerization rate constants with sufficient accuracy. This thesis embodies the subject matter resulting out of this study. It is arranged in six different chapters. A brief introduction about the need for non-degradable polymers and a brief history along with the current industrial status of PLA is given in the introduction. Since it is the lactic acid, which starts the PLA lifecycle, its importance is also discussed. Also the future prospects and advantages of PLA are mentioned. This is followed by an introduction to synthesis of PLA by ring-opening polymerization (ROP) of lactide. Focus is then shifted to a discussion of why are mathematical models useful, in general, followed by the need for mathematical modeling of the ring-opening polymerization of PLA. A brief description of the methodology used is also given. The progress of lactide polymerization has been modeled by assuming a ring opening reaction mechanism comprising of chain initiation, chain propagation, and chain termination. Appropriate differential equations have been developed incorporating the rate controlling reaction(s)/step(s).